The promoting role of lanthanum oxide (La 2 O 3 ) in the catalytic synthesis of mixed higher (C 2 –C 6 ) alcohols from syngas on Co-based catalysts was investigated using a combination of in situ and ex situ X-ray diffraction (XRD), photoelectron spectroscopy (XPS), catalyst reactivity performance studies, and ab initio molecular dynamics (AIMD) simulations. XRD measurements show that doping with La (0.5 wt %) onto activated carbon (AC) supported Co catalyst enhances the Co 2 C phase formation, whereas the Co 2 C phase formation is largely suppressed on alumina supported Co catalyst. A strong correlation of the selectivity toward alcohols with the ratio of Co 2 C/Co particles present in the catalysts was observed. AIMD simulations suggest that on AC supports La exists as an oxide phase in the form of small clusters in the vicinity of Co particles. It was found that Co 2 C formation is energetically favorable, especially for smaller Co particles because of the formation of surface carbide. Theoretical mechanistic studies indicate that oxygenated hydrocarbons can be formed on these catalysts by multiple routes involving the formation of CH x O and CH x CO species at the interface between the La 2 O 3 phase and Co/Co 2 C. A detailed comparison with previous findings in the literature as well as discussion of the implications of these results upon the improvement of the selectivity of these catalysts toward higher alcohols is presented.
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Lebarbier et al. (2011) studied this question.