PNNL

Abstract

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, the promoting role of lanthanum oxide (La2O3) in the catalytic synthesis of mixed higher (C2-C6) alcohols from syngas on Co based catalysts was investigated. XRD measurements show that doping with La (0.5 wt %) onto activated carbon (AC) supported Co catalyst enhances the Co2C phase formation while the Co2C phase formation is largely suppressed on alumina supported Co catalyst. A strong correlation of the selectivity towards alcohols with the ratio of Co2C/Co presented in the catalysts was observed. Our theoretical ab initio molecular dynamics (AIMD) simulations suggest that, on AC supports under the reaction conditions, La exists as an oxide phase in the form of small clusters in the vicinity of Co particles. It was found that Co2C formation is energetically favorable especially for smaller Co particles where La may be influencing the Co particle size. Theoretical mechanistic studies indicate that oxygenated hydrocarbons can be formed on these catalysts by multiple routes involving. the formation of CHxO and CHxCO species at the interface between the La2O3 phase and Co/Co2C. A detailed comparison with previous findings in the literature, as well as discussion of the implications of these results upon the improvement if the selectivity of these catalysts towards higher alcohols, is presented. The Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.