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Acetic Acid Formation from Methane and Carbon Monoxide over a ZnZSM-5 Zeolite Catalyst

Release time:2012-10-12      Source:admin      Reads:1377

NMR-Spectroscopic Evidence of Intermediate-Dependent Pathways for Acetic Acid
  Formation from Methane and Carbon Monoxide over a ZnZSM-5 Zeolite Catalyst

   Xiumei Wang, Guodong Qi, Jun Xu*,Bojie Li, Chao Wang, and Feng Deng*

    we used in situ solid-state NMR spectroscopy to monitor the carbonylation of methane with CO over ZnZSM-5 zeolite catalysts. We found that acetic acid could be generated directly under mild reaction conditions (573–623 K) through two parallel reaction pathways. Namely, CO is activated into methoxy intermediates, which can further interact with CO to generate acetic acid (Koch-type mech-anism), while methane is activated into zinc methyl inter-mediates that can be consequently transformed into methyl groups of acetic acid with CO2 through a typical organome-tallic reactions.
    The present in situ solid-state NMR spectroscopy studies demonstrate for the first time that methane can be directly carbonylated into acetic acid with CO over the ZnZSM-5 catalyst under mild conditions. Two parallel path-ways proceed in a competitive way for the formation of acetic acid. The methoxy intermediate is generated by CO through oxidation and hydrogenation. This species is attacked by residual CO, forming acetic acid through a Koch-type mechanism. On the other hand, methane simultaneously produces a zinc methyl intermediate, which is trapped by CO2 to form acetic acid. Importantly, the two reaction pathways are likely controllable by varying the redox conditions. The present findings may provide a new perspective for selective conversion of small alkanes and co-reactants into more valuable chemicals on Zn- modified zeolite catalysts.