(329d) Ru/TiO2 Based Catalysts As Applied to the Upgrading of Bio-Oils

The upgrading of biomass fast pyrolysis oil, or bio-oil, to transportation fuels is subject to several significant challenges. One of the greatest challenges is to overcome the rapid catalyst deactivation that typically accompanies bio-oil upgrading. In this contribution, we report the use of Ru/TiO₂ based catalysts with significant promise for maximizing stable liquid products from bio-oil, both in the vapor and aqueous phases. Ketonization of carboxylic acids and transalkylation of methoxy groups located on phenolic rings are two desirable reactions readily catalyzed by reducible oxides that enhance the C retention, as opposed to HDT catalysts, which convert them to light gases. Vapor phase studies with the lignin derived model compound, guaiacol, at 400°C indicate that Ru/TiO₂ catalysts show considerable increases in activity and stability over both metal and acid catalysts alone while substantially decreasing the fraction of carbon that is lost to light gases or coke. Ru/TiO₂ catalysts also show significant promise for the ketonization of acetic acid in the aqueous phase under mild conditions of 180°C, a reaction that is typically conducted under substantially higher temperatures in the vapor phase. The influence of catalyst pretreatment conditions, such as calcination and pre-reduction, have important implications on the results obtained with these catalysts for the two systems studied. A combination of analytical techniques including XPS, FTIR, and temperature-programmed techniques (reduction and reaction) are used to characterize the reducibility and nature of the active sites resulting from these catalyst modifications. Comparisons are drawn between the influence of pretreatment conditions on the modification of the active catalyst surface under reaction conditions, and the surprisingly different influence that these modifications have on the two reactions of interest are discussed.