Experimental and computational study of syngas and ethanol conversion mechanisms over K-modified transition metal sulfide catalysts

Abstract

Catalysts with the common composition KCoMoS/C/Al2O3 were synthesized, characterized by physicochemical methods, and tested in the synthesis of alcohols from CO and H2. It was noted that carbon supported on alumina promoted alcohol synthesis by enhancing the CO conversion and the alcohols/hydrocarbons ratio in comparison to pure alumina. The addition of potassium to CoMoS/C/Al2O3 could substantially affect both the morphology of molybdenum disulfide crystallites and catalyst activity in the synthesis of alcohols. According to quantum chemical calculations, using the density functional theory approach, potassium donates electronic density onto the Co atoms of CoMoS phase active sites. Reduction of metal atoms of active sites leads to a decrease in Lewis acidity and in the CO and H2 adsorption energy as well as promoting the oxidative addition of H2. The influence of ethanol addition to synthesis gas on its conversion and the product composition was examined with a view to checking whether the alkyl intermediate interacted with CO in the presence of potassium. A sharp increase of CO conversion in the presence of ethanol was detected. A reaction network of CO conversion on KCoMoS catalyst active sites to various products depending on the catalyst composition and reaction conditions was suggested.