Fundamentals of C–O bond activation on metal oxide catalysts

Abstract

Fundamental knowledge of the active site requirements for the selective activation of C–O bonds over heterogeneous catalysts is required to design multistep processes for the synthesis of complex chemicals. Here we employ reaction kinetics measurements, extensive catalyst characterization, first principles calculations and microkinetic modelling to reveal metal oxides as a general class of catalysts capable of selectively cleaving C–O bonds with unsaturation at the α position, at a moderate temperature and H2 pressure. Strikingly, metal oxides are considerably more active catalysts than commonly employed VIIIB and IB transition metal catalysts. We identify the normalized Gibbs free energy of oxide formation as both a reactivity and a catalyst stability descriptor and demonstrate the generality of the radical-mediated, reverse Mars–van Krevelen C–O bond activation mechanism on oxygen vacancies, previously established only for RuO2. Importantly, we provide evidence that the substrate plays an equally key role to the catalyst in C–O bond activation. Metal oxides have been identified as a promising class of catalysts for carbon–oxygen bond cleavage in the context of biomass valorization, although the systematic understanding of their reactivity remains elusive. Now, a combination of catalytic screening and first principles calculations provide important insights into this family of catalysts.