Influence of surface defects on activity and selectivity: A quantitative study of structure sensitivity of Pd catalysts for acetylene hydrogenation

Abstract

As one of the essential processes in the energy industry, acetylene hydrogenation reactions have been studied extensively in both experiment and theory. However, the fundamentals of structure sensitivity of acetylene hydrogenation over Pd catalysts are still debatable. Herein, a newly developed coverage-dependent microkinetic modelling is utilized to investigate the structure sensitivity of Pd catalysts. The key reaction kinetics are quantitatively examined; for example, a high ethylene activity of 3.92 s-1 and a low selectivity of 0.2 at 300 K are calculated. It is found that the Pd(211) surface is much more active than Pd(111), but exhibits a poor selectivity toward ethylene in contrast to Pd(111) that is intrinsically selective toward ethylene. The high activity of Pd(211) is primarily due to the decisive role of the coverage effect in reducing the reaction barrier of the rate-determining step, while the poor selectivity is a consequence of the inherently high chemisorption energy of ethylene. Furthermore, the ethylene selectivity is found to be more sensitive to the desorption barrier at low temperature. This work provides an atomic-scale understanding of the intrinsic selectivity of the acetylene hydrogenation embodied in different Pd structures.