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

Abstract

In this study, the growth of ZrOx on Au (111) was investigated using scanning tunneling microscopy (STM) and synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS). Nanostructures of ZrOx (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 ZrOx 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 ZrOx 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/ZrOx/Au(111) surfaces could undergo partial decomposition on Zr (CO2, gas → COgas + Oads), or react with oxygen sites from ZrOx to yield carbonates (Zr-CO3, 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.