Journal of Catalysis, Vol.383, 33-41, 2020
Structural evolution of bimetallic Co-Cu catalysts in CO hydrogenation to higher alcohols at high pressure
Bimetallic Co-Cu catalysts are widely applied in higher alcohol synthesis (HAS), but the formation of the final active structure has not yet been fully clarified, especially for Co-rich catalysts. We investigated the structural evolution of a Co-Cu catalyst (Co:Cu = 2) from the hydrotalcite precursor containing additional Al3+ and Zn2+ to the final active state after 80 h under reaction conditions at 280 degrees C and 60 bar. The reconstruction of the bimetallic Co-Cu nanoparticles obtained by H-2 reduction was induced by the feed gas consisting of an equimolar H-2 and CO syngas mixture resulting in fast phase separation and sintering of metallic Cu-0 and Co-0 in the first 2 h time on stream (TOS) and a continuous carbidization of Co-0 forming Co2C and its sintering until steady state was reached after 40 h TOS. An intergrowth of metallic Co-0 nanoparticles with Co2C nanoparticles was observed to occur under reaction conditions. The high selectivity to oxygenates amounting to 41% compared with 29% to hydrocarbons is ascribed to the multifunctional Co-2 C/Cu-0 interface enabling dissociative CO adsorption, hydrogenation and CO insertion. The formation of hydrogenated carbon species (CxHy) originating from dissociative CO chemisorption is assumed to be favored by hydrogen spillover from Cu-0 to Co2C. The adsorption sites for molecular CO provided by both Cu-0 and Co2C facilitate its insertion into the CxHy intermediates thus leading to a higher selectivity to alcohols following the Anderson-Schulz-Flory distribution. (C) 2020 Elsevier Inc. All rights reserved.