Role of Keto Intermediates in the Hydrodeoxygenation of Phenol over Pd on Oxophilic Supports

Abstract

The performance of Pd catalysts supported on SiO2, Al2O3 and ZrO2 for the hydrodeoxygenation (HDO) of phenol has been compared in the gas phase, at 300 °C and 1 atm using a fixed bed reactor. While Pd supported on SiO2 and Al2O3 exhibits high selectivity to cyclohexanone, when supported on an oxophilic support such as ZrO2, it favors the selectivity toward benzene, reducing the formation of ring-hydrogenated products, cyclohexanone and cyclohexanol. Diffuse reflectance infrared Fourier transform spectroscopy experiments support the participation of a keto-tautomer intermediate (2,4-cyclohexadienone) in the reaction. This intermediate can be hydrogenated in two different pathways. If the ring is hydrogenated, cyclohexanone and cyclohexanol are dominant products, as in the case of Pd/SiO2 and Pd/Al2O3 catalysts. By contrast, if the carbonyl group of the keto-intermediate tautomer is hydrogenated, benzene is directly formed via rapid dehydration of the unstable cyclohexadienol intermediate. This is observed in the case of Pd/ZrO2 catalyst. These results demonstrate that the selectivity for HDO of phenol can be controlled by using supports of varying oxophilicity.

Understanding the Performance and Stability of Supported Ni-Co-Based Catalysts in Phenol HDO

“…Most of the mentioned model studies were carried out either in batch autoclaves with short run times [16,[19][20][21][22][23]41] or under gas phase reaction conditions [30][31][32][33]42]. Recent HDO studies reported application of continuous flow reactors using organic solvents (e.g., 1-octanol, 1-octane, 1-hexane) [43][44][45] or supercritical water [46].…”

Directing Reaction Pathways through Controlled Reactant Binding at Pd–TiO2 Interfaces

“…[1] Such interfaces can form the basis of bifunctional catalysis,w here each material contributes its unique functionality to the active site.F or example,b ifunctional catalysts have shown promise for selective hydrodeoxygenation (HDO) of alcohols/aldehydes with aromatic substituents,adesirable path for production of fuels or chemicals from biomass ( Figure 1a). [4][5][6][7][8] Thei mportance of interfacial sites in catalysis suggests that catalyst design should emphasize novel methods for tailoring these interfaces that go beyond using the oxide as as imple catalyst carrier. [4][5][6][7][8] Thei mportance of interfacial sites in catalysis suggests that catalyst design should emphasize novel methods for tailoring these interfaces that go beyond using the oxide as as imple catalyst carrier.…”

“…[4][5][6] The presence of metals capable of hydrogen spillover was found to enhance the reducibility of the metal oxides. [4][5][6] The presence of metals capable of hydrogen spillover was found to enhance the reducibility of the metal oxides.…”

Advances in Upgrading Lignin Pyrolysis Vapors by Ex Situ Catalytic Fast Pyrolysis

“…Souza and co‐workers have synthesized Pd/SiO 2 , Pd/Al 2 O 3 , and Pd/ZrO 2 for the catalytic HDO of phenol to investigate the role of keto intermediates in the HDO reaction. The experiments have been performed in the vapor phase at 300 °C and atmospheric pressure with a fixed‐bed reactor . Pd‐supported on SiO 2 and Al 2 O 3 produce cyclohexanone with high selectivity, and both catalysts demonstrate low deoxygenation activity.…”