G. Centi
Dec 3, 1996
Citations
1
Influential Citations
167
Citations
Quality indicators
Journal
Applied Catalysis A-general
Abstract
Abstract Vanadium oxide supported over titanium oxide is an important example of a transition-metal-oxide ‘monolayer’ catalyst with practical relevance for various industrial applications. After a brief introduction on the concept of monolayer oxide catalysts, this review examines three main topics: (i) the nature of vanadium oxide species over the titanium oxide surface, (ii) their reactivity and structure/activity-selectivity relationships and (iii) modification of the surface properties during the catalytic reactions of o -xylene oxidation and alkylaromatic ammoxidation. An analysis of selected literature data leads to the following main conclusions: (i) the support promotes the formation of an amorphous, hydrated active layer of titanium oxide which may extend up to 3–5 layers; (ii) the reactivity of titanium oxide in this form is enhanced with respect to crystalline vanadium oxide, but the selectivity properties which are a function of the oxidation state of vanadium ion and of the modifications occurring during the catalytic reaction are not significantly different; (iii) in the presence of ammonia, the characteristics of the catalyst surface must be tuned to limit the side reaction of NH 3 combustion. The optimal catalyst composition for ammoxidation reactions is thus different from that for oxidation catalysts. Simultaneous O and N insertion requires instead an intermediate catalyst composition between those optimal for oxidation and ammoxidation of alkylaromatics.