Direct synthesis of V–W–Ti nanoparticle catalysts for selective catalytic reduction of NO with NH3

Abstract

A series of V–W–Ti nanoparticle catalysts with variable V doping amounts were directly synthesized by the sol–gel method, and their catalytic performances were tested for the selective catalytic reduction of NO with ammonia. The catalysts were characterized by means of XRD, Raman, BET, TEM, SEM, NH₃-TPD, H₂-TPR and XPS. SCR kinetic studies were conducted to understand the mechanistic features of V–W–Ti catalysts. It was found that the V_0.02W_0.04Ti catalyst exhibited the highest NO conversion and the lowest apparent activation energy. The characterization results showed that V was incorporated into the TiO₂ framework and the redox cycle of V⁴⁺ + Ti⁴⁺ → V⁵⁺ + Ti³⁺ existed over the V–W–Ti catalysts. A high concentration of reducible and distorted V species could account for the excellent NH₃-SCR catalytic performance of the V_0.02W_0.04Ti catalyst. In situ FT-IR spectroscopy was performed to investigate the mechanism of the NH₃-SCR reaction over the V_0.02W_0.04Ti catalyst. Experimental results showed that both Lewis and Brønsted acid sites over the V_0.02W_0.04Ti catalyst were involved in the NH₃-SCR reaction. The adsorption of nitrate species was significantly limited and the adsorbed NO₂ gaseous molecules were easily formed over the V_0.02W_0.04Ti catalyst, which resulted in the high catalytic activity at low temperature.