Effects of MoOx on dispersion of vanadia and low-temperature NH3-SCR activity of titania supported catalysts: Liquid acidity and steric hindrance.

[Display omitted] • NH 4 Mo 7 O 24 promotes polymerization of VO x with increased solution acidity. • Steric interaction occurs on V-Mo/TiO 2 depending on loading of metal oxides. • More VO x polymers generate on TiO 2 with MoO x addition at low V loading. • Crystalline V 2 O 5 and MoO 3 form due to steric hindrance with excess monolayer loading. • Feasibly reducible VO x species facilitates adsorption and activation of NH 3. Monometallic (V/TiO 2 and Mo/TiO 2) and bimetallic (V-Mo/TiO 2) catalysts were prepared for selective catalytic reduction (SCR) of NO x with NH 3 at low temperatures (100–300 °C). The effect of MoO x on the dispersion of vanadia with different V 2 O 5 loadings was investigated on the basis of X-ray diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), N 2 adsorption–desorption, Raman spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), H 2 temperature-programmed reduction (H 2 -TPR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). As the molybdenum precursor, NH 4 Mo 7 O 24 increased the solution acidity and promoted polymerization of VO x in liquid phase. At a low vanadia loading, polymerization of VO x , the adsorption rate of NH 3 and transformation of active intermediate species NH 2 were enhanced by adding MoO x , while at a high vanadia loading, the steric hindrance became dominant leading to the formation of crystalline V 2 O 5 and MoO 3 and caused decline in SCR activity. [ABSTRACT FROM AUTHOR]