Structure-Directing Role of Support on Hg Oxidation over VO/TiO Catalyst Revealed for NO and Hg Simultaneous Control in an SCR Reactor.

The crystal structure of TiO strongly influences the physiochemical properties of supported active sites and thus the catalytic performance of the as-synthesized catalyst. Herein, we synthesized TiO with different crystal forms (R = rutile, A = anatase, and B = brookite), which were used as supports to prepare vanadium-based catalysts for Hg oxidation. The Hg oxidation efficiency over VO/TiO-B was the best, followed by VO/TiO-A and VO/TiO-R. Further experimental and theoretical results indicate that gaseous Hg reacts with surface-active chlorine species produced by the adsorbed HCl and the reaction orders of Hg oxidation over VO/TiO catalyst with respect to HCl and Hg concentration were approximately 0 and 1, respectively. The excellent Hg oxidation efficiency over VO/TiO-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 and Hg on state-of-the-art VO/TiO catalyst, a combination of anatase and brookite TiO-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 on Hg oxidation.