Shaaban Ehab, Li Gonghu
Department of Chemistry, University of New Hampshire, Durham, NH, 03824, USA.
Commun Chem. 2022 Mar 14;5(1):32. doi: 10.1038/s42004-022-00650-2.
The valorization of carbon oxides on metal/metal oxide catalysts has been extensively investigated because of its ecological and economical relevance. However, the ambiguity surrounding the active sites in such catalysts hampers their rational development. Here, in situ infrared spectroscopy in combination with isotope labeling revealed that CO molecules adsorbed on Ti and Cu interfacial sites in Cu/TiO gave two disparate carbonyl peaks. Monitoring each of these peaks under various conditions enabled tracking the adsorption of CO, CO, H and HO molecules on the surface. At room temperature, CO was initially adsorbed on the oxygen vacancies to produce a high frequency CO peak, Ti-CO. Competitive adsorption of water molecules on the oxygen vacancies eventually promoted CO migration to copper sites to produce a low-frequency CO peak. In comparison, the presence of gaseous CO inhibits such migration by competitive adsorption on the copper sites. At temperatures necessary to drive CO and CO hydrogenation reactions, oxygen vacancies can still bind CO molecules, and H spilled-over from copper also competed for adsorption on such sites. Our spectroscopic observations demonstrate the existence of bifunctional active sites in which the metal sites catalyze CO dissociation whereas oxygen vacancies bind and activate CO molecules.
由于碳氧化物在金属/金属氧化物催化剂上的增值具有生态和经济意义，因此已对其进行了广泛研究。然而，此类催化剂中活性位点的不明确性阻碍了它们的合理开发。在此，原位红外光谱结合同位素标记表明，吸附在Cu/TiO中Ti和Cu界面位点上的CO分子产生了两个不同的羰基峰。在各种条件下监测这些峰中的每一个能够追踪CO、CO₂、H₂和H₂O分子在表面上的吸附情况。在室温下，CO最初吸附在氧空位上以产生高频CO峰，即Ti-CO。水分子在氧空位上的竞争性吸附最终促使CO迁移到铜位点以产生低频CO峰。相比之下，气态CO的存在通过在铜位点上的竞争性吸附抑制了这种迁移。在驱动CO和CO₂加氢反应所需的温度下，氧空位仍可结合CO分子，并且从铜上溢出的H₂也竞争吸附在这些位点上。我们的光谱观察结果证明了双功能活性位点的存在，其中金属位点催化CO解离，而氧空位结合并活化CO分子。
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