Dual-bed catalyst system for C–C coupling of biomass-derived oxygenated hydrocarbons to fuel-grade compounds

Mono-functional intermediates produced by catalytic conversion of sugars and polyols over Pt–Re/C catalysts (consisting of alcohols, ketones, carboxylic acids, and heterocyclic compounds) can be upgraded to fuel-grade compounds using two catalytic reactors operated in a cascade mode. The first reactor achieves C–C coupling of mono-functional intermediates using a dual-bed catalyst system, where the upstream catalyst bed (Ce₁Zr₁O_x) is employed to carry out ketonization of carboxylic acids, and the downstream catalyst bed (Pd/ZrO₂) is used to achieve aldol condensation/hydrogenation of alcohols and ketones. This second bed is not significantly inhibited by CO₂ and H₂O produced during ketonization. The high molecular weight ketones produced by C–C coupling reactions in the dual-bed catalyst system are subsequently converted to alkanes by hydrodeoxygenation (i.e., dehydration/hydrogenation) over a Pt/SiO₂–Al₂O₃ catalyst. Using the aforementioned approach, an aqueous feed containing 60 wt% sorbitol was converted to a liquid stream of alkanes, 53% of which consisted of C₇₊ alkanes with minimal branching, desirable for Diesel fuel.