Thermal Decomposition Of Carboxylates Research Articles

Bio‐oil upgrading via ketonization of carboxylic acids on Na promoted Ca/AlOx catalysts

AbstractKetonization of carboxylic acids is valuable for bio‐oil upgrading and producing bio‐derived chemicals. Ca/AlOx metal oxides with various Ca/Al ratios have been prepared by the low‐cost and natural abundant metals in the process. The addition of alkaline or alkaline‐earth metals could significantly improve the activity of Ca/AlOx catalysts by base‐catalyzed ketonization of carboxylic acids. However, the active sites on alkaline‐metal‐doped Ca/AlOx catalysts are still under debate, and the commercialization of these catalysts often suffers from deactivation in long‐term use. Here Ca(Na)/AlOx catalysts with various Ca/Al molar ratios were prepared and evaluated for the ketonization of acetic acid. Sodium addition resulting in the formation of NaAlO2 has higher basicity than CaO. These strong basic sites could significantly promote the ketonization of acetic acid via the thermal decomposition of carboxylates. The Ca(Na)/AlOx catalyst with NaAlO2 populated on the surface could provide 100% acetone selectivity at the complete conversion of acetic acid at 400°C and exhibit no activity loss after a 400 h reaction, which is the most active and stable catalyst for ketonization reaction hitherto. These Ca(Na)/AlOx catalysts are also stable by adding major bio‐oil model compounds (e.g., phenol) into the reaction mixture, which are promising for future bio‐oil upgrading applications.

Composition-structure-function correlation of Ca/Zn/AlOx catalysts for the ketonization of acetic acid

Abstract Ketonization can efficiently convert carboxylic acids into ketones, promising in bio-oil upgrading. For economic-sustainable bio-refining, Ca/Zn/AlOx (CZA) metal oxides with various Ca/Zn/Al ratios have been prepared by the low-cost and natural abundant metals and are applied in the process here. Mechanistic study on the ketonization of acetic acid revealed the reaction pathways strongly depends on “composition-structure-function” correlation of the Ca/Zn/AlOx catalysts. The reaction is mainly performed on strong base sites (e.g. CaO and ZnO) via thermal decomposition of carboxylates at high temperature (≥375 °C), but depends on acid-base pairs (e.g. amorphous calcium aluminates) significantly at low temperature (≤350 °C). CZA(331) (Ca/Zn/Al = 3/3/1) obtained the highest acetone yield of 97.1% at 425 °C hitherto and retained for over 100 h with simple regeneration process. Adding major bio-oil model compounds (e.g. phenol) into the reaction mixture has minor effect on the CZA catalysts. Therefore, current highly active and stable CZA catalysts are promising in boosting the efficiency and economy of bio-oil upgrading process in future.