Exceptional Activity over the Submonolayer MoO₃ Motif on TiO₂ for Nitrogen Oxide Emission Abatement

Surface restructuring is a useful approach to modulating the properties of nanoparticles. A low-dimensional atomic-thickness active species may exhibit remarkably enhanced activity, in contrast to the inert nature of its bulk counterparts. Here, we report a procedure for growing in situ a low-dimensional monolayer-thick MoO₃ entity from its bulk precursor. Traditional analysis of NO abatement catalyzed by vanadium-based materials implicates vanadium as the active site enhanced by the promoter element W or Mo. However, we report here that the atomic-thickness MoO₃ film can function alone as an efficient NO abatement catalyst by itself; to achieve comparable performance with the industrial catalysts, it is not necessary to add vanadium oxide, which often has serious toxicity issues associated with it. We find that submonolayer MoO₃ is responsible for the observed high activity. Electron microscopy and Raman spectroscopy reveal that the monolayer-thick MoO₃ surface phase is directly attached to the anatase TiO₂ support. The ab initio quantum calculations predict that the bidimensional MoO₃ surface phase would provide more electron back-donation to the antibonding orbital of reactants and thus more efficient reactant activation. The spectral evolution of in situ DRIFTS indicates that the redox mechanism over the low-dimensional MoO₃/TiO₂ involves both Brønsted and Lewis acid sites during the reaction cycle.