CO₂ Reduction by Hydrogen Pre‐Reduced Acceptor‐Doped Ceria

Abstract

The reactivity of H2 pre‐reduced acceptor‐doped ceria materials Gd0.10Ce0.90O2‐δ (GDC10) and Sm0.15Ce0.85O2‐δ (SDC15) was tested with respect to the reduction of CO2 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 CO2. 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 CO2 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 CO2 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 (O2 oxidation or H2 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. Ce4+ reduction to Ce3+ (by H2) and re‐oxidation to Ce4+ (by CO2) on GDC10/SDC15 were directly monitored by infrared spectroscopic analysis of a distinct, IR‐active electronic transition of Ce3+. These results show the complex interplay of oxygen vacancy/dissolved hydrogen reactivity and surface chemical aspects in acceptor‐doped ceria materials.

One-Pot Synthesis of Ni0.05Ce0.95O2−δ Catalysts with Nanocubes and Nanorods Morphology for CO2 Methanation Reaction and in Operando DRIFT Analysis of Intermediate Species

“…In the region between 2200 and 1150 cm −1 , the observed bands are mainly due to the interaction of CO 2 with the CeO 2 surface. It is important to emphasize that pre-reduction up to 500 • C guarantees a Ce 3+ containing layers (surface-subsurface), as evidenced by a negative, although not very intense, peak at 2114 cm −1 corresponding to the Ce 3+ transition, a phenomenon also observed on CeO 2 solid solutions with aliovalent elements, such as Gd 3+ or Sm 3+ by M. Grünbacher et al [54]. At 200 • C, intense bands appeared at 1612, 1390, and 1216 cm −1 assigned to the ν a (CO 3 ), ν s (CO 3 ) and δ(OH) vibrations of bicarbonate species chemisorbed on reduced CeO 2 [12,52,55,56].…”

Coking-resistant dry reforming of methane over Ni/γ-Al2O3 catalysts by rationally steering metal-support interaction

“…All samples got a sharp peak at about 90 C, which was attributed to desorption of weak-bonded bicarbonate (Keturakis et al, 2014). Smooth peaks at 370 C and 550 C, which originated from desorption of monodentate carbonate (weak basic site) and polydentate carbonate (strong basic site), respectively (Ewald and Hinrichsen, 2019;Grü nbacher et al, 2019;Zheng et al, 2019), appeared in L-Ni/g-Al 2 O 3 . The intensity of these two peaks intensified with Ni loading and a new desorption peak at 500 C appeared, which was possibly derived from a kind of bidentate carbonate (Busca and Lorenzelli, 1982 (Ewald and Hinrichsen, 2019).…”

Improvement of Process Conditions for H2 Production by Chemical Looping Reforming

“…A low activation energy of 36 ± 4 kJ/kmol for the oxygen regeneration of ceria was previously reported by Bulfin et al [69], which is compatible with the observed low effect of reaction temperature on kinetics. On the other hand, the mechanism of CeO2 regeneration through H2O or CO2 oxidation has been observed to involve the formation of hydride, hydroxyl, and carbonate species [70][71][72][73]. 1.0 ± 0.1 1.2 ± 0.2 1.44 ± 0.05 The easiness of regeneration, together with a carrier reduction close to the theoretical values, makes ceria a suitable OC to conduct repeated cycles, while 950 °C may be identified as the best operating temperature as it represents a reasonable trade-off between rapid reforming kinetics, carbon deposition, and energy penalties.…”