Oxygen Vacancy Engineering: A Core Strategy for Boosting Ozone Catalytic Oxidation Performance

Oxygen vacancies (O_v) are anionic defects formed by the absence of oxygen atoms in the lattice of metal oxides. Despite their seemingly subtle nature, these defects possess unique electron-rich characteristics that enable them to modulate charge distribution, enhance intermediate adsorption, and accelerate electron transfer—playing multiple critical roles in catalytic cycles. In recent years, oxygen vacancy engineering has emerged as a core strategy for boosting the performance of heterogeneous catalysts, showing great promise in areas such as ozone catalytic oxidation and VOCs catalytic oxidation.

In transition metal oxides like MnO_x, oxygen vacancies have been confirmed as the primary active sites for ozone decomposition. The paradigm shift from simply "creating oxygen vacancies" to "precisely tuning the coordination environment of oxygen vacancies" is driving a leap in catalytic performance. This article systematically reviews the construction strategies, mechanisms of action, and practical application outcomes of oxygen vacancy engineering, providing a reference for further industrial adoption of ozone catalytic oxidation technologies.

2. Strategies for Constructing Oxygen Vacancies

Various methods are available for creating oxygen vacancies, with current mainstream strategies including elemental doping, chemical reduction, crystal facet engineering, and the emerging approach of asymmetric oxygen vacancy construction.

(1) Elemental Doping Strategy

By substituting lattice cations with lower-valence metal ions (e.g., Fe³⁺, Cu²⁺), charge imbalance is induced, generating oxygen vacancies in the lattice. In studies on Fe and Cu co-doped MnO₂, a one-step hydrothermal method using low-valent Cu and Fe ions to replace Mn⁴⁺ drove redox precipitation and created abundant oxygen vacancies on the catalyst surface. The resulting Fe–Cu–MnO₂ catalyst achieved 100% toluene degradation and 100% ozone removal at room temperature, with a mineralization rate of 81.2% and stable performance for over 100 hours. La doping is also an effective means to enhance oxygen vacancy concentration. The La_0.15Mn₁O_x-600 catalyst, prepared via a dual-precipitant-assisted co-precipitation method, maintained >95% ozone conversion for over 6 hours at 90% relative humidity and >98% for over 65 hours at 60% relative humidity. In situ diffuse reflectance infrared spectroscopy revealed that La doping enriched oxygen vacancies, promoted water participation in the catalytic decomposition of ozone, accelerated redox cycling under humid conditions, and significantly alleviated competitive adsorption of water molecules on active sites.

(2) Chemical Reduction Strategy

Treating catalysts with reducing agents (e.g., NaBH₄) partially removes lattice oxygen, directly increasing oxygen vacancy concentration. Studies show that NaBH₄-reduced MnO₂ maintains >90% ozone conversion for up to 318 minutes at an extremely low temperature of −50°C. Density functional theory calculations confirm that the reaction energy barrier at oxygen vacancy sites (0.98 eV) is significantly lower than at Ag sites or Mn sites, making oxygen vacancies the primary active sites for ozone decomposition on MnO₂ under ultra-low temperature conditions.

(3) Crystal Facet Engineering

Differences in atomic arrangement and coordination environments among various crystal facets are exploited to tune oxygen vacancy concentration and reactivity. It was found that although the (111) facet of δ-MnO₂ contains fewer oxygen vacancies than the thermodynamically stable (001) facet, it achieves superior catalytic performance and stability due to accelerated desorption of peroxide intermediates (*O₂). Under harsh conditions of a gas hourly space velocity of 900 L·g⁻¹·h⁻¹ and 35% relative humidity, the Mn-0.2 catalyst retained 95% ozone conversion after 24 hours of reaction.

(4) Asymmetric Oxygen Vacancy Construction

By constructing asymmetric M1–V_o–M2 motifs composed of cations with different electronegativities, charge symmetry is broken and directional electron transfer channels are established. A research team developed a hollow-structured perovskite–metal–organic framework–derived carbon hybrid (CaMnCo@CN) with asymmetric Co–V_o–Mn sites. This structure enhanced O₃ electron capture capability (1.82 eV), strengthened O₃ adsorption (E_ads = −3.56 eV), and elongated the O–O bond to 1.53 Å. Another team from Tsinghua University developed a catalyst with asymmetric Bi–O_v–Mn sites, where the single site lowered the formation energy of the ˙OOOH species. Due to uneven electron distribution when ozone and water coexist, the generation of reactive oxygen species, especially ˙OH, is promoted. This material efficiently degrades various inert VOCs at ambient temperature under realistic humid conditions.

Construction Strategy	Representative Catalyst/System	Key Performance Data
Elemental Doping	Fe–Cu–MnO2	100% toluene degradation, 100% ozone removal, stable >100 h
Elemental Doping	La0.15Mn1Ox-600	>95% conversion at 90% RH (6 h), >98% at 60% RH (65 h)
Chemical Reduction	NaBH4-reduced MnO2	>90% conversion at −50°C (318 min)
Crystal Facet Engineering	δ-MnO2 (111) facet	95% conversion at GHSV 900 L·g−1·h−1, 35% RH (24 h)
Asymmetric Oxygen Vacancy	CaMnCo@CN (Co–Vo–Mn)	99.10% atrazine degradation in 15 min, k = 0.30 min−1
Asymmetric Oxygen Vacancy	Bi–Ov–Mn site catalyst	Efficient degradation of inert VOCs at ambient temperature under humid conditions

3. Multiple Mechanisms of Oxygen Vacancies in Ozone Catalytic Oxidation

Oxygen vacancies play multiple key roles in catalytic cycles, which can be summarized in the following three aspects:

(1) Modulating Electronic Structure to Enhance Electron Transfer

The electron-rich nature of oxygen vacancies makes them efficient electron donors, accelerating the activation of O₃ molecules on the catalyst surface. Combined XPS, EPR, and DFT calculations indicate that oxygen vacancies are the primary reason for the ~200% increase in Lewis acid site concentration, significantly lowering the energy barrier for radical chain reactions (0.17 eV).

(2) Acting as Active Sites to Directly Participate in Reactions

Oxygen vacancies interact with ozone molecules to generate various reactive oxygen species, including radicals (·OH, ·O₂⁻) and non‑radicals (*O, ¹O₂). The oxygen‑vacancy‑rich Ca_1.1MnO_3−δ perovskite catalyst induces superoxide radical (·O₂⁻) generation through oxygen vacancies and constructs a rapid Mn(II/III/IV) cycling mechanism utilizing the redox properties of ·O₂⁻, resulting in a 200% increase in total radical yield. This catalyst achieves COD removal rates of 70–90% for pollutants such as phenol and 2‑chlorophenol.

(3) Exposing More Metal Sites to Enhance Reactivity

The presence of oxygen vacancies exposes additional coordinatively unsaturated metal sites that exhibit higher reactivity. Phosphate quenching experiments combined with DFT calculations demonstrate that oxygen vacancies facilitate the formation of hydrated hydroxyl groups and can also serve as active sites for catalytic ozonation, promoting O–O bond cleavage in ozone to generate *O.

(4) Unique Advantage of Asymmetric Oxygen Vacancies – Dual Oxidation Pathway Activation

Through localized charge polarization, both radical (·OH) and non‑radical (*O/¹O₂) pathways can be activated simultaneously for synergistic oxidation. The CaMnCo@CN catalyst with asymmetric Co–V_o–Mn sites achieved 99.10% atrazine degradation within 15 minutes, with a reaction rate constant k = 0.30 min⁻¹—1.72–5.81 times higher than previously reported catalysts. Even in complex water matrices containing 200 mg/L humic acid or 10 g/L common anions, the removal efficiency remained >94%. Its high stability stems from the reversible Co/Mn redox cycle and the regenerative capacity of oxygen vacancies.

4. Industrial Challenges for Oxygen Vacancy Engineering

Despite significant progress, several key challenges remain for practical industrial applications of oxygen vacancy engineering.

(1) Precise Characterization and Quantitative Analysis of Oxygen Vacancies

Current approaches rely on a combination of techniques including XPS, EPR, XAFS, positron annihilation lifetime spectroscopy (PALS), and aberration‑corrected electron microscopy. Qualitative and quantitative analysis of oxygen vacancies requires cross‑validation among multiple characterization methods, which increases R&D cycles and costs.

(2) Stability and Regeneration of Oxygen Vacancies

During ozone decomposition, catalyst deactivation primarily arises from the accumulation of peroxide intermediates (*O₂) on surface oxygen vacancies. Ag modification can assist oxygen vacancy regeneration by promoting desorption of peroxide intermediates, lowering the desorption energy barrier from 0.98 eV to 0.68 eV. However, excessive Ag may heal oxygen vacancies and cause pore blockage. Recent studies have proposed a liquid‑phase method to regenerate ozone decomposition catalysts by eliminating O₂²⁻ from oxygen vacancies, enabling effective recovery of catalytic activity under mild conditions.

(3) Adaptability Across a Wide Humidity Range

Water molecules compete with ozone for adsorption on oxygen vacancies, leading to rapid catalyst deactivation. Developing stable and effective ozone decomposition catalysts that operate across a broad humidity range remains a major challenge. Strategies such as La doping, which modulates oxygen vacancies while promoting water participation in the catalytic reaction, offer one effective route to mitigate humidity effects.

5. Conclusion

Oxygen vacancy engineering has moved from a laboratory concept to a critical stage toward industrial application. Through strategies such as elemental doping, chemical reduction, crystal facet engineering, and asymmetric oxygen vacancy construction, the ozone catalytic oxidation performance of catalysts can be systematically enhanced. Oxygen vacancies function through multiple synergistic mechanisms—modulating electronic structure, serving as active sites, exposing metal sites, and activating dual oxidation pathways.

Current research is shifting from merely pursuing the quantity of oxygen vacancies to precisely tuning their coordination environment and electronic structure. At the same time, combining multiple strategies—elemental doping, facet engineering, chemical reduction—to develop oxygen‑vacancy‑rich catalysts that operate stably under real industrial conditions (high humidity, high space velocity, complex exhaust components) has become an industry consensus. As understanding of the mechanistic roles of oxygen vacancies deepens and construction strategies continue to innovate, oxygen vacancy engineering will provide an ever more solid foundation for the industrial deployment of ozone catalytic oxidation technologies.

author: Gloria
date:2026/8/04