Methane conversion to higher hydrocarbons over copper loaded BZSM-5 in the presence of oxygen

摘要

The direct conversion of methane to higher hydrocarbons either over metal catalyst or zeolite has not been successful so far in achieving the methane conversion with higher hydrocarbons selectivity within the economic range due to oxidation of the product The present research aims at improving the performance of BZSM-5 catalyst with the addition of copper. Catalytic behaviours at different reaction conditions were investigated. Reaction temperature, oxygen concentration, copper loading and space velocity have been identified as the contributing factors in methane conversion and higher hydrocarbon selectivity. Methane conversion is favourable at higher temperatures which shows 78% conversion at 900 °C. The selectivity of C_5~+ hydrocarbons increases from 650 °C up to 800 °C, but decreases slightly soon after. In methane conversion, the initial step involves an activation of methane to form CH3 free radicals via concerted actions between copper species and acid sites. CH3 radicals react in the gas phase to form C_2~+. The formation of CO_x was derived from the secondary reaction of the CH_3~* radicals with metal oxide catalyst or complete combustion of C_2~+ products. The formation of CO_x was reduced at low oxygen concentration and short residence time.