Biomass to biofuels: Catalytic conversion of biomass-derived synthesis gas to oxygenates

Biomass can be converted to useful fuels and chemicals by two methods: biological (bio) and thermochemical. The bio route is mediated by microorganisms that can process simple sugars as a source of carbon. An example of bio route is the well-established fermentation pathway to ethanol. The thermochemical route is a two-step process and involves: 1) biomass gasification to yield synthesis gas (or syngas), a mixture of CO and H₂, followed by catalytic conversion of syngas into oxygenates. For example, conversion of biomass to ethanol via the thermochemical pathway requires development of highly efficient catalysts to achieve total carbon utility and produce ethanol economically. Since methanol can be produced selectively and in high yields by catalyzed reaction of syngas at low temperatures, we are investigating catalysts that can efficiently convert methanol into ethanol. Mechanistically, the reaction must undergo C-C coupling (homologation). First, Rh-based catalysts are being used because Rh is known to promote methanol homologation to ethanol at 200°C. The reaction is conducted in a 300 mL Parr batch reactor for fast catalyst screening. The goal is to select a non-Rh (less expensive) catalyst that operates in aqueous phase but maintains efficient ethanol conversion under moderate conditions. Ultimately, alcohols can be stored as liquids for hydrogen production. Recent results from our laboratory will be discussed.