(167g) Aqueous-Phase Hydrodeoxygenation Activity of Pd/ZrO2 Catalysts
Aqueous-phase Hydrodeoxygation Activity of Pd/ZrO2 Catalysts
Changjun Liu†, Oscar Marin†, Ayman M. Karim *‡, Heather Brown‡ and Yong Wang *†,‡
† The Gene & Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman Washington 99164, United States
‡ Institute for Interfacial Catalysis, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
Keywords: Aqueous-phase hydrodeoxygenation, bifunctional catalyst, biomass, zirconia
To meet the increase in worldwide energy demand, new processes that use a sustainable resource such as lignocellulosic biomass need to be developed 1. A common step in all the processes that currently exist for the thermochemical conversion of biomass to liquid fuels/chemicals, (e.g. liquefaction fast pyrolysis/catalytic fast pyrolysis, and aqueous phase conversion of carbohydrates), is oxygen removal by hydrodeoxygenation (HDO). Our focus is on the aqueous phase HDO of sugar streams generated from the hydrolysis of biomass. Well-developed hydrolysis processes are capable of deconstructing the cellulose and hemicellulose in lignocellulose into their corresponding sugars (e.g., glucose, fructose, xylose, and et al.) and separate them from lignin2. Selective removal of oxygen from these biomass-derived compounds (monoses/polyols) is one of the key challenges in converting them into fuels and valuable chemicals3. Bifunctional catalysts with appropriate metallic and acidic sites were found capable of catalyzing the aqueous-phase HDO of polyols4. Wide ranges of Pt promoted solid acid catalysts have been tested5. However, in order to improve the selectivity to mono-oxygenates further understanding of the HDO reaction mechanism is required.
In this work, Pd/ZrO2 catalysts promoted by various metal oxides (SnO2, MoO3, WO3) were studied in the aqueous-phase hydrodeoxygenation of polyols with focus on its selectivity to C-O cleavage and C-C cleavage. Ethylene glycol and glycerol were used as model compounds of polyols to simplify the reaction routes and products. The interaction between Pd and WO3-ZrO2, the effects of palladium particle size, and the promotion effect of three metal oxides in aqueous-phase HDO of polyols were elucidated. The structures of the catalysts were characterized by CO FTIR and in situ XAFS. Addition of Sn was found to affect the Pd structure and accessibility due to PdSn alloy formation. The effect of the reaction conditions on the Pd and Sn structure and oxidation state will be discussed and correlated with the reaction pathways.
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