Evolution of the surface species of the V2O5–WO3 catalysts

Promotional effect of antimony on the selective catalytic reduction NO with NH3 over V-Sb/Ti catalyst

The effect of antimony on the selective catalytic reduction (SCR) performance and SO₂ durability of V-Sb/Ti was investigated. The physicochemical characteristics of catalyst were characterized by various techniques, including Brunauer-Emmett-Teller (BET) surface area analysis, X-ray diffraction (XRD), NH₃/SO₂-temperature programmed desorption (TPD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs), X-ray photoelectron spectroscopy (XPS), and H₂-temperature programmed reduction (H₂-TPR). The V-Sb/Ti catalyst showed excellent activity in the range 200-300°C (compared with V/Ti), with an optimum achieved for 2 wt.% antimony. The total amount of acidic sites and NH₃ adsorption characteristics did not affect the catalytic efficiency. The Sb⁵⁺ fraction was highest for V-2.0Sb/Ti and exhibited a positive correlation with the V⁴⁺ fraction. This phenomenon is related to the effect of synergistic between vanadium and antimony, promoting the conversion of V⁵⁺ to V⁴⁺ by Sb⁵⁺. Increasing the V⁴⁺ fraction in V-Sb/Ti increased the catalytic activity, which was mainly attributed to enhanced catalyst re-oxidation capability due to the addition of antimony. Furthermore, the addition of antimony delayed the adsorption of SO₂ onto the V-Sb/Ti catalyst surface, improving the resistance to this gas. Therefore, the addition of antimony to V/Ti improved NO_x conversion and SO₂ durability.

A relationship between the V4+/V5+ ratio and the surface dispersion, surface acidity, and redox performance of V2O5–WO3/TiO2 SCR catalysts

The electron transfer process between vanadium species is omitted and the activated transition state is formed directly.

Effect of the V4+(3+)/V5+ ratio on the denitration activity for V2O5–WO3/TiO2 catalysts

Variation of monolayer dispersed and polymerized VO_x species (a) and apparent activation energy (E_a) of V₃W₈Ti catalysts.