Catalytic Activity of Nb–Si Mixed Oxides Induced by Reduction with Hydrogen

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Abstract
Mixed oxides of niobium and silicon became catalytically active for butene isomerization by a reduction with hydrogen, and their catalytic activities depended on the duration of the reduction. The activity was irreversibly poisoned by oxygen. The formation of Nb4+ by the hydrogen reduction was revealed by ESR technique. Nb4+ was oxidized to Nb5+ by the admission of oxygen gas, and at the same time O2− was formed. It was concluded that the catalytically active site on the mixed oxide surface was Nb4+ ion formed by the reduction. The importance of isolation of Nb4+ ion in silica network was suggested for the retention of the catalytic activity.