(281d) Influence of Support Composition, Base Promoter and Catalyst Passivation On Higher Alcohol Synthesis Over Molybdenum Carbide

Although world-scale catalytic processes have been developed to convert synthesis gas to diesel fuel or methanol, there is a growing need for its direct conversion to higher alcohols for use as fuel additives or chemical precursors. Promoted molybdenum carbide is a promising catalyst for higher alcohol synthesis because of its low cost, slow deactivation, high alcohol selectivity and no requirement for on-stream additives. The current work explores the influences of support composition, base promoter and catalyst passivation on the activity and selectivity of supported-Mo₂C in the synthesis of higher alcohols from syngas at 30 bar and 573 K. Although α-Al₂O₃-supported Mo₂C was more active than MgO-supported Mo₂C, the basic support MgO promoted the formation of alcohols. In addition, higher alcohol synthesis over both α-Al₂O₃-supported and MgO-supported Mo₂C catalysts was substantially improved by adding rubidium as a promoter. The surface of freshly prepared Mo₂C can be highly reactive with oxygen, so the influence of passivation on syngas conversion after carbide preparation was evaluated. Compared to a freshly prepared sample that was never exposed to air, a passivated Mo₂C/α-Al₂O₃ catalyst had lower activity and chain-growth probability. Interestingly, the influence of passivation on Rb-promoted Mo₂C/α-Al₂O₃ was rather minimal. Structural characterization of the catalysts evaluated by X-ray absorption spectroscopy was related to catalytic performance.