Mechanism of Selective Catalytic Reduction of NOx with NH3 over CeO2-WO3 Catalysts

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.

Graphical abstractThe high catalytic activity of CeO2-WO was due to its having more acid sites and active nitrate species. The mechanism of selective catalytic reduction had two pathways.Figure optionsDownload full-size imageDownload as PowerPoint slide