One-step synthesis of 2-cyclopentylcyclopentanone from cyclopentanone catalyzed by NiO-Co3O4/TiO2: reaction pathway†

NiO-Co₃O₄/TiO₂ showed the best catalytic performance for one-step synthesis of 2-cycloamylcyclopentanone from cyclopentanone, which enhanced the competitiveness of cyclopentanone self-condensation. Both intermittent and segmented hydrogenation methods led to increased selectivity for 2-cyclopentenylcyclopentanone. Both acidic and basic substances were added to the reaction integration system, which resulted in a decrease of catalyst activity. The addition of acetic acid could promote the hydrogenation of the CO bond, while the addition of ammonia water reduced the competitiveness of cyclopentanone direct hydrogenation. The by-products in the reaction system were determined, and the reaction network was proposed. Combined with the curve of cyclopentanone conversion-product yield-time, the reaction pathway was speculated. The cyclopentanone self-condensation reaction was catalyzed by NiO-Co₃O₄/TiO₂ at the initial stage of the reaction. Hydrogenation products appeared at a reaction time of 20–30 min, and the yield of 2-cyclopentenylcyclopentanone increased first and then decreased. Combined with XRD and XPS analyses, the valence states of metals were determined.