Direct synthesis of acetic acid by simultaneous co-activation of methane and CO2 over Cu-exchanged ZSM-5 catalysts

The ultimate goal of this study is the development of a new strategy to exploit methane and carbon dioxide resources more efficiently and cleanly. Due to the high stabilities of both methane and CO2, simultaneous C H bond activation of methane and CO2 is one of the toughest challenges in catalysis. Formation of acetic acid was achieved under the continuous flow micro-reactor system by the concurrent feed of methane and carbon dioxide over Cu loaded M+-ZSM-5 catalysts (M = Li+, Na+, K+ and Ca++). The formation of acetic acid was observed in the temperature regime of 425-525 degrees C with a co-feed of CO2 and CH4, under low space velocity of 360 ml h(-1) based on methane. Compared to Cu-0-H-ZSM-5, the M+-ZSM-5 catalyst showed remarkable increment in the formation rate of acetic acid, and the catalytic efficiency was in order K > Na > Ca > Li. The obtained results indicated that the M+ assists in enriching surface active CO2 in the form of carbonates and subsequently reacted with the homolytic activated C H over Cu-0-H-ZSM-5. Gathering Cu-0 and M+, the Cu-0-K-ZSM-5 catalyst showed the highest formation rate of acetic acid (395 mu, mole gcat(-1) h(-1)) at steady state, for 10 h time-on-stream at 500 degrees C. (C) 2017 Elsevier B.V. All rights reserved.