Solid state 51V NMR structural studies of vanadium(V) oxide catalysts supported on TiO 2(anatase) and TiO 2(rutile). The influence of surface impurities on the vanadium(V) coordination

Abstract

Solid state 51V wideline NMR studies show that under ambient conditions the vanadium (V) oxide surface phases on TiO 2(anatase) and TiO 2(rutile) supports predominantly possess distorted-octahedral coordination. However, the coordination environment of vanadia is markedly influenced by the presence of impurities in the support materials. Surface contaminants promote the formation of tetrahedral surface vanadia species, which preferentially form at low surface coverages. The presence of these surface impurities depends on the titania preparation method and overshadows the influence, if any, of the bulk TiO 2 lattice structure (anatase versus rutile). Thus, the strong influence of surface impurities on the V 2O 5/TiO 2 system is most likely responsible for the widely varying claims about differences in the catalytic properties of V 2O 5/TiO 2(anatase) versus V 2O 5/ TiO 2 (rutile) samples.