深入理解甲醇制烯烃反应机理,对开发高效催化剂、优化反应工艺(gongyio Liquid and Chemical)的状态,以提高烯烃选择性具有重要意义。本文对甲醇制烯烃反应机理发展历程进行了综述,对氧离子机理、碳正离子机理、自由基机理、卡宾机理在...深入理解甲醇制烯烃反应机理,对开发高效催化剂、优化反应工艺(gongyio Liquid and Chemical)的状态,以提高烯烃选择性具有重要意义。本文对甲醇制烯烃反应机理发展历程进行了综述,对氧离子机理、碳正离子机理、自由基机理、卡宾机理在内的直接C-C键形成机理进行了简要介绍,详细分析了近期被广泛接受的间接C-C键形成机理(碳池机理),包括初始碳池形成、碳池物质种类、碳池物种反应、碳池失活发展历程。简要介绍了烯烃二次反应机理。展开更多
Periodic density functional theory was applied to investigate the reaction mechanism for the methylation of toluene with methanol over HZSM-5.The results indicated that toluene could be methylated at its para,meta,ort...Periodic density functional theory was applied to investigate the reaction mechanism for the methylation of toluene with methanol over HZSM-5.The results indicated that toluene could be methylated at its para,meta,ortho and geminal positions via a concerted or stepwise pathway.For the concerted pathway,the calculated free energy barriers for the para,meta,ortho and geminal methylation reactions were 167,138,139 and 183 kJ/mol,respectively.For the stepwise pathway,the dehydration of methanol was found to be the rate-determining step with a free energy barrier of145 kj/mol,whereas the free energy barriers for the methylation of toluene at its para,meta,ortho and geminal positions were 127,105,106 and 114 kj/mol,respectively.Both pathways led to the formation of C8H11^＋ species as important intermediates,which could back-donate a proton to the zeolite framework via a reorientation process or form gaseous products through demethylation.Methane was formed via an intramolecular hydrogen transfer reaction from a ring carbon of the C8H11^＋ species to the carbon of the methyl group,with calculated energy barriers of 136,132 and134 kj/mol for the para,meta and ortho C8H11^＋ species,respectively.The calculated free energy barriers for the formation of para-,meta- and ortho-xylene indicated that the formation of the para-xylene had the highest energy barrier for both pathways.展开更多
In order to further improve the catalytic performance of zeolite catalyst for methanol to aromatics(MTA)technology, the double-tier SAPO-34/ZSM-5/quartz composite zeolite films were successfully synthesized via hydrot...In order to further improve the catalytic performance of zeolite catalyst for methanol to aromatics(MTA)technology, the double-tier SAPO-34/ZSM-5/quartz composite zeolite films were successfully synthesized via hydrothermal crystallization. The Si/Al ratio of SAPO-34 film was used as the only variable to study this material. The composite zeolite material with 0.6Si/Al ratio of SAPO-34 has the largest mesoporous specific surface area and the most suitable acid distribution. The catalytic performance for the MTA process showed that 0.6-SAPO-34/ZSM-5/quartz film has as high as 50.3% benzene-toluenexylene selectivity and 670 min lifetime. The MTA reaction is carried out through the path we designed to effectively avoid the hydrocarbon pool circulation of ZSM-5 zeolite, so as to improve the aromatics selectivity and inhibit the occurrence of deep side reactions to a great extent. The coke deposition behavior was monitored by thermogravimetric analysis and gas chromatograph/mass spectrometer, it is found that with the increase of Si/Al ratio, the active intermediates changed from low-substituted methylbenzene to high-substituted methylbenzene, which led to the rapid deactivation of the catalyst. This work provides a possibility to employ the synergy effect of composite zeolite film synthesizing anti-carbon deposition catalyst in MTA reaction.展开更多
The methanol-to-olefin induction reaction over the SAPO-34 was performed using a fluidized-bed system.We found that the whole induction period could be divided into three reaction stages.Further investigation of the r...The methanol-to-olefin induction reaction over the SAPO-34 was performed using a fluidized-bed system.We found that the whole induction period could be divided into three reaction stages.Further investigation of the reaction kinetics revealed that this induction reaction behavior was different from that over H-ZSM-5 catalyst.Compared with the H-ZSM-5,the generation of initial active centers is easier over SAPO-34 because of its limited diffusivity and the spatial confinement effect of the cages.However,the autocatalysis reaction stage is difficult over SAPO-34 because of the continuous formation of inactive methyladamantanes.展开更多
文摘深入理解甲醇制烯烃反应机理,对开发高效催化剂、优化反应工艺(gongyio Liquid and Chemical)的状态,以提高烯烃选择性具有重要意义。本文对甲醇制烯烃反应机理发展历程进行了综述,对氧离子机理、碳正离子机理、自由基机理、卡宾机理在内的直接C-C键形成机理进行了简要介绍,详细分析了近期被广泛接受的间接C-C键形成机理(碳池机理),包括初始碳池形成、碳池物质种类、碳池物种反应、碳池失活发展历程。简要介绍了烯烃二次反应机理。
基金supported by the National Natural Science Foundation of China(21446003)the Specialized Research Fund for the Doctoral Program of Higher Education(20130074110018)~~
文摘Periodic density functional theory was applied to investigate the reaction mechanism for the methylation of toluene with methanol over HZSM-5.The results indicated that toluene could be methylated at its para,meta,ortho and geminal positions via a concerted or stepwise pathway.For the concerted pathway,the calculated free energy barriers for the para,meta,ortho and geminal methylation reactions were 167,138,139 and 183 kJ/mol,respectively.For the stepwise pathway,the dehydration of methanol was found to be the rate-determining step with a free energy barrier of145 kj/mol,whereas the free energy barriers for the methylation of toluene at its para,meta,ortho and geminal positions were 127,105,106 and 114 kj/mol,respectively.Both pathways led to the formation of C8H11^＋ species as important intermediates,which could back-donate a proton to the zeolite framework via a reorientation process or form gaseous products through demethylation.Methane was formed via an intramolecular hydrogen transfer reaction from a ring carbon of the C8H11^＋ species to the carbon of the methyl group,with calculated energy barriers of 136,132 and134 kj/mol for the para,meta and ortho C8H11^＋ species,respectively.The calculated free energy barriers for the formation of para-,meta- and ortho-xylene indicated that the formation of the para-xylene had the highest energy barrier for both pathways.
基金supported by the National Natural Science Foundation of China (51974312, 51974308)the National Key Research & Development Program of China (2019YFE0100100)。
文摘In order to further improve the catalytic performance of zeolite catalyst for methanol to aromatics(MTA)technology, the double-tier SAPO-34/ZSM-5/quartz composite zeolite films were successfully synthesized via hydrothermal crystallization. The Si/Al ratio of SAPO-34 film was used as the only variable to study this material. The composite zeolite material with 0.6Si/Al ratio of SAPO-34 has the largest mesoporous specific surface area and the most suitable acid distribution. The catalytic performance for the MTA process showed that 0.6-SAPO-34/ZSM-5/quartz film has as high as 50.3% benzene-toluenexylene selectivity and 670 min lifetime. The MTA reaction is carried out through the path we designed to effectively avoid the hydrocarbon pool circulation of ZSM-5 zeolite, so as to improve the aromatics selectivity and inhibit the occurrence of deep side reactions to a great extent. The coke deposition behavior was monitored by thermogravimetric analysis and gas chromatograph/mass spectrometer, it is found that with the increase of Si/Al ratio, the active intermediates changed from low-substituted methylbenzene to high-substituted methylbenzene, which led to the rapid deactivation of the catalyst. This work provides a possibility to employ the synergy effect of composite zeolite film synthesizing anti-carbon deposition catalyst in MTA reaction.
文摘The methanol-to-olefin induction reaction over the SAPO-34 was performed using a fluidized-bed system.We found that the whole induction period could be divided into three reaction stages.Further investigation of the reaction kinetics revealed that this induction reaction behavior was different from that over H-ZSM-5 catalyst.Compared with the H-ZSM-5,the generation of initial active centers is easier over SAPO-34 because of its limited diffusivity and the spatial confinement effect of the cages.However,the autocatalysis reaction stage is difficult over SAPO-34 because of the continuous formation of inactive methyladamantanes.
