The enhanced reactivity of graphitic supports for Pd catalyzed toluene hydrogenation

The hydrogenation of toluene to methylcyclohexane has recently been explored as a potential liquid hydrogen carrier system whereby methylcyclohexane can be safely and efficiently transported. Supported metal catalysts are currently being studied and optimized for this application. In this work, a pronounced support effect is demonstrated. Palladium catalysts on graphitic carbons were found to exhibit significantly enhanced toluene hydrogenation rates versus activated carbons and silica supports. Hydrogen temperature programmed desorption results appear to rule out the role of intercalated hydrogen. Using characterization by powder XRD, Raman and x-ray photoelectron spectroscopies, it is suggested that the enhancement in activity arises when a critical degree of crystallinity at the support surface enhances toluene adsorption and opens parallel reaction pathways.