Structure-Directing Role of Support on Hg0 Oxidation over V2O5/TiO2 Catalyst Revealed for NOx and Hg0 Simultaneous Control in an SCR Reactor

The crystal structure of TiO2 strongly influences the physiochemical properties of supported active sites and thus the catalytic performance of the as-synthesized catalyst. Herein, we synthesized TiO2 with different crystal forms (R = rutile, A = anatase, and B = brookite), which were used as supports to prepare vanadium-based catalysts for Hg0 oxidation. The Hg0 oxidation efficiency over V2O5/TiO2-B was the best, followed by V2O5/TiO2-A and V2O5/TiO2-R. Further experimental and theoretical results indicate that gaseous Hg0 reacts with surface-active chlorine species produced by the adsorbed HCl and the reaction orders of Hg0 oxidation over V2O5/TiO2 catalyst with respect to HCl and Hg0 concentration were approximately 0 and 1, respectively. The excellent Hg0 oxidation efficiency over V2O5/TiO2-B can be attributed to lower redox temperature, larger HCl adsorption capacity, and more oxygen vacancies. This work suggests that to achieve the best simultaneous removal of NOx and Hg0 on state-of-the-art V2O5/TiO2 catalyst, a combination of anatase and brookite TiO2-supported vanadyl tandem catalysts is supposed to be employed in the SCR reactor, and the brookite-type catalyst should be on the downstream of the anatase-based catalyst due to the inhibition of NH3 on Hg0 oxidation.