Understanding the morphology and chemical activity of model ZrOx/Au (111) catalysts for CO2 hydrogenation

Abstract

In this study, the growth of ZrO_x on Au (111) was investigated using scanning tunneling microscopy (STM) and synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS). Nanostructures of ZrO_x (x = 1,2) at the sub-monolayer (≤ 0.3 ML) level were prepared by vapor depositing Zr metal onto Au (111) followed by oxidation with O₂ or CO₂. At low coverages of the admetal (< 0.05 ML), the formed ZrO_x nanostructures were dispersed randomly on the terraces and steps of the Au(111) substrate. Strong oxide-metal interactions prevented the formation of islands of zirconia. The ZrO_x nanostructures displayed a reactivity towards CO₂ and H₂ not seen for bulk zirconia. C 1 s AP-XPS results indicated that CO₂ molecules adsorbed on Zr/ZrO_x/Au(111) surfaces could undergo partial decomposition on Zr (CO_{2, gas} → CO_gas + O_ads), or react with oxygen sites from ZrO_x to yield carbonates (Zr-CO_{3, ads}). After exposing ZrO₂/Au (111) surfaces to 1:3 mixtures of CO₂:H₂, the formation of HCOO, CO₃, and CH₃O was detected in AP-XP spectra. These chemical species decomposed at temperatures in the range of 400‒600 K, making them possible reaction intermediates for methanol synthesis.