On the umbrella model for supported vanadium oxide catalysts

An earlier-proposed model for the molecular structure of VO4 species on alumina was tested and compared with the pyramid model on a silica support. The model can be described as a chemisorbed Osupportsingle bondVdouble bond; length as m-dashO(O2) species with a similar geometry as on alumina. Results of DFT calculations on this model are consistent with the experimental Raman and EXAFS data collected on low-loaded silica-supported vanadium oxide catalysts. The band observed at 915 cm−1 is assigned to an Osingle bondO stretch vibration. The thermal motion of the bound O2 molecule can explain the broadness of this band. These findings, in combination with our previous work, demonstrate that the umbrella model is a viable, internally consistent model for supported vanadium oxide catalysts at least at low loadings.