Enhancing Phenol Adsorption on Hydrophobic Pd/SiO2 to Achieve Faster and More Selective Hydrogenation

The effect of catalyst hydrophobicity on the kinetics of hydrogenation of aqueous phenol was investigated. The hydrophobicity of a Pd/SBA-15 catalyst was altered by synthesizing an organosilane with biphenylene framework linkers. Partitioning of phenol between the aqueous solution and the pores favors the hydrophobic catalyst by an order of magnitude at room temperature, relative to the hydrophilic catalyst. The rate of hydrogenation at 75 & DEG;C is higher in the hydrophobic catalyst, as is the selectivity for the partial hydrogenation product, cyclohexanone. Analysis of kinetic profiles measured using operando C-13 NMR reveals that the hydrophobic catalyst has a larger apparent (i.e., composite) adsorption constant for phenol, which results in higher phenol surface coverage and, consequently, faster and more selective hydrogenation to cyclohexanone.