XAFS study of tin modification of supported palladium catalyst for 1,3-butadiene hydrogenation in the presence of 1-butene

Alumina-supported palladium catalyst, which is active for the hydrogenation of 1,3-butadiene, was modified by tin using various tin precursors. The structure of modified catalysts was studied by XAFS and TPR. Before modification, palladium on alumina existed in an electron-deficient hydride state, which was revealed by a shift to a higher Pd K-edge energy in XANES and by an increased Pd-Pd distance in EXAFS fitting. However, tin modification caused the palladium edge energy to decrease to the value of zero valent palladium metal and destroyed the Pd ensembles by making Pd-Sn bonds, irrespective of the nature of tin precursor. This was responsible for the increased 1-butene selectivity in the hydrogenation of 1,3-butadiene in the presence of 1-butene. A carbonaceous species was formed in the catalyst modified with an organic tin precursor, while the inorganic tin modification produced a tin oxide-like species in addition to the formation of Sn-Pd bonds. (C) 2000 Academic Press.