Size-dependent catalytic hydrogen productionviamethane decomposition and aromatization at a low-temperature using Co, Ni, Cu, Mo, and Ru nanometals

Catalysts of methane decomposition to hydrogen and aromatization are inevitable for the development of natural gas applications. Metal catalysts have been developed to achieve highly efficient methane decomposition and aromatization under 1000 K using various substrates, such as zeolites and silica. Here, we performed a consecutive study on methane decomposition using Co-, Ni-, Cu-, Mo-, and Ru-based nanocatalysts in the bulk, on a SiO2 substrate, and in mesoporous SiO2. The crystallite sizes of the bulk nanocatalysts, and nanocatalysts on nonporous and mesoporous SiO2 were controlled to 80-85, 30-70, and 3-11 nm, respectively. The nanocatalysts on mesoporous SiO2 exhibited high activity on hydrogen and benzene productions via methane decomposition, owing to the nanosize effect of the nanocatalysts and adsorption potentials in the SiO2 mesopores. In particular, the Ni nanocatalysts on mesoporous SiO2 exhibited hydrogen production activity from 650 K, which was the lowest temperature, compared with those in previous reports on hydrogen production. In addition, the catalytic activity was maintained for over 15 h at 650 and 800 K with recyclability. The overoxidation of Ni species in the SiO2 mesopores might have promoted the transformation reaction of CH4 to CHx and prevented coking by the largeness of the SiO2 mesopores in comparison with microporous media.