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 Bronsted and Lewis acid sites during the reaction cycle.