Co-reporter:Yanan Tang, Zongxian Yang, Xianqi Dai, Dongwei Ma, and Zhaoming Fu
The Journal of Physical Chemistry C March 14, 2013 Volume 117(Issue 10) pp:5258-5268
Publication Date(Web):February 19, 2013
DOI:10.1021/jp400202e
The geometry, electronic structure, and catalytic properties of Pt catalyst supported on the nonmetal doped-graphene (denoted as D-graphene, where D represents the B, Si, O and P dopant) substrates are investigated using the first-principles method. The nonmetal atoms (NA) have small adsorption energies and prefer to be adsorbed at the bridge site on the pristine graphene. In contrast, they prefer to be anchored at the vacancy site as dopants and form stable D-graphene. The NA dopants can modify the local surface curvature and the electronic properties of graphene and therefore regulate the chemical activity of the D-graphene, which can be used as support for catalysts. The highly stable Pt catalysts supported on the D-graphene substrates (Pt/D-graphene) exhibit good catalytic activity for CO oxidation. By comparing both the Langmuir–Hinshelwood (LH) and Eley–Rideal reaction mechanisms, the LH reaction as the starting state is energetically more favorable. Among the Pt/D-graphene systems studied, CO oxidation reactions are more prone to take place with lower energy barriers on the Pt/Si-graphene. The results provide valuable guidance on selecting dopants in graphene to fabricate carbon-based catalysts for CO oxidation, and validate the reactivity of single-atom catalyst for the designing the atomic-scale catalysts.
Co-reporter:Weimeng Kong;Xilin Zhang;Jianjun Mao;Xiaopei Xu;Yanxing Zhang
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 36) pp:24879-24885
Publication Date(Web):2017/09/20
DOI:10.1039/C7CP04718E
The tolerance of sulfur poisoning of α-Mo2C(0001) surfaces with different Pt coverages is investigated combining the density functional theory (DFT) results with thermodynamics data using the ab initio atomistic thermodynamic method. It is found that on Mo2C(0001), Pt clusters tend to form two dimensional planar structures instead of aggregating. The clean Mo2C(0001) surface interacts with sulfides very strongly and is susceptible to sulfur poisoning. With increasing the coverage of Pt on the Mo2C surface, the interaction between sulfur and substrate is weakened. The sulfur tolerance ability increases in the order of Mo2C ≈ Pt1/Mo2C < Pt4/Mo2C < Pt8/Mo2C, where the coverage of Pt on the Mo2C plays a very effective role. The results provide theoretical guidance for designing Mo2C based catalysts with high activity and high sulfur resistance.
Co-reporter:Shiyan Wang;Xilin Zhang;Yanxing Zhang;Jianjun Mao
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 39) pp:27116-27122
Publication Date(Web):2017/10/11
DOI:10.1039/C7CP05756C
The adsorption and dissociation reactions of H2S on TiC(001) are investigated using first-principles density functional theory calculations. The geometric and electronic structures of the adsorbed S-based species (including H2S, SH and S) on TiC(001) are analyzed in detail. It is found that the H2S is bound weakly, while SH and atomic S are bound strongly on the TiC(001) surface. The transition state calculations show that the formation of SH from H2S (H2S → SH + H) is very easy, while the presence of a co-adsorbed H will inhibit the further dissociation of SH (SH + H → S + H + H). In contrast, the hydrogenation of the adsorbed SH is rather easy (SH + H → H2S). Therefore, the dissociative SH can be removed via the hydrogenation reaction. It is concluded that it is difficult for H2S to dissociate completely to form atomic S and poison the TiC surface. The results will further provide understanding of the mechanism of the sulfur tolerance of the TiC anode of proton exchange membrane fuel cells (PEMFCs).
Co-reporter:Zhansheng Lu;Shuo Li;Chuang Liu;Chaozheng He;Xinwei Yang;Dongwei Ma;Guoliang Xu
RSC Advances (2011-Present) 2017 vol. 7(Issue 33) pp:20398-20405
Publication Date(Web):2017/04/05
DOI:10.1039/C7RA00632B
As an efficient metal-free catalyst, graphene doped with heteroatoms is highly active in promoting electrochemical oxygen reduction reaction (ORR). The detailed kinetic and thermodynamic behaviors of the entire ORR process on sulfur doped monovacancy graphene (SGV), as well as the original mechanism are investigated by the dispersion-corrected density function theory (DFT-D) calculations. It is found that the SGV is rather stable and the sulfur dopant is probably the active center. There are two proposed ORR pathways by kinetic process: the dissociation of OOH and the hydrogenation of OOH with the rate-determining steps of 0.75 eV and 0.62 eV, respectively. And the Gibbs free energy diagram of the entire ORR indicates that the dissociation of OOH is precluded, because the process of reduction step of O into OH is endothermic, while the hydrogenation of HOOH is the most favorable pathway even at high potential of 0.86 V. Our DFT-D simulation suggests that the SGV would be an efficient electrocatalyst for ORR.
Co-reporter:Zhansheng Lu;Peng Lv;Shuo Li;Dongwei Ma;Ruqian Wu
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 25) pp:16795-16805
Publication Date(Web):2017/06/28
DOI:10.1039/C7CP02430D
Single atom catalysts (SACs) have attracted broad research interest in recent years due to their importance in various fields, such as environmental protection and energy conversion. Here, we discuss the mechanisms of CO oxidation to CO2 over single Ag atoms supported on hexagonal boron-nitride sheets (Ag1/BN) through systematic van der Waals inclusive density functional theory (DFT-D) calculations. The Ag adatom can be anchored onto a boron defect (VB), as suggested by the large energy barrier of 3.12 eV for Ag diffusion away from the VB site. Three possible mechanisms (i.e., Eley–Rideal, Langmuir–Hinshelwood, and termolecular Eley–Rideal) of CO oxidation over Ag1/BN are investigated. Due to “CO-Promoted O2 Activation”, the termolecular Eley–Rideal (TER) mechanism is the most relevant one for CO oxidation over Ag1/BN and the rate-limiting reaction barrier is only 0.33 eV. More importantly, the first principles molecular dynamics simulations confirm that CO oxidation via the TER mechanism may easily occur at room temperature. Analyses with the inclusion of temperature and entropy effects further indicate that the CO oxidation via the TER mechanism over Ag1/BN is thermodynamically favorable in a broad range of temperatures.
Co-reporter:Shan Dong, Yanxing Zhang, Xilin Zhang, Jianjun Mao, Zongxian Yang
Applied Surface Science 2017 Volume 426(Volume 426) pp:
Publication Date(Web):31 December 2017
DOI:10.1016/j.apsusc.2017.07.143
•The growth mechanism of small Au clusters on various metal-oxide supports is investigated.•Au adatoms prefer 2D cluster on BaO(100) and TiO2(110) surfaces and 3D cluster on MgO(100), CaO(100) and YSZ(111) surfaces.•A linear relationship between EAu-Support/EAu-Au and Eb is found.•An interesting relationship between association energies and the amount of transferred charge is revealed.The adsorption of Au dimer on MgO(100), CaO(100), BaO(100), TiO2(110) and YSZ(100) surfaces is comparatively studied using ab initio density functional theory calculations. It is found that Au dimer prefers upright adsorption on MgO(100), CaO(100), BaO(100) surfaces and parallel adsorption on TiO2(110) and YSZ(111) surfaces. According to the analysis of the metal-metal cohesive energy (EAu-Au) and the metal-substrate adhesion energy (EAu-Support), we find that Au adatoms prefer 2D cluster on BaO(100) and TiO2(110) surfaces and 3D cluster on MgO(100), CaO(100) and YSZ(111) surfaces. We also find a linear relationship between EAu-Support/EAu-Au and Eb (binding energy of metal atom on the substrate). Furthermore, an interesting correlation between association energies and the amount of transferred charge is found. The findings may help to gain further insight into the structure-property correlation and provide valuable information on crucial parameters in catalyst design.Download high-res image (136KB)Download full-size imageThe simplest Au cluster (dimer) on the most stable metal-oxide surfaces MgO(100), CaO(100), BaO(100), YSZ(111) and TiO2(110).
Co-reporter:Xilin Zhang, Zhansheng Lu, Zongxian Yang
Journal of Power Sources 2016 Volume 321() pp:163-173
Publication Date(Web):30 July 2016
DOI:10.1016/j.jpowsour.2016.04.135
•The catalytic activity of MML/WC(0001) toward ORR is comparatively studied.•The AuML/WC(0001) exhibits the highest activity for ORR.•The rate-determining step of ORR on AuML/WC(0001) is identified.•The deactivation mechanisms of the PtML/WC(0001) and PdML/WC(0001) are addressed.Using the first principles methods, the geometric and electronic structures of the metal monolayers supported on WC(0001) surfaces (MML/WC(0001) (M = Pt, Pd, and Au)) and their catalytic activity toward the oxygen reduction reaction (ORR) were comparatively studied. Both the kinetics and the density of states results demonstrated that the direct dissociation of O2 on all three MML/WC(0001) surfaces are almost impossible. Yet the barriers of the formation and dissociation of OOH on AuML/WC(0001) are much smaller than those on the PtML/WC(0001) and the PdML/WC(0001) surfaces, implying that the AuML/WC(0001) exhibits the highest catalytic activity for ORR via a combination of 2e− hydrogenation of O2 and 4e− dissociation of OOH. The rate-limiting step barrier of 0.83 eV for the hydrogenation of OH forming H2O is also comparable to that on the traditional Pt-based catalysts. The deactivation mechanism of PtML/WC(0001) and the performance of PdML/WC(0001) for ORR were identified. The present study is conductive to designing new efficient catalyst without using of the precious Pt for efficiently promoting ORR.
Co-reporter:Zhansheng Lu, Peng Lv, Yanli Liang, Dongwei Ma, Yi Zhang, Wenjin Zhang, Xinwei Yang and Zongxian Yang
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 31) pp:21865-21870
Publication Date(Web):08 Jul 2016
DOI:10.1039/C6CP02221A
A single metal atom stabilized on two dimensional materials (such as graphene and h-BN) exhibits extraordinary activity in the oxidation of CO. The oxidation of CO by molecular O2 on a single cobalt atom embedded in a hexagonal boron nitride monolayer (h-BN) is investigated using first-principles calculations with dispersion-correction. It is found that the single Co atom prefers to reside in a boron vacancy and possesses great stability. There are three mechanisms for CO oxidation: the traditional Eley–Rideal (ER) and Langmuir–Hinshelwood (LH) mechanisms and the termolecular Eley–Rideal (TER) mechanism proposed recently. Given the relatively small reaction barriers of the rate-limiting steps for the ER, LH and TER mechanisms (0.59, 0.55 and 0.41 eV, respectively), all three mechanisms are able to occur at low temperature. The current study may provide useful clues to develop low cost single atom catalysts.
Co-reporter:Xingli Chu, Zhaoming Fu, Shasha Li, Xilin Zhang and Zongxian Yang
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 19) pp:13304-13309
Publication Date(Web):12 Apr 2016
DOI:10.1039/C6CP00194G
Density functional theory calculations are used to elucidate the catalytic properties of a Pt monolayer supported on a TiC(001) substrate (Pt/TiC) toward NO reduction. It is found that the compound system of Pt/TiC has a good stability due to the strong Pt–TiC interaction. The diverse dissociation paths (namely the direct dissociation mechanism and the dimeric mechanism) are investigated. The transition state searching calculations suggest that NO has strong diffusion ability and small activation energy for dissociation on the Pt/TiC. For NO reduction on the Pt/TiC surface, we have found that the direct dissociation mechanisms (NO + N + O → NO2 + N and NO + N + O → N2 + O + O) are easier with a smaller dissociation barrier than those on the Pt(111) surface; and the dimeric process (NO + NO → (NO)2 → N2O + O → N2 + O + O) is considered to be dominant or significant with even a lower energy barrier than that of the direct dissociation. The results show that Pt/TiC can serve as an efficient catalyst for NO reduction.
Co-reporter:Zhansheng Lu, Shuo Li, Peng Lv, Chaozheng He, Dongwei Ma, Zongxian Yang
Applied Surface Science 2016 Volume 360(Part A) pp:1-7
Publication Date(Web):1 January 2016
DOI:10.1016/j.apsusc.2015.10.219
Highlights
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The NM adatoms belong to embedded adsorption in 18C-hexagon of GDY.
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The Rh and Ir/GDY can be applied to single metal catalysts or sensors.
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A simple linear relationship between Ee-ads and Eb is presented.
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The linear relationship can be used in the noble metal modified GDY.
Co-reporter:Jianjun Mao, Shasha Li, Yanxing Zhang, Xingli Chu, Zongxian Yang
Applied Surface Science 2016 Volume 386() pp:202-209
Publication Date(Web):15 November 2016
DOI:10.1016/j.apsusc.2016.06.022
Highlights
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The surface energies of TiC surfaces vary with the carbon chemical potential, ΔμC.
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Relative stability of TiC surfaces in various ΔμC and vacancy concentration is discussed.
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The surface relaxation leads to moderate relaxation for all surfaces considered.
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The surface carbon vacancies induce vacancy states in the vicinity of Fermi-level.
Co-reporter:Xilin Zhang, Zhansheng Lu, Zongxian Yang
International Journal of Hydrogen Energy 2016 Volume 41(Issue 46) pp:21212-21220
Publication Date(Web):14 December 2016
DOI:10.1016/j.ijhydene.2016.08.011
•Whether the 2e− or 4e− pathway dominates the ORR on CoN4-gra is clarified.•The CoN4-gra could promote the ORR along the 4e− processes.•The minimum energy path of ORR on CoN4-gra is addressed.•The kinetic and thermodynamic rate-determining steps are identified.The kinetic activation barriers and the thermodynamic free energy changes for the probable elementary reaction steps of oxygen reduction reaction (ORR) are calculated by the first principles methods to clarify the debate whether the 2e− or 4e− pathway dominates the ORR on the CoN4 embedded graphene (CoN4-gra). It is found that the CoN4-gra can promote the ORR to proceed along a 4e− pathway and to finally generate two H2O by successive hydrogenation reactions. The reduction of OOH into O and H2O with the largest barrier of 0.69 eV is suggested to be the kinetic rate-determining step (RDS). The thermodynamics results show that the elementary steps of ORR along the 4e− pathway are downhill at the electrode potential lower than 0.58 V. The last step, the reduction of OH into H2O with the largest ΔG value (−0.58 eV), functions as the thermodynamic RDS of the 4e− pathway. The large/small energy barriers and small/large thermodynamic driving forces for the generation/dissociation of HOOH indicate also that the 2e− pathway is less favorable than the 4e− pathway for ORR on CoN4-gra.
Co-reporter:Xilin Zhang, Zhansheng Lu, Zongxian Yang
Applied Surface Science 2016 Volume 389() pp:455-461
Publication Date(Web):15 December 2016
DOI:10.1016/j.apsusc.2016.07.133
Highlights
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The mechanism of CO tolerance and oxidation on PtML/WC(0001) is clarified.
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The high tolerance of PtML/WC(0001) to CO originate from the weak adsorption.
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The minimum energy path and the rate-determining step are identified.
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The activity of PtML/WC(0001) to CO oxidation is comparable to that of Pt(111).
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Some probable strategies are proposed to improve the activity of PtML/WC(0001).
Co-reporter:Xilin Zhang, Zhansheng Lu, Zongxian Yang
Chemical Physics Letters 2016 Volume 649() pp:141-147
Publication Date(Web):April 2016
DOI:10.1016/j.cplett.2016.02.058
Highlights
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The growth mechanisms of Pt nanoparticles on ZrC(100) are clarified.
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The strong interaction with ZrC is beneficial for improving the stability and activity of Pt.
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The Pt modified ZrC surfaces are efficient for both O2 dissociation and O atom removal.
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The current results are in keeping with the previous experiment results.
Co-reporter:Zhansheng Lu;Shuo Li;Dongwei Ma;Yi Zhang;Xinwei Yang
Journal of Materials Science 2016 Volume 51( Issue 23) pp:10400-10407
Publication Date(Web):2016 December
DOI:10.1007/s10853-016-0260-6
SnO2, as a highly stable and carbon-free catalyst, is widely used in proton exchange membrane fuel cell as support. In order to shed light on the mechanism of oxygen reduction reaction on SnO2, the activation of the oxygen atom and molecule on undoped and Pt-doped SnO2 was investigated using the first-principles method in this study. We found that: (a) the Pt dopants in the SnO2(110) surfaces are positively charged; (b) the O-vacancy sites are the most preferable for the adsorption of molecular oxygen; (c) O− species, the most reactive form of oxygen, are easy to be formed through the activation of molecular oxygen on the O-defect sites of the Pt-doped SnO2 surface; and (d) the synergetic effects of Pt dopant and O-vacancy would be the key to the O2 activation. The current results shed light on the activation mechanism of oxygen species on undoped and Pt-doped SnO2 supports.
Co-reporter:Xilin Zhang, Zhansheng Lu, Zongxian Yang
Journal of Molecular Catalysis A: Chemical 2016 Volume 417() pp:28-35
Publication Date(Web):June 2016
DOI:10.1016/j.molcata.2016.03.008
•The non-noble-metal cobalt could be strongly stabilized by pyridinic N vacancy.•The activated sites of Co-N3-gra are identified.•The L-H mechanism is more preferable for CO oxidation than the E-R mechanism.•The Co-N3-gra catalyst exhibits higher catalytic activity for CO oxidation than some other noble metal catalysts.The low operating temperature, high efficiency and noble-metal-free are the goal of the ideal catalysts. In present study, an efficient noble-metal-free catalyst for CO oxidation with a single cobalt atom incorporated with pyridinic nitrogen graphene (Co-N3-gra) is proposed. The catalytic activity for CO oxidation via various mechanisms on the Co-N3-gra catalyst is investigated using the first-principles method. It is found that the CO oxidation occurs preferably following the Langmuir-Hinshelwood mechanism (CO + O2 → OOCO → CO2 + O) with an energy barrier of 0.86 eV for the rate-limiting step of OOCO formation. Our findings prove that the activity of noble-metal-free Co-N3-gra catalyst is comparable to or even higher than some other single noble-metal-graphene based catalysts.CO oxidation catalyzed by the non-noble metal Cobalt coupled with pyridinic N3 graphene along the Langmuir-Hinshelwood mechanism.
Co-reporter:Yanxing Zhang, Zhengyang Wan, Zongxian Yang
Journal of Power Sources 2015 Volume 293() pp:635-641
Publication Date(Web):20 October 2015
DOI:10.1016/j.jpowsour.2015.05.044
•The adsorption and diffusion properties of sulfur on the Ni/YSZ + O are studied.•The adsorbed sulfur doesn't favor to be located at the Ni/YSZ + O interface.•The extra O in YSZ weakens the S adsorption at the vacancy site of Ni/YSZ-Ov.•The extra O in YSZ improves the diffusion of S out of the vacancy of Ni/YSZ-Ov.•The Ni/YSZ + O can help to alleviate the sulfur poisoning as compared with the Ni/YSZ.The sulfur poisoning properties of the nickel/oxygen-enriched yttria-stabilized zirconia (denoted as Ni/YSZ + O) with or without interface O vacancy are studied using the first-principles method based on density functional theory. The effects of the extra O atom at the subsurface vacancy of Ni/YSZ are focused. It is found that S at the Ni/YSZ + O can diffuse easily away from the interface oxygen to the top Ni layer sites. With the formation of O vacancy at the Ni/YSZ + O interface (denoted as Ni/(YSZ + O)-Ov), the adsorbed S prefers to diffuse back to the Ni/YSZ interface O vacancy. Compared with Ni/YSZ-Ov, the Ni/(YSZ + O)-Ov can effectively not only weaken the S adsorption at the interface O vacancy site, but also improve the diffusion of S out of the interface O vacancy. Therefore, the Ni/YSZ + O can help to alleviate the sulfur poisoning at the interface O vacancy site as compared with the Ni/YSZ.Compared with Ni/YSZ-Ov, the Ni/(YSZ + O)-Ov can effectively not only weaken the S adsorption at the interface O vacancy site, but also improve the diffusion of S out of the interface O vacancy. Therefore, the Ni/YSZ + O can help to alleviate the sulfur poisoning at the interface O vacancy site as compared with the Ni/YSZ.
Co-reporter:Zhansheng Lu, Guoliang Xu, Chaozheng He, Tianxing Wang, Lin Yang, Zongxian Yang, Dongwei Ma
Carbon 2015 Volume 84() pp:500-508
Publication Date(Web):April 2015
DOI:10.1016/j.carbon.2014.12.048
Metal-coordinated nitrogen-doped graphene is attractive for its application in oxygen reduction reaction (ORR) at the cathode of hydrogen fuel cells. The detailed paths of ORR on MnN4 embedded graphene (MnN4-gra) have been investigated by using the dispersion-corrected density functional theory (DFT-D) method. It is found that the MnN4-gra can be stable at high temperature from the first-principles molecular dynamics simulation and the MnN4 is the active center for all the possible elementary steps of the ORR. Both the four-electron OOH dissociation and the O2 direct dissociation paths are probable for ORR on the MnN4-gra, which are followed by the two OH’s path or the OH hydrogenation into H2O path. All the proposed paths for the ORR on the MnN4-gra are exothermic with small reaction barriers (17.3 kcal/mol or smaller) to go through the rate-limiting steps. The MnN4-gra may have novel catalytic activity for ORR, which is comparable to that of the Pt catalyst.
Co-reporter:Xilin Zhang, Zhansheng Lu, Guoliang Xu, Tianxing Wang, Dongwei Ma, Zongxian Yang and Lin Yang
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 30) pp:20006-20013
Publication Date(Web):02 Jul 2015
DOI:10.1039/C5CP01922B
Single-atom catalysts, especially with single Pt atoms, have attracted more and more attention due to their high catalytic activity for CO oxidation. The outstanding stability and catalytic activity of a single Pt atom supported on nitrogen doped graphene (Pt/NG) are revealed using first-principles calculations. We find that the stability of a Pt atom on the NG can be promoted by picking an appropriate doping configuration. The exceptionally stable Pt/NG catalyst exhibits excellent catalytic activity for CO oxidation via a new tri-molecular Eley–Rideal mechanism (2CO + O2 → OCO–OCO → 2CO2) with an energy barrier of 0.16 eV for the rate-limiting step of OCO–OCO dissociation, which is more preferable than the other two normal Langmuir–Hinshelwood and Eley–Rideal mechanisms.
Co-reporter:Xiaopei Xu, Yanxing Zhang, Zongxian Yang
Applied Surface Science 2015 Volume 357(Part B) pp:1785-1791
Publication Date(Web):1 December 2015
DOI:10.1016/j.apsusc.2015.10.061
Highlights
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The effects of IB metal dopants on the S poisoning features of Ni are analyzed.
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IB metal dopants can modify the surface electronic structure of Ni.
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IB metal dopants can increase the S tolerance of Ni at an optimized concentration.
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Au is a preferred dopant to increase the resistance to sulfur poisoning of Ni.
Co-reporter:Zhansheng Lu, Peng Lv, Jie Xue, Huanhuan Wang, Yizhe Wang, Yue Huang, Chaozheng He, Dongwei Ma and Zongxian Yang
RSC Advances 2015 vol. 5(Issue 103) pp:84381-84388
Publication Date(Web):25 Sep 2015
DOI:10.1039/C5RA14057A
Single metal atom catalysts exhibit extraordinary activity in a large number of reactions, and some two-dimensional materials (such as graphene and h-BN) are found to be prominent supports to stabilize single metal atoms. The CO oxidation reaction on single Pd atoms supported by two-dimensional h-BN is investigated systematically by using dispersion-corrected density functional theory study. The great stability of the h-BN supported single Pd atoms is revealed, and the single Pd atom prefers to reside at boron vacancies. Three proposed mechanisms (Eley–Rideal, Langmuir–Hinshelwood, and a “new” termolecular Eley–Rideal) of the CO oxidation were investigated, and two of them (the traditional Langmuir–Hinshelwood mechanism and the new termolecular Eley–Rideal mechanism) are found to have rather small reaction barriers of 0.66 and 0.39 eV for their rate-limiting steps, respectively, which suggests that the CO oxidation could proceed at low temperature on single Pd atom doped h-BN. The current study will help to understand the various mechanisms of the CO oxidation and shed light on the design of CO oxidation catalysts, especially based on the concept of single metal atoms.
Co-reporter:Xilin Zhang, Zhansheng Lu, Dongwei Ma, Zongxian Yang
International Journal of Hydrogen Energy 2015 Volume 40(Issue 1) pp:346-352
Publication Date(Web):5 January 2015
DOI:10.1016/j.ijhydene.2014.11.003
•The small iron clusters are efficient for ammonia decomposition.•The stepwise dehydrogenation processes and the rate-limiting steps are addressed.•The study will provide information to tune the reaction rate of NH3 dissociation.The stepwise dehydrogenation of NHx on small iron clusters is investigated from the density functional theory (DFT) calculations. The results indicate that the fewer the H atoms of the NHx (x = 0–3) species, the higher the adsorption energies of NHx on the same Fe cluster are. Also the larger the cluster size, the stronger the adsorption for the same NHx species is. The catalytic activity of small Fe clusters for NH3 dehydrogenation is comparatively studied, and the rate-limiting steps for the reactions are addressed. It is found that the rate-limiting steps for the dehydrogenation of NHx on the Fe and Fe3 are that for the NH decomposition, and those on the Fe2 and Fe4 are that for the NH2 dissociation. The barriers for the rate-limiting steps are 1.06, 1.49, 1.43 and 1.51 eV for the dehydrogenation of NHx on the Fe, Fe2, Fe3 and Fe4 clusters, respectively. The results suggest that the small Fe clusters can be regarded as the potential candidates for NH3 dehydrogenation reactions and can serve as a reference for further investigations on the catalytic activity of small Fe clusters supported by various catalytic materials.The process of ammonia stepwise dehydrogenation on small iron clusters.
Co-reporter:Zhaoming Fu, Jinqi Wang, Na Zhang, Yipeng An, Zongxian Yang
International Journal of Hydrogen Energy 2015 Volume 40(Issue 5) pp:2193-2198
Publication Date(Web):9 February 2015
DOI:10.1016/j.ijhydene.2014.12.063
•Doping Cu in Fe3O4 catalyst can control the adsorbed reactant ratios in WGS reaction.•Doping Cu in Fe3O4 can improve the activity of Fe ions for adsorbing CO and H2O.•Doping Cu in Fe3O4 can enhance the co adsorption of CO and H2O in WGS reaction.The effects of the addition of Cu to a Fe3O4 catalyst on water-gas shift reactions (WGS) are investigated using first-principle calculations. To elucidate the doping effect, the adsorption of CO and H2O (the reactants in WGS) molecules is studied on the surfaces of pure Fe3O4 and Cu doped Fe3O4. The results reveal that Cu dopants in the Fe3O4(1 1 1) surface are effective in enhancing the adsorption strength of CO molecules as well as in inhibiting excess water molecules from covering active sites. Simultaneously, it is found that Cu dopants improve the activity of the Fe ions adjacent to dopants for adsorbing both CO and H2O. Therefore, it is possible to control the adsorbance of CO and H2O to reach a proper proportion for WGS through changing the concentration of Cu promoters in the catalysts. The mechanism of doping effects is discussed based on the chemical bond theory and Bader charge analysis. Additionally, the co adsorption of CO and H2O is studied on pure and Cu doped Fe3O4(1 1 1) surfaces. The calculated results also suggest that doping of Cu atoms in Fe3O4 would improve the stability of the reactants co adsorbed on catalysts, which is beneficial for the WGS reaction.
Co-reporter:Yanxing Zhang, Zongxian Yang
Computational and Theoretical Chemistry 2015 Volume 1071() pp:39-45
Publication Date(Web):1 November 2015
DOI:10.1016/j.comptc.2015.08.011
•The global minima of the PdnAg(8−n) clusters are determined by first principle calculations.•The HOMO–LUMO gap of the PdnAg(8−n) clusters can be controlled by turning the Pd ratio.•The activity of the PdnAg(8−n) clusters towards H2 adsorption and dissociation are studied.•The Pd5Ag3 is a proper candidate for H2 dissociation with the lowest Pd usage.•The Pd2Ag6 is a promising candidate with important applications for H2 storage.The global minima of the PdnAg(8−n) clusters are determined based on the particle swarm optimization algorithm, merging density functional theory calculations. It is found that the HOMO–LUMO gap of the PdnAg(8−n) clusters can be controlled from 0.06 to 0.91 eV by turning the Pd ratio. The activity of the optimized PdnAg(8−n) clusters towards H2 adsorption and dissociation at low coverage are studied. We propose that the Pd5Ag3 is a proper candidate for H2 dissociation with the lowest Pd usage. We also find that the Pd2Ag6 can serve as a promising candidate for H2 storage, because it has the largest compositional stability and is the most efficient cluster for H2 adsorption and disfavored for H2 dissociation.We propose that the Pd5Ag3 is a proper candidate for H2 dissociation with the lowest Pd usage small H2 dissociation barrier and negative reaction energy.
Co-reporter:Yanxing Zhang, Zhaoming Fu, Mingyang Wang, Zongxian Yang
Journal of Power Sources 2014 Volume 261() pp:136-140
Publication Date(Web):1 September 2014
DOI:10.1016/j.jpowsour.2014.03.056
•The carbon deposition at the Ni/YSZ interface with O vacancy is studied.•The adsorption and diffusion properties of CH on the Ni/YSZ are studied.•The CH can easily diffuse and be trapped at the interface O vacancy.•The CH can dissociate to C and H atom easily at the interface O vacancy.The carbon deposition at the Triple Phase Boundary (TPB) of the Nickel/Yttrium-Stabilized Zirconia (YSZ) interface is studied using the first-principles method based on density functional theory, with consideration of the interface oxygen vacancy. It is found that the CH fragment (the most stable dissociation products of CH4 on Ni catalyst) can easily diffuse and be trapped at the O vacancy. The trapped CH can dissociate to C and H with a much lower dissociation barrier (0.74 eV) as compared with that (1.39 eV) on the pure Ni (111) surface. Therefore, we propose that the carbon deposition may form easily at the interface oxygen vacancy of TPB as compared with that on the pure Ni (111) surface, which offers new understanding on the carbon deposition of the Ni/YSZ anode of solid oxide fuel cell.It is found that the CH fragment can easily diffuse and be trapped at interface O vacancy site. The trapped CH can dissociate to C and H atoms with lower dissociation barrier (0.74 eV) as compared as that (1.39 eV) on the pure Ni (111) surface. Therefore the interface oxygen vacancy may induce the formation of carbon deposition at the TPB of the Ni/YSZ anode.
Co-reporter:Yanxing Zhang, Zongxian Yang and Meng Wu
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 38) pp:20532-20536
Publication Date(Web):01 Aug 2014
DOI:10.1039/C4CP02662D
The adsorption and dissociation of O2 on the core–shell M@Pd nanowires (M = 3d, 4d, 5d transition metals) are studied using the first-principles density functional method. Suitable core atoms are determined based on the stability of the core–shell NWs and their efficiency for O2 dissociation. With the consideration of the stability and cost, we found that Fe, Co, Ni, Cu, Ru, Ir atoms have lower price than Pd and favor at the core even with O adatom at the surface. The formed M@Pd core–shell nanowires are active for O2 dissociation with activation barriers no larger than 0.25 eV. The results may serve as a guide for the design of efficient Pd-based nanocatalysts for O2 dissociation.
Co-reporter:Zhansheng Lu, Dongwei Ma, Lin Yang, Xiaobing Wang, Guoliang Xu and Zongxian Yang
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 24) pp:12488-12494
Publication Date(Web):28 Apr 2014
DOI:10.1039/C4CP00540F
As a noble-metal-free catalyst for CO oxidation, SnO2 has sparked worldwide interest owing to its highly reactive lattice oxygen atoms and low cost. The current density functional theory (DFT) results demonstrate the process of CO oxidation by lattice oxygen on the SnO2(110) surface and the recovery of the reduced surface by O2. It is found that CO can be easily oxidized on the SnO2(110) surface following the Mars–van Krevelen mechanism. The adsorbed oxygen turns into various oxygen species by transferring electron(s) to the chemisorbed oxygen, which is only found on the partially reduced SnO2−x surface, but not on the perfect SnO2(110) surface: O2(gas) ↔ O2(ad) ↔ O2−(ad) ↔ O22−(ad) ↔ O2−(lattice) + O−(ad). The calculated stretching frequencies would help to distinguish the various adsorbed species observed in experiment and of course help in the assignment of vibrational modes in the experimental spectra.
Co-reporter:Zhaoming Fu, Mingyang Wang, Pengju Zuo, Zongxian Yang and Ruqian Wu
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 18) pp:8536-8540
Publication Date(Web):07 Feb 2014
DOI:10.1039/C3CP55076A
Using first principles simulations and the Monte Carlo method, the optimal structure of the triple-phase boundaries (TPB) of the Ni/Yttria-Stabilized Zirconia (YSZ) anode in solid oxide fuel cells (SOFCs) is determined. Based on the new TPB microstructures we reveal different reaction pathways for H2 and CO oxidation. In contrast to what was believed in previous theoretical studies, we find that the O spillover from YSZ to Ni plays a vital role in electrochemical reactions. The H2 oxidation reaction can proceed very rapidly, by means of both the H and O spillovers, whereas the CO oxidation can only proceed through the O spillover pathway. Further understanding of the roles of defects and dopants allows us to explain puzzling experimental observations and to predict ways to improve the catalytic performance of SOFCs.
Co-reporter:Yanxing Zhang, Zhaoming Fu, Shan Dong and Zongxian Yang
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 3) pp:1033-1040
Publication Date(Web):29 Oct 2013
DOI:10.1039/C3CP53824A
The mechanisms for the resistance to sulfur poisoning at the triple phase boundary (TPB) of the Ni/yttria-stabilized zirconia (YSZ) system treated with Sn vapor are studied using the first-principles method based on density functional theory. Models with Sn dopant or adsorbate are proposed. It is found that the TPB model of the Ni/YSZ system with Sn dopant in Ni can to some extent restrain the diffusion of sulfur from the Ni part to the interface O vacancy by forcing the sulfur atom to diffuse along a longer path, which increases the time for which sulfur remains at the Sn doped Ni surface and allows the O ion to diffuse to the O vacancy at the interface. Once the O ion diffuses to the O vacancy, it forms interface O2−, which repels the sulfur adsorbate and eliminates the sulfur poisoning. However, as the barriers of sulfur diffusion to the vacancy are still small (0.25 eV or smaller), the Sn dopant in Ni does not efficiently eliminate the sulfur poisoning at the TPB. In contrast, the TPB model of the Ni/YSZ system with an Sn adatom on the Ni can form a physical barrier and prevent effectively sulfur diffusion to the O vacancy at the interface. The diffusion barriers are as large as 1.41 eV, which therefore eliminates the sulfur poisoning at the TPB. The results give a detailed dynamic picture of the mechanism of the high tolerance to sulfur poisoning of the Ni/YSZ anode at the TPB after the pre-exposures to metallic tin vapor.
Co-reporter:Xilin Zhang, Zhansheng Lu, Yanan Tang, Zhaoming Fu, Dongwei Ma and Zongxian Yang
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 38) pp:20561-20569
Publication Date(Web):29 Jul 2014
DOI:10.1039/C4CP02873B
The mechanisms for the catalytic reduction of NO on the metal-free nitrogen doped graphene (NG) support are investigated using the density function theory (DFT) calculations both with and without the van der Waals (vdW) correction. The results indicate that the dimer mechanism is more facile than the direct decomposition mechanism. In the dimer mechanism, a three-step reaction is identified: (i) the coupling of two NO molecules into a (NO)2 dimer, followed by (ii) the dissociation of the (NO)2 dimer into N2O + Oad, then (iii) the O adatom is taken away easily by the subsequent NO. Once the NO2 is desorbed, the remaining N2O can be reduced readily by NO on NG. The reaction processes are also confirmed from the first principles molecular dynamics simulations. The results suggest that the NG is an efficient metal-free catalyst for catalytic reduction of NO.
Co-reporter:Shasha Li, Zhansheng Lu, Zongxian Yang, Xingli Chu, Yanxing Zhang, Dongwei Ma
International Journal of Hydrogen Energy 2014 Volume 39(Issue 5) pp:1957-1966
Publication Date(Web):4 February 2014
DOI:10.1016/j.ijhydene.2013.11.132
•The dissociation of H2S molecule leads to atomic S absorbed preferentially at the Cu strip.•Adsorbed sulfur could be removed at suitable partial pressure of water.•The sulfur poisoning to the Cu/CeO2 system can be avoided.•The sulfur tolerance mechanism of the Cu/CeO2 system is discussed.The interaction of H2S with the Cu/CeO2 system is investigated using the first-principles method. It is found that the formation energy of surface oxygen vacancies is lower than that of interface oxygen vacancies and the spillover of an oxygen ion from ceria to Cu strip is an exothermic process, suggesting that the oxygen ions in the substrate are extremely active. The dissociation of H2S molecule forms atomic S, which is absorbed preferentially at the Cu strip on both unreduced and reduced Cu/CeO2(110), instead of interacting with the ceria and diffusing into the ceria bulk, alleviating the deactivation of the ceria. On the other hand, the sulfur atom at the Cu strip could be removed by forming SO2 at suitable partial pressure of water as suggested by our thermodynamics prediction. Therefore the accumulation of sulfur at the Cu strip and the sulfur poisoning to the Cu/CeO2 system can be avoided.The sulfur at the Cu strip from the dissociation of H2S could be removed at suitable partial pressure of water, thus the accumulation of sulfur at the Cu strip and the sulfur poisoning to the anodes can be avoided.
Co-reporter:Xingli Chu, Yanxing Zhang, Shasha Li, Zongxian Yang
Surface Science 2014 Volume 622() pp:16-23
Publication Date(Web):April 2014
DOI:10.1016/j.susc.2013.12.002
•There exist both molecular and dissociative adsorption for the H2S and SH.•Sulfur has stronger interaction with the surface and forms SO and SO22 − species.•The bond cleavage processes of H2S on YSZ + O surface are exothermic with small barriers.•The dissociating S atom from H2S may result in the surface poisoning.•Sulfur can be removed from the surface by introducing oxidizing reagents.The first-principles method based on density functional theory (DFT) is used to investigate the reaction mechanism for the adsorption of H2S on the oxygen-enriched yttria-stabilized zirconia (YSZ + O) (111) surface. It is found that the H2S dissociation processes have low energy barriers (< 0.5 eV) and high exothermicities (2.5 eV), and the dissociative S atoms may result in the poisoning of the YSZ + O surface by forming the SO and the hyposulfite (SO22 −) species with very strong bonds to the surface. In addition, using the ab initio atomistic thermodynamics method, the surface regeneration or de-sulfurization process of a sulfur-poisoned (i.e. sulfur-covered) YSZ + O(111) surface is studied. According to the phase diagram, the adsorbed atomic sulfur can be oxidized to SO2 and removed from the YSZ + O surface by introducing oxidizing reagents, e.g. O2 and H2O.
Co-reporter:Xilin Zhang;Zhansheng Lu;Yanan Tang;Dongwei Ma
Catalysis Letters 2014 Volume 144( Issue 6) pp:1016-1022
Publication Date(Web):2014 June
DOI:10.1007/s10562-014-1232-6
The integrated mechanism of the catalytic oxidation of NO by N2O on the metal-free support of nitrogen doped graphene (NG) is investigated using density function theory calculations. The results indicate that the N2O can be intensively adsorbed on NG support, while the NO, N2, NO2 are all weakly adsorbed. In the oxidation process, a two-step mechanism is identified: the dissociation of N2O followed by the oxidation of NO with the dissociative O-atom. The present work suggests that the NG support, as a high-efficient and metal-free catalyst, is one of the promising candidates for removing the nitrogen oxides gases exhaust.
Co-reporter:Pengju Zuo, Zhaoming Fu, Zongxian Yang
Journal of Power Sources 2013 Volume 242() pp:762-767
Publication Date(Web):15 November 2013
DOI:10.1016/j.jpowsour.2013.05.151
•On pure Ni or IB metals (M), C-dimer configurations are preferred.•On the Ni/M alloy, the separated C-atoms configurations are preferred.•The C atoms tend to be adsorbed far away from the dopant atoms on Ni/M(111) surfaces.•The M dopants in the Ni(111) enhance the energy barriers for the C-dimer formation.Focusing on the mechanisms of coking inhibition properties of the nickel-based alloy catalysts, the adsorption and diffusion of single C atoms and C dimer on the (111) surfaces of pure metals (Ni, Cu, Ag and Au), as well as the bimetallic systems (Ni/M) with 1/4 ML of M atoms in the surface layer of Ni(111) are studied based on spin-polarized density functional theory calculations, where M represents the IB metals (Cu, Ag and Au). It is confirmed that C atoms are energetically favorable to be adsorbed at the three-fold hollow sites on the pure Ni and M surfaces. Introducing M into Ni surface can weaken the adsorption of C due to the 3d-bands of the dopant atoms are farther from the Fermi level than those of Ni, which makes the three-fold hollow sites with IB dopant neighbor(s) unstable for carbon adsorption. The diffusion barriers for the process of C-dimer formation (C + C → C dimer) on the bimetallic surface are all higher than that on pure nickel. The results provide a proper explanation on the suppression effects of carbon deposition on the nickel-based alloy catalysts.The IB-metal dopants on the Ni(111) surface enhance the reaction barriers for the transition of C + C → C dimer, which means that the separated C atoms are difficult to form C dimer on the Ni/M(111) surfaces.
Co-reporter:Xingli Chu, Zhansheng Lu, Yanxing Zhang, Zongxian Yang
International Journal of Hydrogen Energy 2013 Volume 38(Issue 21) pp:8974-8979
Publication Date(Web):17 July 2013
DOI:10.1016/j.ijhydene.2013.05.008
•The H2S and SH are weakly bound on the surface via physical adsorption.•Sulfur has stronger interaction with the YSZ and forms oxido-sulfate species (SO2−).•Hydrogen will inhibit the formation of sulfur from the dissociation of H2S.•Sulfur-removing on YSZ(111) surface is feasible by hydrodesulfurization.The adsorption and dissociation of H2S on the yttria-stabilized zirconia (YSZ) (111) surface are studied using the first-principles methods. It is found that H2S and SH species are bound weakly on the YSZ(111) surface. Sulfur atom is essentially immobile both into the YSZ bulk and along the surface. Instead, it is stably anchored on the O atop of the YSZ surface with the formation of the SO2− fragment. The nudged elastic band (NEB) calculations show that the formation of SH from H2S (H2S → SH + H) is very easy, while the presence of a co-adsorbed H would inhibit the further dissociation of SH. In contrast, the hydrogenation of the adsorbed sulfur is rather easy. It is concluded that H could inhibit the formation of sulfur, thus the sulfur poisoning of the YSZ surface would be prevented by hydrogen.H could inhibit the formation of sulfur, thus the sulfur poisoning of the YSZ surface would be prevented by hydrogen.
Co-reporter:Yanan Tang, Zongxian Yang, Xianqi Dai, Dongwei Ma, and Zhaoming Fu
The Journal of Physical Chemistry C 2013 117(10) pp: 5258-5268
Publication Date(Web):February 19, 2013
DOI:10.1021/jp400202e
The geometry, electronic structure, and catalytic properties of Pt catalyst supported on the nonmetal doped-graphene (denoted as D-graphene, where D represents the B, Si, O and P dopant) substrates are investigated using the first-principles method. The nonmetal atoms (NA) have small adsorption energies and prefer to be adsorbed at the bridge site on the pristine graphene. In contrast, they prefer to be anchored at the vacancy site as dopants and form stable D-graphene. The NA dopants can modify the local surface curvature and the electronic properties of graphene and therefore regulate the chemical activity of the D-graphene, which can be used as support for catalysts. The highly stable Pt catalysts supported on the D-graphene substrates (Pt/D-graphene) exhibit good catalytic activity for CO oxidation. By comparing both the Langmuir–Hinshelwood (LH) and Eley–Rideal reaction mechanisms, the LH reaction as the starting state is energetically more favorable. Among the Pt/D-graphene systems studied, CO oxidation reactions are more prone to take place with lower energy barriers on the Pt/Si-graphene. The results provide valuable guidance on selecting dopants in graphene to fabricate carbon-based catalysts for CO oxidation, and validate the reactivity of single-atom catalyst for the designing the atomic-scale catalysts.
Co-reporter:Yanan Tang, Zongxian Yang and Xianqi Dai
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 48) pp:16566-16572
Publication Date(Web):25 Jun 2012
DOI:10.1039/C2CP41441D
The catalytic oxidation of CO on Pt/X-graphene (X = “pri” for pristine- or “SV” for defective-graphene with a single vacancy) is investigated using the first-principles method based on density functional theory. In contrast to a Pt atom on pristine graphene, a vacancy defect in graphene strongly stabilizes a single Pt adatom and makes the Pt adatom more positively charged, which helps to weaken the CO adsorption and facilitates the O2 adsorption, thus enhancing the activity for CO oxidation and alleviating the CO poisoning of the platinum catalysts. The CO oxidation reaction on Pt/SV-graphene has a low energy barrier (0.58 eV) by the Langmuir–Hinshelwood (LH) reaction (CO + O2 → OOCO → CO2 + Oads) which is followed by the Eley–Rideal (ER) reaction with an energy barrier of 0.59 eV (CO + Oads → CO2). The results validate the reactivity of catalysts on the atomic-scale and initiate a clue for fabricating carbon-based catalysts with low cost and high activity.
Co-reporter:Yanan Tang;Xianqi Dai
Journal of Nanoparticle Research 2012 Volume 14( Issue 5) pp:
Publication Date(Web):2012 May
DOI:10.1007/s11051-012-0844-2
Adsorption energies and stable configurations of CO on the Pt clusters are investigated using the first-principles density-functional theory method. It is found that the adsorption of CO on the top site of the Pt4 cluster is more stable than that on the bridge site. The atomic charges are unevenly distributed within the charged Pt4 cluster, and the structural positions of the Pt atoms determine their charge states and therefore their activity. A systematic study on the effects of electrons and holes doping in the Pt4 clusters suggest an effective method to prevent the CO poisoning through regulating the total charge in Pt4 clusters. The graphene-based substrate is an ideal catalyst support, which makes the Pt catalyst lose electron and weakens the CO adsorption. The results would be of great importance for designing high active nanoscale Pt catalysts used for fuel cells.
Co-reporter:Zongxian Yang, Yanxing Zhang, Zhaoming Fu, and Ruqian Wu
The Journal of Physical Chemistry C 2012 Volume 116(Issue 36) pp:19586-19589
Publication Date(Web):August 24, 2012
DOI:10.1021/jp306454q
Density functional calculations and ab initio molecular dynamics simulations are performed to investigate adsorption and dissociation of O2 molecules on the DI (double icosahedron) Pd19 nanocluster. Exceptionally high activity is found for oxygen bond cleavage over its waist region, with an energy barrier of only 0.06 eV and a reaction time of 0.5 ps. This stems from the availability of valley-like Pd4 ensembles and the large weights of LUMO and HOMO. Moreover, this cluster is highly stable in reaction conditions up to 500 K, so it can be a good candidate for the development of excellent nanocatalysts.
Co-reporter:Zhansheng Lu, Jolla Kullgren, Zongxian Yang, and Kersti Hermansson
The Journal of Physical Chemistry C 2012 Volume 116(Issue 15) pp:8417-8425
Publication Date(Web):April 10, 2012
DOI:10.1021/jp2092913
Even very low levels of sulfur contaminants can degrade the catalytic performance of cerium oxide. Here, the interaction of atomic sulfur with the ceria (111) and (110) surfaces has been studied using first-principles methods. Two sulfoxy species are identified: oxido-sulfate(2-) species (SO2–) on both the CeO2(111) and (110) surfaces and hyposulfite (SO22–) on the (110) surface. Sulfide (S2–) is formed when a surface or a subsurface oxygen atoms is replaced by sulfur. These sulfide species are more stable at the surface. Furthermore, sulfite (SO32–) structures are found when sulfur is made to replace one Ce in the ceria (111) and (110) surfaces. The calculated sulfur diffusion barriers are larger than 1.4 eV for both surfaces, and thus sulfur is essentially immobile, providing a possible explanation for the sulfidation phenomena of the ceria-based catalyst. Thus, we find three different species from interaction of S with ceria which are all, due to their strong binding, capable of poisoning the surface, reduced or unreduced. Our results suggest that under reducing conditions sulfur is likely to be found in the (111) surface (replacing oxygen) but on the (110) surface (as SO22–).
Co-reporter:Zongxian Yang, Yanxing Zhang, and Ruqian Wu
The Journal of Physical Chemistry C 2012 Volume 116(Issue 25) pp:13774-13780
Publication Date(Web):June 8, 2012
DOI:10.1021/jp300971e
Structural stability and catalytic reactivity of M@Pt12 core–shell nanoclusters with different core atom (M) are systematically investigated using ab initio density functional theory calculations with the generalized gradient approximation. We found that the pure D5h-Pt13 cluster is venerable to reactants and may loss its activity in reaction conditions. The insertion of Fe, Co, Tc, Ru, Rh, Re, Os, or Ir into its core, forming D5h M@Pt12 core–shell nanoclusters, may significantly enhance the structural stability and may also further improve its catalytic activity. Our findings provide useful insights for the design of robust bimetallic nanocatalysts.
Co-reporter:Qing-Gao Wang ; Jia-Xiang Shang
The Journal of Physical Chemistry C 2012 Volume 116(Issue 44) pp:23371-23376
Publication Date(Web):October 19, 2012
DOI:10.1021/jp306606g
The initial oxidization of a Nb(100) surface is investigated using a first-principles method based on the density functional theory. Our theoretical results indicate that the symmetry of the Nb(100) surface is changed with the adsorption of O atoms. The p(2 × 2)-O0.50 and p(2 × 2)-O1.00 are stable for the on-surface adsorption at the O coverages of 0.50 and 1.00 monolayer (ML), respectively. The (4 × 1)-O and (3 × 1)-O are stable for the multilayer adsorption at the O coverages of 1.75 and 2.00 ML, respectively, which, according to the work function and local atomic structure, are the NbO(100) precursors formed on the Nb(100) surface. In addition, the thermodynamic analysis reveals that the NbO oxide is stable in a vacuum [e.g., log(Po2/PO) = −18] at high temperature (e.g., T > 1200 K), in agreement with the formation of NbO precursors on a Nb(100) surface.
Co-reporter:Zongxian Yang, Qinggao Wang, Shuyi Wei
Surface Science 2011 Volume 605(3–4) pp:351-360
Publication Date(Web):February 2011
DOI:10.1016/j.susc.2010.11.001
The interaction of water molecules with the Zr-doped ceria (111) surface is investigated by using the DFT + U method. For the stoichiometric Zr-doped ceria (111) surface, a water molecule can be adsorbed not only through a one-H-bond configuration with its O* (oxygen of water) binding to a surface Ce ion, but also preferably through a nearly dissociated configuration with its O* binding to a surface Zr ion, at variance with that on the pure ceria (111) surface, where only a one-H-bond configuration is observed. While Zr-doping enhances the interaction of water with the unreduced CeO2(111), it reduces the tendency of water dissociation on the reduced ceria. On the first kind Ce0.75Zr0.25O2 − x(111) surface (VI, with a surface oxygen vacancy not neighboring a Zr dopant), water molecules prefer to dissociate around the Ce sites with the formation of the O*–Ce bond. On the second kind Ce0.75Zr0.25O2 − x(111) surface (VII, with a surface oxygen vacancy neighboring a Zr dopant, which has a much higher formation probability than VI), the tendency of water dissociation (although preferred) is reduced compared with those on the CeO2 − x(111) and the first kind Ce0.75Zr0.25O2 − x(111).Additionally, the electronic interaction of water and the Zr-doped ceria (111) surface or the reduced Zr-doped ceria (111) surface is mainly from the interaction of the O*–Ce bond and the Hb–O bond because the charge affinity of Ce ions is stronger than that of Zr ions. Although the O* fills the vacancy site when a water molecule dissociates on the Ce0.75Zr0.25O2 − x(111), it does not oxidize the surface.Research Highlights► The water/Zr-doped ceria interaction is investigated by using the DFT+U method. ► Zr-doping enhances the interaction of water with the unreduced CeO2(111). ► Zr-doping reduces the tendency of water dissociation on the reduced ceria. ► Although the O* fills the vacancy site when a water molecule dissociates on the Ce0.75Zr0.25O2-x(111), it does not oxidize the surface.
Co-reporter:Zhansheng Lu, Zongxian Yang, Bingling He, Christopher Castleton, Kersti Hermansson
Chemical Physics Letters 2011 Volume 510(1–3) pp:60-66
Publication Date(Web):24 June 2011
DOI:10.1016/j.cplett.2011.03.091
Abstract
DFT + U calculations of Cu-doped bulk ceria are presented. The first oxygen vacancy in Cu-doped ceria forms almost spontaneously and the second vacancy is also easily created. Whether zero, one or two oxygen vacancies, the Cu dopant is in the form Cu(+II), and prefers to be 4-coordinated in a close to planar structure. Charge compensation, structural relaxation and available Cu–O states all play roles in lowering the O vacancy formation energies, but to different degrees when the first and second oxygen vacancies are formed. The Cu-doped ceria(1 1 1) surface system behaves in a similar fashion.
Co-reporter:Zongxian Yang, Zhixia Geng, Yanxing Zhang, Jinlong Wang, Shuhong Ma
Chemical Physics Letters 2011 Volume 513(1–3) pp:118-123
Publication Date(Web):6 September 2011
DOI:10.1016/j.cplett.2011.07.088
Abstract
The adsorption, diffusion and dissociation properties of O2, as well as adsorption and diffusion properties of O on the Ih Cu@Pt12 core–shell nanoparticle are studied using the ab initio density functional theory (DFT) calculations. It is found that the O2 can easily dissociate and the O can easily diffuse on the Ih Cu@Pt12 with much lower barriers as compared those on the Pt(1 1 1) surface, which demonstrates the much higher oxygen reduction activity of the Ih Cu@Pt12 core–shell nanoparticles.
Co-reporter:Yun Zhao ; Botao Teng ; Zongxian Yang ; Yue Zhao ; Leihong Zhao ;Mengfei Luo
The Journal of Physical Chemistry C 2011 Volume 115(Issue 33) pp:16461-16466
Publication Date(Web):July 22, 2011
DOI:10.1021/jp203640f
The adsorption behaviors and electronic properties of Sn on the CeO2(111) surface were systematically investigated using the density functional theory (DFT) method. Our results suggested that Sn on the hollow site is more stable than that on the top oxygen site at the coverage of 0.25 ML, while Sn on the top oxygen site is the most stable configuration when the coverage of Sn is equal to or higher than 0.5 ML. Charge density difference (CDD) analysis indicates that electrons transfer from the Sn adatom to the substrate, leading to the reduction of Ce4+ to Ce3+ ion, which is in agreement with the experimental spectroscopy. The reduction degree of the substrate increases with the Sn coverage, which is well supported by the CDD and spin-resolved density of states (DOS) of the most stable xSn/CeO2(111) configurations. The adsorption of Sn can partially activate the surface oxygen of ceria. The tentative study of a probe molecule CO adsorption on the Sn/CeO2(111) surface indicates that CO adsorption is enhanced due to the strong tin–ceria interactions.
Co-reporter:Zongxian Yang;Zhaoming Fu;Yanning Zhang;Ruqian Wu
Catalysis Letters 2011 Volume 141( Issue 1) pp:78-82
Publication Date(Web):2011 January
DOI:10.1007/s10562-010-0446-5
Systematic density-functional calculations have been performed to address an important issue for CO oxidation on redox ceria: the role of lattice oxygen. One major findings is that CO easily grasps one lattice oxygen atom to form CO2− and CO2 on CeO2 (111) and Ce0.75Zr0.25O2 (111) with small activation energies. Zr dopants facilitate the reduction of Ce+4 to Ce+3 and hence weaken the Ce–O bonds, which benefit the direct formation and release of CO2.
Co-reporter:Zongxian Yang ; Luogang Xie ; Dongwei Ma ;Guangtao Wang
The Journal of Physical Chemistry C 2011 Volume 115(Issue 14) pp:6730-6740
Publication Date(Web):March 9, 2011
DOI:10.1021/jp200005r
Ceria-supported copper is a wonderful catalyst for the water−gas shift (WGS) reaction which has been demonstrated experimentally. Using first-principles calculations based on density functional theory (DFT), we identify the mechanisms for the growth of small Cu clusters (Cux, x = 1−4) on ceria and the dissociation of H2O on the Cu4/CeO2 catalyst. Our calculations indicate that the strong copper−oxygen interaction at the Cu4/CeO2 interface is comparable to the copper−copper intracluster interactions, and the competitions between them determine the morphologies of Cu clusters on ceria. H2O dissociates with small barriers (0.19−0.31 eV) on the Cu4/CeO2 catalyst, and the highly catalytic activity originates from the enhanced electrostatic interaction between the positively charged Cu sites and the polar H2O molecule. The Cu/O interface sites of the ceria-supported copper catalyst are identified as the active sites for H2O dissociation. As a buffer to accept/release electrons, the ceria support not only activates the Cu sites but also participates in the H2O dissociation reaction at the Cu/O interface.
Co-reporter:Bo-Tao Teng, Shi-Yu Jiang, Zong-Xian Yang, Meng-Fei Luo, You-Zhao Lan
Surface Science 2010 Volume 604(Issue 1) pp:68-78
Publication Date(Web):1 January 2010
DOI:10.1016/j.susc.2009.10.024
The effects of different oxygen species and vacancies on the adsorption and oxidation of formaldehyde over CeO2(1 1 1) surface were systematically investigated by using density functional theory (DFT) method. On the stoichiometric CeO2(1 1 1) surface, the C–H bond rupture barriers of chemisorbed formaldehyde are much higher than that of formaldehyde desorption. On the reduced CeO2(1 1 1) surface, the energy barriers of C–H bond ruptures are less than those on the stoichiometric CeO2(1 1 1) surface. If the C–H bond rupture occurs, CO and H2 form quickly with low energy barriers. When O2 adsorbs on the reduced (1 1 1) surface (O2/Ov species), the C–H bond rupture barriers of formaldehyde are greatly reduced in comparison with those on the stoichiometric CeO2(1 1 1) surface. If O2 adsorbs on oxygen vacancy at sub-layer surface, its oxidative roles on formaldehyde are much similar to that of O2/Ov species.
Co-reporter:Zongxian Yang, Jinlong Wang, Xiaohu Yu
Chemical Physics Letters 2010 Volume 499(1–3) pp:83-88
Publication Date(Web):20 October 2010
DOI:10.1016/j.cplett.2010.09.021
Abstract
The adsorption, diffusion and dissociation of O2 on the Pt-skin Pt3Ni(1 1 1) surface were investigated using the ab initio density functional theory (DFT) calculation. The adsorption of O2 is less stable and the diffusion and dissociation of the adsorbed O2 are weakened as compared to those on the Pt(1 1 1) surface. The mechanism for the high oxygen reduction reaction (ORR) activity of the Pt3Ni(1 1 1) surface is attributed to the weakening the adsorption of OH and other oxygenous intermediates produced by ORR, which therefore alleviates the poisoning to the catalyst.
Co-reporter:Zongxian Yang, Qinggao Wang, Shuyi Wei, Dongwei Ma and Qiang Sun
The Journal of Physical Chemistry C 2010 Volume 114(Issue 35) pp:14891-14899
Publication Date(Web):August 18, 2010
DOI:10.1021/jp101057a
The interaction of a water molecule with the (111) surfaces of stoichiometric and reduced ceria is investigated using first principle density functional theory with the inclusion of the on-site Coulomb interaction (DFT+U). It is found that on the stoichiometric ceria(111) surface, the water molecule is adsorbed spontaneously through single hydrogen bond configuration. In contrast, on the lightly reduced ceria(111), there exist both molecular adsorption (no-H-bond configuration) and dissociative adsorption (surface hydroxyl) modes. It is obvious that oxygen vacancies can enhance the interaction of water with the substrate. Phase diagrams for stoichiometric and reduced ceria(111) surfaces in equilibrium with water vapor in the complete range of experimentally accessible gas phase condition are calculated and discussed combining the DFT results and thermodynamics data using the ab initio atomistic thermodynamic method. We present a detailed analysis of the stability of the water−ceria system as a function of the ambient conditions, and focus on two important surface processes for water adsorption on the stoichiometric and on the lightly reduced surfaces, respectively.
Co-reporter:Zongxian Yang, Bingling He, Zhansheng Lu and Kersti Hermansson
The Journal of Physical Chemistry C 2010 Volume 114(Issue 10) pp:4486-4494
Publication Date(Web):February 18, 2010
DOI:10.1021/jp909174u
With the use of the DFT+U method, the properties of Cu adsorbed on the stoichiometric CeO2(111) surface, Cu-doped CeO2(111) (denoted as Cu0.08Ce0.92O2) surface, and CO oxidation on the stoichiometric Cu0.08Ce0.92O2 surface are studied systematically. It is found that (i) Cu is stable both as an adsorbed atom on the surface and as dopant in the surface region. Cu adsorbed at the surface is Cu(+I) while Cu as a dopant atom is Cu(+II). (ii) The Cu dopant facilitates O-vacancy formation considerably, while Cu adsorption on the stoichiometric CeO2(111) surface may suppress oxygen vacancy formation. (iii) Physisorbed CO, physisorbed CO2, as well as chemisorbed CO (carbonate) species are observed on the Cu-doped CeO2(111) surface, in contrast, on the clean ceria(111) surface, only physisorbed CO was previously observed. C−O distances, adsorption energies, and surface-induced C−O vibrational frequency shifts were used to characterize these species.
Co-reporter:Zongxian Yang, Dongwei Ma
Surface Science 2009 Volume 603(Issue 16) pp:2413-2421
Publication Date(Web):15 August 2009
DOI:10.1016/j.susc.2009.05.017
Co-reporter:Zongxian Yang, Yanwei Wei, Zhaoming Fu, Zhansheng Lu, Kersti Hermansson
Surface Science 2008 Volume 602(Issue 6) pp:1199-1206
Publication Date(Web):15 March 2008
DOI:10.1016/j.susc.2008.01.013
The effects of Zr doping on the atomic and electronic properties of the ceria(1 1 1) surface are studied using first-principles density functional theory with the inclusion of on-site Coulomb interaction. The atomic structures, electronic structure, and the vacancy formation energies of the Zr-doped and undoped ceria(1 1 1) surfaces are compared. It is found that (i) Zr doping induces a severe distortion of the unreduced surface structure; (ii) at the reduced Zr-doped ceria(1 1 1) surface, the oxygen anions around the oxygen vacancy show much larger displacements than those on the pure CeO2(1 1 1) surface; (iii) an oxygen vacancy is more easily formed around the Zr dopant, and the reduction energy is lowered by about 0.5 eV; (iv) the excess electrons left by the removed oxygen atom localize on the two Ce cations neighboring the vacancy and thus brings about the reduction of the two Ce4+ ions; and (v) the atomic structure modification induced by the Zr doping plays a vital role in facilitating the reduction of the ceria–zirconia solid solution as compared to the pure ceria.
Co-reporter:Zongxian Yang ; Zhaoming Fu ; Yanwei Wei ;Zhansheng Lu
The Journal of Physical Chemistry C 2008 Volume 112(Issue 39) pp:15341-15347
Publication Date(Web):September 4, 2008
DOI:10.1021/jp711154k
With use of the first-principles density functional theory with the inclusion of the on-site Coulomb interaction of the Ce4f electrons (DFT+U) method, the adsorption of CO on the (110) surface of a stoichiometric Ce0.75Zr0.25O2 system is studied systematically. It is found that, (1) in addition to the carbonate-like CO3 structures, there exists a new adsorption species (a bent CO2− structure) on the Ce0.75Zr0.25O2(110) surface, and (2) the Zr-dopant can enhance the adsorption of CO and improve the CO oxidation process on the ceria surface by promoting the desorption of CO2.
Co-reporter:Zongxian Yang, Tom K. Woo, Kersti Hermansson
Surface Science 2006 Volume 600(Issue 22) pp:4953-4960
Publication Date(Web):15 November 2006
DOI:10.1016/j.susc.2006.08.018
The adsorption of NO on the (1 1 1) and (1 1 0) surfaces of ceria (CeO2) was studied using projector-augmented wave (PAW) method based density-functional theory within the generalized gradient approximation (GGA). Several adsorption sites for NO on the stoichiometric surfaces are found, all with weak molecule-surface interaction. The adsorption on the reduced surfaces is much stronger. The O-ends of the adsorbed NO molecules fill the oxygen vacancies and the N–O bonds are elongated. If two such adsorbed NO molecules, residing at neighbouring sites, meet, their N-ends will form a strong N–N bond with little or no barrier. This is an intermediate step towards dissociation of free N2 which is calculated to be strongly thermodynamically driven.
Co-reporter:Shan Dong, Yanxing Zhang, Xilin Zhang, Jianjun Mao, Zongxian Yang
Applied Surface Science (30 April 2017) Volume 402() pp:
Publication Date(Web):30 April 2017
DOI:10.1016/j.apsusc.2017.01.057
•The catalytic activity of supported metal catalysts is closely related to the size of metal particles.•The dissociation of O2 on the YSZ (111) surface is largely enhanced by the supported Ni cluster.•The supported Ni dimer is predicted to be the smallest Ni cluster needed for efficient O2 dissociation.•The results would provide an important reference to improve the activity and efficiency of the Ni/YSZ(111) nanocomposite catalysts in cost-effective materials.The adsorption and dissociation of O2 on the supported small nickel clusters with one-, two-, three-Ni atoms on yttria-stabilized zirconia (YSZ) (111) surfaces, as well as those on the bare YSZ(111) and Ni(111) surfaces are comparatively studied using ab initio density functional theory calculations. It is found that the dissociation of O2 on the YSZ(111) surface is largely enhanced by the supported Ni dimer, which is predicted to be the smallest Ni cluster needed for efficient O2 dissociation. The results would provide an important reference to improve the activity and efficiency of the Ni/YSZ(111) nanocomposite catalysts in cost-effective materials.The minimum energy paths (MEPs) for the dissociation process of O2 on the surfaces of bare YSZ (111) and Nin/YSZ (111) (n = 1, 2 and 3).
Co-reporter:Xiaopei Xu, Yanxing Zhang, Zongxian Yang
Physics Letters A (12 February 2017) Volume 381(Issue 6) pp:671-678
Publication Date(Web):12 February 2017
DOI:10.1016/j.physleta.2016.12.002
•The electric field and Cu dopant effects on S poisoning feature of Ni are analyzed.•The present of large electric field can enhance S tolerance.•Cu dopant concentration affect the surface electronic structure of Ni.•100% Cu doping on surface Ni layer can mostly decrease the sulfur poison.The effects of sulfur poisoning on the (1 0 0), (1 1 0) and (1 1 1) surfaces of pure Ni and Cu/Ni alloy are studied in consideration of the effect of electric field. The effects of Cu dopants on the S poisoning characteristics are analyzed by the means of the density functional theory results in combination with thermodynamics data using the ab initio atomistic thermodynamic method. When the Cu concentration increases to 50% on the surface layer of the Cu/Ni alloy, the (1 1 0) surface becomes the most vulnerable to the sulfur poisoning. Ni with a copper skin can mostly decrease the sulfur poisoning effect. Especially under the electric field of 1.0 V/Å, the sulfur adsorption and phase transition temperature can be further reduced. We therefore propose that Ni surfaces with copper skin can be very effective to improve the resistance to sulfur poisoning of the Ni anode under high electric field.
Co-reporter:Zhansheng Lu, Peng Lv, Zongxian Yang, Shuo Li, Dongwei Ma and Ruqian Wu
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 25) pp:NaN16805-16805
Publication Date(Web):2017/06/02
DOI:10.1039/C7CP02430D
Single atom catalysts (SACs) have attracted broad research interest in recent years due to their importance in various fields, such as environmental protection and energy conversion. Here, we discuss the mechanisms of CO oxidation to CO2 over single Ag atoms supported on hexagonal boron-nitride sheets (Ag1/BN) through systematic van der Waals inclusive density functional theory (DFT-D) calculations. The Ag adatom can be anchored onto a boron defect (VB), as suggested by the large energy barrier of 3.12 eV for Ag diffusion away from the VB site. Three possible mechanisms (i.e., Eley–Rideal, Langmuir–Hinshelwood, and termolecular Eley–Rideal) of CO oxidation over Ag1/BN are investigated. Due to “CO-Promoted O2 Activation”, the termolecular Eley–Rideal (TER) mechanism is the most relevant one for CO oxidation over Ag1/BN and the rate-limiting reaction barrier is only 0.33 eV. More importantly, the first principles molecular dynamics simulations confirm that CO oxidation via the TER mechanism may easily occur at room temperature. Analyses with the inclusion of temperature and entropy effects further indicate that the CO oxidation via the TER mechanism over Ag1/BN is thermodynamically favorable in a broad range of temperatures.
Co-reporter:Zhaoming Fu, Mingyang Wang, Pengju Zuo, Zongxian Yang and Ruqian Wu
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 18) pp:
Publication Date(Web):
DOI:10.1039/C3CP55076A
Co-reporter:Zhansheng Lu, Dongwei Ma, Lin Yang, Xiaobing Wang, Guoliang Xu and Zongxian Yang
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 24) pp:
Publication Date(Web):
DOI:10.1039/C4CP00540F
Co-reporter:Yanxing Zhang, Zongxian Yang and Meng Wu
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 38) pp:NaN20536-20536
Publication Date(Web):2014/08/01
DOI:10.1039/C4CP02662D
The adsorption and dissociation of O2 on the core–shell M@Pd nanowires (M = 3d, 4d, 5d transition metals) are studied using the first-principles density functional method. Suitable core atoms are determined based on the stability of the core–shell NWs and their efficiency for O2 dissociation. With the consideration of the stability and cost, we found that Fe, Co, Ni, Cu, Ru, Ir atoms have lower price than Pd and favor at the core even with O adatom at the surface. The formed M@Pd core–shell nanowires are active for O2 dissociation with activation barriers no larger than 0.25 eV. The results may serve as a guide for the design of efficient Pd-based nanocatalysts for O2 dissociation.
Co-reporter:Xingli Chu, Zhaoming Fu, Shasha Li, Xilin Zhang and Zongxian Yang
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 19) pp:NaN13309-13309
Publication Date(Web):2016/04/12
DOI:10.1039/C6CP00194G
Density functional theory calculations are used to elucidate the catalytic properties of a Pt monolayer supported on a TiC(001) substrate (Pt/TiC) toward NO reduction. It is found that the compound system of Pt/TiC has a good stability due to the strong Pt–TiC interaction. The diverse dissociation paths (namely the direct dissociation mechanism and the dimeric mechanism) are investigated. The transition state searching calculations suggest that NO has strong diffusion ability and small activation energy for dissociation on the Pt/TiC. For NO reduction on the Pt/TiC surface, we have found that the direct dissociation mechanisms (NO + N + O → NO2 + N and NO + N + O → N2 + O + O) are easier with a smaller dissociation barrier than those on the Pt(111) surface; and the dimeric process (NO + NO → (NO)2 → N2O + O → N2 + O + O) is considered to be dominant or significant with even a lower energy barrier than that of the direct dissociation. The results show that Pt/TiC can serve as an efficient catalyst for NO reduction.
Co-reporter:Yanan Tang, Zongxian Yang and Xianqi Dai
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 48) pp:NaN16572-16572
Publication Date(Web):2012/06/25
DOI:10.1039/C2CP41441D
The catalytic oxidation of CO on Pt/X-graphene (X = “pri” for pristine- or “SV” for defective-graphene with a single vacancy) is investigated using the first-principles method based on density functional theory. In contrast to a Pt atom on pristine graphene, a vacancy defect in graphene strongly stabilizes a single Pt adatom and makes the Pt adatom more positively charged, which helps to weaken the CO adsorption and facilitates the O2 adsorption, thus enhancing the activity for CO oxidation and alleviating the CO poisoning of the platinum catalysts. The CO oxidation reaction on Pt/SV-graphene has a low energy barrier (0.58 eV) by the Langmuir–Hinshelwood (LH) reaction (CO + O2 → OOCO → CO2 + Oads) which is followed by the Eley–Rideal (ER) reaction with an energy barrier of 0.59 eV (CO + Oads → CO2). The results validate the reactivity of catalysts on the atomic-scale and initiate a clue for fabricating carbon-based catalysts with low cost and high activity.
Co-reporter:Zhansheng Lu, Peng Lv, Yanli Liang, Dongwei Ma, Yi Zhang, Wenjin Zhang, Xinwei Yang and Zongxian Yang
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 31) pp:NaN21870-21870
Publication Date(Web):2016/07/08
DOI:10.1039/C6CP02221A
A single metal atom stabilized on two dimensional materials (such as graphene and h-BN) exhibits extraordinary activity in the oxidation of CO. The oxidation of CO by molecular O2 on a single cobalt atom embedded in a hexagonal boron nitride monolayer (h-BN) is investigated using first-principles calculations with dispersion-correction. It is found that the single Co atom prefers to reside in a boron vacancy and possesses great stability. There are three mechanisms for CO oxidation: the traditional Eley–Rideal (ER) and Langmuir–Hinshelwood (LH) mechanisms and the termolecular Eley–Rideal (TER) mechanism proposed recently. Given the relatively small reaction barriers of the rate-limiting steps for the ER, LH and TER mechanisms (0.59, 0.55 and 0.41 eV, respectively), all three mechanisms are able to occur at low temperature. The current study may provide useful clues to develop low cost single atom catalysts.
Co-reporter:Yanxing Zhang, Zhaoming Fu, Shan Dong and Zongxian Yang
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 3) pp:NaN1040-1040
Publication Date(Web):2013/10/29
DOI:10.1039/C3CP53824A
The mechanisms for the resistance to sulfur poisoning at the triple phase boundary (TPB) of the Ni/yttria-stabilized zirconia (YSZ) system treated with Sn vapor are studied using the first-principles method based on density functional theory. Models with Sn dopant or adsorbate are proposed. It is found that the TPB model of the Ni/YSZ system with Sn dopant in Ni can to some extent restrain the diffusion of sulfur from the Ni part to the interface O vacancy by forcing the sulfur atom to diffuse along a longer path, which increases the time for which sulfur remains at the Sn doped Ni surface and allows the O ion to diffuse to the O vacancy at the interface. Once the O ion diffuses to the O vacancy, it forms interface O2−, which repels the sulfur adsorbate and eliminates the sulfur poisoning. However, as the barriers of sulfur diffusion to the vacancy are still small (0.25 eV or smaller), the Sn dopant in Ni does not efficiently eliminate the sulfur poisoning at the TPB. In contrast, the TPB model of the Ni/YSZ system with an Sn adatom on the Ni can form a physical barrier and prevent effectively sulfur diffusion to the O vacancy at the interface. The diffusion barriers are as large as 1.41 eV, which therefore eliminates the sulfur poisoning at the TPB. The results give a detailed dynamic picture of the mechanism of the high tolerance to sulfur poisoning of the Ni/YSZ anode at the TPB after the pre-exposures to metallic tin vapor.
Co-reporter:Xilin Zhang, Zhansheng Lu, Yanan Tang, Zhaoming Fu, Dongwei Ma and Zongxian Yang
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 38) pp:NaN20569-20569
Publication Date(Web):2014/07/29
DOI:10.1039/C4CP02873B
The mechanisms for the catalytic reduction of NO on the metal-free nitrogen doped graphene (NG) support are investigated using the density function theory (DFT) calculations both with and without the van der Waals (vdW) correction. The results indicate that the dimer mechanism is more facile than the direct decomposition mechanism. In the dimer mechanism, a three-step reaction is identified: (i) the coupling of two NO molecules into a (NO)2 dimer, followed by (ii) the dissociation of the (NO)2 dimer into N2O + Oad, then (iii) the O adatom is taken away easily by the subsequent NO. Once the NO2 is desorbed, the remaining N2O can be reduced readily by NO on NG. The reaction processes are also confirmed from the first principles molecular dynamics simulations. The results suggest that the NG is an efficient metal-free catalyst for catalytic reduction of NO.
Co-reporter:Xilin Zhang, Zhansheng Lu, Guoliang Xu, Tianxing Wang, Dongwei Ma, Zongxian Yang and Lin Yang
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 30) pp:NaN20013-20013
Publication Date(Web):2015/07/02
DOI:10.1039/C5CP01922B
Single-atom catalysts, especially with single Pt atoms, have attracted more and more attention due to their high catalytic activity for CO oxidation. The outstanding stability and catalytic activity of a single Pt atom supported on nitrogen doped graphene (Pt/NG) are revealed using first-principles calculations. We find that the stability of a Pt atom on the NG can be promoted by picking an appropriate doping configuration. The exceptionally stable Pt/NG catalyst exhibits excellent catalytic activity for CO oxidation via a new tri-molecular Eley–Rideal mechanism (2CO + O2 → OCO–OCO → 2CO2) with an energy barrier of 0.16 eV for the rate-limiting step of OCO–OCO dissociation, which is more preferable than the other two normal Langmuir–Hinshelwood and Eley–Rideal mechanisms.
