Abstract:

ZrO₂ catalysts with different Ce contents were synthesized by sol-gel method and used for carrying out to achieve the photothermal catalytic direct synthesis of dimethyl carbonate (DMC) from CO₂ and methanol. Experimental results revealed that the DMC yield via photothermal catalysis was obviously higher than single thermal catalysis, and Ce_0.25Zr_0.75O₂ had the best effect with the DMC yield of 3.084mmol/g, which was 1.9 times that of pure ZrO₂. XRD and TEM analysis results showed that Ce atoms were doped into the crystal lattice of ZrO₂, which led to the formation of cerium-zirconium solid solution and the increasing concentration of surface oxygen vacancies, improving the CO₂ adsorption capacity. The solid solution had smaller nano size and larger specific surface area, and its formation of mesoporous structure was more conducive to CO₂ diffusion. The energy band structure and optical absorption spectra confirmed that the photoresponse of solid solution was widened and the light utilization efficiency was raised. Besides, with the assistance of oxygen vacancy in the narrow band gap prompts, the efficient separation of photo-generated carriers would provide more photo-generated electrons and held for activating methanol and CO₂, and combine with acid-base sites on the surface of solid solution, realizing the highly efficient synthesis and selectivity of DMC. Finally, the reaction mechanism of photothermal catalysis synthesis of DMC from CO₂ and methanol over Ce_0.25Zr_0.75O₂ solid solution was proposed, which should provide excellent theoretical basis and experimental data for the research and development on the photothermal catalytic synthesis of DMC.

Key words: carbon dioxide(CO₂), dimethyl crbonate(DMC), photothermal co-catalysis, ceria-zirconia solid solution, oxygen vacancies

摘要：

采用溶胶-凝胶法合成不同铈含量的ZrO₂催化剂，用于光热协同催化CO₂与甲醇直接合成碳酸二甲酯（DMC）。实验发现，光热催化的DMC产率明显高于热催化，且Ce_0.25Zr_0.75O₂具有最高DMC产率3.084mmol/g，是纯ZrO₂的1.9倍。XRD和TEM分析表明：Ce原子掺入ZrO₂晶格形成铈锆固溶体同时增加其表面氧空位浓度，提高吸附CO₂能力；固溶体的纳米尺寸减小、比表面积增大和介孔结构丰富，有利于CO₂扩散。能带结构和光吸收光谱表明：铈锆固溶体光响应范围拓宽且有效利用率提高；氧空位辅助窄带隙特征可促使光生载流子有效分离，允许更多光生电子和空穴参与CO₂及甲醇的活化，加之固溶体表面酸碱位点的协同作用，最终实现高效率高选择性合成DMC。最后，提出了铈锆固溶体光热催化CO₂与甲醇合成DMC的反应机理，为光协同热催化合成DMC的研究提供良好的理论基础和实验数据。

关键词: 二氧化碳, 碳酸二甲酯, 光热协同催化, 铈锆固溶体, 氧空位