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    ZnxCe2−yZryO4/SAPO−34双功能催化剂上CO2加氢合成低碳烯烃

    CO2 synthesis of lower olefins over ZnxCe2−yZryO4/SAPO−34 bifunctional catalyst

    • 摘要: CO2加氢经接力催化转化为高附加值化学品是实现绿色低碳化工的重要路径之一。系统探讨了ZnxCe2−yZryO4/SAPO−34双功能催化剂在CO2加氢制备低碳烯烃(C2=~C4=)中的催化性能,重点考察了金属氧化物的制备方法(溶胶凝胶法、共沉淀法、水热法)对其结构特性、表面氧空位浓度、加氢能力及催化行为的影响。通过XRD、H2-TPR、CO2-TPD、Raman、原位DRIFTS等多种表征手段,系统分析了不同合成方法对ZnxCe2−yZryO4物相结构、还原性能、CO2吸附能力及反应中间体演化规律的影响。进一步优化了反应温度、压力、空速、氧化物与分子筛质量比及耦合方式等工艺条件,揭示了双功能催化剂中甲醇/乙烯酮中间体的生成与转化机制。结果表明,采用溶胶凝胶法(以葡萄糖为络合剂)制备的Zn0.5Ce0.2Zr1.8O4氧化物与SAPO−34分子筛机械混合后,在反应温度为350 ℃、压力为4 MPa、空速为6000 mL/(g·h)的条件下表现出最优的催化性能:CO2转化率达12.44%,烃类产物中低碳烯烃(C2=~C4=)选择性高达78.47%,副产物CO的选择性仅为36.23%。与之相比,水热法制备的样品CO选择性较高、低碳烯烃选择性较低;共沉淀法虽能形成良好固溶体结构,但氧空位浓度与加氢能力均弱于溶胶凝胶法。Raman与CO2-TPD结果表明:溶胶凝胶法制备的催化剂具有最高的表面氧空位浓度,有利于CO2的吸附与活化;原位DRIFTS进一步证实,该方法制备的氧化物表现出最强的中间体加氢能力,能够高效促进甲醇/甲酸盐物种向低碳烯烃的转化。系统揭示了金属氧化物制备方法对ZnCeZrOx/SAPO−34双功能催化剂结构与性能的调控机制,为高性能CO2加氢制低碳烯烃催化剂的设计提供了理论依据与试验支撑。

       

      Abstract: CO2 hydrogenation via relay catalysis to produce high-value chemicals is one of the important pathways for achieving green and low-carbon chemical processes. This study systematically investigates the catalytic performance of ZnxCe2−yZryO4/SAPO−34 bifunctional catalysts for CO2 hydrogenation to light olefins (C2=~C4=), with a focus on the effects of different preparation methods of metal oxides (sol-gel, co-precipitation, and hydrothermal methods) on their structural properties, surface oxygen vacancy concentration, hydrogenation capacity, and catalytic behavior. Various characterization techniques, including XRD, H2-TPR, CO2-TPD, Raman spectroscopy, and in situ DRIFTS, were employed to systematically analyze the influence of different synthesis methods on the phase structure, reducibility, CO2 adsorption capability, and evolution of reaction intermediates of ZnxCe2−yZryO4. Furthermore, the reaction temperature, pressure, gas hourly space velocity (GHSV), mass ratio of oxide to zeolite, and coupling mode were optimized, and the generation and conversion mechanism of methanol/ketene intermediates over the bifunctional catalyst were elucidated. The results indicate that the catalyst prepared by the sol-gel method (using glucose as a complexing agent) combined with SAPO−34 zeolite via physical mixing exhibits the best catalytic performance under the conditions of 350 ℃, 4 MPa, and a GHSV of 6000 mL/(g·h): CO2 conversion reaches 12.44%, the selectivity for light olefins (C2=~C4=) in hydrocarbon products is as high as 78.47%, and the selectivity for the byproduct CO is only 36.23%. In contrast, the sample prepared by the hydrothermal method shows higher CO selectivity and lower light olefin selectivity. Although the co-precipitation method can form a well-defined solid solution structure, its oxygen vacancy concentration and hydrogenation capacity are both inferior to those of the sol-gel method. Raman and CO2-TPD results demonstrate that the catalyst prepared by the sol-gel method possesses the highest surface oxygen vacancy concentration, which facilitates CO2 adsorption and activation. In situ DRIFTS further confirms that the oxide prepared by this method exhibits the strongest hydrogenation capability for intermediates, efficiently promoting the conversion of methanol/formate species to light olefins. This study systematically reveals the regulatory mechanism of metal oxide preparation methods on the structure and performance of ZnCeZrOx/SAPO−34 bifunctional catalysts, providing theoretical insights and experimental support for the design of high-performance catalysts for CO2 hydrogenation to light olefins.

       

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