(416d) Hydrogenation of Biomass-Derived Furans Over Noble Metal Catalysts

The production of furan derivatives from hemicellulose and cellulose is one of the major routes for biomass- based sustainable energy supply and valuable chemicals. Using cellulose will largely produce 2,5-dimethylfuran (DMF), while 2-methylfuran (2MF) results by hydrolysis, dehydration and hydrogenation reactions starting from hemicellulose.  Although DMF and 2MF have been considered as next-generation biofuels, very little is known about their hydrogenation or hydrogenolysis reactions leading to higher-value added chemicals.

The hydrogenation and hydrogenolysis reactions of two methyl-substituted furans, DMF and 2MF, were studied over noble metal catalysts supported on carbon. We determined the conversion and product selectivity over the Pt and Pd catalysts for each furan under different reaction conditions. Over the entire temperature range of 50−300°C, the hydrogenated species, ring-opening products (alcohols and ketones), and cracked products were produced by hydrogenation of furans.

We further investigated the decomposition of hydrogenated methyl-substituted furans in the absence of hydrogen, because as the reaction temperature increases the decomposition of hydrogenated furans can affect the product selectivity. It is also possible that the furan hydrogenation reactions proceed via partial or full hydrogenation of the furan ring. Therefore, to probe the sequence of hydrogenation, hydrogenolysis and decomposition events during hydrogenation of these substituted furans, hydrogenation and decomposition of 2,5-dimethyltetrahydrofuran and 2-methyltetrahydrofuran were investigated over the same noble metal catalysts. The DMF and 2MF hydrogenation results showed that over a Pt/C catalyst the main reaction was furan ring opening and the primary hydrogenation products were ketones. We also observed various cracked hydrocarbons resulting from the hydrogenolysis reaction. These results indicated that the Pt/C catalyst was active in both the furan ring opening as well as ring saturation reactions. In contrast to the Pt/C catalyst, the Pd/C catalyst exhibited a completely different behavior in furan hydrogenation reactions. It showed a high selectivity to furan ring saturation products with only traces of other products. Also, the Pd/C catalyst showed deactivation due to carbon deposition, especially at high reaction temperatures, and the original catalytic activity could not be regained after attempted regeneration in hydrogen. We also observed that the Pt/C catalyst displayed high selectivity to 2-hexanol during DMF hydrogenation below 100^oC.

In contrast to DMF, 2MF hydrogenation showed high cracking tendency even at low reaction temperatures. We propose that the steric hindrance caused by an additional methyl group in the furan ring of DMF affects the mode of furan ring adsorption on the catalytic surface causing a reduction in the cracking tendency. Therefore, this study sheds new light onto the nature of reaction intermediates and pathways during DMF and 2MF hydrogenation over noble metal catalysts.