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The exhaust gas contains harmful products, including fuel-additive elements such as compounds of sodium, which cause dramatic catalyst deactivation of catalysts during selective catalytic reduction (SCR) of NO with NH3. There is an increasing demand to synthesize alkali-poisoning-resistant catalysts for industrial NH3-SCR applications. In this study, the as-synthesized Fe2O3/MoO3/TiO2 exhibits a high degree of resistance toward Na2SO4 poisoning during the NH3-SCR reaction. With 500 μmol g–1 Na+ poisoning, Fe2O3/MoO3/TiO2 showed approximately 95% (or more) of its original activity throughout the entire temperature rage. Even with 700 μmol g–1 Na+ poisoning, Fe2O3/MoO3/TiO2 still performed well. The 500 and 700 μmol g–1 Na+ loadings dictate that, on average, SCR catalysts could be exposed to alkali-rich and highly dusty environments for more than 14 000 and 20 000 h, respectively. The layered MoO3 building block is used as a binding buffer and sandwiched between the active phase and TiO2 support to provide sufficiently stable binding sites for Na2SO4 poison and to present alkali blocking of the surface active phase. Our findings provide useful information regarding the use of MoO3 as a safety buffer for developing functional NH3-SCR catalysts with enhanced alkali-poisoning-resistant performance and long lifetimes.

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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 MoO 3 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 atomicthickness MoO 3 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 MoO 3 is responsible for the observed high activity. Electron microscopy and Raman spectroscopy reveal that the monolayer-thick MoO 3 surface phase is directly attached to the anatase TiO 2 support. The ab initio quantum calculations predict that the bidimensional MoO 3 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 MoO 3 /TiO 2 involves both Brønsted and Lewis acid sites during the reaction cycle.

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Submonolayer Mo-decorated V2O5–WO3/TiO2 provides abundant vanadia species and unsaturated V4+ species, accelerating the acid and redox cycling of low-temperature NH3-SCR.

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