One-pot synthesis of iron-doped ceria catalysts for tandem carbon dioxide hydrogenation

Abstract

We report on the one-pot synthesis of inexpensive and abundant CeO₂ and 1.5, 4.5, and 9 mol% Fe-doped ceria (Ce_1−xFe_xO_2−δ) systems and their catalytic activity for tandem CO₂ hydrogenation. XAFS and XRD demonstrate that oxygen vacancies are generated via two mechanisms: firstly, by the substitution of Ce⁴⁺ by Fe³⁺ in the lattice and the subsequent loss of oxygen anions. Secondly, by the partial reduction of Ce⁴⁺ to Ce³⁺, which is enhanced by the presence of Fe. All the samples tested show high activity for CO₂ hydrogenation and the production of CO, CH₄, and light (C₂–C₄) alkanes and alkenes, with the 9 mol% Fe-doped CeO₂ showing the best performance in terms of CO₂ reaction rate and product selectivity. During reaction, Fe exsolves/seggregates from the ceria, resulting in particles decorating the surface of the catalyst and increasing the reaction rates of CO₂. This system is composed of two functionalities, the oxygen vacancy and the Fe, whose close vicinity results in a high selectivity toward CO and CH₄ detrimental to the more valuable hydrocarbons. A rather complex interplay between the two functionalities, their interface, and the particle size of the catalysts exists for this tandem reaction network on this catalytic system and deserves further studies.