Highly selective semi-hydrogenation of acetylene over porous gold with twin boundary defects

Abstract

Porous gold prepared by dealloying Al2Au (PG(Al2Au)) exhibits much higher catalytic performance in the semi-hydrogenation of acetylene than gold powder or porous gold prepared from Ag3Au (PG(Ag3Au)). The selectivity of PG(Al2Au) for ethylene production is above 95% in the temperature range 350–523 K. The high catalytic performance correlates with the presence of a high density of twinning defects in the fcc lattice of PG(Al2Au). In contrast, such defects are barely detectable in PG(Ag3Au) or gold powder using powder X-ray diffraction measurements. On the stepped {211} surfaces of PG (Al2Au) twinning defects create long closed-packed rows of highly reactive low-coordinated atoms denoted as W-chains, which are responsible for the observed high activity and selectivity during acetylene semi-hydrogenation. Ab initio density functional theory (DFT) calculations confirm that these low-coordinated Au sites (CN = 6 or 5) systematically created by twinning defects facilitate hydrogen adsorption, dissociation and subsequent hydrogenation reactions. On the basis of these experimental and DFT results, we propose a reaction scenario for semi-hydrogenation of acetylene over PG(Al2Au).