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

Abstract

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.

Alkali-Poisoning-Resistant Fe2O3/MoO3/TiO2 Catalyst for the Selective Reduction of NO by NH3: The Role of the MoO3 Safety Buffer in Protecting Surface Active Sites

“…Fe 2 O 3 /MoO 3 /TiO 2 shows irregular, rough shapes and has a large size variation (see the SEM image in Figure S1). The submonolayer structured MoO 3 on TiO 2 has been evidenced by our previous work . However, when MoO 3 /TiO 2 was mixed with Fe 2 O 3 , it was difficult to distinguish the MoO 3 surface layer by TEM because of the strong signals from Fe 2 O 3 and TiO 2 .…”

“…The origin of the extremely high resistance to Na 2 SO 4 is elucidated. Recently, we have shown that MoO 3 with a layered structure has important implications in catalysis . Moreover, the intercalation of Na + ions into MoO 3 is expected, according to the report of a previous study .…”

“…Two active building blocks, Fe 2 O 3 and MoO 3 /TiO 2 , were prepared separately and then mixed to form the Fe 2 O 3 /MoO 3 /TiO 2 catalyst. MoO 3 /TiO 2 was synthesized according to our recently published procedure . This method is based on the self-assembly of uniform, two-dimensional MoO 3 submonolayers on a commercially available TiO 2 support.…”

Single Mo atoms paired with neighbouring Ti atoms catalytically decompose ammonium bisulfate formed in low-temperature SCR

“…3b, only a peak at ∼1600 cm −1 assigned to the adsorbed gas NH 3 on Lewis sites appears in the spectrum of TiO 2 . 29 However, when single Mo atoms were anchored on TiO 2 , significant signals at ∼1670 and ∼1455 cm −1 appeared, manifesting the increased NH 3 coordination of Brønsted sites in the form of NH 4 + , 29,38 i.e. , Mo–O–H structures were formed on the surface of Mo 1 /TiO 2 , which are totally different from that in bulk MoO 3 where no relevant peak was observed.…”

“…27,28 Hence, a catalyst with Mo–Ti acid–base dual sites should readily adsorb NH 4 + and HSO 4 − , respectively. Moreover, owing to the unsaturated coordination configuration, the surface Mo ions often have the desired ability to facilitate the oxidation of NH 4 + , 29 generating reduced Mo species. Due to the charge transfer between Mo and Ti atoms via Mo 5+ + Ti 4+ → Mo 6+ + Ti 3+ , 30 the produced Ti 3+ , which often has a higher electron state density near the Fermi level ( E f ), 31 favourably accelerates the reduction of HSO 4 − .…”