Structure sensitivity: Hydrogenolysis of n-butane and hydrogenation of ethylene on nickel clusters condensed onto amorphous silica

Abstract

The crystallite size dependence of n-butane hydrogenolysis and ethylene hydrogenation has been studied over silica supported nickel catalysts. The samples were prepared by vapour condensation of nickel atoms onto a flat amorphous silica substrate. The support was grown by thermal oxidation of the silicon (111) surface. The growth mechanism and the crystalline and electronic structures of the nickel particles were followed by in-situ RHEED and AES techniques, while the absolute coverage, ranging from 10 13 to 10 16 atoms cm −2, and the size distribution of the metal particles, have been measured independently by RBS and TEM techniques respectively. The dependence of turnover frequency on crystallite size has been studied for n-butane hydrogenolysis and ethylene hydrogenation. Maximum turnover frequency for n-butane hydrogenolysis and ethylene hydrogenation is observed for nickel crystallite sizes in the range of 15–20 and 5–7 Å respectively. It has been found that the hydrogenolysis of n-butane requires a minimum number of atoms.