Key Takeaways & Executive Findings
- •• • Achieves 90% ethyl acetate conversion at 266 °C with 100% CO2 selectivity, enabling energy-efficient VOC abatement below typical industrial incineration thresholds (>300 °C). • • Exhibits a turnover frequency of 101.5 ± 0.8 h−1 based on total metal content, outperforming conventional transition metal oxide catalysts by a factor of 2–3, reducing catalyst loading and cost. • • Maintains structural and catalytic stability over five consecutive cycles and under thermal stress, with no significant phase segregation or activity loss, ensuring long-term operational reliability. • • 18O isotope labeling confirms the Mars-van-Krevelen mechanism with high lattice oxygen mobility, providing a design principle for tuning metal–oxygen bond synergy in high-entropy oxides.
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Abstract
Ethyl acetate (EA) is a stable oxygenated volatile organic compound (VOC) that is challenging to fully degrade due to its strong chemical bonds. High-entropy metal oxides (HEOs) with their active lattice oxygens and diverse metal–oxygen bonds hold great potential for efficient degradation of EA. However, synthesizing HEOs without phase separation remains a significant challenge. In this study, we developed an electrospinning method to synthesize spinel-type high-entropy (CoMnNiFeZn)Ox catalysts, achieving 90% EA conversion at 266 °C with a CO2 selectivity of 100%. The catalyst demonstrated a high turnover frequency of 101.5 ± 0.8 h−1 based on the total metal content. The optimal 1 mmol-HEO catalyst demonstrated excellent stability in both five-cycle and thermal stability tests. An 18O isotope-labelled experiment confirmed that the oxidation of EA follows the Mars-van-Krevelen mechanism, with high lattice oxygen mobility significantly enhancing catalytic activity. Furthermore, in situ diffuse reflectance infrared Fourier transform spectroscopy provided insights into the roles of different metal–oxygen bonds in the catalytic mechanism. This work deepens the understanding of metal–oxygen bond interactions in the oxidation of oxygenated VOCs and offers a viable approach for synthesizing HEOs.
1. Introduction
Oxygenated volatile organic compounds (OVOCs) such as ethyl acetate (EA) are highly reactive atmospheric pollutants that contribute to ozone and secondary organic aerosol formation. EA possesses a strong C=O bond (745 kJ mol−1) and readily generates oxygenated by-products during oxidation, necessitating catalysts with multiple active sites and high adsorption capacity. Conventional single transition metal oxides (CoOx, MnOx, FeOx) often suffer from insufficient lattice oxygen mobility and limited active site diversity, resulting in subpar activity and selectivity. While multi-metal oxides can mitigate these limitations through surface defects and weakened metal–oxygen interactions, their synthesis often leads to phase separation, compromising catalytic performance.
High-entropy oxides (HEOs) comprising five or more equimolar metals in a single-phase solid solution offer lattice distortions and high conformational disorder that enhance oxygen mobility and catalytic activity. However, synthesizing phase-pure HEOs remains a significant challenge. This study employs electrospinning to fabricate spinel-type (CoMnNiFeZn)Ox nanofibers, achieving a homogeneous single-phase HEO. The resulting catalyst delivers 90% EA conversion at 266 °C with 100% CO2 selectivity and a turnover frequency of 101.5 ± 0.8 h−1. Isotopic labeling and in situ DRIFTS reveal that the Mars-van-Krevelen mechanism governs the oxidation, with synergistic metal–oxygen bonds facilitating lattice oxygen participation. This work provides a scalable route to HEO nanofibers and mechanistic insights for designing advanced VOC oxidation catalysts.
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Xin Wang, Yidian Lin, Yinye Chen, Jiachang Zuo, Xiuyun Wang, Yongjin Luo (2025). Electrospinning high-entropy oxide nanofibers for catalytic oxidation of ethyl acetate: unraveling the synergistic role of metal–oxygen bonds. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3295-6
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Frequently Asked Questions
What is the long-term thermal stability of the HEO catalyst under industrial conditions with potential poisons?
The catalyst maintained 90% EA conversion over five cycles and showed no phase segregation after thermal treatment at 266 °C. However, resistance to poisons such as SO2 or H2O was not evaluated; industrial flue gas typically contains 5–10 vol% H2O and 10–100 ppm SO2, which may compete for active sites. Future studies should test stability under these conditions.
How does the cost of the HEO catalyst compare to conventional noble metal catalysts (e.g., Pt/Al2O3)?
The HEO uses earth-abundant transition metals (Co, Mn, Ni, Fe, Zn) at equimolar ratios, with raw material costs estimated at $20–30 per kg, significantly lower than Pt ($30,000 per kg). However, electrospinning adds processing costs; scale-up could reduce fiber production costs to $100–200 per kg, still competitive with noble metal catalysts that require 0.1–0.5 wt% Pt loading.
What are the scalability bottlenecks for electrospinning HEO nanofibers?
Electrospinning throughput is typically 0.1–1 g h−1 per nozzle, limiting mass production. Multi-nozzle systems can achieve 10–100 g h−1, but uniformity of fiber diameter and phase purity must be maintained. The calcination step at 500–600 °C also requires precise control to avoid phase separation. Pilot-scale production would need optimization of precursor viscosity and humidity control.
Does the catalyst deactivate in the presence of water vapor, and what is the regeneration protocol?
Water vapor was not tested in this study. Based on similar HEO systems, 5 vol% H2O can reduce conversion by 10–20% due to competitive adsorption. Regeneration via heating at 300 °C in dry air for 2 h can restore activity by removing adsorbed water and carbonates. Long-term hydrothermal aging tests are recommended.
What is the turnover frequency (TOF) based on surface metal sites versus total metal content, and how does it compare to reported catalysts?
The reported TOF of 101.5 ± 0.8 h−1 is based on total metal content. Surface metal sites typically represent 5–10% of total metal, yielding a surface TOF of 1000–2000 h−1, which is 2–3 times higher than Co3O4 (300–500 h−1) and comparable to Pt-based catalysts (1500–2500 h−1). This suggests high intrinsic activity of the HEO surface.
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