Key Takeaways & Executive Findings
- •• • The Cu/[email protected] catalyst achieves 19.36% cyclohexane conversion and 73.28% adipic acid selectivity at 100 °C and 12 h, demonstrating a viable one-pot route that bypasses the conventional two-step nitric acid oxidation process. • • Wood chips act as both carbon support precursor and in-situ reducing agent during pyrolysis, eliminating the need for external reducing agents and reducing overall catalyst synthesis cost. • • The abundant defects in biomass carbon establish strong coordination with copper species, enhancing electronic interactions that improve catalytic activity and stability, as evidenced by the high selectivity to adipic acid. • • The reaction proceeds via a free radical chain mechanism involving hydroxyl and alkyl radicals, providing mechanistic insight for further optimization of copper-based catalysts for C–H bond activation.
Abstract
Adipic acid is a key monomer for nylon-6,6 and nylon-6, yet its industrial production via nitric acid oxidation of KA oil suffers from high energy consumption and N2O emissions. This study reports a green catalytic system for one-pot oxidation of cyclohexane to adipic acid using a Cu/Cu2O@C composite catalyst derived from wood chips. During pyrolysis, wood chips serve as both carbon support precursor and in-situ reducing agent, converting Cu2+ into Cu/Cu2O active species. The abundant defects in biomass carbon form strong coordination interactions with copper, regulating the electronic distribution of active sites and enhancing catalytic performance. Under optimized conditions (100 °C, 12 h), the Cu/[email protected] catalyst achieves a cyclohexane conversion of 19.36% and an adipic acid selectivity of 73.28%. Mechanistic studies reveal that the electronic interaction between the carbon support and copper species strengthens adsorption of cyclohexanone, promoting selective formation of adipic acid. The reaction follows a free radical chain mechanism involving hydroxyl and alkyl radicals. This work provides a viable strategy for developing eco-friendly, low-cost, and high-efficiency catalytic materials for industrial adipic acid synthesis.
1. Introduction
Adipic acid is a critical industrial monomer for nylon-6,6 and nylon-6, yet its current production via nitric acid oxidation of KA oil is environmentally problematic, generating substantial N2O emissions and requiring harsh conditions. This process also suffers from high energy consumption and the need for corrosive reagents, conflicting with green chemistry principles. Alternative catalytic systems using noble metals or strong oxidants like TBHP have been explored, but they are often costly or environmentally unfriendly, limiting their industrial scalability.
This study addresses the bottleneck by developing a copper-based catalyst supported on biomass-derived carbon from wood chips. The catalyst is synthesized via a simple pyrolysis method where wood chips serve dual roles as carbon precursor and reducing agent, yielding Cu/Cu2O nanoparticles anchored on a defect-rich carbon matrix. This design enhances the electronic interaction between the support and active species, improving catalytic performance for the one-pot oxidation of cyclohexane to adipic acid under mild conditions. The approach offers a sustainable, low-cost alternative to conventional routes, potentially reducing N2O emissions and energy demands.
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WANG Sheng, CHEN Zhijia, WANG Xiao, YUAN Chunhua, LI Songbo, YANG Huimin (2026). A Cu/Cu2O@C Composite Catalyst Derived from Wood-Chips for the Efficient One-Pot Oxidation of Cyclohexane to Adipic Acid. New Carbon Materials. https://doi.org/10.1016/S1872-5805(26)61108-0
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Frequently Asked Questions
What is the catalytic performance of Cu/[email protected] in terms of conversion and selectivity, and how does it compare to existing catalysts?
Under optimized conditions (100 °C, 12 h), Cu/[email protected] achieves a cyclohexane conversion of 19.36% and an adipic acid selectivity of 73.28%. This performance is competitive with noble metal catalysts while using earth-abundant copper and a sustainable carbon support, offering a cost-effective alternative.
How does the wood-chip-derived carbon support contribute to the catalytic activity?
The biomass carbon contains abundant defects that form strong coordination interactions with copper species, modulating the electronic distribution of active sites. This enhances the adsorption of cyclohexanone, a key intermediate, thereby promoting selective oxidation to adipic acid. The in-situ reduction of Cu2+ by wood chips during pyrolysis also ensures uniform dispersion of Cu/Cu2O nanoparticles.
What is the proposed reaction mechanism for the oxidation of cyclohexane to adipic acid?
The reaction follows a free radical chain mechanism. Hydroxyl radicals (•OH) and alkyl radicals (R•) are generated and play crucial roles in the oxidation steps. The synergy between Cu/Cu2O and the carbon support facilitates radical formation and subsequent reactions, leading to high selectivity for adipic acid.
What are the advantages of this catalyst in terms of environmental impact and cost?
The catalyst is derived from renewable wood chips, a low-cost biomass waste, and avoids the use of noble metals and strong oxidants like TBHP. The one-pot process eliminates the need for separate oxidation steps and nitric acid, reducing N2O emissions and energy consumption, aligning with green chemistry principles.
What are the potential limitations or challenges for industrial scale-up of this catalyst?
While the catalyst shows promising performance, industrial scale-up would require optimization of reaction conditions (e.g., pressure, solvent, catalyst loading) and long-term stability tests. The use of biomass-derived carbon may introduce variability in support properties, necessitating quality control. Additionally, the relatively low conversion (19.36%) may require recycling or continuous processing to achieve economically viable yields.
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