| Nitrogen oxides are one of the most common and the greatest impact atmospheric pollutants. It is the key and difficult point of atmospheric environmental governance. With our industry have been expanding, especially the development of thermal power industry, their emissions are increasing quickly. It also brought a lot of environmental problems. Selective Catalytic Reduction(SCR) technology, with ammonia as a reducing agent and V2O5-WO3/TiO2 as catalyst, has become the most mature and the most widely used thermal power plant flue gas denitrification technology. However, since the active temperature of V2O5-WO3/TiO2 catalyst is,between 300~400℃, so the SCR reactor can only be arranged in high-sulfur and high-dust position which is between dust catcher and economizer. High concentration of SO2 and fly ash in flue gas greatly shorten the life of the catalyst.Therefore, the development of low-temperature SCR technology has aroused extensive attention from researchers both at home and abroad. Low temperature SCR catalyst is the core technology of low-temperature SCR, so research the catalyst that can be arranged after the dedusting or desulfurization and has high activity and strong anti-toxic will be the key of the Low Temperature SCR technology. There are many metal Mn oxides with different valences and can be converted to each other cycle, this feature makes the catalyst with manganese oxide as the active component has better low-temperature activity. Ce is often used as additives to improve the performance of the activity of the catalyst as it has good oxygen storage performance. TiO2 its stability and ease-of-form strong interactions with the active ingredient of which is often used as a carrier of the catalyst. Therefore, Mn-Ce/TiO2 catalyst has good application prospects when it is used as low-temperature SCR catalyst. However, the flue gas often contains a certain concentration of SO2 and H2 O, and both have certain inhibitory effect on the activity of the catalyst, so to research the effect that SO2 and H2 O have on the catalyst activity and explore the causes, and thus improve the performance of catalyst have important practical significance.This article was prepared Mn-Ce/TiO2 low temperature SCR catalyst by sol-gel. Add CTAB, Al2O3 and SiO2 modified its optimization and studied the effects on the catalytic activity and the presence of co-catalyst alone in SO2 and H2 O. BET, SEM, XRD, FT-IR and XPS characterization methods were used to explore the modification effects of optimization of the catalyst as well as the causes of SO2 and H2 O poisoning effect on the catalyst. The results showed that, CTAB modification acts best, when there is no SO2 and H2 O and the reaction temperature is 140℃,the NOx removal efficiency is about 84% and it shows good stability.However, with the addition of simulated flue gas SO2 or H2 O concentration on the catalyst activity increases produce significant inhibition. When the SO2 concentration is 900×10-6, NOx removal rate is only about 41%. And when H2 O concentration is 9%, NOx removal rate is only about 57%.The catalyst deactivation caused by high concentration SO2 cannot recover while H2 O inhibition can restore. When SO2 and H2 O exit together, the competitive adsorption of H2 O will weaken the poisoning effect of SO2 on the catalyst. The results showed the ammonium salt catalysts and surface deposition caused a significant reduction in pore size hole 5-10 nm and covering Lewis acid sites on the catalyst surface adsorption properties of the catalyst leaving NH3 weakened. Effect of SO2 poisoning also caused a lot of carriers TiO2 generated from anatase into rutile type, and the active substance MnOx crystallization and Mn-Ti generated into MnTiO3 which due to the destruction of the interaction. These changes caused the path that adsorbed oxygen transforms into lattice oxygen blocked, which causes a large number of low-cost state MnOx emergence and role of oxygen storage CeOx decline, and these both caused the catalytic activity decrease. The presence of H2 O can weaken the effect of SO2 on the catalyst. |
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