(435d) Catalytic Hydrodeoxygenation on Metal Carbides
Stoichiometric removal of oxygen is required for the chemical transformation of renewable biomass feedstock to energy carriers and other substitutes for petroleum derived products. Oxygen removal from biomass can be performed under catalytic hydrotreatment conditions (25-70 bar H2, 300 – 400˚C) using noble metal catalysts, but oxygen removal is often concurrent with excessive H2 usage through hydrogenolysis and/or alkene/aromatic hydrogenation, producing low-value short-chain alkanes as opposed to light alkenes and aromatics.
We report vapor phase hydrodeoxygenation (HDO) of acetone, anisole, guaiacol, and m-cresol, representative of cellulose and lignin pyrolysis products over Mo2C-based non-precious metal catalyst formulations that enable selective HDO at ambient pressure and low temperatures (98 – 200˚C). The dominant HDO reaction products were unsaturated, deoxygenated hydrocarbons including propylene, benzene, phenol, and toluene with carbon selectivity ranging from 60-90%, and <1% selectivity to C-C bond scission products.
The HDO kinetics of these probe molecules were investigated as functions of contact time, reactant partial pressures, and temperature. This work proposes HDO mechanistic models to fit experimentally measured rates, and these kinetic models were further probed using transient isotopic experiments and the kinetic isotope effect. The HDO site requirements were probed via in situ titration experiments using pyridine, CO and CO2 to assess the number and identity of active sites. The active catalytic phase for HDO was investigated as a function of catalyst oxygen content via in situ O2 dosing experiments and systematic oxygen inclusion during catalyst synthesis to probe the effects of near-surface and bulk oxidation on catalytic HDO activity. The kinetics, mechanism, and site requirements of low pressure HDO on Mo2C formulations will be presented.