Li Na, Zhang Shenghan, Cheng Zedong, Wu Wenfei
North China Electric Power University, School of Environmental Science and Engineering Baoding 071000 Hebei China
Inner Mongolia University of Science & Technology, School of Energy and Environment Baotou 014010 Inner Mongolia China.
RSC Adv. 2021 Aug 13;11(44):27607-27619. doi: 10.1039/d1ra05435j. eCollection 2021 Aug 9.
The group has shown that Baiyun Ebo rare earth concentrate has excellent performance in NH-SCR denitrification when used as a carrier, where rare earth elements are mainly present in cerium fluorocarbon ore (CeCOF) and monazite (CePO) mineral phases. In this paper, a new low-temperature NH-SCR catalyst of Mn-Fe/CeCOF-monazite was prepared by an impregnation method, using synthetic CeCOF and purified monazite as carriers. By exploring its denitrification performance and mechanistic analysis, it provides theoretical guidance for the use of rare earth concentrates as low-temperature NH-SCR catalysts. Our previous studies have determined the optimum loading of Fe, so this paper needs to be investigated for the optimum doping ratio of the active substance Mn. The results of the activity tests, XRD and BET have determined that the best denitrification rate and catalytic performance was achieved at a ratio of Mn : Ce of 1 : 5. The denitrification activity of the different catalysts was investigated by loading Fe, Mn and Fe and Mn together. The results obtained by means of experimental analyses such as XRD, SEM, BET and activity tests showed that the composite catalyst loaded with Fe and Mn at the same time, had the highest activity and its denitrification rate could reach 94.8% at 250 °C. This is mainly attributed to the fact that the interaction of Fe, Mn can promote the dispersion of each other on the carrier surface, which greatly improves the specific surface area of the catalyst. The introduction of Fe and Mn increases the acidic sites and the amount of acid on the catalyst surface, which results in the formation of a large number of oxygen vacancies and the presence of more oxygen species on the catalyst surface, which facilitate the migration of oxygen. The new catalyst was investigated by Fourier transform infrared (FTIR) spectroscopy to characterise the adsorption and transformation behaviour of the reactive species on the surface of the catalyst, and to investigate the reaction mechanism. The results showed that the entire reaction process followed the L-H mechanism, with the gaseous NO adsorption and activation on the catalyst surface generating bidentate nitrate, bridging nitrate species and NH/NH species as the main intermediate species involved in the reaction, both of which underwent redox reactions on the catalyst surface to produce N and HO. The above results indicated that the CeCOF-monazite carrier has excellent performance, and provided a theoretical basis for the high-value utilization of rare earth concentrates.
该团队已经表明，白云鄂博稀土精矿作为载体在NH-SCR脱硝中具有优异性能，其中稀土元素主要存在于氟碳酸铈矿（CeCOF）和独居石（CePO）矿相中。本文采用浸渍法，以合成的CeCOF和提纯的独居石为载体，制备了一种新型的Mn-Fe/CeCOF-独居石低温NH-SCR催化剂。通过探索其脱硝性能并进行机理分析，为稀土精矿作为低温NH-SCR催化剂的应用提供了理论指导。我们之前的研究已经确定了Fe的最佳负载量，因此本文需要研究活性物质Mn的最佳掺杂比例。活性测试、XRD和BET的结果表明，当Mn∶Ce的比例为1∶5时，脱硝率和催化性能最佳。通过负载Fe、Mn以及同时负载Fe和Mn来研究不同催化剂的脱硝活性。通过XRD、SEM、BET和活性测试等实验分析获得的结果表明，同时负载Fe和Mn的复合催化剂活性最高，其在250℃时的脱硝率可达94.8%。这主要归因于Fe、Mn之间的相互作用能够促进彼此在载体表面的分散，从而大大提高了催化剂的比表面积。Fe和Mn的引入增加了催化剂表面的酸性位点和酸量，导致形成大量氧空位且催化剂表面存在更多的氧物种，这有利于氧的迁移。通过傅里叶变换红外（FTIR）光谱对新型催化剂进行研究，以表征催化剂表面活性物种的吸附和转化行为，并研究反应机理。结果表明，整个反应过程遵循L-H机理，气态NO在催化剂表面的吸附和活化产生双齿硝酸盐、桥连硝酸盐物种以及NH/NH物种作为反应中涉及的主要中间物种，二者均在催化剂表面发生氧化还原反应生成N和HO。上述结果表明CeCOF-独居石载体具有优异性能，为稀土精矿的高值利用提供了理论依据。
