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    非均相催化以胺/芳烃为底物的CO2还原功能化研究进展

    Progress on heterogeneous catalysis for reductive functionalization of CO2 with amines/aromatics and H2

    • 摘要: CO2还原功能化反应将CO2还原和C—X键的形成相偶联,从而将CO2以甲酰基、甲基等形式引入有机分子,极大地扩展了CO2转化可获得的产物范围。其中非均相催化以胺类化合物或芳香烃为底物、H2为还原剂的CO2还原功能化反应,有望用于工业规模甲酰胺、甲基胺和甲基芳烃等重要化学品的生产,因而是近年来的研究热点。在以胺类化合物为底物的CO2还原功能化反应中,常采用Pd、Au、Pt、Ru、Re、Ir、Cu和Co等金属纳米材料,通过载体种类及载体表面官能团修饰、有机配体或金属氧化物修饰金属纳米颗粒以及形成合金等策略,有效调控活性金属中心的电子结构并在载体上引入多个活性位点,提高金属中心对H2的活化能力以及催化剂对CO2、胺类底物以及还原功能化中间体的吸附活化能力,从而提高催化剂活性和稳定性并调控N−甲酰化和N−甲基化产物选择性。对于以芳香烃为底物的CO2还原功能化反应,则采用金属混合氧化物或Re/TiO2与分子筛组成的双功能催化剂,其中金属混合氧化物或Re/TiO2将CO2还原至甲醇,而分子筛中的酸性位点则活化甲醇和芳香烃并促进C—C偶联,形成甲基化产物。通过调控金属混合氧化物的组成、分子筛的种类以及分子筛中酸性位点的种类、密度和分布,优化混合氧化物和分子筛的混合比例和混合方式等策略,能有效提高CO2催化加氢和芳香烃甲基化效率,并使甲醇生成、迁移和消耗速率相匹配,从而提高原料转化率和目标产品选择性;目前,CO2和芳香烃的转化率达到30%以上,产物选择性超过90%。目前,CO2还原功能化反应在非均相催化剂设计和产物调控方面积累了系统的研究成果,为后续技术革新与应用奠定了坚实基础。

       

      Abstract: The reductive functionalization of CO2 couples CO2 reduction with C—X bond formation, incorporating CO2 into organic molecules as formyl, methylene, hydroxymethyl, or methyl groups, thereby significantly expanding the product scope of CO2 conversion. Particularly, the heterogeneous catalyzed reductive functionalization of CO2 with amines/aromatics using H2 as reductant shows great potential for industrial-scale production of valuable chemicals such as formamides, methylamines, and methylated aromatics, which makes it a research hotspot. In the reductive functionalization of CO2 with amines, supported metal nanomaterials (e.g., Pd, Au, Pt, Ru, Re, Ir, Cu, and Co) are widely used. Strategies such as support selection and surface modification, decoration of metal nanoparticles with organic ligands or metal oxides, and alloy formation have been utilized to tune the electronic structure of active metal centers and introduce multiple active sites on the support. These strategies can promote H2 activation at the metal centers and enhance the adsorption and activation of CO2, amine substrates, and the corresponding intermediates on the catalyst. Consequently, the catalytic activity, cyclic stability and the selectivity to N-formylation or N-methylation product can be improved. In the methylation reactions of aromatics with CO2 and H2, dual-functional catalysts composed of mixed metal oxides (or Re/TiO2) and zeolites are employed. In the reaction, the mixed metal oxides (or Re/TiO2) reduce CO2 to methanol while the acidic sites of the zeolite activate methanol and aromatics to promote C—C coupling and thus produce methylated products. By tailoring the composition of the mixed metal mixed oxide and the acidic sites (type, density, and distribution) of the zeolite, as well as optimizing the mixing ratio and mode of these two components, the efficiency of CO2 hydrogenation and aromatics methylation can be significantly improved and the methanol generation, migration, and consumption rates are balanced, thereby enhancing both feedstock conversion and target product selectivity. By far, the CO2 and aromatics conversion rates can exceed 30% with product selectivity surpassing 90%. Currently, systematic research achievements have been obtained for CO2 reductive functionalization in the heterogeneous catalyst design and product regulation, laying a solid foundation for subsequent technological innovation and applications.

       

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