原位红外光谱法研究沸石催化剂上苯与乙烯烷基化反应

Study on Alkylation of Benzene with Ethylene over βZeolite Catalyst by in situ IR

采用原位红外光谱技术 ,于 1 2 0～ 2 0 0℃下 ,对沸石催化剂上苯与乙烯烷基化的反应机理进行了探讨 .结果表明 ,乙烯、苯和乙苯吸附在催化剂的同一类活性中心上 ,它们之间存在着竞争吸附 ,乙烯的吸附能力较苯和乙苯强 ;吸附的乙烯可与吸附的苯或乙苯发生烷基化反应 .催化剂上已吸附乙烯时 ,由于乙烯在强吸附位上吸附较牢 ,苯和乙苯不易吸附 ,烷基化反应难以进行 ,且吸附的乙烯间可发生反应 .乙烯与乙苯的反应较丙烯与异丙苯的反应难于进行 .

The alkylation of benzene with ethylene over β zeolite catalyst was studied by using in situ IR method at 120, 160, 200 ℃. Benzene or ethylbenzene and ethylene were injected sequentially or vice versa into in situ IR cell and the changes of IR spectra were investigated. The alkylation mechanism has been referred as follows: Adsorbed ethylene may reacts with adsorbed benzene or ethylbenzene. They are adsorbed competitively at the same kind of sites. Ethylene adsorbs more strongly than benzene and ethylbenzene. At lower temperature, such as 120～160 ℃, when the sites of catalyst are occupied by ethylene, benzene and ethylbenzene are hardly to be adsorbed at the sites, therefore alkylation can not take place. Adsorbed ethylene can react with each other, and replace adsorbed benzene and ethylbenzene, so reaction occurs. At 200 ℃, benzene and ethylbenzene can replace a part of adsorbed ethylene and reaction can take place. By comparison with the reaction of cumene with propylene, the reaction of ethylbenzene with ethylene takes place more difficult at the same temperature.