基于钛锡载体的SCR低温脱硝催化剂的表面性质研究

摘要

TiO2-SnO2 mixed oxide was prepared by a co-precipitation method and xCeO2/TiO2-SnO2 catalysts were prepared using the impregnation method. The physicochemical properties were investigated by X-ray diffraction ( XRD) , BET specific surface area measurement, H2 temperature-programmed reduction ( H2-TPR) , NH3 temperature-programmed desorption ( NH3-TPD ) , high-resolution transmission electron microscopy ( HRTEM ) , and in situ diffuse reflectance infrared spectroscopy ( DRIFTS ) . Meanwhile, their catalytic performance for the selective catalytic reduction of NOx with NH3 ( NH3-SCR) was tested. It was found that 0. 1Ce/TiO2-SnO2 had higher NOx conversion and wider temperature range of 250 ~350℃. Excess loading of CeO2 could lead to the decrease of specific surface area, redox ability and adsorption capacity of ammonia as well as the shrink of effective catalytic temperature range. NH3-TPD result showed that the adsorption of NH3 in weak acid and medium acid sites were significantly enhanced by CeO2 , which was related to the decrease of NH3-SCR reaction temperature. In situ DRIFTS indicated that the strength of Lewis acid sites and Brφnsted acid Sites were markedly enhanced for xCeO2/TiO2-SnO2 catalyst. Besides, new Brφnsted acid Sites appeared at 1 657 ~1 666 cm-1 and NH+4 played the dominant role in the SCR reaction.%采用共沉淀法制备TiO2-SnO2固溶体,浸渍法负载CeO2得到一系列xCeO2/TiO2-SnO2负载型催化剂,在模拟NH3选择性催化还原NOx( NH3-SCR)反应条件下考察催化剂低温脱硝活性。通过X射线衍射( XRD)、比表面积测定( BET)、程序升温还原(H2-TPR)、程序升温脱附(NH3-TPD)、高分辨率透射电子显微镜(HRTEM)、原位漫反射傅里叶变换红外光谱(in situ DRIFTS)等表征技术,研究了氧化铈负载后催化剂的微观结构、表面物种的存在状态、表面酸位等表面性质及NH3吸附特性。结果表明,Ce：Ti 物质的量比为0.1时,催化剂催化脱硝反应活性最高,同时具有较宽的温度窗口(250~300℃)和热稳定性；铈的过量负载会导致催化剂比表面积减小、活性窗口变窄,同时其氧化还原能力和NH3吸附能力也减弱。 NH3-TPD结果显示,CeO2的负载导致催化剂NH3在弱酸及中等酸位的吸附显著增强,与催化剂NH3-SCR最佳反应物温度降低有关。 in situ DRIFTS表明,xCeO2/TiO2-SnO2催化剂的Lewis酸位和Brφnsted酸位强度均明显增强,同时,在1657~1666 cm-1处出现新的Brφnsted酸位,参与SCR反应的主要物质是NH+4分子。