Bio-oil upgrading via ketonization of carboxylic acids on Na promoted Ca/AlO_x catalysts

Ketonization of carboxylic acids is valuable for bio-oil upgrading and producing bio-derived chemicals. Ca/AlO_x 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/AlO_x catalysts by base-catalyzed ketonization of carboxylic acids. However, the active sites on alkaline-metal-doped Ca/AlO_x catalysts are still under debate, and the commercialization of these catalysts often suffers from deactivation in long-term use. Here Ca(Na)/AlO_x 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)/AlO_x 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)/AlO_x 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.