Multifunctional Cascade Catalysis of Itaconic Acid Hydrodeoxygenation to 3-Methyl-tetrahydrofuran

Hybrid production of isoprene from biomass-derived sugar as a feedstock for renewable rubber is a three-part process comprising glucose fermentation to itaconic acid, liquid-phase hydrodeoxygenation to 3-methyl-tetrahydrofuran, followed by vapor-phase dehydra-decyclization to isoprene. Here, we investigate a multifunctional catalyst design for itaconic acid hydrodeoxygenation to 3-methyl-tetrahydrofuran. The production of 3-methyl-tetrahydrofuran from itaconic acid is a multistep process involving hydrogenation, acid-catalyzed dehydration, and hydrodeoxygenation of multiple organic functionalities. A detailed kinetic analysis of this multistep reaction network over a Pd/C catalyst revealed a kinetic bottleneck in the reduction of methyl-γ-butyrolactone to 1,4-methylbutanediol, which was accelerated through the use of Re as an oxophillic promoter. Varying ratios of Pd:Re indicated a maximum overall rate of lactone ring opening with a 3.5:1.0 Pd:Re ratio, likely due to the combined capability of Pd to hydrogenate double bonds and Re to open the lactone ring. Applying this insight, the overall rate of itaconic acid hydrodeoxygenation to 3-methyl-tetrahydrofuran increased by more than an order of magnitude.