A promising route for upgrading biomass-derived carboxylic acids is catalytic conversion into olefins, alcohols, or H2 using the ketonization reaction as an intermediate step. Ketonization of carboxylic acids may be advantageously performed in the condensed phase in order to eliminate the need to supply a large amount of energy to vaporize the aqueous stream. However, catalysts and catalytic supports studied to date are not stable under aqueous condensed hydrothermal reaction conditions. Common ketonization catalysts such as ZrO2-, CeO2-, and TiO2-based catalysts have been reported to lose surface area, undergo phase transformation, and lose catalytic activity upon exposure to condensed dry and aqueous acetic acid at temperatures higher than 473 K. Therefore, developing hydrothermally stable catalyst and catalytic supports is paramount for the catalytic upgrading of carboxylic acids. In this work, we synthesized a series of LaxZryOz mixed-metal oxides with different La:Zr atomic ratios between 0.035 and 0.23 with the goal of enhancing the catalytic activity and stability for the ketonization of acetic acid in condensed aqueous media at 568 K. We synthesized a hydrothermally stable LaxZryOz mixed-metal oxide catalyst with ketonization activity 265 and 45 times more active than La2O3 and ZrO2, respectively. Further, the LaxZryOz catalysts with La:Zr atomic ratio between 0.10 and 0.17 were stable over 1000’s of hours under hydrothermal reaction conditions and maintained a surface area of 80-90 m2 g-1. Catalyst characterization techniques suggest that the enhanced stability of the LaxZryOz catalysts is observed with the formation of a phase isomorphic with tetragonal ZrO2. DRIFTS spectroscopy measurements indicated the enhanced catalytic activity of LaxZryOz catalysts correlated with greater acetic acid surface population in the presence of H2O versus pure ZrO2. Further characterization via XRD to elucidate the crystalline/amorphous ratio and TEM measurements investigating an increase in “terraced” planes on the metal-oxide catalyst surface will be discussed in the context of activity/structure relationship.

Development of hydrothermally stable materials for the catalytic upgrading of biomass-derived carboxylic acids in the presence of condensed water

255th National Meeting (2018)

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