摘要
对负载在硅铝胶上的钯催化剂分别在175℃(LTR)和400℃(HTR)下进行还原预处理。采用原位IR谱研究了He和H_2气氛中苯在载体和负载钯催化剂上的吸附和反应行为。结果表明,对苯氢化反应,载体SiO_2-Al_2O_3没有活性,Pd/SiO_2-Al_2O_3中LTR的活性比HTR的高。在70℃下反应比25℃下快。文中提出了可能存在两类活性中心的看法。
In situ FT-IR spectroscopy was employed to characterize adsorbed benzene species under steady state flow reaction in the presence of H2, and also under equilibrium adsorption in the presence of He. The IR spectra were recorded over the range of 4000 to 1000 cm-1.
The effect of low or high temperature reduction pretretment ( LTR or HTR) of Pd/SiO2-Al2O3 on the activity of benzene hydrogenation was strongly dependent on the reduction temperatures. The present work showed that the catalytic activity of support ( SiO2-Al2O3 ) for the hydrogenation of benzene is negligible, and the catalytic activity of the LTR Pd/SiO2-Al2O3 was higher than that of the HTR one. As the temperature increased from 25 to 70℃, the rate of hydrogenation was increased remarkably. According to IR experimental data we considered that benzene adsorbed on Pd/SiO2-Al2O3 have two configurations: one bent,most probably, in the molecular plane of benzene, second configuration bent in side-on bonding. Only the second configuration participated in the hydrogenation reaction, and we also found that the first configuration would transfer into second configuration during the reaction. Correspondently, there may be two kinds of active sites on the Pd/SiO2-Al2O3 surface. On the relatively more active center, due to the deformation of benzene ring the band at 1479 cm-1 was weakened, and the band at 1389 cm-1 was strengthened.
出处
《分子催化》
EI
CAS
CSCD
1991年第2期147-153,共7页
Journal of Molecular Catalysis(China)
