Enhancement of Boehmite‐derived Aluminum Oxide Catalysis for Intramolecular Aldol Condensation of 2,5‐hexanedione to 3‐methyl‐2‐cyclopentenone by Lanthanum Loading and Thermal Treatment

Abstract Improvement of boehmite (AlOOH)‐derived aluminum oxide catalyzed intramolecular aldol condensation of 2,5‐hexanedione (HDN) to 3‐methyl‐2‐cyclopentenone (MCP) is examined by addition of another element (M: Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Sr, In, La, Ce, Gd, and none) as 3 wt% (in theory) with thermal treatment at 600 °C. It is particularly interesting that only the La‐loaded AlOOH exhibited positive performance of 49% yield for MCP in comparison to pristine AlOOH of 40% yield under the same reaction condition (3.0 mmol HDN). The calcination temperature and loading amount of La were surveyed further to assess the unique trends of La‐derived reactivity. Findings indicate 5 wt% La‐loaded AlOOH calcined at 500 °C as the best catalyst affording 60% yield and 71% selectivity for MCP production among the various La‐loaded Al 2 O 3 categories. As generated La/Al 2 O 3 also possesses good stability for continuous transformation of HDN to MCP, which is appreciable for more than 20 h while maintaining greater than 80% selectivity in a liquid‐flow reactor system.