To the nature of the support effect in palladium-catalyzed aqueous-phase hydrogenation of maleic acid

Abstract

Influence of the support nature on catalytic properties of the supported Pd nanoparticles in liquid-phase (water, ethanol) hydrogenation of maleic acid (MA) to succinic one was extensively studied. Different oxides (SiO2, diatomites, WO3, Ta2O5, Nb2O5, V2O5, TiO2, CeO2, ZrO2, Ga2O3, In2O3, Cr2O3, Fe2O3, Al2O3), salts (CaF2, BaSO4) and carbon supports either with extremely low or high porosity were employed as the catalyst supports. XPS studies of the catalysts revealed no significant support-induced changes of the electronic state of the active component. For palladium on non-porous supports, its TOF values in MA hydrogenation turned to be constant in ethanol medium but varied with the support nature in water. In the case of porous supports, the TOFs diminished in both media and were governed by mean pore size and surface acidity of the supports. The dependence of TOF values on mean distance between adjacent Pd nanoparticles is also revealed. The catalytic results are explained by the presence of the electric double layer at the catalyst-solution interface, which affect its catalytic performance.