Hydrogenolysis of alkanes. Part 2.—Hydrogenolysis of n-butane over variously treated Ru/TiO2 catalysts

Abstract

The hydrogenolysis of n-butane has been studied on 1 and 5% ruthenium/titania catalysts pretreated in hydrogen at various temperatures and in air at 623 K. Increasing the temperature of reduction of impregnated ruthenium trichloride from 623 to 758 K gives an increase in activity attributed to removal of chloride, but the low activities associated with a strong metal–support interaction (SMSI) are not found until a reduction temperature of 893 K is used. Subsequent oxidation followed by low-temperature reduction gives much higher activities: this is ascribed to spreading of ruthenium oxide over the support, reduction of which affords more highly dispersed metal which easily succumbs to SMSI on a further high-temperature reduction. This interpretation receives some support from temperature-programmed-reduction results. Product distributions are interpreted according to the scheme devised by Kempling and Anderson. The oxidation treatment and low-temperature reduction creates a new type of active site which appears to favour terminal bond splitting in adsorbed n-butane and has greater reactivity for bond splitting in adsorbed C₂ and C₃ species. This analysis also leads to the conclusions that a second reduction at 623 K does not wholly convert the well dispersed metal to the SMSI state and that not quite all of the oxide formed at 623 K spreads over the support. The strange behaviour of this system is contrasted with that of ruthenium and of platinum supported on silica.