Low-temperature isotopic exchange of molecular hydrogen over films of hafnium and dysprosium alloys with copper, silver, and gold

Catalytic properties of films of hafnium and dysprosium alloys with the metals of Group 1B, i.e., Cu, Ag, and Au, were examined in the model reaction H-2 + D-2 = 2HD. The reaction was studied at 66.6 Pa over the temperature range 77-170 K, where the isotopic exchange follows the Eley mechanism. The specific catalytic activity (K-sp) Of the Dy alloys with Group 1B metals increased, while for hafnium alloys, K-sp decreased as compared to Individual Dy and Hf, respectively. As a result, K-sp values for all alloys were close to each other, except for that of Dy-Ag. This fact was accounted for by the acceptor character of Dy, resulting from the incomplete 4f level of this rare-earth element, unlike Hf. The difference in the electronegativity of Group 1B metals had no effect on the catalytic activity of their alloys with Dy and Hf. It was shown that electronegativity plays a minor role in the formation of intermetallic compounds (IMC). On the basis of the kinetic data, the energy of interatomic bonds in IMC alloys is determined. The reasons for the variation of the activation energy of low-temperature exchange, resulting from alloying Dy and Hf with the Group 1B metals, are discussed.