经PPh3修饰的Rh/SiO2催化剂的吸附-脱附性能

 应用程序升温技术研究了氢甲酰化反应物CO,H2和C2H4在经PPh3修饰的Rh/SiO2(PPh3-Rh/SiO2)催化剂上的吸附-脱附行为. CO-TPD结果显示, Rh/SiO2催化剂在348, 398和525 K处有3个脱附峰, PPh3-Rh/SiO2催化剂仅在368 K处出现脱附峰,表明催化剂的吸附性能发生了明显变化. 采用原位红外光谱研究了PPh3-Rh/SiO2催化剂上CO的吸附态. 结果表明, 2040 cm-1处吸收峰归属于PPh3修饰的Rh粒子上线式吸附的CO. 这种吸附态既不同于Rh/SiO2多相催化剂表面Rh粒子上的CO吸附态,也不同于相应均相催化剂中的羰基配位态. TPD和FT-IR结果表明,在低压下PPh3-Rh/SiO2催化剂对氢甲酰化反应已具有相当的催化性能.

Adsorption-Desorption Behavior of Rh/SiO2 Catalyst Modified with PPh3 Ligand

The temperature-programmed desorption(TPD) was employed to investigate the adsorption-desorption behavior of CO,H_2 and C_2H_4 on the Rh/SiO_2 catalyst modified with PPh_3 ligand(PPh_3-Rh/SiO_2).The result showed that there were three CO desorption peaks at 348,398 and 525 K on Rh/SiO_2,while only one CO desorption peak at 368 K was observed on PPh_3-Rh/SiO_2.Analogously,only one desorption peak of H_2 and C_2H_4 appeared on PPh_3-Rh/SiO_2.These results implied that the adsorption-desorption behavior of CO,H_2 and C_2H_4 on PPh_3-Rh/SiO_2 was different from that on Rh/SiO_2.The adsorption states of CO on PPh_3-Rh/SiO_2 were studied using in situ FT-IR technique.The result revealed that the IR absorption peak at(2?040) cm~(-1),corresponding to the CO-TPD desorption peak at 368 K on PPh_3-Rh/SiO_2,was assigned to the linear CO state on the surface PPh_3-modified Rh particles.This adsorption-desorption behavior of CO on PPh_3-Rh/SiO_2 was not only different from that of Rh/SiO_2,but also distinguished from that of carbonyl on homogeneous catalysts.The TPD and FT-IR results indicated that the PPh_3-Rh/SiO_2 had catalytic performance for hydroformylation at lower pressure.