Stabilization of furanics to cyclic ketone building blocks in the vapor phase

Furanics are produced in high abundance from the decomposition of biomass. The thermal and chemical instability of these species leads to the formation of humins upon condensation. The ring rearrangement of furfural to form 2-cyclopentenone and cyclopentanone is known to occur in the condensed aqueous phase, but this requires operation in condensed acidic media where humin formation readily occurs. High hydrogen pressures are typically used to offset rapid polymerization reactions, limiting the yields of stable unsaturated products that result. Here we report that furfural can be selectively converted to 2-cyclopentenone and cyclopentanone in a single step over supported TiO2 catalysts with both model compounds and real biomass-derived streams in the vapor phase. Selectivity for ring rearrangement vs. C-O cleavage over TiO2 supported Ru and Pd catalysts can be tuned by manipulating the water partial pressure. The formation of these products in the absence of a condensed acidic stream also enables the tuning of reaction environments to favor the selective formation of unsaturated ketones, which could be valuable diolefin precursors. The incorporation of a TiO2 support in the catalysts tested leads to the suppression of C-C hydrogenolysis/decarbonylation and enhancement of ring rearrangement reactions. The nature of the active sites for selective C-O cleavage as well as vapor phase ring rearrangement are discussed.