Fine-tunable Ni@porous silica core–shell nanocatalysts: Synthesis, characterization, and catalytic properties in partial oxidation of methane to syngas

Ni nanoparticles (NPs) of narrow size distribution encapsulated inside meso- and microporous silica were prepared through in situ reduction of NiO NPs coated with silica. By varying preparation parameters, the mean size of Ni NPs can be fine-tuned in the range 6–45 nm. It was found that with variation in core size, microcapsular cavity, and shell porosity, the as-obtained Ni@meso-SiO2 catalysts for the partial oxidation of methane to synthesis gas are notably different in catalytic activity and durability. The catalyst activity and durability are essentially determined by the size of the Ni cores, and also somewhat by the porosity of SiO2 shells, as well as the extent of core–shell interaction, which is influenced by the microcapsular cavity structure. The Ni-350@meso-SiO2 catalyst with Ni NPs of ca. 6 nm and SiO2 shells with 3–4 nm mesopores is superior in both activity and durability, giving CH4 conversion of ∼93%, H2 selectivity of 92–93% (750 °C and GHSV = 72,000 mL g−1 h−1), and TOFCH4 of 37.9 s−1.