Supported Ni catalysts on three mesoporous SiO2 supports (i.e., SBA-15, MCM-41, and HMS) were prepared using a solid-state reaction between Ni(NO3)2 and organic template-occluded mesoporous SiO2. For comparison, supported Ni catalysts on mesoporous SiO2 synthesized by the conventional impregnation method were also included. The catalysts were characterized by scanning electron microscopy, X-ray diffraction, UV–vis diffuse reflectance spectroscopy, N2 adsorption, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, transmission electron microscopy, and transmission electron microscopy–energy-dispersive X-ray. The catalytic properties of the catalysts were evaluated using gas-phase catalytic hydrodechlorination of 1,2-dichloroethane. The results showed that upon grinding Ni(NO3)2 with template-occluded mesoporous SiO2, strong coordination between Ni2+ and dodecylamine was identified in the Ni(NO3)2–HMS system. Additionally, the results of H2 temperature-programmed reduction revealed that NiO in calcined NiO/HMS was reduced at higher temperature than those in calcined NiO/SBA-15 and NiO/MCM-41, reflecting the presence of a strong interaction between NiO and mesoporous SiO2 in NiO/HMS. Consistently, the average particle sizes of metallic Ni were found to be 2.7, 3.4, and 9.6 nm in H2-reduced Ni/HMS, Ni/SBA-15, and Ni/MCM-41, respectively, indicative of a much higher Ni dispersion in Ni/HMS. For the catalytic hydrodechlorination of 1,2-dichloroethane, Ni/MCM-41 synthesized by the solid-state reaction method exhibited a catalytic activity similar to that prepared by the impregnation method, while higher catalytic activities were observed on Ni/HMS and Ni/SBA-15 than on their counterparts prepared by the impregnation method. Furthermore, a higher conversion was identified on Ni/HMS than on Ni/SBA-15 and Ni/MCM-41, highlighting the importance of template type for the preparation of highly dispersed metal catalysts on mesoporous SiO2.Keywords: 1,2-dichloroethane; gas-phase catalytic hydrodechlorination; solid-state reaction; supported Ni catalysts; template-occluded mesoporous SiO2;

•Au@Pd/TiO2 catalysts were prepared by two-step photodeposition.•Pd was atomically dispersed on Au surface in the catalysts.•Au@Pd(0.049)/TiO2 had a highest TOF for catalytic oxidation of benzyl alcohol.In this study, bimetallic Au@Pd/TiO2 catalysts with an Au loading amount of 0.94 wt.% and Pd loading amounts varying from 0.017 to 0.13 wt.% were prepared using a two-step photocatalytic deposition method, and the solvent-free aerobic oxidation of benzyl alcohol was investigated on the catalysts. For comparison, monometallic Pd/TiO2 with a Pd loading amount of 0.048 wt.% (denoted as Pd(0.048)/TiO2) and Au/TiO2 with a Au loading amount of 0.94 wt.% were also prepared. The catalysts were characterized using X-ray diffraction, transmission electron microscope, UV–Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, infrared spectroscopy of CO adsorption, and energy dispersive spectroscopy. Characterization results suggested that in the bimetallic catalysts Pd atoms were preferentially deposited on exposed Au surface and core-shell structured Au@Pd particles with atomically dispersed Pd as the shell were formed. Additionally, monomeric and paired Pd sites were dominated in bimetallic catalysts with Pd contents below 0.066 wt.%, and increasing Pd deposition amount led to gradual development of Pd ensembles. For the solvent-free aerobic oxidation of benzyl alcohol, Au/TiO2 had negligible catalytic activity, while Pd(0.048)/TiO2 exhibited marked conversion of benzyl alcohol. As for bimetallic catalysts, the conversion of benzyl alcohol increased with the increase of Pd deposition amount from 0.017 to 0.049 wt.%, whereas kept constant when Pd deposition amount was further increased to 0.13 wt.%. Accordingly, Au@Pd(0.049)/TiO2 had a highest turnover frequency value of 21961 h−1 for the oxidation of benzyl alcohol among the test bimetallic catalysts.Download high-res image (130KB)Download full-size image

Pd catalysts supported on graphene and N-doped graphene (GN-1, GN-2 and GN-3) with varied N-doping amounts were prepared using the deposition–precipitation method, and liquid phase catalytic hydrodechlorination (HDC) of 2,4-dichlorophenol (2,4-DCP) was investigated over these catalysts. The catalysts were characterized by X-ray diffraction, elementary analysis, N2 adsorption–desorption isotherms, transmission electron microscopy, and X-ray photoelectron spectroscopy. Characterization results showed that graphene could be successfully doped by N using the heat treatment method with melamine as precursor, and N doping amounts were determined to be 5.7, 8.6 and 11.3% for GN-1, GN-2 and GN-3, respectively. Additionally, Pd2+/Pd0 ratios and Pd dispersions in the Pd/GN catalysts were much higher than those in Pd/graphene. For a similar Pd loading, the Pd dispersion of Pd/GN first increased and then decreased with the increase of N-doping amount, and the highest Pd dispersion was observed on Pd(2.9)/GN-2. Accordingly, GN supported Pd catalysts exhibited much higher catalytic activities than Pd/graphene, the catalytic reaction first increased and then decreased slightly in activity with the increase of nitrogen doping amount, and the highest activity was identified on Pd(2.9)/GN-2. Moreover, the dechlorination of 2,4-DCP over supported Pd catalysts proceeded via both a stepwise and concerted pathway, and the concerted pathway became predominant upon N doping.

Palladium catalysts supported on Al2O3, activated carbon (AC), SiO2 and CeO2 were prepared using the impregnation and deposition–precipitation methods. The liquid phase catalytic hydrodechlorination of diclofenac on the catalysts was investigated, and the toxicity of the original and treated diclofenac solutions was evaluated using Daphnia magna. Characterization results indicated that the Pd catalyst supported on CeO2 had a higher Pd dispersion than those supported on Al2O3, AC and SiO2. The binding energy of Pd 3d5/2 in Pd/CeO2 was higher than Pd/Al2O3 with a similar Pd loading amount. Additionally, for Pd/CeO2 prepared by the deposition–precipitation method the binding energy of Pd 3d5/2 slightly decreased with the Pd loading amount. As for catalytic diclofenac reduction, Pd/SiO2 exhibited a nearly negligible catalytic activity, whereas diclofenac concentration decreased by 100, 86, and 29% within 50 min of reaction on Pd/CeO2, Pd/Al2O3, and Pd/AC, respectively, indicative of a catalytic activity order of Pd/CeO2 > Pd/Al2O3 > Pd/AC > Pd/SiO2. The hydrodechlorination of diclofenac on Pd/CeO2 could be well described using the Langmuir–Hinshelwood model. Diclofenac hydrodechlorination processed via a combined stepwise and concerted pathway, and increasing Pd loading amount in Pd/CeO2 favoured the concerted pathway. In comparison with original diclofenac, catalytic hydrodechlorination of diclofenac led to markedly decreased toxicity to Daphnia magna.

A novel TiO2 supported core–shell (Pd@Ag) bimetallic catalyst was fabricated via the sequential photodeposition method. The Ag shell effectively blocks the high coordination sites on the Pd core, and therefore pronouncedly enhances the ethylene selectivity for the catalytic hydrogenation of acetylene in excess ethylene.

The presence of pharmaceutical antibiotics in aquatic environments poses potential human health and ecological risks. We synthesized ordered micro- and mesoporous carbons, and further conducted batch experiments to systematically examine their adsorption properties toward three antibiotics, sulfamethoxazole, tetracycline, and tylosin, in aqueous solution. In comparison, nonporous graphite, single-walled carbon nanotubes, and two commercial microporous activated carbons were included as additional adsorbents. Adsorption of low-sized sulfamethoxazole was stronger on the activated carbons than on other carbonaceous adsorbents resulting from the pore-filling effect; in contrast, due to the size-exclusion effect adsorption of bulky tetracycline and tylosin was much lower on the activated carbons, especially for the more microporous one, than on the synthesized carbons. After normalizing for adsorbent surface area, adsorption of tetracycline and tylosin on the synthesized carbons was similar to that on nonporous graphite, reflecting complete accessibility of the adsorbent surface area in adsorption. Additionally, compared with other porous adsorbents the synthesized carbons showed faster adsorption kinetics of tetracycline and tylosin, which was attributed to their regular-shaped, open and interconnected three-dimensional pore structure. The findings indicate that template-synthesized micro- and mesoporous carbons are promising adsorbents for the removal of antibiotics, particularly, the bulky and flexible-structured compounds, from aqueous solution.

Humic acid is generally considered as one of ubiquitous pollutants in surface and ground water. In this study, aminopropyl functionalized SBA-15 adsorbents with varied aminopropyl contents were prepared via the co-condensation method and characterized by elemental analysis, X-ray diffraction, N2 adsorption, IR spectroscopy and zeta-potential measurements. The adsorption behaviors of the adsorbents for humic acid were investigated using batch experiments and adsorption kinetic tests. SBA-15 exhibited low humic acid adsorption amount. In contrast, substantially enhanced humic acid adsorption was observed over aminopropyl functionalized SBA-15 adsorbents. Humic acid adsorption over the adsorbents could be well described using Langmuir adsorption model and the maximum humic acid adsorption capacities were found to be 8.5, 72.5 and 117.6 mg g−1 for SBA-15, APTS-SBA-15-5% and APTS-SBA-15-10%, respectively. In addition, increasing solution pH led to monotonically decreased humic acid adsorption over aminopropyl functionalized SBA-15. Humic acid adsorption process over functionalized SBA-15 could be well described using pseudo-second-order kinetic model and HA adsorption was controlled by both external and intraparticle diffusion based on the fitting results using Weber–Morris model.

Nitrate and benzene are commonly identified contaminants in groundwater. In this study, a series of TiO2 supported Pt–Cu bimetallic catalysts were prepared and photocatalytic nitrate reduction in the presence of benzene was investigated. The catalysts were characterized by XRD, N2 adsorption, TEM, X-ray photoelectron spectroscopy and IR spectroscopy of CO adsorption. The results showed that Pt–Cu alloy was formed in TiO2 supported bimetallic catalysts except for the bimetallic catalyst with TiO2 calcined at 700 °C as the support. In addition, higher alloy dispersion and smaller metal particle sizes could be obtained on TiO2 calcined at 300 °C compared to those calcined at 500 and 700 °C. For photocatalytic nitrate reduction in the presence of benzene, nitrate was mainly converted to ammonia or nitrite over Pt/TiO2 or Cu/TiO2, respectively, whereas TiO2 supported Pt–Cu bimetallic catalysts exhibited a considerable N2 selectivity for photocatalytic nitrate reduction. The catalytic activity and N2 selectivity of the supported bimetallic catalyst was strongly dependent on TiO2 calcination temperature, Pt/Cu ratio and metal loading amount. The bimetallic catalyst with TiO2 calcined at 300 °C as the support, Pt loading amount of 5 wt.% and Pt/Cu ratio of 4/1 displayed higher N2 selectivity compared with other bimetallic catalysts. The present results demonstrate the selective nitrate reduction over Pt–Cu/TiO2 catalysts with benzene as the hole scavenger, highlighting the validity of simultaneous removal of aqueous nitrate and benzene by photocatalysis.

Selenite (SeO32−) is an oxyanion of environmental significance due to its toxicity when taken in excess. In the present study, a hybrid adsorbent (HFO-201) was prepared by irreversibly impregnating hydrated ferric oxide (HFO) nanoparticles within a commercial available anion-exchange resin (D-201), and its adsorption towards selenite from water was investigated in batch and column tests. HFO-201 exhibited improved sorption selectivity toward selenite as compared to the polymeric anion exchanger D-201. Two possible adsorption interactions were responsible for selenite removal by HFO-201, the electrostatic interaction from the ammonium groups bound to the D-201 matrix, and the formation of inner-sphere complexes between the loaded HFO nanoparticles and selenite. In a wide pH range (i.e., 3–8), increasing solution pH was found to result in a decrease of selenite removal on HFO-201. Adsorption isotherms fit the Freundlich model well, and selenite adsorption increased with increasing ambient temperature, indicating its endothermic nature. Column adsorption tests suggested that satisfactory removal of selenite from 2 mg/L to less than 0.01 mg/L could be achieved by HFO-201 even in the presence of the commonly encountered anionic competition at greater concentration, with the treatment capacity of ∼1200 bed volume (BV) per run, while that for D-201 was only less than 30 BV under otherwise identical conditions. Furthermore, the exhausted HFO-201 was amenable to efficient in situ regeneration with a binary NaOH–NaCl solution.

A microporous carbon with very high specific surface area and narrow pore size distribution was synthesized using Y zeolite as a template. The structural, porosity, and surface characteristics of the material were investigated by elemental analysis, N2 adsorption, powder X-ray diffraction, and Raman spectroscopy. The batch adsorption technique was performed to assess adsorption of three monoaromatic compounds, phenol, 1,3-dichlorobenzene, and 1,3-dinitrobenzene, on the synthesized carbon. Nonporous graphite, single-walled carbon nanotubes, and two commercial microporous activated carbons were also included as comparative adsorbents. The synthesized microporous carbon showed extraordinarily high adsorption affinity (comparable or higher than activated carbons and carbon nanotubes) for the three adsorbates, and very fast adsorption/desorption kinetics (equilibrium reached less than 3 h) and complete adsorption reversibility for phenol. These adsorption properties were attributed to the large hydrophobic surface area and the regular-shaped, open and interconnected three-dimensional pore structure of the synthesized microporous carbon. Additionally, with normalization of adsorbent surface area adsorption of a bulky solute, 1,2,4,5-tetrachlorobenzene, was prominently higher on the synthesized carbon than on the activated carbons, due to alleviated size exclusion effect. Findings of the present work highlight the potential of using zeolite-templated carbons as effective adsorbents for removal of hydrophobic organic contaminants in water treatment.

ZrO2 supports with different properties were prepared, and the hydrogenation of aqueous nitrate catalyzed by ZrO2 supported Pd−Cu bimetallic catalysts was investigated. The results showed that ZrO2 support calcined at 573 K was unstable during the preparation of the bimetallic catalyst. Increasing calcination temperature led to the increase of particle size of ZrO2 support. In addition, using ZrO2 calcined at 973 K as the support resulted in the increase of metal particle sizes and the increased content of bimetallic ensembles at the expense of monometallic Pd. The bimetallic catalyst with ZrO2 calcined at 773 K as the support exhibited higher catalytic activity and N2 selectivity for the reduction of aqueous nitrate as compared to the bimetallic catalyst with ZrO2 calcined at 573 or 973 K as the support. The activity and selectivity of ZrO2 supported bimetallic catalysts for nitrate reduction also depended on the Pd/Cu ratio. Decreasing Pd/Cu ratio led to the decrease of the amount of monometallic Pd sites and to the increase of the content of Pd−Cu ensembles. The bimetallic catalyst with Pd/Cu ratio of 4/1 showed the optimum activity and N2 selectivity for the reduction of aqueous nitrate.

Mesoporous carbon CMK-3 was prepared using a mesoporous silica SBA-15 as the template, and the adsorption of aqueous direct yellow 12 (DY-12) on CMK-3 and commercial powdered activated carbon (PAC) was studied. X-ray diffraction, N2 adsorption, and transmission electron microscopy results demonstrate that CMK-3 with ordered structure is a true replica of its template SBA-15. CMK-3 and PAC have comparable pore volumes, whereas CMK-3 mainly consists of mesopores, and PAC contains both micropores and mesopores. The adsorption of DY-12 over CMK-3 and PAC could be well-described by the Langmuir isotherm model. The maximum adsorption amounts of CMK-3 and PAC for DY-12 at 25 °C were found to be (303.0 and 161.3) mg·g−1, respectively, indicative of a substantially higher adsorption capacity of CMK-3 compared to that of PAC. DY-12 adsorption processes over CMK-3 and PAC obey pseudosecond-order kinetics. For DY-12 adsorption on CMK-3, the rate constants were (2.82·10−4, 4.43·10−5, and 9.77·10−6) g·mg−1·s−1 at initial DY-12 concentrations of (17.7, 44.3, and 145) mg·dm−3, respectively. In the case of PAC, the rate constants were found to be (1.78·10−5, 9.8·10−7, and 6.7·10−7) g·mg−1·s−1 at initial concentrations of (17.7, 44.6, and 339) mg·dm−3, respectively, reflecting much lower adsorption rates over PAC than those over CMK-3. Furthermore, the intraparticle diffusion of DY-12 over CMK-3 and PAC was elucidated using the Weber−Morris model. The present results clearly verify the importance of mesopores in the adsorption of aqueous DY-12.

Bromate is recognized as an oxyhalide disinfection byproduct in drinking water. In this study, supported noble metal (Pd, Pt) catalysts with different supports of SiO2, Al2O3 and activated carbon (AC) were prepared and the catalytic hydrogenation of aqueous bromate was first investigated. Characterization results showed the isoelectric points (IEPs) of Pd/SiO2 and Pd/Al2O3 catalysts were around 2.0 and 8.0, respectively, whereas the IEP of Pd/AC was much lower than 2.0. In comparison with Pd/SiO2 and Pd/AC, Pd/Al2O3 exhibited a substantially higher catalytic activity at pH 5.6 for bromate reduction due to the electrostatic attractive interaction between the bromate ion and the catalyst. Moreover, bromate with an initial concentration of 0.39 mM was removed by 80.2% over Pt/Al2O3 and nearly 100% over Pd/Al2O3 after reaction for 2 h, indicative of a higher catalytic activity of Pd/Al2O3. For Pd/Al2O3, the bromate reduction followed the Langmuir–Hinshelwood model, reflecting an adsorption controlled reduction mechanism. Increasing Pd loading amount resulted in enhanced bromate reduction. In addition, the bromate reduction was found to be strongly pH-dependent and enhanced reduction rate could be achieved at low pH. In the presence of coexisting anions (Cl−, Br− and SO42−) the bromate reduction was suppressed, wherein SO42− exhibited the most marked inhibition effect, attributed to competitive adsorption for active surface sites. The present results indicate that catalytic hydrogenation can be used as a potential treatment technique for the removal of bromate in drinking water.

•Ag-Pd/ZrO2 with trace Pd was prepared using the co-impregnation method.•Isolated Pd sites dominated in the Ag-Pd/ZrO2 catalysts.•Ag-Pd/ZrO2 with trace Pd exhibited high ethylene selectivities.Gas-phase catalytic hydrodechlorination is one of the most efficient and economic methods for the removal of volatile chlorinated alkanes. Novel Ag-based bimetallic catalysts with high ethylene selectivities were prepared using the co-impregnation method. The catalysts were characterized by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and IR spectroscopy of CO adsorption. The catalytic performance, in particular the selectivities of the catalysts was examined on hydrodechlorination of 1,2-dichloroethane. Two supported monometallic catalysts (Ag/ZrO2 and Pd/ZrO2) were included as comparative catalysts. Ag/ZrO2 exhibited a low 1,2-dichloroethane coversion and high chloroethylene selectivity for the gas-phase hydrodechlorination of 1,2-dichloroethane, while Pd/ZrO2 had a high conversion and ethane selectivity. In contrast to monometallic catalysts, Ag-Pd/ZrO2 with trace Pd had substantially enhanced ethylene selectivity, and the bimetallic catalyst with a Pd loading amount of 0.099 wt.% (denoted as Ag(1.99)-Pd(0.099)/ZrO2) exhibited nearly 100% ethylene selectivity. The excellent ethylene selectivity can be attributed to the highly dispersed metallic Pd in Ag particles of Ag(1.99)-Pd(0.099)/ZrO2 as evidenced by the IR spectra of CO adsorption. The findings in this study indicate that Ag-Pd/ZrO2 with trace Pd can be used as promising catalyts for highly effective and selective hydrodechlorination of volatile chlorinated alkanes.Download high-res image (174KB)Download full-size image

Lv et al. [L. Lv, J. He, M. Wei, D.G. Evans, X. Duan, Factors influencing the removal of fluoride from aqueous solution by calcined Mg–Al–CO3 layered double hydroxides, J. Hazard. Mater. B 133 (2006) 119–128] previously investigated the fluoride removal using calcined Mg–Al–CO3 layered double hydroxides (CLDH) as the sorbents. The present comment further discusses the mechanism of fluoride adsorption onto CLDH.

Supported Pd catalysts on ordered mesoporous carbon (OMC) and activated carbon (AC) were prepared and their catalytic behavior for the liquid phase catalytic hydrodechlorination (HDC) of 2,4-dichlorophenol was investigated. In comparison with Pd/AC, Pd particles of Pd/OMC were effectively confined in the mesopores of OMC, resulting in high Pd dispersion and Pd2+ content. Accordingly, Pd/OMC exhibited higher catalytic activity than Pd/AC. Moreover, increasing catalyst reduction temperature lowered the catalytic activities and favored stepwise HDC of 2,4-dichlorophenol.Download full-size imageResearch highlights“research highlights should consist of only 85 characters per bullet point, includingspaces. however, the research highlights provided for this item exceed the maximum requirement.kindly provide the necessary corrections. for more information, please see guide forauthors.”► Pd/OMC has higher Pd dispersion and Pd2+ content than Pd/AC. ► Pd/OMC displays higher catalytic activity than Pd/AC for the liquid phase catalytic HDC of 2,4-DCP. ► Increasing catalyst reduction temperature lowers the catalytic activities of the catalysts and favors stepwise HDC of 2,4-DCP.

Selenite (SeO32−) is an oxyanion of environmental significance due to its toxicity when taken in excess. In the present study, a hybrid adsorbent (HFO-201) was prepared by irreversibly impregnating hydrated ferric oxide (HFO) nanoparticles within a commercial available anion-exchange resin (D-201), and its adsorption towards selenite from water was investigated in batch and column tests. HFO-201 exhibited improved sorption selectivity toward selenite as compared to the polymeric anion exchanger D-201. Two possible adsorption interactions were responsible for selenite removal by HFO-201, the electrostatic interaction from the ammonium groups bound to the D-201 matrix, and the formation of inner-sphere complexes between the loaded HFO nanoparticles and selenite. In a wide pH range (i.e., 3–8), increasing solution pH was found to result in a decrease of selenite removal on HFO-201. Adsorption isotherms fit the Freundlich model well, and selenite adsorption increased with increasing ambient temperature, indicating its endothermic nature. Column adsorption tests suggested that satisfactory removal of selenite from 2 mg/L to less than 0.01 mg/L could be achieved by HFO-201 even in the presence of the commonly encountered anionic competition at greater concentration, with the treatment capacity of ∼1200 bed volume (BV) per run, while that for D-201 was only less than 30 BV under otherwise identical conditions. Furthermore, the exhausted HFO-201 was amenable to efficient in situ regeneration with a binary NaOH–NaCl solution.

A novel TiO2 supported core–shell (Pd@Ag) bimetallic catalyst was fabricated via the sequential photodeposition method. The Ag shell effectively blocks the high coordination sites on the Pd core, and therefore pronouncedly enhances the ethylene selectivity for the catalytic hydrogenation of acetylene in excess ethylene.