Effect of Zirconia Polymorph on Vapor-Phase Ketonization of Propionic Acid

Vapor-phase ketonization of propionic acid derived from biomass was studied at 300–375 °C over ZrO 2 with different zirconia polymorph. The tetragonal ZrO 2 (t-ZrO 2) are more active than monoclinic ZrO 2 (m-ZrO 2). The results of characterizations from X-ray diffraction (XRD) and Raman suggest m-ZrO 2 and t-ZrO 2 are synthesized by the solvothermal method. NH 3 and CO 2 temperature-programmed desorption (NH 3-TPD and CO 2-TPD) measurements show that there were more medium-strength Lewis acid base sites with lower coordination exposed on m-ZrO 2 relative to t-ZrO 2, increasing the adsorption strength of propionic acid. The in situ DRIFTS (Diffuse reflectance infrared Fourier transform spectroscopy) of adsorbed propionic acid under ketonization reaction reveal that as the most abundant surface intermediates, the monodentate propionates are more active than bidentate propionates. In comparison with m-ZrO 2, the t-ZrO 2 surface favors monodentate adsorption over bidentate adsorption. Additionally, the adsorption strength of monodentate propionate is weaker on t-ZrO 2. These differences in adsorption configuration and adsorption strength of propionic acid are affected by the zirconia structure. The higher surface concentration and weaker adsorption strength of monodentate propionates contribute to the higher ketonization rate in the steady state. View Full-Tex