Theoretical investigation of the selectivity of alcohols and aldehydes on Co-based catalysts in syngas conversion

Abstract

Syngas conversion to long chain alcohols and aldehydes by Co-based catalysts offers green route for synthesizing value-added chemicals. Cobalt carbides (Co2C) has been proven promoting oxygenates formation, and the Co/Co2C interface exhibited synergetic effects on increasing selectivity of higher alcohols. However, the underlying mechanism that determines the ratio of aldehydes and alcohols in oxygenate products is less understood. In this work, the hydrogenation of oxygenate intermediate was studied from first principles on metallic Co, Co2C surfaces and Co/Co2C interface to investigate the formation processes of alcohols and aldehydes. First-principles calculations show that: On Co2C(111) facet of Co2C nanosphere, aldehyde desorption as the final product has a slight advantage over its subsequent hydrogenation to alcohol; hydrogenation of oxygenate on Co2C(020) facet of Co2C nanoprism is difficult, whereas aldehyde on Co2C(101) facet of Co2C nanoprism is very easy to be hydrogenated to alcohol; and the synergistic effect between metallic and carbide surfaces on the Co/Co2C interface model promotes the selectivity of alcohol as the final product during hydrogenation of oxygenate intermediates. This study provides theoretical insights into the rational design of catalysts for controlling the selectivity between aldehydes and alcohols in syngas conversion to oxygenates.