The production of oxygenates such as esters and organic acids from alcohols is an attractive route to high value industrial chemicals. In particular, routes that do not require the addition of oxidants, volatile or toxic reactants, base co-catalyst, or precious metal catalysts are highly desirable. Acceptorless dehydrogenative coupling (ADC) has been commercialized over copper based catalysts but current systems suffer from the requirement that bio-ethanol be dried before introduction to the catalyst bed and from the co-production of aldehydes and ketones requiring re-hydrogenation over a Ru based secondary catalyst. Previous reports have indicated that sulfated Mo/C could be a potentially promising material for this class of reactions. In this work, we demonstrate that nanoparticulate bulk MoS2 is active for conversion of ethanol to ethyl acetate and hydrolysis to acetic acid. In high pressure batch reactions equilibrium yield of ethyl acetate (44%) is achieved in 24 hours at 230oC. Upon addition of water, total acetate yield (ethyl acetate and acetic acid) increases to 82%. MoS2 from a variety sources was tested for this reaction. Structure-function correlations were developed by combining atmospheric pressure flow reactions and material characterization based on x-ray absorption spectroscopy and infrared spectroscopy with CO as a probe molecule. Based on these correlations, it is postulated that formation of ethyl acetate occurs via a hemiacetal intermediate over two sites, a coordinatively unsaturated Mo site for dehydrogenation of ethanol to acetaldehyde, and a basic site (likely an -SH group) for formation of the hemiacetal. This is the first report of ADC on bulk MoS2 as well as the first application of these characterization techniques to a class of reactions outside of the hydrotreating literature.

Acceptorless dehydrogenative coupling of ethanol over bulk MoS2 and spectroscopic structure-function correlations

255th National Meeting (2018)

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