Ce1-xMnxO2表面性质对催化CO2和甲醇直接合成DMC反应活性的影响

通过共沉淀法制备了一系列Mn掺杂量不同的Ce_1-xMn_xO₂催化剂, 并将其用于催化CO₂和甲醇直接合成碳酸二甲酯(DMC). 通过X射线衍射(XRD)、 氮气吸附-脱附、 透射电子显微镜(TEM)、 X射线光电子能谱(XPS)和程序升温脱附(TPD)等手段研究了Ce_1-xMn_xO₂表面性质对催化CO₂和甲醇直接合成DMC反应活性的影响. 结果表明, Mn离子进入CeO₂晶格中形成固溶体, 随着Mn掺杂量增加, 催化剂表面弱酸碱位数量逐渐降低, 中强酸碱和强酸碱位数量增加, 催化剂表面氧空位含量呈先增加后减少的变化趋势, 当Mn掺杂量较少时, 催化剂表面Mn²⁺比例较高, 有利于Ce⁴⁺+Mn²⁺→Ce³⁺+Mn³⁺反应的进行, 促进催化剂表面氧空位生成; 进一步提高Mn掺杂量时, 催化剂表面Mn⁴⁺比例提高, 有利于Ce³⁺+Mn⁴⁺→Ce⁴⁺+Mn³⁺反应的进行, 导致催化剂表面氧空位含量减少. 研究发现Ce_1-xMn_xO₂催化剂活性与表面氧空位含量线性相关.

Surface Properties of Ce1-xMnxO2 Catalyst on the Catalytic Activities for Direct Synthesis of DMC from CO2 and Methanol

A series of Ce_1-xMn_xO₂ catalysts with different Mn doping amounts were prepared by coprecipitation method and applied to catalyze direct synthesis of dimethyl carbonate(DMC) from CO₂ and methanol. The effects of surface properties of Ce_1-xMn_xO₂ on the direct synthesis of DMC from CO₂ and methanol were studied by means of X-ray diffraction(XRD), N₂ adsorption-desorption, transmission electron microscopy(TEM), X-ray photoelectron spectroscopy(XPS) and programmed temperature desorption(TPD). The results indicated that Mn ions successfully entered into the lattice of CeO₂ and formed a uniform solid solution. With the increase of Mn doping, the number of weak acid and base sites on the catalyst surface decreased gradually, while the number of medium and strong acid and base sites increased. Meanwhile, the oxygen vacancy content on the catalyst surface increased first and then decreased with the increase of Mn doping. When the doping of Mn was low, the ratio of Mn²⁺ on the catalyst surface was high, which was beneficial for the reaction of Ce⁴⁺+ Mn²⁺→Ce³⁺+ Mn³⁺ and the formation of oxygen vacancies. With further increase of Mn doping, the ratio of Mn⁴⁺ on the catalyst surface increase, which was conducive to the reaction of Ce³⁺+Mn⁴⁺→Ce⁴⁺+Mn³⁺, resulting in the decrease of oxygen vacancy. The catalytic activity of Ce_1-xMn_xO₂ catalyst was linearly correlated with the content of oxygen vacancy on surface.