(435c) Acid/Metal Balance in Bifunctional Conversion of Cresol to Hydrodeoxygenated Compounds Via Alkylation, Dehydration, and Hydrodeoxygenation

The hydrodeoxygenation of phenolics has been a matter of great interest in recent studies as part of the biomass conversion efforts. We have recently proposed a mechanism that includes a fast enol-keto tautomerization step that precedes the ring hydrogenation.  An unstable ketone intermediate forms over the catalyst surface and it can be hydrogenated via two possible paths. a) when the CO of this intermediate gets hydrogenated instead of the ring, a very reactive unsaturated alcohol (3-methyl-3,5-cyclohexadienol) is formed and it can be readily dehydrated to toluene, b) when the C=C bonds in the ring are hydrogenated, methylcyclohexanone is formed. The latter can be further hydrogenated to methylcyclohexanol.  Over acidic supports, this alcohol dehydrates to methylcyclohexene; sub-sequent dehydrogenation produces toluene.  A detailed kinetics study of the conversion of each of the possible intermediates yields strong support to the proposed mechanism. 

Interestingly, when the reaction is conducted in the liquid phase on zeolite-supported metals (Pt or Pd), alkylation of the aromatic ring by the saturated alcohol becomes an important reaction pathway that produces C11 hydrocarbons of potential value as fuel components.  In this contribution, we will discuss the importance of maintaining a suitable acid/metal balance and a favorable zeolite porous structure to maximize the yield of alkylated compounds.