Interplay between Defect Structure and Catalytic Activity in the Mo 10− x V x O y Mixed‐Oxide System

The Mo 10− x V x O y solid‐solution systems (0≤ x ≤10) were studied by electron paramagnetic resonance spectroscopy. The results show the existence of paramagnetic vanadyl VO 2+ species, whose concentration becomes maximal for Mo 5 V 5 O y . A quantitative analysis of the [VO 2+ ] concentration as a function of the Mo/V ratio allows it to characterize the prevailing defect chemistry in the Mo 10− x V x O y system. In this respect, the semi‐conducting properties of Mo 10− x V x O y are p‐type in an interval of Mo 9 V 1 O y –Mo 5 V 5 O y and switch into n‐type because of the conduction electrons in a composition range of Mo 5 V 5 O y –Mo 1 V 9 O y . 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 VO 2+ centers in the bulk have to be considered too for heterogeneous catalysis.