Selective Hydrogenation Of Acetylene Over Pd/ZnAl₂O₄

Selective hydrogenation of acetylene is one of the challenging areas in catalyst design.Reaction mechanisms and structure-function studies have been reported on several working catalysts.Here we report our studies on Pd/ZnAl2o4 single atom catalysts which are highly active and selective for selective hydrogenation of acetylene compared with PdZn nanoparticles.In this work,Pd/Zn catalysts were prepared on ZnAl2O4 spinel by incipient wetness impregnation method.The influence of reduction conditions,Pd loading,and support on the catalyst performance was studied.Characterization of catalysts led to the conclusion that the formation of by-product green oil does not negatively impact catalyst activity,instead promotes the activity through hydrogen transfer mechanism during the induction period.The effect of ethylene in feedstock on selective hydrogenation of acetylene and the role of green oil in the induction period were further investigated.Ethylene can act as a hydrogen-transfer medium to transport the dissociated hydrogen ions on Pd to green oil,creating new reaction sites where acetylene adsorbed is hydrogenated mainly to ethylene.The excelled reactivity and superior selectivity can both be achieved in the late induction period,only if the amount of PdZn catalysts employed is controlled not in excess to cause the complete conversion of acetylene.Hence,the uncovered mechanism associated with the induction period can be used as a novel approach to generate more efficient catalysts.Our studies on PdZn catalysts provide new insight on the design of Pd catalysts for selective acetylene hydrogenation with improved Pd atom economy.