Hydrodeoxygenation of Phenol over Zirconia-Supported Catalysts: The Effect of Metal Type on Reaction Mechanism and Catalyst Deactivation

Abstract

This work aims at investigating the effect of the type of metal (Pt, Pd, Rh, Ru, Cu, Ni, Co) on the performance of ZrO₂-supported catalysts for the hydrodeoxygenation of phenol in the gas phase at 573 K and 1 atm. Two different reaction pathways take place depending on the type of the metal. For Pt/ZrO₂ and Pd/ZrO₂ catalysts, phenol is mainly tautomerized, followed by hydrogenation of the C=C bond of the tautomer intermediate formed, producing cyclohexanone and cyclohexanol. By contrast, the direct dehydroxylation of phenol followed by hydrogenolysis might also occur over more oxophilic metals such as Rh, Ru, Co, and Ni. In addition to the metals, the oxophilic sites of this support represented by Zr⁴⁺ and Zr³⁺ cations near the perimeter of the metal particles also increased the selectivity to deoxygenated products. All catalysts were significantly deactivated mainly owing to the growth of metal particle size and the decrease in the density of oxophilic sites.

Metal effects: The product distribution in the hydrodeoxygenation of phenol is investigated as a function of the type of the metal. Two different reaction pathways take place depending on the type of the metal in the ZrO₂-supported catalysts; phenol tautomerization, followed by hydrogenation of the C=C bond (Pt,Pd) and direct dehydroxylation of phenol followed by hydrogenolysis (Rh,Ru,Co,Ni).

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