Catalytic Oxidation of Cycloalkanes

Catalytic oxidation of cycloalkanes represents a pivotal route to convert inert C–H bonds into more functional oxygenated products, notably cycloalkanols and cycloalkanones, which serve as precursors for polymers, fine chemicals and pharmaceutical intermediates. The archetypal reaction is the partial oxidation of cyclohexane to a mixture of cyclohexanol and cyclohexanone—often termed KA oil—under molecular oxygen. The challenge arises from the high bond dissociation energy of the C–H bond and the propensity for over-oxidation, requiring catalysts that balance activity, selectivity and stability under mild conditions. Traditional industrial processes employ homogeneous radical initiators and operate at elevated temperatures and pressures, leading to separation challenges and safety concerns. Recent advances focus on heterogeneous systems that harness nanostructured supports, earth-abundant metal oxides or noble-metal nanoparticles to activate O₂ at lower temperatures, suppress radical chain runaway and promote sustainable operation. Progress in mechanistic understanding—particularly of oxygen vacancy formation, surface-active oxygen species and single-site active centres—has underpinned the design of catalysts capable of high KA oil selectivity, catalyst recyclability and reduced environmental footprint.

Research from Nature Portfolio

Recent studies have demonstrated the power of redox-tuned metal oxide solid solutions to achieve aerobic C–H activation under mild conditions. A mesoporous Mn₀.₅Ce₀.₅Oₓ solid solution was engineered to combine high manganese doping within a CeO₂ lattice, creating abundant surface oxygens and mobile oxygen vacancies. This catalyst achieved cyclohexane conversion exceeding 17 % at 100 °C—outperforming commercial counterparts operated at 140–160 °C—while maintaining high cyclohexanol/cyclohexanone selectivity through rapid oxygen vacancy migration and C–H bond activation. Complementing this, immobilisation of gold nanoparticles on mesoporous silica via a one-pot organosilane route generated highly dispersed low-coordinated Au⁰ sites. These sites proved exceptional at activating molecular oxygen, accelerating the formation of surface oxygen species and driving solvent-free oxidation of cyclohexane with enhanced turnover frequencies. Together, these developments illustrate how controlled dopant incorporation and nanoparticle dispersion on tailored supports can reconcile high activity with selectivity in cycloalkane oxidation.

Catalytic Oxidation of Cycloalkanes publication trend

The graph below shows the total number of articles in catalytic oxidation of cycloalkanes across all publications each year (not limited to Nature Index journals).

Technical terms

Cycloalkane: A saturated hydrocarbon ring such as cyclohexane, notable for strong C–H bonds and industrial relevance.

Catalytic oxidation: A process in which a catalyst facilitates the addition of oxygen to organic substrates, enabling selective functionalisation.

KA oil: The mixture of cyclohexanol and cyclohexanone produced by cyclohexane oxidation, used as a key intermediate.

Heterogeneous catalyst: A catalyst in a different phase from the reactants (typically solid), enabling easy separation and reuse.

Oxygen vacancy: A lattice defect in metal oxides where an oxygen atom is missing, enhancing redox activity and oxygen mobility.

Mesoporous: A descriptor for materials containing pores with diameters between 2 and 50 nm, offering high surface area for catalyst dispersion.

References

1. Mesoporous MnCeOx solid solutions for low temperature and selective oxidation of hydrocarbons. Nature Communications (2015).
2. Gold nanoparticles supported on mesoporous silica: origin of high activity and role of Au NPs in selective oxidation of cyclohexane. Scientific Reports (2016).
3. Synthesis and characterization of novel transition metal complexes with L-Proline and their catalytic activity evaluation towards cyclohexane oxidation. Materials Research Express (2020).
4. Ionic liquids modified cobalt/ZSM-5 as a highly efficient catalyst for enhancing the selectivity towards KA oil in the aerobic oxidation of cyclohexane. Open Chemistry (2019).
5. Sustainability in Catalytic Cyclohexane Oxidation: The Contribution of Porous Support Materials. Catalysts (2019).