Different Product Distributions and Mechanistic Aspects of the Hydrodeoxygenation of m-Cresol over Platinum and Ruthenium Catalysts

Experimental measurements of the conversion of m-cresol over Pt and Ru/SiO2 catalysts show very different product distributions, even when the reaction is conducted at similarly low conversions and the same operating conditions (300 °C, 1 atm). That is, although ring hydrogenation to 3-methylcyclohexanone is dominant over Pt, deoxygenation to toluene and C–C cleavage to C1–C5 hydrocarbons prevail over Ru. For understanding the differences in reaction mechanisms responsible for this contrasting behavior, the conversion of m-cresol over the Pt(111) and Ru(0001) surfaces has been analyzed using density functional theory (DFT) methods. The DFT results show that the direct dehydroxylation of m-cresol is unfavorable over the Pt(111) surface with an energy barrier of 242 kJ/mol. In turn, the calculations suggest that the reaction could proceed through a keto tautomer intermediate, which undergoes hydrogenation of the carbonyl group followed by dehydration to form toluene and water. At the same time, a low energy...