(243e) Hydrodeoxygenation of Phenol Over Zeolite-Supported Metal Catalysts

Bio-oil from fast pyrolysis of biomass cannot be used directly as a transportation fuel or fuel additive because of low heating value, high viscosity, incomplete volatility, and chemical instability due to its large oxygen content. Numerous studies of zeolitic upgrading of bio-oil have been reported, but nearly all studies focused on the use of zeolite itself as a catalyst. In this work, hydrodeoxygenation (HDO) has been studied over bifunctional zeolite-supported noble metal catalysts.

To get a better understanding of HDO reaction pathways on bifunctional zeolite catalysts, aqueous phenol was tested as a model compound (of bio-oil species derived from fast pyrolysis of lignocellulosic biomass) in a fixed bed reactor at elevated hydrogen pressures. The catalysts were prepared by simple impregnation methods and were characterized by a number of complementary techniques to generate understanding of the catalyst structure, allowing correlation of the catalytic behavior as a function of the physicochemical properties of the catalysts.

Data on the product distribution during HDO show that cyclohexane was produced through two parallel pathways, the first being the hydrogenation of the aromatic ring followed by hydrogenolysis, and the second pathway being the hydrogenolysis followed by hydrogenation of aromatic ring. During the reaction, condensation and alkylation pathways were also observed, but no products of cracking reactions were observed under the conditions used in this study.

The catalysts showed high initial HDO activity (~ 100% conversion) even at high space velocity (20 h^-1), but the catalysts deactivated rapidly. Various characterization techniques such as solid state ²⁷Al NMR and FT-IR shed light on the catalyst deactivation processes. Deactivation of the bifunctional zeolite catalysts in HDO of aqueous phenol was caused mainly by coke deposition and not by dealumination . Coke deposits can be removed by air treatment, and the regeneration process completely restores catalytic activity.