Structure-Directing Role of Support on Hg 0 Oxidation over V 2 O 5 /TiO 2 Catalyst Revealed for NO x and Hg 0 Simultaneous Control in an SCR Reactor.

The crystal structure of TiO 2 strongly influences the physiochemical properties of supported active sites and thus the catalytic performance of the as-synthesized catalyst. Herein, we synthesized TiO 2 with different crystal forms (R = rutile, A = anatase, and B = brookite), which were used as supports to prepare vanadium-based catalysts for Hg 0 oxidation. The Hg 0 oxidation efficiency over V 2 O 5 /TiO 2 -B was the best, followed by V 2 O 5 /TiO 2 -A and V 2 O 5 /TiO 2 -R. Further experimental and theoretical results indicate that gaseous Hg 0 reacts with surface-active chlorine species produced by the adsorbed HCl and the reaction orders of Hg 0 oxidation over V 2 O 5 /TiO 2 catalyst with respect to HCl and Hg 0 concentration were approximately 0 and 1, respectively. The excellent Hg 0 oxidation efficiency over V 2 O 5 /TiO 2 -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 NO x and Hg 0 on state-of-the-art V 2 O 5 /TiO 2 catalyst, a combination of anatase and brookite TiO 2 -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 NH 3 on Hg 0 oxidation.