Preparation of mesoporous CeO₂ and monodispersed NiO particles in CeO₂, and enhanced selectivity of NiO/CeO₂ for reverse water gas shift reaction

The preparation of mesoporous ceria (CeO₂) and NiO/CeO ₂ was investigated using a simple calcination method. Though the oxidation of Ce³⁺ ions, the hydrolysis of Ce⁴⁺ ions, polymerization and precipitation in melted liquid, the nanosized mesoporous CeO₂ and NiO/CeO₂ could be obtained after calcination. The mesoporous CeO₂ and NiO/CeO₂ that were obtained had high surface areas, narrow pore size distributions and uniform mesopores. The mesoporous CeO₂ had very high thermal stability and a surface area of 100 m² g^-1 even after calcination at 600 C. The mesoporous CeO₂ and NiO/CeO₂ had nanoarrays with uniform mesopores (intercrystalline voids). The reverse water gas shift reaction was studied using mesoporous NiO/CeO₂ as a catalyst. The CO₂ conversion increased with increasing temperature and NiO amount. With less than 3 wt% NiO, NiO particles were monodispersed in mesoporous CeO₂, and provided a CO selectivity of 100%, regardless of temperature. These monodispersed NiO particles in mesoporous CeO₂ were observed for the first time. NiO particles that aggregated in the presence of more than 3.5 wt% NiO, resulted in a CO selectivity of 100% at temperatures above 700 C, whereas the CO selectivity is less than 100% at temperatures below 650 C. Therefore, the mondispersion of NiO particles in mesoporous CeO₂ enhanced CO selectivity.