Poisoning and competitive adsorption effects during phenol hydrogenation on platinum in water-alcohol mixtures

The effect of other bio-oil components on the aqueous phase hydrogenation of phenol on a Pt/C catalyst was investigated at a temperature of 353 K and a total pressure of 250 psi. Cyclohexanone and cyclohexanol were primary products; cyclohexanone was further converted to cylcohexanol. Methanol or ethanol as additives in water could completely stop ring hydrogenation in phenol (and in other test compounds: benzene, toluene) and decelerated the hydrogenation of cyclohexanone. Formic acid also suppressed hydrogenation reactions. The poisoning effect resulted from CO, formed by decomposition of alcohols or formic acid on platinum. Ab initio density-functional theory calculations afforded adsorption geometries, binding energies and diffusion barriers of relevant species. Phenol hydrogenation on platinum is more susceptible to CO poisoning than cyclohexanone hydrogenation because it needs a large ensemble site. The poisoning effect of alcohols can be avoided by mixing the components in a specific order.