Role of Reduced CeO₂(110) Surface for CO₂ Reduction to CO and Methanol

Abstract

Density functional theory (DFT) calculations were performed to study the mechanism of carbon dioxide (CO 2 ) reduction to carbon monoxide (CO) and methanol (CH 3 OH) on CeO 2 (110) surface. CO 2 dissociates to CO on interacting with the oxygen vacancy on reduced ceria surface.The oxygen atom heals the vacancy site and regenerates the stoichiometric surface via a redox mechanism with intrinsic activation and reaction energies of 259.2 kJ/mole and 238.6 kJ/mole respectively. Lateral interaction of oxygen vacancies were studied by the generation of two oxygen vacancies per unit of CeO 2 surface. Compared to a single isolated vacancy, the activation and reaction energies of CO 2 dissociation on a di-vacancy were approximately reduced to half of its value. Hydrogen atom co-adsorbed on the surface was observed to assist CO 2 dissociation by forming a carboxyl intermediate, CO 2 +H→COOH (∆E act = 39.0 kJ/mole, ∆H = -69.2 kJ/mole) which on subsequent dissociation produces CO via the redox mechanism. On hydrogenation, CO is likely to produce methanol. The energetics of CO hydrogenation to produce methanol showed exothermic steps with activation barriers comparable to the DFT calculations reported for Cu (111) and CeO 2-x /Cu(111) interface. While on the stoichiometric surface, COOH dissociation COOH→CO+OH (∆E act = 55.6 kJ/mole, ∆H =5.7 kJ/mole) is likely to be difficult as compared to rest of the elementary steps, whereas on the reduced surface the energetics of the same step were significantly lowered (∆E act = 47.4 kJ/mole, ∆H = -80.4 kJ/mole). In comparison, hydrogenation of methoxy, H 3 CO+H→H 3 COH, appears to be relatively difficult (∆E act = 58.7 kJ/mole) on the reduced surface.

The Synergistic Effect of CuZnCeOx in Controlling the Formation of Methanol and CO from CO2 Hydrogenation

“…also discovered the promotion role of Ce in methanol generation in their research . To understand the promotion mechanism of Ce from the theoretical level, many research groups performed DFT calculations and they have proved the activation ability of CO 2 at the Cu−CeO 2 interface ,,. However, there is still no systematic study of CeO x as a catalyst promoter in CuZnCeO x catalyst.…”

H2 Dissociation and Oxygen Vacancy Formation on Ce2O3 Surfaces

“…The former is related to the presence of oxygen vacancies without change of the crystalline structure (typically a fluorite) whereas the latter corresponds to the limit case where all the Ce atoms are reduced into Ce 3+ with a sesquioxide A-type (hexagonal) structure. 10 In the last years, much effort was put in the comprehension of the partial reduction impact on the ceria surface property [11][12][13][14][15][16] and reactivity [17][18][19][20][21] , with much less insight in Ce 2 O 3 compositions. In standard conditions of pressure and temperature, Ce 2 O 3 is not a stable material but recent development of new experimental techniques and protocols make possible the synthesis of Ce 2 O 3 particles.…”

CO2 Reduction by Hydrogen Pre‐Reduced Acceptor‐Doped Ceria

“…This was also found in the present work for both GDC10 and SDC15, as a relative increase of the carboxylate signal was observed on the pre‐reduced samples. Surface carboxylate or formate are suspected to be the reaction intermediates for the hydrogenation of CO 2 to methanol . As we observed carboxylates (but no formates) on reduced GDC10/SDC15 after CO 2 RT adsorption and subsequent CO 2 ‐TPO, this result might be interpreted in favor of the carboxylate mediated route.…”

“…Surface carboxylate or formate are suspected to be the reaction intermediates for the hydrogenation of CO 2 to methanol. [34,35,36] As we observed carboxylates (but no formates) on reduced GDC10/SDC15 after CO 2 RT adsorption and subsequent CO 2 -TPO, this result might be interpreted in favor of the carboxylate mediated route. However, it must be emphasized that our experiments showed the formation of CO (which is the product of the reverse water-gas shift reaction) and not the formation of methanol.…”