Porous NiO Prepared by Flame Spray Pyrolysis for 80 wt% Ni–CeO 2 Catalyst and Its Activity for CO 2 Methanation

NiO and CeO 2 were prepared via flame spray pyrolysis. The specific surface area and total pore volume were 251 m 2 g –1 and 2.3 cm 3 g –1 for NiO and 338 m 2 g –1 and 3.3 cm 3 g –1 for CeO 2 , respectively. The high porosity and surface area of the NiO allowed deposition of small CeO 2 particles ( 〜 5 nm) by the impregnation of cerium acetate monohydrate. The particles were reduced using 5 % H 2 at 500 °C for 1 h which converted NiO to metallic Ni. During the reduction, the growth of Ni particles was hindered by CeO 2 particles. Consequently, the Ni size was relatively small ( 〜 20 nm) despite the extremely high Ni content (80 wt%), as observed by scanning transmission electron microscopy. In contrast, incorporation of Ni using nickel acetate tetrahydrate into the CeO 2 support resulted in formation of inhomogeneous Ni particles (20-100 nm) after H 2 reduction. H 2 chemisorption measurement showed the surface area of Ni particles in the former catalyst was 13.7 m 2 g –1 , which was 2.4 times larger than that in the latter catalyst. The former catalyst exhibited remarkable performance for CO 2 methanation (47 % CO 2 conversion at 250 °C), 2 times higher than in the latter catalyst.