Simultaneous catalytic oxidation of CO and Hg0 over Au/TiO2 catalysts: Structure and mechanism study

Abstract

Au/TiO2 catalysts with different morphologies were prepared by the modulation of chlorine via a hydrothermal method, which were used for the simultaneous catalytic removal of CO and Hg0. Results showed that the Au/TiO2 catalyst with a structure of submicron sphere and ascorbic acid modification (denoted as AuV/2 M T) showed 38.2% (41.1%, without H2O) CO conversion at 50 °C and nearly 100% CO conversion at 275-350℃ (225-350℃, without H2O). This catalyst also exhibited stable catalytic efficiency of approximately 88% (95.7%, without H2O) for Hg0 removal at 300℃. The high catalytic activity of the AuV/2 M T was ascribed to a series of superior properties, including a high specific surface area, a large amount of adsorbed oxygen species and a large brookite/rutile TiO2 ratio. Moreover, the AuV/2 M T also exhibited excellent stability. The AuV/2 M T continued to exhibit nearly 90.5% CO conversion efficiency and 84.5% Hg0 conversion efficiency after continuous testing with 6 vol.% H2O for 120 h. Therefore, this catalyst is expected to be used in coal-fired power plants. The mechanism of CO removal over AuV/2 M T was in-depth investigated. The presence of chlorine promoted the catalytic oxidation of Hg0 while the presence of CO has no great effect on desorption of Hg0. Moreover, catalytic oxidation of CO over AuV/2 M T catalyst was found to follow L-H mechanisms. The formate was the intermediate species for CO catalytic oxidation, and it transformed to CO2 quickly by consuming the oxygen species (O2−, O− and −OH) adsorbed onto the catalyst surface. The oxygen species consumed on the surface of catalyst was supplied by oxygen, and it was the key factor in determining the reaction rate.