Chapter 15: Solar-thermal Catalytic CO₂ Splitting

With increasing demand for renewable energy and fuels there is much interest in solar thermochemical fuel production (STFP), the use of concentrated solar power (CSP) to power the splitting of water and carbon dioxide into H₂ and CO for sustainable fuels. This is usually a two-step process: the reduction of a catalyst at high temperatures followed by oxidation at lower temperatures utilising CSP to provide the high reaction temperatures (up to 1500 °C). Since it was first explored as a solar-driven redox catalyst to split CO₂ in 2010, there has been an increasing interest in cerium oxide as the catalyst for the solar-driven production of CO from CO₂. This chapter looks at pure CeO₂, and especially the effects of its stoichiometry on the redox process, as ceria will partially reduce from Ce⁴⁺ → Ce³⁺ to create CeO_2–δ with oxygen deficiencies (δ). It also looks at the extensive work on the doping or substitution of ceria, which has been explored with a wide range of transition metal and rare earth ions, with particularly interesting results for tetravalent Hf⁴⁺ and Zr⁴⁺.