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 typeo fm etal (Pt, Pd, Rh, Ru, Cu, Ni, Co) on the performanceofZ rO 2 -supported catalystsf or the hydrodeoxygenation of phenol in the gas phase at 573 Ka nd 1atm. Twod ifferent reactionp athways take place depending on the typeo ft he metal. For Pt/ZrO 2 and Pd/ZrO 2 catalysts, phenol is mainly tautomerized,f ollowed by hydrogenation of the C=Cb ond of the tautomer intermediate formed, producing cyclohexanonea nd cyclohexanol.B y contrast, the directd ehydroxylation of phenol followed by hydrogenolysis might alsoo ccur over more oxophilic metalss uch as Rh,R u, Co, and Ni. In addition to the metals, the oxophilic sites of this support represented by Zr 4 + and Zr 3 + cations near the perimeter of the metal particles also increasedt he 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.

Phenol Catalytic Hydrogenation over Palladium Nanoparticles Supported on Metal‐Organic Frameworks in the Aqueous Phase

“…Noronha et al. investigated the effect of the type of metal (Pt, Pd, Rh, Ru, Cu, Ni, Co) on the performance of ZrO 2 ‐supported catalysts for phenol hydrodeoxygenation . Pd/ZrO 2 provided the best catalytic activity among the prepared catalysts.…”

Effect of Strong Metal‐Support Interaction of Pt/TiO2 on Hydrodeoxygenation of m‐Cresol

“…Various types of catalysts have been investigated for HDO of phenolics . Among those catalysts, transition metal (such as Pd, Pt and Ru) supported on reducible metal oxides (such as TiO 2 , CeO 2 and ZrO 2 ) have been extensively studied,, since they have shown increased selective deoxygenation to aromatics. The possible reason has been ascribed to the oxiphilic site of reducible oxide favors tautomerization of phenol and, therefore, facilitates the formation of aromatics,, or the metal/support interface site favors direct cleavage of C aromatic ‐OH bond toward aromatics ,.…”

“…Among those catalysts, transition metal (such as Pd, Pt and Ru) supported on reducible metal oxides (such as TiO 2 , CeO 2 and ZrO 2 ) have been extensively studied,, since they have shown increased selective deoxygenation to aromatics. The possible reason has been ascribed to the oxiphilic site of reducible oxide favors tautomerization of phenol and, therefore, facilitates the formation of aromatics,, or the metal/support interface site favors direct cleavage of C aromatic ‐OH bond toward aromatics ,. By varying particle sizes of Ru on TiO 2 via changing Ru loadings, Omotoso et al suggested that the perimeter site of Ru‐TiO 2 interface is the active site for deoxygenation of m‐cresol to toluene at 400 °C .…”

Liquid‐phase Hydrodeoxygenation of 4‐Propylphenol to Propylbenzene: Reducible Supports for Pt Catalysts

“…The change in product distribution was explained with the loss of Pd and support interaction due to carbon deposition; metal sintering; and loss of Lewis acid sites on the support. [36] Teles et al [22] also reported deactivation of various metals (Pt, Pd, Rh, Ru, Cu, Ni and Co) on ZrO 2 . The main reasons for deactivation were metal sintering and the decrease of the number of oxophilic sites caused by strong adsorption of reaction intermediates.…”

“…Recently, the HDO of phenolics has been studied extensively to produce aromatics with base metal [18][19][20] or noble metal [14,15,[21][22][23][24] catalysts. Cyclohexane and other non-aromatics have also been obtained with base [16,25] and noble [15,22,23,[26][27][28] metal catalysts. Product selectivities and reaction rates can be strongly influenced by the solvent and the phase distribution of the components in the reaction mixture.…”