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/CeO2 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.