Revisiting dispersion and reactivity of active sites via a restricted random distribution model over supported vanadia catalysts for NO reduction

The structure and dispersion of active sites substantially impact the performance of supported metal oxide catalysts, as exemplified by the V2O5/TiO2 catalysts used for NH3-SCR reaction. Due to the complexity of the active site dispersion on the catalyst surface, the intrinsic law of this structure-activity relationship remains controversial. Herein, we proposed a restricted random distribution model to describe the stochastic anchoring behavior of active sites on the TiO2 surface during the loading process of vanadia. The structures of monomeric, dimeric, and polymeric VOx sites were determined by DFT calculations and verified with spectroscopy and adsorption information experimentally. The calculated reaction pathways and energy profiles for these structures indicated that the dual sites configuration and terminal V(=O)2 bond are responsible for the high reactivity of aggregated VOx sites. Combining the reactivity of these various sites and the random distribution method, we built a general profile of the correlation between the V2O5/TiO2 catalyst surface and its reaction performance. The reactivity results obtained from experimental in situ DRIFTS and kinetic tests validate our theoretical model. The random distribution method links DFT calculations and experiments, coupling the structure and dispersion of the VOx active sites to the catalyst reactivity.