SO2对NO催化氧化过程的影响V.NiO/γ-Al2O3上SO2的作用机理

采用程序升温脱附(TPD)及漫反射原位红外光谱(DRIFT)技术分析比较了SO2存 在前后，NO—02反应气体在NiO／γ—Al2O3催化剂上所形成吸附物种的变化情况， 发现SO2能促使硝酸盐物种在低温分解并释放出NO2，而且耐热稳定的硝酸盐物种也 比单纯NO-02吸附时多．室温时催化剂表面上的SO2以弱吸附物种为主，特征红外吸 收峰位于1324cm^-1附近，温度升高后表面硫酸盐物种数量增多．关联SO2气氛中 NO2的生成规律后得出，类似于铅室反应中间体的多分子吸附物种NO2(SO3)x]是产 生N02的活性物种，由SO2在载体或催化剂表面弱碱位吸附后吸引气相NO所产生，解 离O^-起到稳定活性物种和补充弱碱位的作用．同时该物种也是毒性物质SO4^2-的 前驱体，当KO氧化反应发生后催化剂的失活也开始了．

Effect of SO2 on NO Catalytic Oxidation V. MechaniSm of SO2 Promotion over NiO/

The influence of SO2 on the adsorption of NO-O2 on the surface of NiO/γ-Al2O3 was investigated by use of temperature programmed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). It was found that there are a large quantity of nitro and nitrites as well as monodentate nitrates formed after NO-O2 adsorption at room temperature, while the bidentate and bridged nitrates are predominant and the desorption of NO2 increases after NO- O2-SO2 adsorption. SO2 is adsorbed in significant amounts as weakly bonded species, which is characterized by an intense and broad band near 1324 cm-1. Small amounts of sulfates are present on the catalyst surface even at room temperature and grow with increasing adsorption temperature and treatment time. The decomposition of nitrates at low temperatuies can account for the release of NO2 during reaction in the presence of SO2. A mechanism is proposed to explain the role of SO2 in NO catalytic oxidation at low temperatures. Several types of multi- molecular intermediate species such as NO2 (SO3 ),. ] the composition of which is similar to the chamber crystals are suggested as active species for producing NO2. These species are formed by combining NO in the structure of coordinated nitrates with SO2 adsorbed on either weakly basic O2- sites or the basic OH- groups. Adsorbed O2 species dissociated on neighboring active metal sites such as Ni2 + also participate in the formation of the multi-molecular intermediate and are helpful to the stability of the intermediate structures. The continuous adsoiption of SO2 on the freesites, especially on the Lewis acid sites near the intermediate species finally breaks down the intermediate structures. The decomposition of multi-molecular intermediates, which is responsible for the release of NO2 > however, leads to the sulfation of the catalyst at the same time. As a result, the deactivation of the catalyst occurs.