| NOx is one of the main air pollutants, now selective catalytic reduction of NOx by ammonia (NH3-SCR) is the main control technology for NOx removal, in which the key issue is the catalyst with high-efficiency. The SCR catalyst most commonly used is V2O5-WO3(MoO3)/TiO2. In industrial application, the activity of the catalysts decreased with the running time prolonged. Furthermore, as the operating temperature of the catalysts was lower in the non-power industry, ammonium bisulfate would generate and deposite on the surface of the catalysts. Moreover, that would cover the active sites of the catalysts, resulting in catalytic activity decreased faster. Besides, the alkali metals and arsenic in the fly ash or flue gases also enabled the catalysts deactivation. Therefore, we investigated the NH3-SCR activity over the vanadium-titanium catalysts with different metal impurities. The decomposition of NH4HSO4 over the catalysts was also studied. That was considered important to the application and regeneration of the catalysts in the industry.In this paper, the NH3-SCR performance of V2O5-MoO3/TiO2 catalysts with rare earth elements (Pr, La and Ce), alkali metal element (Cs and Rb), Bi and Sb modified was investigated. The reaction mechanism of the catalysts and the decomposition of NH4HSO4 over the CeO2 doped the vanadium-titanium catalysts were studied also. The main results are as follows:(1) Pr, La and Ce doped the V2O5/TiO2 and V2O5-MoO3/TiO2 catalysts were prepared by sol-gel and impregnation methods. Ce doped the V2O5/TiO2 catalysts exhibited higher NH3-SCR activity comparing with Pr and La doped catalysts. Moreover, Pr doped the V2O5-MoO3/TiO2 catalysts showed high activity and N2 selectivity in the temperature range of 200～400℃, also exhibited good resistance to SO2 and H2O. Addition of La and Ce on V2O5-MoO3/TiO2 catalyst could improve the catalytic activity NOx removal. When the La and Ce doping content were 4 wt% and 10 wt% respectively, the catalysts showed best performance of SCR. Furthermore, the addition of rare earth elements (mainly analysis Pr and La) could increase the specific surface area, give more NH3 adsorption species, chemisorbed oxygen species, bridged nitrate species and the numbers of Br(?)nsted acid sites, resulting in an enhancement in the catalytic activity for NH3-SCR of NOx.(2) We prepared Pr doped the industrial TiO2 and the V2O5-MoO3/TiO2 catalysts with different Pr doping and V loading by impregnation method. The performance showed that an addition of a few Pr on V2O5-MoO3/TiO2 catalyst could enhance the catalytic activity for NH3-SCR of NOx at low temperature (100～180℃) and high temperature (300～400℃). At 180 ℃, the NO conversion over IM-3 V6MolPrTi catalyst could reach 93%. With increasing the loading of V2O5 (0.3～3 wt%), the NO conversion over V2O5-MoO3/1 wt%Pr6O11-TiO2 increased.(3) Cs, Rb, Bi and Sb modified the 3% V2O5-6% MoO3/TiO2 catalysts were prepared through impregnation method. The results showed that a small amount of Cs2O and Rb2O loaded on 3V6MoTi catalyst, a little influence on the NO conversion over 3V6MoTi catalyst appeared. But with increasing the loading of Cs2O and Rb2O, the catalytic activity decreased. When an addition of Sb2O5 on the 3 V6MoTi catalyst, the catalytic activity was decreased at low temperature and improved at high temperature (>350℃). When the loading content of Bi2O5 was 0.1-0.5 wt%, the catalytic activity of the catalyst was improved. But with increasing the loading of Bi2O5, the catalytic activity decreased.(4) We investigated the decomposition of NH4HSO4 over V2O5-MoO3/CeO2-TiO2 catalysts using TG-MS technique. It’s showed that a portion of NH4HSO4 decomposed into NH3 and H2O over V2O5-MoO3/CeO2-TiO2 catalysts before 200℃, while the SO2 adsorbed over the catalysts. A portion of adsorbed SO2 was desorbed at 415℃. Furthermore, the temperature of SO2 signal peak was decreased and appeared around 720℃ with CeO2 doping content was 10 wt%. So, Ce doped could promote the decomposition of NH4HSO4 over the V2O5-MoO3/TiO2 catalyst and reduce the decomposition temperature. The reaction equations are as follows:... |
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