In Situ FT-IR Spectroscopic Study of CO₂ and CO Adsorption on Y₂O₃, ZrO₂, and Yttria-Stabilized ZrO₂

In situ FT-IR spectroscopy was exploited to study the adsorption of CO₂ and CO on commercially available yttria-stabilized ZrO₂ (8 mol % Y, YSZ-8), Y₂O₃, and ZrO₂. All three oxides were pretreated at high temperatures (1173 K) in air, which leads to effective dehydroxylation of pure ZrO₂. Both Y₂O₃ and YSZ-8 show a much higher reactivity toward CO and CO₂ adsorption than ZrO₂ because of more facile rehydroxylation of Y-containing phases. Several different carbonate species have been observed following CO₂ adsorption on Y₂O₃ and YSZ-8, which are much more strongly bound on the former, due to formation of higher-coordinated polydentate carbonate species upon annealing. As the crucial factor governing the formation of carbonates, the presence of reactive (basic) surface hydroxyl groups on Y-centers was identified. Therefore, chemisorption of CO₂ most likely includes insertion of the CO₂ molecule into a reactive surface hydroxyl group and the subsequent formation of a bicarbonate species. Formate formation following CO adsorption has been observed on all three oxides but is less pronounced on ZrO₂ due to effective dehydroxylation of the surface during high-temperature treatment. The latter generally causes suppression of the surface reactivity of ZrO₂ samples regarding reactions involving CO or CO₂ as reaction intermediates.