Insights into the Major Reaction Pathways of Vapor-Phase Hydrodeoxygenation of m-Cresol on a Pt/HBeta Catalyst

Conversion of m-cresol was studied on a Pt/HBeta catalyst at 225-350 degrees C and ambient hydrogen pressure. At 250 degrees C, the reaction proceeds through two major reaction pathways: (1)direct deoxygenation to toluene (DDO path); (2)hydrogenation of m-cresol to methylcyclohexanone and methylcyclohexanol on Pt, followed by fast dehydration on BrOnsted acid sites (BAS) to methylcyclohexene, which is either hydrogenated to methylcyclohexane on Pt or ring-contracted to dimethylcyclopentanes and ethylcyclopentane on BAS (HYD path). The initial hydrogenation is the rate-determining step of the HYD path as its rate is significantly lower than those of subsequent steps. The apparent activation energy of the DDO path is 49.7kJmol(-1) but the activation energy is negative for the HYD path. Therefore, higher temperatures lead to the DDO path becoming the dominant path to toluene, whereas the HYD path, followed by fast equilibration to toluene, is less dominant, owing to the inhibition of the initial hydrogenation of m-cresol.