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 this work, 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/CuO_x/Cu(111) system, which has the potential to achieve a high selectivity for a direct CO₂ to methanol transformation. The morphology of ZrO₂ was strongly affected by the preparation method. The ZrO₂/CuO_x/Cu(111) model catalyst prepared by the oxidation at 600 K of Zr pre-deposited on Cu(111) exhibited substantial mixing of ZrO₂ and CuO_x. In contrast, the direct deposition of Zr under an O₂ ambient over CuO_x/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/CuO_x/Cu(111) surfaces. The model catalyst prepared by the direct deposition of Zr in O₂ was annealed up to 700 K in ultra-high vacuum. Both STM and XPS results suggest no apparent change in ZrO₂, while CuO_x was reduced at such annealing conditions. The island size of 10-12 nm observed for ZrO₂ on Cu(111) is much smaller than island sizes seen for CeO₂ (30-50 nm) and ZnO (300-500 nm) on the same substrate, opening the possibility for unique chemical properties.

Jindong Kang

Appearances