Key factors that affect catalytic activity of activated carbon-based catalyst in chemical looping methane decomposition for H2 production

Abstract

Chemical looping methane decomposition for hydrogen production is widely discussed, and activated carbon (AC) is widely studied as a cheap, easily-available catalyst with high initial activity. In this study, 10%, 30% and 50% HNO3 was used to treat AC to change its specific surface area, pore structure, and surface functional groups. After reactions at 900 °C and 950 °C, the AC is characterized and analyzed, and key factors affecting its catalytic performance are assessed. After acid treatment, the specific surface areas and pore volumes of AC are decreased, the number of oxygen-containing and nitrogen-containing functional groups is increased. It may be expected that increases of functional groups would increase the number of active surface sites, however, experiments have shown surface areas and pore volumes are representative and perhaps linearly correlated with methane conversions. The decreases in surface areas and pore volumes are predominantly associated with the elimination of micropores. Simultaneously, conclusions from molecular simulations are that smaller pore sizes in AC promotes adsorption of methane molecules on the AC and their conversion to hydrogen. Therefore, the unfavorable influences of decreased specific surface area and changed pore structure are detrimental to the initial steps of methane adsorption and then decomposition.