Preparation and Structural Characterization of ZrO₂/CuOₓ/Cu(111) Inverse Model Catalysts
2020
Shi, Rui | Mahapatra, Mausumi | Kang, Jindong | Orozco, Iván | Senanayake, Sanjaya D. | Rodríguez, José A.
CO₂ hydrogenation to methanol is regarded as a promising reaction to catalytically convert a major greenhouse gas (CO₂) into a value-added product (methanol). In the current study, scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) were applied to investigate the growth mode of low coverages (<0.2 ML) of ZrO₂ in an inverse ZrO₂/CuOₓ/Cu(111) system, which has the potential to achieve high selectivity for a direct CO₂-to-methanol transformation. It was found that the morphology of ZrO₂ was strongly affected by the preparation method. The ZrO₂/CuOₓ/Cu(111) model catalyst prepared by the oxidation at 600 K of Zr predeposited on Cu(111) exhibited substantial mixing of ZrO₂ and CuOₓ. In contrast, the direct deposition of Zr under an O₂ ambient over CuOₓ/Cu(111) at 600 K produced small ZrO₂ islands (10–12 nm in size) with a two-dimensional structure (i.e., only one layer of ZrO₂). XPS studies indicate that both preparation methods lead to ZrO₂/CuOₓ/Cu(111) surfaces. The model catalyst prepared by the direct deposition of Zr in an O₂ ambient was annealed up to 700 K in an ultrahigh vacuum. Both STM and XPS results suggest no apparent change in ZrO₂, while CuOₓ was reduced at such annealing conditions. The island size of 10–12 nm observed for ZrO₂ on Cu(111) is much smaller than those seen for CeO₂ (30–50 nm) and ZnO (300–500 nm) on the same substrate, opening the possibility for unique chemical properties.
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