Modification of ruthenium catalysts for alkane hydrogenolysis

Modification of the properties of small Ru particles by species emanating either from the support, or from a third substance added to the metal on a supposedly inert support, is sensitively revealed by observing the kinetics and product selectivities in the hydrogenolysis of the lower alkanes. Besides inhibiting rates, modification by a number of species causes (i) high ethane selectivities from n-butane, (ii) a low temperature coefficient of all product selectivities, (iii) stronger H-2 chemisorption, deduced by analysing the dependence of rate on H-2 pressure, and (iv) a weak dependence of selectivities on H-2 pressure. There is some indication of a modifying effect with Ru/SiO2 after the first reduction of the precursor; it is clearly present with Ru/TiO2 as a 'strong metal-support interaction', and very marked with Ru/Al2O3, after reduction at high temperature. Quite generally the modifying influence is removed by oxidation and low temperature reduction. TiO2 added to Ru/SiO2 or Ru/Al2O3 does not act as a strong modifier; but K2O and especially V2O5 have large effects on rates and kinetics, their effects remaining after an oxidation step. (C) 2000 Elsevier Science B.V. All rights reserved.