H/D exchange experiments on a Cu/ZnO/Al₂O₃ catalyst have shown that methanol synthesis and RWGS display a strong thermodynamic isotope effect, which is attributed to differences in the zero-point energy of hydrogenated vs. deuterated species. The effect is larger for methanol synthesis and substantially increases the equilibrium yield in deuterated syngas. In the kinetic regime of CO₂ hydrogenation, an inverse kinetic isotope effect of H/D substitution was observed, which is stronger for methanol synthesis than for CO formation suggesting that the two reactions do not share a common intermediate. Similar observations were also made on other catalysts such as Cu/MgO, Cu/SiO₂, and Pd/SiO₂. In contrast to CO₂ hydrogenation, the CO hydrogenation on Cu/ZnO/Al₂O₃ did not show such a strong kinetic isotope effect indicating that methanol formation from CO₂ does not proceed via consecutive reverse water gas shift and CO hydrogenation steps. The inverse KIE is consistent with formate hydrogenation being the rate-determining step of methanol synthesis from CO₂. Differences in the extent of product inhibition by water, observed for methanol synthesis and reverse water gas shift indicate that the two reactions proceed on different surface sites in a parallel manner. The consequences for catalyst design for effective methanol synthesis from CO₂ are discussed.

中文翻译：

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在Cu / ZnO / Al2O3上将CO2加氢为甲醇和CO：是否存在常见的中间体？

在Cu / ZnO / Al ₂ O ₃催化剂上进行的H / D交换实验表明，甲醇合成和RWGS表现出很强的热力学同位素效应，这归因于氢化物种与氘代物种的零点能量差异。对于甲醇合成，效果更大，并大大提高了氘代合成气的平衡收率。在CO ₂氢化的动力学过程中，观察到H / D取代的逆动力学同位素效应，这对于甲醇合成而言比对CO形成更强，表明这两个反应没有共同的中间体。对其他催化剂如Cu / MgO，Cu / SiO ₂和Pd / SiO ₂也有类似的观察。与CO相反_在图2的氢化中，在Cu / ZnO / Al ₂ O ₃上的CO氢化没有显示出如此强的动力学同位素效应，表明由CO ₂形成的甲醇没有通过连续的反向水煤气变换和CO氢化步骤进行。逆KIE与甲酸酯加氢是一致的，甲酸酯加氢是由CO ₂合成甲醇的速率确定步骤。观察到的甲醇合成和逆向水煤气变换对水的产物抑制程度的差异表明，这两个反应在平行的不同表面上进行。讨论了由CO ₂有效合成甲醇的催化剂设计结果。