H2‐D2 Exchange Kinetics in the Presence of H2S over Pd4S, Pd70Cu30, and Pd47Cu53 Surfaces

H2S retards H2 transport across Pd membranes used for H2 separation by forming a Pd4S scale that has both low H2 dissociation activity and low H-atom permeability. As hydrogen purification membranes, alloys such as Pd70Cu30 and Pd47Cu53 are attractive alternatives to pure Pd due to their resistance to formation of bulk sulfides. Nonetheless, exposure to H2S can decrease the permeability of Pd70Cu30 and Pd47Cu53 membranes, presumably by poisoning the catalytic activity of their surfaces for H2 dissociation. In this work, the effect of H2S on H2 dissociation on Pd4S, Pd70Cu30, and Pd47Cu53 surfaces is investigated by microkinetic analysis of H2-D2 exchange kinetics over Pd4S, Pd70Cu30, and Pd47Cu53 surfaces in the presence of varying concentrations of H2S at nearambient H2+D2 pressure. We show that the rate of H2-D2 exchange over all three surfaces is significantly suppressed when H2S is added to H2/D2/Ar reactant mixtures and that the suppression of H2-D2 exchange increases with increasing H2S concentration. Microkinetic analysis of the H2-D2 exchange kinetics reveals that H2S decreases the rate of H2-D2 exchange by two distinct mechanisms: (1) increasing the intrinsic barrier to H2 dissociation and (2) blocking H2 dissociation sites.