Adsorption of CO2 and Facile Carbonate Formation on BaZrO3 Surfaces

Abstract

The adsorption of CO2 and CO on BaZrO3 (0 0 1) was investigated by first-principles calculations with a focus on the BaO termination. CO2 was found to strongly chemisorb on the surface by formation of carbonate species with an adsorption enthalpy of up to −2.25 eV at low coverage and −1.05 eV for a full monolayer. An adsorption entropy of −8.8 × 10–4 eV K–1 was obtained from the vibrational properties of the adsorbates. Surface coverages were evaluated as a function of temperature and CO2 partial pressure, and the obtained coverage under 1 bar CO2 was more than 0.8 at 1000 K (conditions relevant for steam methane reforming). The fully saturated surface was stable up to about 400 K under ambient atmosphere, i.e., 400 ppm of CO2. The initial stage of BaCO3 formation was evaluated according to migration of barium to the carbonate overlayer, which was found to result in a significant stabilization of the system. The barium migration was found to be essentially unobstructed with a barrier of only ∼5 meV. In light of the stability of carbonate adsorbates at the surface, the prospect of bulk dissolution of carbonate species was evaluated but ultimately found to be negligible in acceptor-doped BaZrO3.