EFFECT OF THE K-MO INTERACTION IN K-MOO3 GAMMA-AL2O3 CATALYSTS ON THEPROPERTIES FOR ALCOHOL SYNTHESIS FROM SYNGAS

A series of K-MoO3/gamma-Al2O3 catalysts was prepared by varying the K /Mo atomic ratios between 0 and 1.5, maintaining molybdenum content as constant. The structures of the samples were characterized by several techniques (LRS, XRD, XPS, ESR, TPR, 02, CO and H-2 chemisorption, an d TPD) and accounted for the catalytic properties for alcohol synthesi s from synthesis gas. It is revealed that for the potassium-promoted s amples an interaction between the potassium promoter and the supported molybdenum component occurs. The amount of the species resulting from this interaction gets saturated at a K/Mo ratio of 0.8. On the oxidic samples, K-Mo interaction species which may contain potassium cations and an Mo7O246- Unit are formed. This retards, to some extent, the su lfidation and reduction of Mo(VI) to Mo(IV). The sulfidation of the in teraction species leads to the aggregation of MoS2 and the formation o f surface ''K-Mo-S'' species. At K/Mo ratios above 0.8, KCl crystallit es form; some amount of KCl, which is not aggregated, covers the expos ed molybdenum surface, and decreases the amount of ''K-Mo-S'' species and Mo(CUS) sites. The activity toward alcohol formation over the sulf ided samples is in parallel with the extent of the K-Mo interaction, w ith the maximum achieved at K/Mo ratio of 0.8, while alcohol selectivi ty monotonically increases with K/Mo ratio. It is tentatively proposed that the surface ''K-Mo-S'' species and Mo(CUS) sites are responsible for the alcohol and hydrocarbon formations, respectively. The large i ncrease in alcohol selectivity at K/Mo ratios above 0.8 could be attri buted to the effect of the unaggregated KCl which preferentially cover s the Mo(CUS) sites. The high C2+OH/C1OH ratio in the alcohol product distribution is probably due to the substantial amount of the SH speci es present on the surface of the sulfided samples during reaction. (C) 1994 Academic Press. Inc.