Abstract
Ketonization of biomass-derived propionic acid was investigated at 270–350 °C over CexZr1–xO2 mixed oxides with varying Ce/Zr ratios. The acidity of CexZr1–xO2 increases as Zr content is increased. The density of the strong base sites is reduced with increasing Zr content, while the density of the medium-strength base sites is maximized on Ce0.5Zr0.5O2. Diffuse reflectance infrared spectroscopy of propionic acid adsorption indicated that increasing Zr content in CexZr1–xO2 favors monodentate adsorption over bidentate adsorption. The reaction rate varies with the composition of CexZr1–xO2. The intrinsic reaction rate can be correlated with the medium-strength acid/base ratio. The rate maximizes at a medium-strength acid/base ratio of ∼1.07 on Ce0.1Zr0.9O2. This value is close to 1, indicating that the balanced medium-strength acid–base sites play a crucial role in the ketonization. The balanced acid–base property influences propionic acid adsorption, enolate formation, and C–C coupling and therefore affect...
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