Al2O3 microrods supported Pd catalysts for semi-hydrogenation of acetylene: Acidic properties tuned reaction kinetics behaviors

The acidic properties of the support show remarkable effects on Pd-catalyzed reactions including the semi-hydrogenation of acetylene. Herein, Al2O3 microrods with distinct acidic properties are synthesized as the supports for Pd catalysts to address the acidic properties dominated kinetics behavior of acetylene hydrogenation. The acidic properties of Al2O3 microrods decrease with the calcination temperature, in the order of Al2O3-1400 < Al2O3-1200 < Al2O3-800, in which the numbers denote the temperature for calcination process. Catalytic performance show that the hydrogenation activities of the corresponding Pd catalysts increase by Pd/Al2O3-1400 < Pd/Al2O3-800 < Pd/Al2O3-1200, while the selectivities to the target ethylene decrease by Pd/Al2O3-1400 > Pd/Al2O3-1200 > Pd/Al2O3-800. A quantitative analysis combined with structure characterizations are further performed to elucidate the underlying origin of such acidic-property dependent performances. It is demonstrated that the different electronic structures of Pd caused by the acidic properties contribute to distinct adsorption properties for the reactant and the target products, which can be quantitatively described by the entropy of activation (Delta S*).