氧化硅载体对Ir-Re双金属的结构及其催化甘油氢解的影响

Effect of silica chemistry on structure of Ir-Re bimetallic catalysts and catalysis for glycerol hydrogenolysis

采用3种氧化硅载体KIT-6、G-6和FS制备了Ir-Re双金属催化剂,并应用于甘油选择性氢解制备1,3-丙二醇,采用TEM、XRD、H2-TPR、CO-DRIFTS和NH3-TPD等手段详细表征了催化剂结构,并探讨其构效关系。研究结果表明:3种催化剂表面的Ir-Re双金属催化剂均形成了Ir-Re合金结构,合金化程度为Ir-Re/KIT-6>Ir-Re/FS>Ir-Re/G-6;载体表面羟基含量显著影响Ir-Re纳米粒子的分散度及其与载体的相互作用。Ir-Re/FS的金属分散度最高,甘油氢解的初始活性最高但稳定性最差;而具有良好合金结构的Ir-Re/KIT-6在甘油氢解中表现出良好的氢解活性和最高的1,3-丙二醇选择性。

As an alternative process to petroleum based processes, hydrogenolysis of biomass-derived glycerol to 1, 3-propanediol（1, 3-PD） can be effectively catalyzed by bimetallic Ir-Re catalyst. However it still suffers from low selectivity of 1, 3-PD and low reaction rate. With extension of our previous study, silica was selected as a promising catalyst support to investigate the role of silica chemistry in the Ir-Re catalyst for glycerol hydrogenolysis. Bimetallic Ir-Re catalysts supported on three kinds of silica supports of KIT-6, G-6 and FS were prepared for glycerol hydrogenolysis to produce desired 1, 3-PD. The structure of catalysts were characterized by varied techniques of N2 adsorption-desorption, transmission electron microscopy（TEM）, X-ray diffraction（XRD）, H2 temperature-programmed reduction（H2-TPR）, in-situ CO adsorption diffuse reflectance infrared Fourier transform spectroscopy（DRIFTS） and temperature-programmed desorption（TPD） of ammonia. Also, the structure-activity relationship of the catalysts was discussed. It showed that the bimetallic catalysts on three silica supports possessed alloy structure of Ir-Re on surface, of which the order of alloy degree follows Ir-Re/KIT-6Ir-Re/FSIr-Re/G-6. Hydroxyl groups on support surfaces significantly affected the degree of metal dispersion and the interaction between active metallic components and support. The Ir-Re/FS catalyst possessed the highest degree of metal dispersion and exhibited the best initial activity but the worst stability for glycerol hydrogenolysis, while the Ir-Re/KIT-6 catalyst featured the highest degree of alloy thus showed excellent catalytic performance and the highest selectivity to 1, 3-PD of desired product.