CO 2 Reduction by Hydrogen Pre‐Reduced Acceptor‐Doped Ceria

The reactivity of H 2 pre‐reduced acceptor‐doped ceria materials Gd 0.10 Ce 0.90 O 2‐δ (GDC10) and Sm 0.15 Ce 0.85 O 2‐δ (SDC15) was tested with respect to the reduction of CO 2 to CO in the context of the reverse water‐gas shift reaction. It was demonstrated that not only oxygen vacancies, but also dissolved hydrogen is a reactive species for the reduction of CO 2 . Dissolved hydrogen must be considered upon discussion of the mechanism of the reverse water‐gas shift reaction on ceria‐derived materials apart from oxygen vacancies and formates. The reduction of CO 2 is preceded by the formation of carbonate species of different thermal stability and reactivity. The stability of these carbonates was directly demonstrated by in situ infrared spectroscopy and revealed the largely reversible nature of CO 2 ad‐ and desorption. In comparison to pre‐reduced samples, decreased carbonate coverage is obtained after oxidative treatments of GDC10 and SDC15. No significant effect of the sample treatment (O 2 oxidation or H 2 reduction) on the surface carbonate stability was noticed. Mono‐dentate carbonates and carboxylates appear to be more easily formed on pre‐reduced (i. e. defective) samples. Ce 4+ reduction to Ce 3+ (by H 2 ) and re‐oxidation to Ce 4+ (by CO 2 ) on GDC10/SDC15 were directly monitored by infrared spectroscopic analysis of a distinct, IR‐active electronic transition of Ce 3+ . These results show the complex interplay of oxygen vacancy/dissolved hydrogen reactivity and surface chemical aspects in acceptor‐doped ceria materials.