(606b) Improving Performance of K-MoS2 Catalysts for Syngas Conversion to Higher Alcohols: Effect of Supports & Synthesis Methods

The recent energy debate and demand for renewable fuels has intensified research activities for conversion of biomass derived feedstocks to fuels and fuel additives. Synthesis of ethanol and lower aliphatic alcohols from syngas (CO + H2) is therefore receiving renewed interest. An important objective is to develop commercially competitive catalysts and understand the fundamental issues affecting their performance. Molybdenum Sulfide (MoS2) class of catalysts have been investigated extensively [1, 2] which indicate that the challenges are in improving the C2+ alcohol productivity and selectivity. In this presentation, some recent experimental results will be presented to demonstrate the influence of preparation methods, conditions of calcination in preparing precursors and the metal content on the catalytic activity and selectivity in syngas to alcohols. The experiments were carried out in a continuously operated high pressure fixed bed reactor with provision for online analysis of the products. The experiments involved extended period tests to evaluate the steady state performance, which usually required more than 15-20 hrs for most of the catalysts tested. It was observed that the calcination of a catalyst precursor, metal content, support type and its acidity, source of Mo precursor as well as the reaction conditions have a strong influence on the catalytic activity as well as selectivity to alcohols in comparison to hydrocarbons. By only changing the support type and its composition, selectivity for alcohols as well as overall yield could be improved by 3 times at temperatures > 300oC; C2+/C1 alcohol ratios could be enhanced from of 1 to 4. At higher temperatures (>320 oC), methane and higher alkanes formation is significantly enhanced reducing the alcohols selectivity. The alcohol selectivity at higher temperatures was however, improved by modifying the catalyst synthesis procedure and adding certain metallic promoters. The results on the effect of CO/H2 ratio, GHSV and temperature on the conversion of syngas and selectivity of alcohols will also be discussed.

References

[1] Subramani, V.; Gangwal, S. K. A Review of Recent Literature to Search for an Efficient Catalytic Process for the Conversion of Syngas to Ethanol, Energy & Fuels, 2008,22 (2),814

[2] Spivey, J.J.; Egbebi, A. Heterogeneous catalytic synthesis of ethanol from biomass-derived syngas, Chem. Soc. Rev., 2007, 36, 1514.