The Kinetics of H2–D2 Exchange over Pd, Cu, and PdCu Surfaces

Abstract

PdCu alloy membranes are promising candidates for hydrogen separation from H2S-containing gas mixtures. Dissociative H2 adsorption and associative desorption are important steps in the process of hydrogen transport across PdCu membranes; however, the kinetics of H2 adsorption and desorption on PdCu surfaces are not well understood. In this work, the kinetics and energetics of H2 adsorption and desorption on Pd, Cu, and PdCu surfaces are investigated by microkinetic analysis of H2–D2 exchange (H2 + D2 → 2HD) over fixed beds of Pd, Cu, Pd70Cu30, and Pd47Cu53 foils at near-ambient pressure and temperatures in the range 300–900 K. The rate of H2–D2 exchange over Cu, which is the least active H2–D2 exchange catalyst used in this study, is limited by the rate of H2 adsorption due to the large activation barrier to dissociative H2 adsorption on Cu (ΔEads⧧ = 0.54 ± 0.06 eV). The Cu content of the PdCu alloys and the crystal structures of the Pd-hydride phases (α- and β-PdH) and of Pd47Cu53 (body-centered cubic an...