The relationship between valence state of cerium ion and the catalytic activity for dimethyl carbonate (DMC) synthesis directly from carbon dioxide and methanol was investigated by using four CeO₂ catalysts calcined at the different temperatures, which showed different concentrations of Ce⁴⁺ analyzed by XPS. In situ Fourier transform infrared spectroscopy (FTIR) was used to probe CO₂ and methanol adsorption species on ceria surface. With the calcination temperature increasing from 323 to 973 K, the concentration of Ce⁴⁺ increased, leading to larger proportion of active methanol adsorptions (Types I and II methoxy) and CO₂ adsorptions (bidentate carbonate). Meanwhile, high‐calcination temperature also led to small surface area and more –OH group dehydration, which resulted in the less formation of active Types I and II methoxy and bidentate carbonate. As a result, the ceria calcined at 773 K showed the highest activity and the one calcined at 973 K performed the lowest.

中文翻译：

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CeO2上铈离子价态对甲醇和二氧化碳合成碳酸二甲酯的影响

通过使用四种在不同温度下煅烧的CeO ₂催化剂，研究了铈离子的价态与直接由二氧化碳和甲醇合成碳酸二甲酯（DMC）的催化活性之间的关系，这表明XPS分析了不同浓度的Ce ⁴⁺。 。原位傅立叶变换红外光谱（FTIR）用于探测二氧化铈表面的CO ₂和甲醇吸附物质。随着煅烧温度从323 K升高到973 K，Ce ⁴⁺的浓度增加，导致活性甲醇（I和II型甲氧基）和CO _2的吸附比例增加吸附（二元碳酸盐）。同时，高煅烧温度还导致较小的表面积和更多的–OH基团脱水，从而导致活性I型和II型甲氧基和双齿碳酸盐的形成较少。结果，在773 K下煅烧的二氧化铈显示出最高的活性，而在973 K下煅烧的二氧化铈表现出最低的活性。