Interplay between Defect Structure and Catalytic Activity in the Mo10−xVxOy Mixed‐Oxide System

AbstractThe Mo10−xVxOy solid‐solution systems (0≤x≤10) were studied by electron paramagnetic resonance spectroscopy. The results show the existence of paramagnetic vanadyl VO2+ species, whose concentration becomes maximal for Mo5V5Oy. A quantitative analysis of the [VO2+] concentration as a function of the Mo/V ratio allows it to characterize the prevailing defect chemistry in the Mo10−xVxOy system. In this respect, the semi‐conducting properties of Mo10−xVxOy are p‐type in an interval of Mo9V1Oy–Mo5V5Oy and switch into n‐type because of the conduction electrons in a composition range of Mo5V5Oy–Mo1V9Oy. Highest catalytic activity is obtained when vanadium acts as an acceptor center and oxygen vacancies ${\left( {\upsilon _{\rm{O}}^{ \bullet \bullet } } \right)}$ are formed for reasons of charge compensation. In addition to the surface, ${\upsilon _{\rm{O}}^{ \bullet \bullet } }$ and VO2+ centers in the bulk have to be considered too for heterogeneous catalysis.