Activation of the Highly-Selective Pd₁₁Bi₂Se₂ during the Semi-Hydrogenation of Acetylene

Abstract

Pd₁₁Bi₂Se₂ was prepared as single-phase material and used in an unsupported state as catalyst in the semi-hydrogenation of acetylene in ethylene excess. After an initial inactive time-period, Pd₁₁Bi₂Se₂ activated and showed high acetylene conversion and selectivity towards ethylene at 473 K. In addition, after the initial inactive state, the compound revealed high stability during 100 h time on stream. At 80 % conversion the selectivity to ethylene is higher than 90 %. Post-catalysis investigations by powder X-ray diffraction (p-XRD) and X-ray photoelectron spectroscopy (XPS) exclude the formation of intermetallic hydrides, decomposition, and the presence of elemental palladium. Furthermore, comparison of XPS before and after catalysis revealed the reason of the inactive state of the intermetallic compound during the first hours of catalysis. An initial surface layer of bismuth oxide is reduced and re-incorporated into the intermetallic compound. This material change is responsible for the initially observed activation of Pd₁₁Bi₂Se₂ during the semi-hydrogenation of acetylene.