Hydrogen Adsorption and Absorption with Pd–Au Bimetallic Surfaces

Abstract

Pd−Au bimetallic catalysts have shown promising performance in numerous reactions that involve hydrogen. Fundamental studies of hydrogen interactions with Pd−Au surfaces could provide useful insights into the reaction mechanisms over Pd−Au catalysts, which may, in turn, guide future catalyst design. In this study, the interactions of hydrogen (i.e., adsorption, absorption, diffusion, and desorption) with Pd/Au(111) model surfaces were studied using temperature-programmed desorption (TPD) under ultrahigh-vacuum conditions. Our experimental results reveal Pd−Au bimetallic surfaces readily dissociate H 2 and yet also weakly bind H adatoms, properties that could be beneficial for catalytic reactions involving hydrogen. The presence of contiguous Pd sites, characterized by reflection−absorption infrared spectroscopy using CO as a probe molecule (CO-RAIRS), was found to be vital for the dissociative adsorption of H 2 at 77 K. The H adatom binds to Pd−Au alloy sites more strongly than to Au(111) but more weakly than to Pd(111) as indicated by its desorption temperature (∼200 K). With hydrogen exposure at slightly higher temperatures (i.e., 100−150 K), extension of a low-temperature desorption feature was observed, suggesting the formation of subsurface H atoms (or H absorption). Experiments using deuterium indicate that H−D exchange over the Pd−Au bimetallic surface obeys Langmuir−Hinshelwood kinetics and that H/D adatoms are mobile on the surface at low temperatures.

Preparation and structure-property relationships of supported trimetallic PdAuAg catalysts for the selective hydrogenation of acetylene

“…8. The peak below 100°C is attributed to the desorption of physically adsorbed hydrogen, and the peak around 200°C is ascribed to the desorption of chemisorbed hydrogen [60]. It is worth noting that the desorption temperature of chemisorbed H 2 in the m-PdAuAg 2 catalyst is about 20°C lower that of the c-PdAuAg 2 catalyst, indicating that H 2 dissociation occurs more easily in the m-PdAuAg 2 catalyst.…”

Determination of mass transfer resistances of fast reactions in three‐phase mechanically agitated slurry reactors

“…12,19,20 1. Dissociative and molecular chemisorption onto the catalyst surface A. Hydrogen dissociative chemisorption [21][22][23][24][25] At the equilibrium,…”

Effect of annealing in oxygen on alloy structures of Pd–Au bimetallic model catalysts

“…52,[56][57][58] The growth of the Pd overlayer on the Au(111) surface at 77 K has been suggested to obey a layer-by-layer mechanism. 52,[56][57][58] The growth of the Pd overlayer on the Au(111) surface at 77 K has been suggested to obey a layer-by-layer mechanism.…”

“…52,56,57 The Pd−Au surface was first heated to 500 K at 1 K/s to desorb any surface contaminants such as CO. After the sample had cooled to 77 K, an IR background scan was taken. 52,56,57 The Pd−Au surface was first heated to 500 K at 1 K/s to desorb any surface contaminants such as CO. After the sample had cooled to 77 K, an IR background scan was taken.…”