Co-reporter:Xiaolong Liu, Yueying Chu, Qiang Wang, Weiyu Wang, Chao Wang, Jun Xu, Feng Deng
Solid State Nuclear Magnetic Resonance 2017 Volume 87(Volume 87) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.ssnmr.2017.05.002
•The solid state synthesis method was applied to ITQ-13 zeolites.•The factors affecting the crystallization of pure silica ITQ-13 and Ge-ITQ-13 were explored.•The detailed configurations of the Ge-D4R units in ITQ-13 were determined.•The SiOSi bonds in the D4R units connecting the layers of ITQ-13 framework were identified.Well-crystallized Ge-free and Ge-ITQ-13 were successfully obtained by solid state synthesis method. The Ge/Si ratio and the water content that are the two important factors in the synthesis of germanosilicate zeolites were explored for the formation of ITQ-13. The effect of the mineralizing agents (NH4F and NH4Cl) on the ITQ-13 synthesis was investigated as well. The obtained pure silica ITQ-13 and Ge-ITQ-13 were characterized by one- and two-dimensional solid- state NMR techniques. One-dimensional (1D) 19F MAS, 1H→29Si CP/MAS and 19F→29Si CP/MAS NMR spectroscopy evidenced the formation of pure Si-D4R (double four ring) and Ge-D4R units, with the latter being generated by substitution of Si atom from the former units. The detailed configurations of the Ge-D4R units in ITQ-13 was revealed by two-dimensional (2D) 29Si{19F} HETCOR NMR spectroscopy. With the help of theoretical calculations on the 19F and 29Si NMR chemical shifts, six types of D4R units were determined. The formation of the specific D4R unit confirms the structural directing roles of Ge atom and F ions in the formation of the D4R units in zeolite framework. The identification of the SiOSi bonds in the D4R units that connects the layers of ITQ-13 framework provided rationale for the high stability of the ITQ-13 in the degermanation treatment.Download high-res image (288KB)Download full-size image
Co-reporter:Chao Wang, Xianyong Sun, Jun Xu, Guodong Qi, Weiyu Wang, Xingling Zhao, Wenzheng Li, Qiang Wang, Feng Deng
Journal of Catalysis 2017 Volume 354(Volume 354) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.jcat.2017.08.003
•The distribution and reactivity of retained hydrocarbon pool species varies with reaction time and contact time.•The reaction is accelerated by the accumulation of hydrocarbon pool species.•The product selectivity is related to different hydrocarbon pool species.•A cyclopentenyl cations-based cycle is proposed.•The distribution of hydrocarbon pool species in the catalyst bed dictates the reaction pathways.The hydrocarbon pool (HP) species in methanol-to-olefins (MTO) reactions over zeolite H-ZSM-5 were investigated by solid-state NMR spectroscopy and GC–MS. The distribution and reactivity of retained HP species such as carbocations and methylbenzenes (MBs) were found to evolve with reaction time and their positions in the catalyst bed. The underlying mechanism of the typical S-shaped methanol conversion curve was revealed, in which the dominating reaction route was found to be dependent on the formation and reactivity of different HP species that were varied at different reaction time. During the induction period, cyclopentenyl cations served as the precursor to MBs and exhibited higher reactivity than the latter. The reaction was accelerated by the accumulation of alkenes and further enhanced by consequent involvement of the cyclopentenyl cations and aromatics, which eventually led to a steady state reaction. The interconversions of the reaction cycles based on alkenes, cyclopentenyl cations, and MBs were proposed for the formation of light olefins. The co-catalysis of HP species in the MTO reactions showed that the cyclopentenyl cations and alkenes favored propene formation, while the light MBs such as xylene and triMB facilitated ethene formation. Within the catalyst bed, both cyclopentenyl cations and MBs were dominantly formed in the upper catalyst layers. The experiments indicated that both cyclopentenyl cations and alkenes maintained high reactivity throughout the catalytic bed, while MBs exhibited high reactivity only in the upper catalyst position.Download high-res image (94KB)Download full-size image
Co-reporter:Weiyu Wang;Yanxi Zhao;Guodong Qi;Qiang Wang;Chao Wang;Jinlin Li;Feng Deng
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 14) pp:9349-9353
Publication Date(Web):2017/04/05
DOI:10.1039/C7CP00352H
We demonstrated the facet dependence of pairwise addition of hydrogen in heterogeneous catalysis over Pd nanocrystal catalysts via NMR using para-hydrogen-induced polarization.
Co-reporter:Dr. Chao Wang;Dr. Qiang Wang; Jun Xu;Dr. Guodong Qi;Pan Gao;Weiyu Wang;Yunyun Zou;Dr. Ningdong Feng;Dr. Xiaolong Liu ; Feng Deng
Angewandte Chemie 2016 Volume 128( Issue 7) pp:2553-2557
Publication Date(Web):
DOI:10.1002/ange.201510920
Abstract
Hydrocarbon-pool chemistry is important in methanol to olefins (MTO) conversion on acidic zeolite catalysts. The hydrocarbon-pool (HP) species, such as methylbenzenes and cyclic carbocations, confined in zeolite channels during the reaction are essential in determining the reaction pathway. Herein, we experimentally demonstrate the formation of supramolecular reaction centers composed of organic hydrocarbon species and the inorganic zeolite framework in H-ZSM-5 zeolite by advanced 13C–27Al double-resonance solid-state NMR spectroscopy. Methylbenzenes and cyclic carbocations located near Brønsted acid/base sites form the supramolecular reaction centers in the zeolite channel. The internuclear spatial interaction/proximity between the 13C nuclei (associated with HP species) and the 27Al nuclei (associated with Brønsted acid/base sites) determines the reactivity of the HP species. The closer the HP species are to the zeolite framework Al, the higher their reactivity in the MTO reaction.
Co-reporter:Dr. Chao Wang;Dr. Qiang Wang; Jun Xu;Dr. Guodong Qi;Pan Gao;Weiyu Wang;Yunyun Zou;Dr. Ningdong Feng;Dr. Xiaolong Liu ; Feng Deng
Angewandte Chemie 2016 Volume 128( Issue 7) pp:
Publication Date(Web):
DOI:10.1002/ange.201511880
Co-reporter:Dr. Chao Wang;Dr. Qiang Wang; Jun Xu;Dr. Guodong Qi;Pan Gao;Weiyu Wang;Yunyun Zou;Dr. Ningdong Feng;Dr. Xiaolong Liu ; Feng Deng
Angewandte Chemie International Edition 2016 Volume 55( Issue 7) pp:
Publication Date(Web):
DOI:10.1002/anie.201511880
Co-reporter:Dr. Chao Wang;Dr. Qiang Wang; Jun Xu;Dr. Guodong Qi;Pan Gao;Weiyu Wang;Yunyun Zou;Dr. Ningdong Feng;Dr. Xiaolong Liu ; Feng Deng
Angewandte Chemie International Edition 2016 Volume 55( Issue 7) pp:2507-2511
Publication Date(Web):
DOI:10.1002/anie.201510920
Abstract
Hydrocarbon-pool chemistry is important in methanol to olefins (MTO) conversion on acidic zeolite catalysts. The hydrocarbon-pool (HP) species, such as methylbenzenes and cyclic carbocations, confined in zeolite channels during the reaction are essential in determining the reaction pathway. Herein, we experimentally demonstrate the formation of supramolecular reaction centers composed of organic hydrocarbon species and the inorganic zeolite framework in H-ZSM-5 zeolite by advanced 13C–27Al double-resonance solid-state NMR spectroscopy. Methylbenzenes and cyclic carbocations located near Brønsted acid/base sites form the supramolecular reaction centers in the zeolite channel. The internuclear spatial interaction/proximity between the 13C nuclei (associated with HP species) and the 27Al nuclei (associated with Brønsted acid/base sites) determines the reactivity of the HP species. The closer the HP species are to the zeolite framework Al, the higher their reactivity in the MTO reaction.
Co-reporter:Guodong Qi, Qiang Wang, Yueying Chu, Jun Xu, Anmin Zheng, Jihu Su, Jiafu Chen, Chao Wang, Weiyu Wang, Pan Gao and Feng Deng
Chemical Communications 2015 vol. 51(Issue 44) pp:9177-9180
Publication Date(Web):27 Apr 2015
DOI:10.1039/C5CC02601F
The structure and reactivity of a room temperature stable zinc carbonyl complex in Zn-modified H-ZSM-5 zeolite were revealed by solid-state NMR spectroscopy.
Co-reporter:Chao Wang;Xianfeng Yi;Dr. Jun Xu;Dr. Guodong Qi;Pan Gao;Weiyu Wang;Dr. Yueying Chu;Dr. Qiang Wang;Dr. Ningdong Feng;Dr. Xiaolong Liu;Dr. Anmin Zheng ;Dr. Feng Deng
Chemistry - A European Journal 2015 Volume 21( Issue 34) pp:12061-12068
Publication Date(Web):
DOI:10.1002/chem.201501355
Abstract
The methanol to olefins conversion over zeolite catalysts is a commercialized process to produce light olefins like ethene and propene but its mechanism is not well understood. We herein investigated the formation of ethene in the methanol to olefins reaction over the H-ZSM-5 zeolite. Three types of ethylcyclopentenyl carbocations, that is, the 1-methyl-3-ethylcyclopentenyl, the 1,4-dimethyl-3-ethylcyclopentenyl, and the 1,5-dimethyl-3-ethylcyclopentenyl cation were unambiguously identified under working conditions by both solid-state and liquid-state NMR spectroscopy as well as GC-MS analysis. These carbocations were found to be well correlated to ethene and lower methylbenzenes (xylene and trimethylbenzene). An aromatics-based paring route provides rationale for the transformation of lower methylbenzenes to ethene through ethylcyclopentenyl cations as the key hydrocarbon-pool intermediates.
Co-reporter:Xiumei Wang, Jun Xu, Guodong Qi, Chao Wang, Qiang Wang and Feng Deng
Chemical Communications 2014 vol. 50(Issue 77) pp:11382-11384
Publication Date(Web):04 Aug 2014
DOI:10.1039/C4CC03621B
Using in situ solid-state NMR spectroscopy we show that CO can act as an alkylating reagent and react with benzene to produce toluene over a Zn/H-ZSM-5 zeolite. In the alkylation reaction, CO provides the methyl group of toluene via a methoxy intermediate.
Co-reporter:Chao Wang ;Dr. Yueying Chu ;Dr. Anmin Zheng;Dr. Jun Xu;Dr. Qiang Wang;Pan Gao;Guodong Qi; Yanjun Gong;Dr. Feng Deng
Chemistry - A European Journal 2014 Volume 20( Issue 39) pp:
Publication Date(Web):
DOI:10.1002/chem.201483972
Co-reporter:Chao Wang ;Dr. Yueying Chu ;Dr. Anmin Zheng;Dr. Jun Xu;Dr. Qiang Wang;Pan Gao;Guodong Qi; Yanjun Gong;Dr. Feng Deng
Chemistry - A European Journal 2014 Volume 20( Issue 39) pp:12432-12443
Publication Date(Web):
DOI:10.1002/chem.201403972
Abstract
Over zeolite H-ZSM-5, the aromatics-based hydrocarbon-pool mechanism of methanol-to-olefins (MTO) reaction was studied by GC-MS, solid-state NMR spectroscopy, and theoretical calculations. Isotopic-labeling experimental results demonstrated that polymethylbenzenes (MBs) are intimately correlated with the formation of olefin products in the initial stage. More importantly, three types of cyclopentenyl cations (1,3-dimethylcyclopentenyl, 1,2,3-trimethylcyclopentenyl, and 1,3,4-trimethylcyclopentenyl cations) and a pentamethylbenzenium ion were for the first time identified by solid-state NMR spectroscopy and DFT calculations under both co-feeding ([13C6]benzene and methanol) conditions and typical MTO working (feeding [13C]methanol alone) conditions. The comparable reactivity of the MBs (from xylene to tetramethylbenzene) and the carbocations (trimethylcyclopentenyl and pentamethylbenzium ions) in the MTO reaction was revealed by 13C-labeling experiments, evidencing that they work together through a paring mechanism to produce propene. The paring route in a full aromatics-based catalytic cycle was also supported by theoretical DFT calculations.
Co-reporter:Guodong Qi ; Jun Xu ; Jihu Su ; Jiafu Chen ; Xiumei Wang ;Feng Deng
Journal of the American Chemical Society 2013 Volume 135(Issue 18) pp:6762-6765
Publication Date(Web):April 25, 2013
DOI:10.1021/ja400757c
We report the low-temperature catalytic reactivity of Zn+ ions confined in ZSM-5 zeolite toward CO oxidation. In situ DRIFT and ESR spectroscopy demonstrated that molecular O2 is readily activated by Zn+ ion to produce O2– species at room temperature (298 K) via facile electron transfer between Zn+ ion and O2 and that the formation of the active O2– species is responsible for the high activity of the ZnZSM-5 catalyst toward CO oxidation.
Co-reporter:Xiumei Wang, Jun Xu, Guodong Qi, Bojie Li, Chao Wang, and Feng Deng
The Journal of Physical Chemistry C 2013 Volume 117(Issue 8) pp:4018-4023
Publication Date(Web):February 6, 2013
DOI:10.1021/jp310872a
Alkylation of benzene with methane was studied under oxidization condition over ZnZSM-5 zeolites by using in situ solid-state NMR spectroscopy and GC-MS analysis. The experimental results indicate that the alkylation reaction occurs with selective formation of toluene at temperatures of 523–623 K using O2 or N2O as the oxidant. Using 13C isotope labeled reactants, the conversions of methane and benzene were independently monitored, and their respective role in the reaction was determined. It was found by NMR spectroscopy that methane was first activated into methoxy species and zinc methyl intermediates. As an electrophilic agent, the methyl group of methoxy species could directly attack phenyl ring to produce toluene via electrophilic substitution reaction, while the zinc methyl species was not directly involved in the alkylation reaction. However, the similar nature of zinc methyl species (Zn–CH3) to organozinc compounds allowed the facile oxidization of zinc methyl species (Zn–CH3) into methoxy species. As confirmed by GC-MS experiments, methane exclusively provided the methyl group of toluene product while benzene afforded the phenyl ring. Experimental results also indicated that neither methane nor benzene alone could generate toluene.
Co-reporter:Bojie Li, Jun Xu, Bing Han, Xiumei Wang, Guodong Qi, Zhengfeng Zhang, Chao Wang, and Feng Deng
The Journal of Physical Chemistry C 2013 Volume 117(Issue 11) pp:5840-5847
Publication Date(Web):March 1, 2013
DOI:10.1021/jp400331m
Carbonylation of dimethyl ether (DME) with CO over H-mordenite (H-MOR) zeolites from 423 to 573 K was studied by in-situ 13C solid-state NMR spectroscopy. The reaction was monitored separately in the 8-membered ring (MR) and in the 12-MR channels of the zeolite under identical conditions. The experimental results indicated that both 8-MR and 12-MR channels were capable of producing methyl acetate product but with remarkably different selectivities. At low-reaction temperature, surface acetyl species (CH3CO−) as stabilized acylium cation was solely identified in the 8-MR channels, which was confirmed by measurement of its characteristic chemical shift anisotropy (CSA) parameters. Additionally, the intermediate role of the acetyl species was evidenced by the fact that it could react with DME to form methyl acetate. This demonstrated the theoretically proposed specificity of the 8-MR channels for generation and stabilization of the acetyl intermediate which was considered as the rate-limiting step of carbonylation reaction. While in the 12-MR channels, the acetyl intermediate was not found during the reaction, and formation of hydrocarbons was favored. The absence of acetyl intermediate might account for the lower reactivity of the 12-MR channels to generate methyl acetate product.
Co-reporter:Xiumei Wang;Guodong Qi;Dr. Jun Xu;Bojie Li;Chao Wang ;Dr. Feng Deng
Angewandte Chemie International Edition 2012 Volume 51( Issue 16) pp:3850-3853
Publication Date(Web):
DOI:10.1002/anie.201108634
Co-reporter:Xiumei Wang, Jun Xu, Guodong Qi, Chao Wang, Weiyu Wang, Pan Gao, Qiang Wang, Xiaolong Liu, Ningdong Feng, Feng Deng
Journal of Catalysis (January 2017) Volume 345() pp:228-235
Publication Date(Web):1 January 2017
DOI:10.1016/j.jcat.2016.11.009
•The mechanism of ethane co-reaction with CO to produce carboxylic acids is revealed.•Surface zinc–ethyl and methoxy species are identified as key intermediates.•The zinc–ethyl species shows reactivity similar to that of organometallic compounds.•Redox conditions affect the activation of ethane and CO.•Bifunctionality of ZnZSM-5 zeolite is essential for the co-reaction.The carbonylation reaction of ethane with CO to produce carboxylic acid was studied over zinc-modified ZSM-5 zeolite (denoted as Zn/ZSM-5) using in situ solid-state NMR spectroscopy. 13C-isotope-labeled reactants were alternatively used to monitor the co-reaction at temperatures of 298–623 K. The NMR experimental results demonstrated that surface zinc-ethyl and methoxy species were formed and identified as key intermediates in the reaction. The reactivity of these intermediates was further explored under both oxidizing and reducing conditions by adding O2 and H2 into the reaction system. It was found that ethane was initially activated into zinc–ethyl species that show reactivity similar to that of organometallic compounds such as diethyl zinc. The interaction of zinc–ethyl species with CO2 resulting from the oxidation of CO produces propanoic acid. Side products such as aromatics were formed by dehydrogenation of zinc–ethyl species via the formed ethene intermediates. We also found that hydrogenolysis of ethane occurred and gave rise to byproduct methane, which led to the formation of acetic acid by carboxylation with CO2. Additionally, CO was converted into surface methoxy species, which could react with CO to produce acetic acid via a Koch-type carbonylation reaction.Download high-res image (77KB)Download full-size image
Co-reporter:Guodong Qi, Qiang Wang, Yueying Chu, Jun Xu, Anmin Zheng, Jihu Su, Jiafu Chen, Chao Wang, Weiyu Wang, Pan Gao and Feng Deng
Chemical Communications 2015 - vol. 51(Issue 44) pp:NaN9180-9180
Publication Date(Web):2015/04/27
DOI:10.1039/C5CC02601F
The structure and reactivity of a room temperature stable zinc carbonyl complex in Zn-modified H-ZSM-5 zeolite were revealed by solid-state NMR spectroscopy.
Co-reporter:Weiyu Wang, Jun Xu, Yanxi Zhao, Guodong Qi, Qiang Wang, Chao Wang, Jinlin Li and Feng Deng
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 14) pp:NaN9353-9353
Publication Date(Web):2017/01/19
DOI:10.1039/C7CP00352H
We demonstrated the facet dependence of pairwise addition of hydrogen in heterogeneous catalysis over Pd nanocrystal catalysts via NMR using para-hydrogen-induced polarization.
Co-reporter:Xiumei Wang, Jun Xu, Guodong Qi, Chao Wang, Qiang Wang and Feng Deng
Chemical Communications 2014 - vol. 50(Issue 77) pp:NaN11384-11384
Publication Date(Web):2014/08/04
DOI:10.1039/C4CC03621B
Using in situ solid-state NMR spectroscopy we show that CO can act as an alkylating reagent and react with benzene to produce toluene over a Zn/H-ZSM-5 zeolite. In the alkylation reaction, CO provides the methyl group of toluene via a methoxy intermediate.
