Hydrogen–Deuterium Exchange on Iso-structural Sesquioxides of the First Long Period

Abstract

INVESTIGATIONS of the relationship between the electronic structure and the catalytic activity of transition metal oxides have tended to centre around either the electron (or positive hole) concentration¹ or the population of atomic dorbitals²; but there have been no attempts so far to follow up in this field the newer studies on electrical and magnetic properties which reflect the extent of d orbital overlap in the oxides of the first long period^3,4. Moreover, although it is now widely recognized that the energy-levels of transition metal ions in solids are strongly influenced by the symmetry of the crystal field, there are no correlative studies of catalytic activity in which this important parameter has been standardized. It is for these reasons that we have undertaken a short study of the H₂–D₂ exchange on sintered specimens of titanium, vanadium and chromium sesquioxides. The ions Ti³⁺, V³⁺and Cr³⁺ follow in the sequence d¹, d² and d³, and in the almost cubic field of the corundum lattice (which is common to all three oxides) one would expect the progressive filling of the degenerate dɛ set to ensure a gradual decrease in the amount of orbital overlap along this sequence.