| Mercury is one of toxic heavy metals, which can cause serious harm on human health and natural environment. Coal-fired power plants are major sources of anthropogenic mercury emissions. China has promulgated laws and regulations to limit mercury emissions from coal-fired power plants. Research and development of mercury control technologies in coal-fired power plants is urgent. Among current mercury pollution control technologies, catalytic oxidation of mercury is a promising method. Considering that the majority of power plants have installed denitration equipment, dust removal equipment and desulfurization equipment, we can take use of SCR catalyst to oxide Hg0to Hg2+, and then effectively remove Hg2+in the subsequent pollution control equipments. Consequently, this method can significantly reduce the cost of pollution control and has a much greater prospect. In this paper, aiming at the problems and shortcomings of mercury catalytic oxidation catalyst, mercury oxidation of MOx/TiO2catalyst was studied. Afterwards, metal M’s oxide was doped to V2O5/TiO2catalyst in order to improve the mercury oxidation ability of V2O5/TiO2catalyst. The modified V2O5/TiO2catalyst is investigated for cooperative control of NOx and mercury. The main results are shown as following:1. A series of MOx/TiO2catalysts containing different amounts of metal M’s oxide were prepared by equal volume impregnation method. Activity tests showed that MOx/TiO2catalysts exhibit excellent mercury oxidation ability in low HCl concentration even at high gas hourly space velocity. The excellent catalytic performance is mainly due to the outstanding oxidation ability of metal M’s oxide. X-ray power diffraction results showed that metal M’s oxide exist in amorphous state on catalyst surface. The influence of different flue gas components (O2, HCl, NO, SO2, H2O) on mercury oxidation performance were investigated. It was discovered that O2and HCl can greatly promote mercury oxidation, and NO also has a promoting effect. SO2can inhibit mercury oxidation due to competitive adsorption with Hg0on the catalyst surface. H2O also has an inhibiting effect on mercury oxidation. The reaction over MOx/Ti02catalyst followed Mars-Maessen mechanism when only O2existed. Hg0was initially adsorbed on the catalyst surface, then reacting with lattice oxygen. The consumed lattice oxygen was recovered by gas-phase oxygen. When O2and HCl both existed, mercury oxidation was promoted due to active chlorine species generated on the catalyst surface and the mechanism altered.2. The effect of metal M doping on denitration performance and mercury oxidation of V2O5/TiO2catalyst was investigated. It was found that mercury oxidation increased together with reaction temperature and metal M’s oxide loading in the experimental temperature (300～400℃) and load capacity (0.1-5wt%). For denitration performance, metal M’s oxide loading is significantly helpful to low temperature activity, but when metal M’s oxide loading is further increased, high temperature activity decreased. X-ray power diffraction results showed that metal M’s oxide and vanadium oxide exist in amorphous state on catalyst surface. The improvement of catalytic performance is mainly due to the interaction between metal M’s oxide and vanadium oxide and the outstanding oxidation ability of metal M’s oxide. H2temperature programmed reduction results showed that the reduction peak of modified catalyst was shifted to low temperature, which indicating that the redox ability of catalyst was improved. X-ray photoelectron spectra results showed that there is an interaction between metal M’s oxide and vanadium oxide. After the addition of metal M’s oxide, the ratio of V5+increased, and the ratio of V4+decreased.3. The influence of different flue gas components (O2, HCl, NO, SO2, H2O) on mercury oxidation performance of modified catalyst were investigated. It was found that O2and HCl can greatly promote mercury oxidation, and NO also has a promoting effect. SO2can inhibit mercury oxidation due to competitive adsorption with Hg0on the catalyst surface. H2O also has an inhibiting effect on mercury oxidation. In addition, NH3has a strong inhibitory effect on mercury oxidation. NH3can cause Hg0desorption from catalyst surface. The adsorption and desorption of HCl and Hg0on doped catalyst was studied to explore the mechanism of promoting effect of metal M’s oxide on V2O5/TiO2catalyst. Experimental results showed that HCl adsorption was promoted on V2O5-MOx/TiO2catalyst and adsorbed HCl on the catalyst surface have a better reactivity. HCl can cause Hg0desorption from catalyst surface, which indicated that HCl and Hg0have same adsorption sites on catalyst surface and HCl has stronger adsorption ability than Hg0on these adsorption sites. Besides, Hg0can react with pre-adsorbed HCl. |
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