反应过程中Cu物种演变对其催化甲醇氧化羰基化反应活性的影响

以NH₄Y分子筛为载体、 乙酰丙酮铜为铜源, 采用固相反应法制备了无氯CuY催化剂, 并用于催化甲醇氧化羰基化合成碳酸二甲酯(DMC). 结合不同反应时间催化剂的X射线衍射(XRD)、 N₂吸附-脱附、 热重(TG)、 程序升温脱附/还原(NH₃-TPD/H₂-TPR)、 透射电子显微镜(TEM)和X射线光电子能谱(XPS)等表征结果, 分析了反应过程中Cu物种演变对其催化活性的影响. 结果表明, 新鲜催化剂中铜物种主要以Cu⁺形式存在, 占铜物种的48%; 随着反应的进行, 活性中心Cu⁺逐渐被氧化为Cu²⁺, 进而生成CuO物种, 部分CuO逐渐迁移至催化剂外表面. 在反应100 h内, Cu⁺含量逐渐减小至36.7%, CuO含量增加, 导致DMC的时空收率及选择性不断下降, 副产物二甲氧基甲烷(DMM)和甲酸甲酯(MF)的选择性逐渐提高. 当反应时间延长至190 h时, Cu⁺含量为33.6%, 略有下降, DMC的时空收率和选择性趋于平稳. 继续延长反应时间至300 h, 催化剂中铜物种状态基本不变, 催化剂催化性能保持稳定.

Influence of Structure Evolution of CuY Catalyst During the Reaction Process on Its Catalytic Performance for Oxidative Carbonylation of Methanol†

Chloride-free CuY catalyst prepared by solid state reaction with NH₄Y zeolites as support and copper acetylacetone as copper source was evaluated for oxidative carbonylation of methanol to dimethyl carbonate(DMC). Combining the results of X-ray diffraction(XRD), N₂ adsorption-desorption isotherm, thermogravimetric(TG) analysis, NH₃-temperature-programmed desorption(NH₃-TPD), transmission electroon microscopy(TEM) and X-ray photoelectron spectroscopy(XPS) characterization, the influence of copper species evolution during the reaction process on its catalytic performance was disclosed. The results indicated that Cu⁺ was the dominant Cu species of fresh catalyst with the percentage of 48%. As the reaction proceeded, the active center Cu⁺ was gradually oxidized to Cu²⁺, and then formed CuO, part of which gradually migrated to the outer surface of the catalyst. With the reaction time extended to 100 h, the percentage of Cu⁺ gradually decreased to 36.7%, while the percentage of CuO continued to increase, accordingly resulting in the decrease of the space-time yield and selectivity of DMC and the increase of the selectivity of byproducts dimethoxymethane(DMM) and methyl formate(MF). With the reaction time extended to 190 h, the percentage of Cu⁺ decreased slowly to 33.6%, the space time yield and selectivity of DMC tended to be stable. When the reaction time extended to 300 h, the copper species in the catalyst remained unchanged, and the catalytic performance of the catalyst remained stable.