Design of Active and Stable Catalysts for the Hydrodeoxygenation of m-Cresol

Pyrolysis is an emerging technology for the conversion of biomass to liquid fuel products. However, due to the oxygen content of these biomass-derived liquids they are acidic, highly viscous, prone to polymerization, and have a low heating value (1). For these reasons, oxygenates present in “pyrolysis oils” must be upgraded to hydrocarbons before consideration as potential transportation fuels. Hydrodeoxygenation (HDO) is a potential route for the oxygenate upgrading, but the design of active, stable HDO catalysts that operate with minimal H₂ consumption is still a challenge (2).

Phenolic compounds account for a large fraction of biomass pyrolysis oils. The phenolic C-O bond is particularly strong, and thus HDO must occur by hydrogenation of the phenolic aromatic ring followed by dehydration to remove oxygen (3). This path suggests the need for a catalyst active for hydrogenation of aromatics and with acid sites able to catalyze dehydration reactions. As a model for the phenolics from pyrolysis oil, we have studied the HDO of m-Cresol (3-methylphenol) over Pt-based supported catalysts in a lab-scale flow reactor. Modification of the Pt catalyst by bimetallic formation with 3d metals has a significant impact on the overall activity for HDO. Pt-Ni/Al₂O₃ and Pt-Co/Al₂O₃ are both more active (63% and 60% conversion of m-Cresol, respectively, under conditions tested) for HDO than a monometallic Pt catalyst (38% conversion), but also are more selective towards fully hydrogenated products. Similarly, increasing the acidity of the Al₂O₃ support by F^- washing increases HDO activity, and improves selectivity towards the aromatic hydrocarbon product. We have further investigated the role of the support by testing alternative supports such as SiO₂ and ZrO₂. We will report an investigation of the structure-function properties of the metal particles in the catalysts and their synergy with acid sites on the support to maximize stability and selectivity for desired products.

References

1. Zhang Q, Chang J, Wang T, Xu Y. Review of biomass pyrolysis oil properties and upgrading research. Energy Conversion and Management. 2007;48:87-92.

2. Elliott DC. Historical Developments in Hydroprocessing Bio-oils. Energy & Fuels. 2007;21(3):1792-815.

3. Massoth FE, Politzer P, Concha MC, Murray JS, Jakowski J, Simons J. Catalytic Hydrodeoxygenation of Methyl-Substituted Phenols: Correlations of Kinetic Parameters with Molecular Properties. Journal of Physical Chemistry B. 2006;110:14283-91.