Condensation of pentose-derived furan compounds to C₁₅ fuel precursors using supported phosphotungstic acid catalysts: Strategy for designing heterogeneous acid catalysts based on the acid strength and pore structures

The selective condensation of 2-methylfuran and furfural to C₁₅ compounds is performed using supported phosphotungstic acid catalysts in a continuous-flow fixed-bed reactor. The formation of unwanted viscous tetramers (C₂₀) is suppressed when the continuous-flow reaction system is used. Stronger acids, as measured by pK_a, improved the condensation of furans, but the number of acid sites was rather weakly correlated with the catalytic activity. Suppressed catalytic activity in tiny pores smaller than 2.8–6.3 nm was also observed. Based on the observations of the acidity and pore structures, a strategy with which to design optimum catalysts for the condensation of furan compounds is suggested.