Shape-Selective Isopropylation of Aromatic Hydrocarbons over H-Mordenite in Supercritical Carbon Dioxide Medium
作者:Subhash Chandra Laha、Hiroaki Naiki、Kenichi Komura、Yoshihiro Sugi
DOI:10.1246/bcsj.20110214
日期:2011.11.15
The isopropylation of aromatic hydrocarbons isobutylbenzene (IBB), naphthalene (NP), and biphenyl (BP) was examined over H-mordenite (MOR), H-β (BEA), and H-Y (FAU) zeolites in supercritical carbon dioxide (sc-CO2) medium. MOR was only selective for the formation of the least bulky 4-isobutylcumene (4-IBC) in the isopropylation of IBB. In particular, the catalytic activity and selectivity for 4-IBC were enhanced by the dealumination of MOR; MOR with 110 of SiO2/Al2O3 ratio rendered the highest performance; however, the catalytic activity was decreased by further dealumination. Thermogravimetric analyses confirmed the reduction of coke formation on the catalysts in sc-CO2 medium, preventing the deactivation of MOR. Shape-selective formation of the least bulky isomers, 2,6-diisopropylnaphthalene (2,6-DIPN) and 4,4′-diisopropylbiphenyl (4,4′-DIPB), was also observed in the isopropylation of NP and BP over MOR in sc-CO2. sc-CO2 works as an efficient medium to access and/or replace substrates and their products to/from acidic sites in the MOR channels. In particular, the removal of coke precursors from acidic sites on the zeolite is enhanced by the sc-CO2 medium, resulting in decreased coke formation.
芳烃异丙基化反应中,异丁基苯(IBB)、萘(NP)和联苯(BP)在超临界二氧化碳(sc-CO2)介质中进行了对H-莫来石(MOR)、H-β(BEA)和H-Y(FAU)沸石的研究。MOR在对IBB的异丙基化反应中仅对形成体积最小的4-异丁基倍氯烷(4-IBC)具有选择性。特别地,通过去铝化处理MOR可以增强其对4-IBC的催化活性和选择性;具有110 SiO2/Al2O3比的MOR表现出最高的性能;然而,进一步的去铝化会降低催化活性。热重分析证实,在sc-CO2介质中催化剂上的焦炭形成减少,从而防止了MOR的失活。在对NP和BP的异丙基化反应中,也观察到在MOR上形状选择性形成体积最小的异构体2,6-二异丙基萘(2,6-DIPN)和4,4'-二异丙基联苯(4,4'-DIPB)。sc-CO2作为一种高效介质,可以访问和/或替代MOR通道中的酸性位点的底物及其产物。特别是,sc-CO2介质增强了从沸石酸性位点去除焦炭前驱体的能力,从而减少了焦炭的形成。