Thermal analysis of catalyst precursors. Part 1. Temperature-programmed evolution of hydrogen chloride during the reduction of supported ruthenium trichloride

Abstract

The evolution of hydrogen chloride during temperature-programmed reduction (TPR) of RuCl 3 supported on silica and alumina (0.5 and 5% Ru) and on titania (0.1, 0.6 and 5% Ru) has been followed in parallel with conventional TPR measurements of hydrogen uptake from 6% hydrogen in nitrogen. Reduction of Ru III to Ru o begins in every case at 330 ±10 K, but the breadth of the TPR peak increases with metal content so that the temperatures of the peak maxima also increase. There is evidence of more than one type of precursor species in the majority of cases. Hydrogen chloride evolution during TPR varies greatly with the support and with the metal content. With silica, it begins shortly after hydrogen uptake starts, and is virtually complete at 900 K. Hydrogen chloride is much more strongly retained on alumina, and is not completely eliminated even at 1073 K. With titania having 5% Ru as RuCl 3, some two-thirds of the total hydrogen chloride is evolved during the hydrogen uptake phase; as the metal content is decreased, the minimum temperature for its appearance increases. Hydrogen chloride is thought to be chiefly retained through reaction with surface hydroxyl groups on the supports; mechanisms of its elimination are discussed.