STRUCTURE AND DISTRIBUTION OF ALKALI PROMOTER IN K/MOS2 CATALYSTS AND THEIR EFFECTS ON ALCOHOL SYNTHESIS FROM SYNGAS

Potassium-promoted MoS2 catalysts were investigated by scanning Auger electron spectroscopy, electron probe microanalysis, X-ray energy dispersive spectroscopy, and elementary chemical analysis to elucidate the role of potassium on MoS2. Fresh samples exhibited a uniform distribution of the alkali elements by CO hydrogenation, whereas the oxidized sample showed a segregation of the potassium component in the bulk of the catalyst. The fresh K2CO3-, K2O2-, and K2S-promoted MoS2 catalysts show high selectivities to alcohols and their IR spectra present two characteristic bands at 1650 and 1400 cm-1 assigned to a bicarbonate-like species which is believed to be an active intermediate for the synthesis of alcohols. No such IR bands appear in the cases of K2SO4- and KCl-promoted MoS2 and oxidized K2CO3/MoS2 catalysts which mainly produce hydrocarbons instead of alcohols. A mechanism based on this intermediate is proposed for the alcohol formation from CO-H2. In addition, the enhanced catalytic activity and high selectivity to C2+, hydrocarbons of the oxidized K2CO3/MoS2 is believed to be due to the transfer of electron from the alkali metal diffused into the bulk of MoS2, resulting in an increase in electron density as well as in the density of states at the Fermi surface. The alkali metal on the MoS2 acts as a medium for oxygen supply ("sponge") in the atmosphere and promotes oxidation of Mo(IV) to Mol(VI) and S2- to S6+ states. © 1993 Academic Press. All rights reserved.close33363