Ozone Decomposition Catalyst Low-Temperature Activity Retention Strategies: From Deactivation Mechanisms to Engineering Implementation

Ozone catalytic decomposition technology is widely applied in fields such as industrial waste gas treatment, aircraft cabin air purification, and air quality control in semiconductor manufacturing facilities due to its low energy consumption and ease of operation. However, the ozone decomposition efficiency of most transition metal oxide catalysts drops significantly when the ambient temperature falls below 15°C. Ozone elimination in aircraft cabins serves as a prime example: the ozone concentration in outside air intake at cruising altitudes (up to 13,700 meters) is far higher than at ground level. With the Federal Aviation Administration (FAA) and the World Health Organization (WHO) setting an upper limit of 0.056 ppm for ozone exposure over an 8-hour period, catalytic decomposition stands as the core technical approach for ozone control in cabins.
Catalyst deactivation under low-temperature conditions is not caused by a single factor but results from the coupling of two mechanisms: inhibited oxygen vacancy regeneration and competitive adsorption by water molecules. Starting with the reaction mechanism, this paper systematically reviews strategies for maintaining catalytic activity across four dimensions—material modification, support design, system optimization, and regeneration technology—and proposes a framework for combining these strategies based on specific temperature and humidity scenarios.

I. Mechanisms of Low-Temperature Deactivation: Imbalance in the Oxygen Vacancy Cycle and Competitive Adsorption by Water Molecules
The ozone decomposition reaction over manganese-based catalysts follows a Mars-van Krevelen cycle: ozone adsorbs onto surface oxygen vacancies (Ov) and decomposes to form peroxo intermediates (O₂²⁻); subsequently, O₂ desorbs, regenerating the oxygen vacancies. The rate-determining step of this cycle is the desorption of peroxo species, and the energy barrier associated with this step dictates the catalyst's maximum activity.

This cycle faces dual constraints at low temperatures. Under dry conditions, the desorption rate of peroxo species decreases further; oxygen atoms fail to desorb rapidly, accumulating at active sites and poisoning the oxygen vacancies. In the presence of water vapor, water molecules—structurally similar to ozone—compete for adsorption at oxygen vacancies; additionally, water molecules can form a water film that hinders effective contact between ozone and the active sites. The coupling of these two deactivation mechanisms leads to a drastic reduction in catalyst lifespan under low-temperature conditions.

It is worth noting that the role of water molecules in ozone decomposition is temperature-dependent. Research indicates that in an ozone atmosphere containing water vapor, manganese (Mn) in Mn-based catalysts is oxidized to higher valence states. A reaction pathway has been proposed wherein water molecules form surface OH₂⁺ species via electrostatic forces and hydrogen bonding, subsequently binding with O₃ to create a six-membered ring intermediate. This implies that, under appropriate conditions, water molecules may participate in the reaction rather than merely inhibiting activity; however, at low temperatures, this promoting pathway is suppressed, and competitive adsorption becomes the dominant factor.

II. Material Modification: Regulating Oxygen Vacancy Concentration and Regeneration Efficiency
2.1 Increasing Oxygen Vacancy Density via Chemical Reduction
Oxygen vacancy concentration is the primary determinant of low-temperature activity. Chemical reduction treatment can significantly increase the content of low-valence manganese (Mn²⁺, Mn³⁺) and enhance oxygen migration capability. An ε-MnO₂ catalyst reduced with NaBH₄ maintained a 100% ozone removal rate for 300 minutes at -25°C and retained a conversion rate exceeding 90% for 318 minutes at the ultra-low temperature of -50°C. ε-MnO₂ exhibits a specific surface area of 199.48 m²/g and an oxygen migration capacity of 7.23×10²¹ atom·g⁻¹, outperforming the other five MnO₂ crystal forms.

2.2 Synergistic Promotion of Oxygen Vacancy Regeneration by Noble Metals
Although reduction treatment increases oxygen vacancy concentration, it fails to resolve the difficulty of desorbing peroxo species; consequently, the catalyst still deactivates rapidly due to hindered oxygen vacancy regeneration. Silver (Ag) loading facilitates the desorption of peroxo intermediates by weakening the orbital overlap between oxygen vacancies (Ov) and O₂ as well as reducing Mn-O bond strength. DFT calculations reveal that the introduction of Ag lowers the desorption energy barrier for peroxo species from 0.98 eV to 0.68 eV.

By combining NaBH₄ reduction with 1 wt.% Ag loading, the 1Ag-MnO₂-NaBH₄ catalyst maintained an ozone removal rate above 80% for 600 minutes at -50°C, achieving a synergistic balance between increasing active sites and lowering energy barriers. The core of this strategy lies in the precise control of Ag loading: excessive Ag can repair oxygen vacancies and cause pore blockage, thereby negating the beneficial effects on desorption. 2.3 Synergistic Effects in Composite Oxides and Multimetallic Systems
In Mn-Ce composite oxides, the complementary effect of Ce's 4f-orbital electrons lowers the energy required for the catalytic generation of hydroxyl radicals from ozone. At a Mn/Ce molar ratio of 1:1, the yield of hydroxyl radicals increases by more than 40% compared to single-component oxides under low-temperature conditions (5–10°C). The formation of structural defects within the Mn-Ce composite system enhances oxygen vacancy density, while the modulation of surface acidic sites further facilitates low-temperature catalytic ozonation.

III. Support and Structural Design: Suppressing Competitive Water Adsorption
3.1 Encapsulation of Manganese-Oxygen Clusters in Zeolites
Encapsulating manganese-oxygen clusters within zeolite supercages represents one of the most significant breakthroughs in support strategies in recent years. The [Mn₃O₃]ⁿ⁺ clusters housed within FAU zeolite supercages provide abundant charge-transfer pathways; this facilitates electron distribution during the rate-limiting step, lowers the reaction energy barrier, and stabilizes the manganese oxidation state. This catalyst maintains an ozone decomposition efficiency exceeding 95% for 98 hours at -5°C and a space velocity of 720,000 h⁻¹. Crucially, the catalyst can be reversibly regenerated by treatment in air at 180°C for one hour—the lowest regeneration temperature reported to date for ozone catalysts—thereby providing the material foundation for an application model combining "direct cold-air treatment" with "periodic in-situ regeneration."

3.2 Hydrophobic Modification to Suppress Water Adsorption
Modulating surface hydrophobicity through organosilane grafting offers another effective approach. A Mn/ZSM-5 catalyst modified with butyltriethoxysilane (C4) maintains an O₃ conversion rate of over 85% for 6 hours at 80% relative humidity. Characterization results indicate that the organosilane reacts with surface hydroxyl groups (Si-OH-Al, Si-OH, Mn-OH) on the Mn/ZSM-5 to form siloxane bonds; this significantly enhances surface hydrophobicity while simultaneously promoting the formation of low-valence manganese species and oxygen vacancies. DFT calculations further reveal that the energy barrier for the rate-determining step at MnOH sites (0.704 eV) is lower than that at oxygen vacancies (0.842 eV); the coexistence of these two sites accelerates ozone decomposition.

The carbon-coating strategy also demonstrates potential for moisture resistance. A hydrophobic carbon layer prevents water vapor from accumulating on the catalyst surface, thereby avoiding competitive adsorption of water molecules at active sites.

IV. System-Level Activity Maintenance
4.1 Space Velocity Matching and Temperature Compensation
Reducing the space velocity at low temperatures to extend contact time is a direct method to compensate for insufficient reaction rates. For installed catalytic systems, this can be achieved by adjusting airflow rates or increasing the catalyst loading. The low pressure-drop characteristic of monolithic honeycomb catalysts offers advantages in high-airflow scenarios; studies have reported that zeolite-based honeycomb monolith catalysts maintain a decomposition efficiency of over 99% for more than 1,000 hours at 170°C and a space velocity of 50,000 h⁻¹, while retaining stable mechanical strength.

4.2 Optimization of Ozone Dosage Methods
In liquid-phase catalytic ozonation systems, the combined use of micro-bubbles for ozone dosing can significantly enhance ozone dispersion and dissolution efficiency. Operational data shows that employing a micro-bubble/catalytic ozonation process allows the COD removal rate for textile dyeing wastewater to remain above 75% even at a water temperature of 10°C—an improvement of 25 percentage points over conventional aeration methods. The essence of this strategy is to compensate for reaction kinetic limitations at low temperatures by improving mass transfer.

4.3 Synergistic Auxiliary Energy Fields
Combining ultraviolet (UV) light with catalytic ozonation can promote ozone photolysis at low temperatures, generating more hydroxyl radicals, while ultrasonic cavitation enhances liquid-phase mass transfer. These auxiliary measures can serve as system-level supplements in specific scenarios, though the balance between additional energy consumption and equipment complexity must be evaluated.

V. Regeneration Strategies: Lifespan Management under Low-Temperature Conditions
The deactivation of ozone catalysts is fundamentally caused by oxygen vacancies being occupied by peroxy species or blocked by water molecules; regeneration is the process of restoring the accessibility of these oxygen vacancies.

Thermal regeneration is the most traditional method. Research indicates that heat treatment within the 100–500°C range can restore approximately 57.5% of activity at 300°C; however, high-temperature treatment may lead to reduced breakthrough times and irreversible structural damage. Hydrogen reduction offers a viable low-temperature alternative: ~55% activity recovery can be achieved at just 60°C, as hydrogen selectively reacts with surface-adsorbed oxygen species to form water and liberate active sites, requiring significantly less energy than traditional thermal regeneration.

Zeolite-encapsulated manganese-oxide cluster catalysts achieve reversible regeneration after just one hour of air treatment at 180°C; this temperature range aligns well with low-temperature operating conditions, making them suitable for in-situ regeneration. Optimizing regeneration frequency requires a comprehensive assessment of catalyst type, the extent of deactivation, and the costs associated with operational downtime.

VI. Scenario-Specific Strategy Combinations
Temperature, humidity, and operational conditions vary significantly across applications, necessitating tailored strategies.

Aviation cabin ozone abatement (-40 to -5°C; ultra-high space velocity; maintenance-free requirement): A zeolite-encapsulated manganese-oxide cluster catalyst combined with a "direct cold-air treatment + periodic in-situ regeneration" approach is the optimal solution. Its long-term stability at -5°C and a space velocity of 720,000 h⁻¹, alongside low-temperature regeneration at 180°C, perfectly meet the aviation industry's strict requirements for maintenance without disassembly and minimal pressure drop.
Winter wastewater treatment ozone off-gas (0–15°C; high humidity; continuous operation): An Mn-Ce composite oxide system utilizing a hydrophobic support modification, paired with low-temperature hydrogen regeneration (60°C) for periodic maintenance. Micro-bubble dosing can simultaneously optimize mass transfer within the liquid-phase system.
Cold-chain disinfection ozone treatment (-20 to 0°C; intermittent operation): Data showing that an NaBH₄-reduced ε-MnO₂ catalyst maintains a 100% removal rate for 300 minutes at -25°C demonstrate its suitability for this temperature range; synergistic modification via Ag loading can further extend the single-run operational cycle. For ozone purification in semiconductor cleanrooms (operating at 10–25°C with low ozone concentrations and stringent cleanliness requirements), the high specific surface area and abundant oxygen vacancies of ε-MnO₂ ensure sufficient catalytic activity near room temperature, while its monolithic honeycomb structure accommodates high airflow rates with manageable pressure drop.
Conclusion
The fundamental logic for maintaining ozone catalyst activity under low-temperature conditions can be summarized in three parallel strategies: lowering energy barriers to facilitate the desorption of peroxy species, increasing active sites to boost oxygen vacancy concentration, and enhancing resistance to interference to suppress competitive adsorption by water molecules. At the material level, chemical reduction and synergistic modification with noble metals resolve the trade-off between oxygen vacancy concentration and regeneration efficiency; at the support level, zeolite encapsulation and hydrophobic modification provide the structural foundation for moisture-resistant, low-temperature operation; and at the system level, space velocity matching and optimized ozone dosing compensate—through engineering measures—for the limitations of low-temperature reaction kinetics. The synergy among these three approaches, rather than the isolated application of any single strategy, is the key to achieving engineering reliability in low-temperature catalytic ozone decomposition technology.

Author: Gloria
Date: 2026-09-24