(235f) Acetone Condensation over Ion-Exchanged Hydroxyapatite Catalysts
In this work, we investigate the gas-phase condensation of acetone to mesityl oxide over HAP as a model reaction. Using a post-synthesis ion-exchange method, a series of divalent cation-substituted HAP catalysts were prepared to understand how different elements influence reaction rates. Initial characterization by XRD and BET suggest that the surfaces of exchanged-HAP catalysts are enriched with the introduced dopant while retaining an apatitic structure. To overcome equilibrium limiations, catalysts were tested in a fixed bed reactor using a physical mixture of HAP and Pd/SiO2 to hydrogenate unsaturated products with H2. Our results show that the nature of the cation in HAP plays a key role in governing catalytic activity. Isotopic labeling and KIE experiments reveal that enolate formation and C-C coupling are fast and reversible under the range of reaction conditions tested. The rate-limiting step occurs after the formation of diacetone alcohol, which is an intermediate in the reaction. A relationship between key descriptors of HAP structure and microkinetic parameters of acetone condensation will be discussed.
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