Abstract
The adsorption of CO2 on the Fe3O4(001)-(2 × 2)R45° surface was studied experimentally using temperature programmed desorption (TPD), photoelectron spectroscopies (UPS and XPS), and scanning tunneling microscopy. CO2 binds most strongly at defects related to Fe2+, including antiphase domain boundaries in the surface reconstruction and above incorporated Fe interstitials. At higher coverages,CO2 adsorbs at fivefold-coordinated Fe3+ sites with a binding energy of 0.4 eV. Above a coverage of 4 molecules per (2 × 2)R45° unit cell, further adsorption results in a compression of the first monolayer up to a density approaching that of a CO2 ice layer. Surprisingly, desorption of the second monolayer occurs at a lower temperature (≈84 K) than CO2 multilayers (≈88 K), suggestive of a metastable phase or diffusion-limited island growth. The paper also discusses design considerations for a vacuum system optimized to study the surface chemistry of metal oxide single crystals, including the calibration and characterisation of a molecular beam source for quantitative TPD measurements.
Highlights
CO2 is one of the most common components in the atmosphere of planets and at the surfaces of interstellar dust grains, which makes understanding both the gaseous and solid phases important for astrophysical research.1–3 On Earth, emissions of CO2 into the atmosphere are rising, and there is a growing effort to develop carbon-capture and storage technologies (CO2 sequestration) to mitigate global warming
We study the adsorption of CO2 on the Fe3O4(001) surface utilizing an experimental ultrahighvacuum (UHV) setup optimized to study the surface chemistry of single-crystal metal-oxide samples
The paper begins with a description of the new vacuum system, with a focus on how we combine an effusive molecular beam (MB) source and a special sample mount to perform quantitative temperature programmed desorption (TPD) measurements of bulk oxide single crystals
Summary
CO2 is one of the most common components in the atmosphere of planets and at the surfaces of interstellar dust grains, which makes understanding both the gaseous and solid phases important for astrophysical research. On Earth, emissions of CO2 into the atmosphere are rising, and there is a growing effort to develop carbon-capture and storage technologies (CO2 sequestration) to mitigate global warming. On Earth, emissions of CO2 into the atmosphere are rising, and there is a growing effort to develop carbon-capture and storage technologies (CO2 sequestration) to mitigate global warming. As such there is much interest in the interaction of CO2 with components of the environment including water and Earth abundant minerals.. We study the adsorption of CO2 on the Fe3O4(001) surface utilizing an experimental ultrahighvacuum (UHV) setup optimized to study the surface chemistry of single-crystal metal-oxide samples. Additional CO2 molecules initially compress the monolayer before a complete second layer is formed. This second monolayer is less strongly bound than multilayer CO2 ice
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