Ethanol dehydrogenation over (K)(Co)MoS2[sbnd]catalysts supported on activated carbon: Effect of active phase composition

Abstract

The conversion of ethanol to synthesize various oxygenated hydrocarbons was studied over monometallic-, bimetallic-, and trimetallic-(K)(Co)MoS2-based catalysts supported on activated carbon. The catalysts were synthesized using the incipient wetness impregnation method and sulfidized with H2S. The catalysts were characterized by the following techniques: N2 adsorption-desorption, UV spectroscopy of pyridine-adsorption; scanning electron microscopy (SEM); SEM energy dispersive X-ray (EDX). SEM/EDX results revealed that the active metals formed a uniform phase. Synthesized catalysts were tested in a fixed-bed tubular reactor. It was established that the addition of K and Co significantly altered the physical-chemical properties, activity and selectivity of sulfide catalysts. The addition of K decreased the catalytic activity (i.e., over KMoS2/C and KCoMoS2/C) relative to the reference MoS2/C and CoMoS2/C samples. The incorporation of a promoter atom, Co, and an alkali metal, K, inhibited ethanol dehydration (into ethene) and intermolecular dehydration (into diethyl ether). K incorporation led to the formation of active sites for higher alcohol synthesis (HAS) and other oxygenates, namely (aldol-) condensation and coupling processes, and increased the ratio of liquids to hydrocarbons. Ethanol was transformed into ethyl acetate, ethyl acetoacetate, acetaldehyde, butonal-1, propanol-1, and short-chain hydrocarbons. The acidity of the catalysts did not have a direct influence on conversion. The obtained results led us to conclude that product yields are highly dependent on the active phase composition, with ethyl acetate being the most preferred product.