Comparison of HMF Hydrodeoxygenation over Different Metal Catalysts in a Continuous Flow Reactor

Abstract

The three-phase hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF) and hydrogenation of 2,5-dimethylfuran (DMF) were studied over six carbon-supported metal catalysts (Pt, Pd, Ir, Ru, Ni, and Co) using a tubular flow reactor with 1-propanol solvent, at 180 degrees C and 33 bar. By varying the space time in the reactor, the reaction of HMF is shown to be sequential, with HMF reacting first to furfuryl ethers and other partially hydrogenated products, which then form 2,5-dimethylfuran (DMF). Ring-opened products and 2,5-dimethyltetrahydrofuran (DMTHF) were produced only from reaction of DMF. Rate constants for the pseudo-first-order sequential reactions were obtained for each of the metals. The selectivities for the reaction of DMF varied with the metal catalyst, with Pd forming primarily DMTHF, Ir forming a mixture of DMTHF and open-ring products, and the other metals forming primarily open-ring products. Catalyst stabilities followed the order Pt similar to Ir > Pd > Ni > Co > Ru. Since the stability order correlated with carbon balances in the product (>93% for Pt; <75% for Ru), deactivation appears to be caused by deposition of humins on the catalyst.