TPD Study of Mordenite-Type Zeolites for Selective Catalytic Reduction of NO by NH 3
ABSTRACT The effect of the adsorption of NO and NH3on catalytic activity has been examined by temperature-programmed desorption over a series of cation-exchanged mordenite catalysts for selective catalytic reduction (SCR) of NO by NH3. The catalytic activity observed in a packed-bed flow reactor was well correlated with the cation content of the catalyst and its adsorption properties, making it possible to elucidate the role of metals and acidity in this reaction system. The amount of NH3and NO adsorbed on the catalyst surface proportionally increased with the degree of cation exchange of the catalyst, especially at the Brønsted acid site (H+) and the metal site (Cu2+). SCR activity also gradually increased with the acidity of the catalyst and/or its degree of catalyst cation exchange. Surface acidity of the mordenite catalysts appears to be a dominant factor in the high performance of the SCR reaction system. The common activation energy is observed to be about 12 kcal/mole for NaHM and CuHM catalysts, independent of their cation content on the catalyst surface. The active sties of this catalytic system are both the Brønsted acid site and the metal site. Furthermore, the reaction occurred in a Langmuir–Hinshewood manner with a dual-site catalysis mechanism.
- SourceAvailable from: Rajamani GounderJournal of Catalysis 04/2014; 312:26–36. · 6.07 Impact Factor
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ABSTRACT: Ammonia oxidation has been studied between 298 to 800 K on zeolite NaY and copper-based catalysts (Cu(x)-NaY, x being the exchange degree). The main product of the reaction was N2. The rates of NH3 conversion in selective catalytic reduction (SCR) of NO by NH3 (NH3 + O2 + NO) and in NH3 oxidation (NH3 + O2) were similar on Cu(195)-NaY, but differed at lower temperature on Cu(76)-NaY. On Cu(25)-NaY, the rate of NH3 conversion in SCR of NO was always much faster. During the SCR of NO on Cu(76)-NaY, two waves of N2O formation were observed, while on Cu(25)-NaY, no N2O was detected. The formation of N2O at low temperature was ascribed to the decomposition of ammonium nitrate formed on CuO aggregates. The second N2O formation at a higher temperature resulted from the ammonia oxidation which occurred either on next-neighbour isolated Cu2+ or on [CuOCu]2+ dimers.Comptes Rendus de l Académie des Sciences - Series IIC - Chemistry 04/1998; 1(4):229–235.
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ABSTRACT: The mechanism of NH3-selective catalytic reduction (SCR) over a CeO2-WO3 catalyst was investigated by temperature-programmed desorption (TPD) analysis and in situ diffuse reflectance infrared Fourier transform spectroscopy. The active sites were on CeO2, while WO3 greatly enhanced the amount and strength of the surface Brönsted acid sites and the NO oxidation ability. Both NH4+ and coordinated NH3 contributed to the SCR reaction. Bridging nitrate and monodentate nitrate were confirmed as the reactive nitrate species. Under SCR reaction conditions, surface NH4NO3 was formed, which played the role of an important intermediate species. Two different pathways for the SCR reaction were suggested for the CeO2-WO3 catalyst.摘要摘要：采用共沉淀法制备了新型 CeO2-WO3 复合氧化物催化剂, 并用于氨选择性催化还原 (NH3-SCR) NOx 反应中. 活性测试表明, 在 200∼450 ºC NOx 转化率接近 100%. 采用程序升温脱附和原位漫反射红外光谱研究了该催化剂上的 NH3-SCR 反应机理. 结果表明, 该催化剂的主要活性位是 CeO2, 而 WO3 的加入大大提高了其表面 Brönsted 酸位的数量与强度及其氧化 NO 的能力. 另外还发现, 除了催化剂表面 Lewis 酸与 Brönsted 酸参与反应外, 表面的桥式与单齿硝酸盐也是活性很高的物种. 整个 SCR 反应可通过以上两种途径进行.Chinese Journal of Catalysis 05/2011; 32(5):836–841. · 1.30 Impact Factor