(55d) Characterization of Potassium-Promoted Cobalt Molybdenum Sulfide Mixed Alcohol Catalysts After Extended Time On-Stream

Alkali-promoted cobalt-molybdenum sulfide (K-CoMoS_x) catalysts have been the focus of both industrial and academic research over the past 20+ years due to their promising performance for mixed alcohol production from syngas. The catalyst is stable in sulfur and tolerant of ammonia, which makes it particularly attractive for conversion of biomass-derived syngas without necessitating costly upgrading of the syngas. When considering the commercial viability of a catalyst, it is important to understand its stability under working conditions, signs of and reasons for deactivation, and methods for maintaining or recovering catalyst performance. However, the literature offers little information on K-CoMoS_x stability and lifetime. Because K-CoMoS_x is widely used for desulfurization of aromatic rings, it is reasonable to assume that gas phase aromatics will not harm the catalyst. Therefore, we suggest that catalyst deactivation under normal operation results from loss of sulfur, and that catalyst lifetime studies are synonymous with sulfur maintenance studies. This presentation will compare the suitability of various sulfiding co-feeds (hydrogen sulfide, dimethyl disulfide, and dimethyl sulfide), and their abilities to maintain a sulfided mixed alcohol catalyst in a fresh state. Characterization of fresh and discharged catalysts via N₂ porosimetry, XRD, XPS, and TEM will be preseneted. The catalysts examined under extended reaction times exhibited BET surface areas of 7–12 m²/g. Powder XRD studies show that the fresh catalyst consists of crystalline MoS₂, CoS₂, and a small amount of Co₉S₈. Catalysts tested for >500h retain the MoS₂ and Co₉S₈ phases, but do not contain crystalline CoS₂, suggesting dispersion of this phase during the reaction. TEM analyses of discharged catalysts revealed a similar layered morphology as fresh catalysts, suggesting little morphological change even at long reaction times (>1000 h on stream). The results of an XPS investigation to identify and differentiate surface sulfide, carbide, and oxide species of discharged catalysts will also be presented.