Hydrodeoxygenation of Guaiacol over Ceria-Zirconia Catalysts

Sarah McNew Schimming1, Chukwuemeka Okolie1 and Carsten Sievers*

Georgia Institute of Technology â?? School of Chemical & Biomolecular Engineering
Biomass is the only renewable source that can meet the demand for carbon-based liquid fuels and chemicals. Upgrading of bio-oils obtained from pyrolysis of biomass involves removal of oxygen. Catalytic hydrodeoxygenation (HDO) is becoming a very important technology for this purpose. The removal of oxygen containing functional groups from aromatic rings is among the more difficult reaction steps in HDO. In this study, guaiacol which is a major component of pyrolysis oil, is chosen as a model compound. Ceria-Zirconia catalysts are chosen as an alternative to expensive noble metal catalysts and transition metal sulfides, which would require a continuous H2S supply.
Ceria-zirconia catalysts were prepared by coprecipitation and characterized by different techniques. The presence of oxygen vacancies and the availability of dissociated hydrogen were identified as essential prerequisites for HDO activity over ceria-zirconia. The concentration of oxygen vacancies was titrated at different temperatures, and the availability of dissociated hydrogen was assessed using H2-D2 isotopic exchange as a test reaction. Further characterization by XRD and N2 physisorption showed that the crystallite size and the resulting surface area are key descriptors for the performance of ceria-zirconia catalysts.
The conversion of guaiacol over ceria-zirconia in the presence of H2 was investigated with a flow reactor at 101 kPa. Conversion and selectivity data showed that phenol and cresol were the most abundant reaction products at all contact times and temperatures that were studied. At long contact time the yield of benzene increased. The activation energy of guaiacol conversion was lowered by incorporating zirconia into the ceria lattice. Structure property-relationships will be discussed.