(435g) Liquid Phase Hydrodeoxygenation of Phenolic Compounds on Platinum and Palladium Catalysts

The hydrodeoxygenation of phenolic compounds, which constitute a substantial portion of bio-oils, was investigated. Noble metals have been reported to be suitable catalysts for vapor phase or aqueous phase processing of phenolic compounds, but have not been tested in more complex reaction environments. The goal was to reveal the influence of other bio-oil components on catalyst stability and reaction kinetics. In situ attenuated total reflection IR spectroscopy was used to monitor the course of the reaction with high time resolution. Platinum and palladium supported on carbon served as the catalysts; typical reactions temperatures were 80 to 115 °C at a H₂ pressure of 250 psig.

The addition of small amounts (as little as 2 wt%) of alcohols to the aqueous reaction mixture suppressed conversion of phenol and of its hydrogenation product cyclohexanone. This effect can be ascribed to decomposition of the alcohol and poisoning of the catalyst and was more pronounced for primary than secondary alcohols. Conversion of phenol was more susceptible to this poisoning effect than conversion of cyclohexanone, which can be explained by different demands of these molecules on the reaction site. Another observation was that the performance of the noble metal catalysts varied strongly with the conditions of the reductive pretreatment, indicating that significant catalyst restructuring in water can occur.

The data demonstrate that competitive adsorption and structure-sensitivity are the dominating factors in the noble metal-catalyzed conversion of phenolic compounds and their hydrogenation products.