The synthesis of anisole by vapor phase methylation of phenol with methanol over activated alumina（AA） supported catalysts was investigated in a fixed bed reactor. KH2PO4/AA gave the best performance among the eight...The synthesis of anisole by vapor phase methylation of phenol with methanol over activated alumina（AA） supported catalysts was investigated in a fixed bed reactor. KH2PO4/AA gave the best performance among the eight tested catalysts. The catalyst was prepared by loading KH2PO4 on AA and then calcining at the optimized temperature of 700 °C for 8 h. In the vapor phase reaction, the level of anisole yield（LAY） has a maximum at 400–450 °C when the temperature varied from 300 to 500°C, which decreased slightly with increasing WHSV and increased distinctly with increasing mole fraction of methanol. On comparing O‐methylation and C‐methylation of phenol, a low temperature,high WHSV（short residence time）, and a low methanol concentration over the KH2PO4/AA catalyst with higher K contents were found to increase anisole selectivity by O‐methylation of phenol. The reaction routes to the major products and the catalytic mechanism were suggested, and a ‘K‐acid＇bifunctional process may be a critical factor to the formation of anisole.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
基金supported by the National Natural Science Foundation of China(51476180)the National Basic Research Program of China(973Program2014CB744304)~~
文摘The synthesis of anisole by vapor phase methylation of phenol with methanol over activated alumina（AA） supported catalysts was investigated in a fixed bed reactor. KH2PO4/AA gave the best performance among the eight tested catalysts. The catalyst was prepared by loading KH2PO4 on AA and then calcining at the optimized temperature of 700 °C for 8 h. In the vapor phase reaction, the level of anisole yield（LAY） has a maximum at 400–450 °C when the temperature varied from 300 to 500°C, which decreased slightly with increasing WHSV and increased distinctly with increasing mole fraction of methanol. On comparing O‐methylation and C‐methylation of phenol, a low temperature,high WHSV（short residence time）, and a low methanol concentration over the KH2PO4/AA catalyst with higher K contents were found to increase anisole selectivity by O‐methylation of phenol. The reaction routes to the major products and the catalytic mechanism were suggested, and a ‘K‐acid＇bifunctional process may be a critical factor to the formation of anisole.
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.
