No abstract

Continuous hydrogenation of aqueous furfural (4.5%) was studied using a monolith form (ACM) of an activated carbon Pd catalyst (∼1.2% Pd). A sequential reaction pathway was observed, with ACM achieving high selectivity and space time yields (STYs) for furfuryl alcohol (∼25%, 60–70 g/L-cat/h, 7–15 1/h liquid hourly space velocity, LHSV), 2-methylfuran (∼25%, 45–50 g/L-cat/h, 7–15 1/h LHSV), and tetrahydrofurfuryl alcohol (∼20–60%, 10–50 g/L-cat/h, <7 1/h LHSV). ACM showed a low loss of activity and metal leaching over the course of the reactions and was not limited by H2 external mass transfer resistance. Acetic acid (1%) did not significantly affect furfural conversion and product yields using ACM, suggesting Pd/ACM’s potential for conversion of crude furfural. Limited metal leaching combined with high metal dispersion and H2 mass transfer rates in the composite carbon catalyst (ACM) provides possible advantages over granular and powdered forms in continuous processing.

Activated carbon monolith (ACM) catalysts were impregnated with Pd, Pd−Cu, and Pd−Fe for continuous hydrogenation of aqueous furfural (FUR). The effect of temperature, pressure, and liquid residence time on product selectivity and space-time yield (STY) was determined. Adding a second metal to Pd/ACM shifted the selectivity of the catalyst from 2methylfuran (2MF) and 2-methyltetrahydrofuran (2MTHF) to furfuryl alcohol (FA) and tetrahydrofurfuryl alcohol (THFA), respectively, over the range of tested temperatures and pressures. High STYs of 272 g/Lcat/h (1089 g/kg-cat/h) for THFA and 143 g/Lcat/h (574 g/kg-cat/h) for FA were achieved using Pd−Fe/ ACM at 180 °C and 300 psig. Similarly, adding Fe increased the FUR, FA, and THFA turnover frequency by a factor of 3, 4, and 60, respectively. The effect was not as pronounced when adding Cu. The effect of acetic acid, an impurity present in crude FUR, on FUR conversion and product selectivity was determined. The surface area analysis indicated a relatively low loss of surface area over 13 hydrogenation reactions on each catalyst. The presence of a second metal on the monolith catalyst stabilized the Pd particles, reduced the leaching, and altered the product selectivity.