Oxygen Vacancy over CoMnOx Catalysts Boosts Selective Ethanol Production in the Higher Alcohol Synthesis from Syngas
Higher alcohol synthesis (HAS) from syngas is highly attractive but still challenging due to the complexity of the reaction system and the difficulty in modulating the carbon number distribution of products, especially in improving the selectivity toward ethanol or short-chain alcohols over a single catalyst. Herein, we propose a CoMnOx nanocomposite catalyst with the Co/Mn molar ratio of 1/2 prepared by the facile sol–gel method and found that it could selectively produce short-chain alcohols in the HAS. The C2-5OH proportion in the total alcohol reached 75.5 C%, in which the ethanol proportion was as high as 48.0 C%, breaking through the Anderson-Schulz–Flory distribution and outperforming most of the reported cobalt-based catalysts for HAS. Multiple characterizations and contrast experiments indicated that oxygen vacancies in MnOx that formed during reduction and reaction can dissociate CO but are inactive in C–C coupling, thus generating lots of CHx* monomers. The CHx* intermediates could react with the CO* species adsorbed on the neighboring Co2C species, greatly stimulating the production of ethanol. It is also demonstrated that the oxygen vacancies possibly facilitated the carbonization of cobalt and enhanced the alcohol selectivity, while the untransformed CoxMn1–xO was not active in the reaction. These findings may provide potentials in designing catalysts for highly selective production of ethanol and short-chain products in HAS from syngas.
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