Pd-Cu双金属催化剂上加氢反应的仲氢诱导超极化研究

Hydrogenation Reaction on Pd-Cu Bimetallic Catalysts:A Parahydrogen-Induced Polarization Study

本文通过多相催化-仲氢诱导超极化(HET-PHIP)核磁共振(NMR)技术研究了Pd-Cu/SiO_2双金属催化剂上丙炔选择性加氢反应.首先利用等体积浸渍法和连续浸渍法合成了一系列不同Pd/Cu比例和形貌的Pd-Cu/SiO_2双金属催化剂.通过ALTADENA(Adiabatic Longitudinal Transport After Dissociation Engenders Net Alignment)方法发现,催化剂的Pd/Cu比例和形貌均对PHIP的极化效率有较大影响.随着Pd-Cu双金属催化剂中Pd比例的增大,PHIP极化效率降低,同时反应活性增强.在同Pd/Cu比例下,相对于等体积浸渍法,连续浸渍法制备的层叠形貌催化剂具有较弱的极化效率以及较强的催化活性,这是由于催化剂表面暴露出的Pd数量增多,导致催化活性增强;同时单个Pd集簇表面积增大,使得氢原子移动范围扩大,从而造成极化效率降低.

Hydrogenation reaction of propyne on Pd-Cu bimetallic catalysts was studied using the heterogeneous parahydrogen-induced polarization(PHIP)nuclear magnetic resonance(NMR)technique.Incipient-wetness impregnation and sequential impregnation were used to prepare Pd-Cu/SiO2 bimetallic catalysts with different composition and morphology.With the ALTADENA(Adiabatic Longitudinal Transport After Dissociation Engenders Net Alignment)method,it was observed that both the composition and morphology of the bimetallic catalysts had significant influence on the efficiency of PHIP.The catalysts with lower Pd/Cu atom ratio had lower activity but higher polarization efficiency.Compared to isometric impregnation method,the palladium atoms in the Pd-Cu/SiO2 catalyst synthesized with the sequential impregnation method mostly stayed on the surface of bimetallic nanoparticles,generating larger Pd ensembles and leading to higher catalytic activity and lower polarization efficiency.