CeO2 is a promising catalytic oxidation material for flue gas mercury removal. Density functional theory (DFT) calculations and periodic slab models are employed to investigate mercury adsorption and oxidation by oxygen over the CeO2 (111) surface. DFT calculations indicate that Hg0 is physically adsorbed on the CeO2 (111) surface and the Hg atom interacts strongly with the surface Ce atom according to the partial density of states (PDOS) analysis, whereas, HgO is adsorbed on the CeO2 (111) surface in a chemisorption manner, with its adsorption energy in the range of 69.9–198.37 kJ/mol. Depending on the adsorption methods of Hg0 and HgO, three reaction pathways (pathways I, II, and III) of Hg0 oxidation by oxygen are proposed. Pathway I is the most likely oxidation route on the CeO2 (111) surface due to it having the lowest energy barrier of 20.7 kJ/mol. The formation of the HgO molecule is the rate-determining step, which is also the only energy barrier of the entire process. Compared with energy barriers of Hg0 oxidation on the other catalytic materials, CeO2 is more efficient at mercury removal in flue gas owing to its low energy barrier.
Arsenic, a toxic component in coal-fired flue gas, is poisonous to the commercial selective catalytic reduction (SCR) denitrification catalysts. To unveil the arsenic poisoning mechanism on commercial SCR catalysts, fresh and 1 year used arsenicpoisoned plate-type V 2 O 5 −MoO 3 /TiO 2 catalysts from a coal-fired power plant in the Inner Mongolia Province of China were systematically analyzed with SCR activity and characterization experiments. The results indicated that the plate-type V 2 O 5 −MoO 3 / TiO 2 catalysts possessed a certain ability to resist arsenic poisoning. The average denitrification efficiency of the poisoned catalysts was maintained over 70% at 350 °C, even though the arsenic content was as high as 7 wt %, compared to the denitrification efficiency of 87.35% for the fresh catalyst. Characterization results indicated that both physical and chemical factors resulted in the deactivation of catalysts by arsenic. The surface area and amount of surface acid sites of the used catalysts decreased, which inhibited the adsorption of ammonia. The redox capacity of the used catalysts also decreased as a result of the increase of tetravalent vanadium (V 4+ ) and the decrease of surface chemisorbed oxygen. Furthermore, catalysts at different installation positions in the SCR system had different denitrification activities and deactivation mechanisms. The major deactivation factor for the catalysts in the top layer was physical blockage, while the chemical deactivation was dominant for the catalysts in the middle layer.
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