Humidity is one of the key factors affecting the catalytic efficiency and long-term stability of ozone decomposition catalysts in practical industrial applications. Engineering experience shows that gases treated in ozone systems are rarely completely dry. In applications such as water treatment, industrial oxidation, and off-gas treatment, relative humidity often remains above 50% RH, and some operating conditions may approach saturated humidity.
If a catalyst performs well only under low-humidity conditions but lacks moisture resistance, problems such as reduced ozone removal efficiency, increased pressure drop, and shortened catalyst service life may occur during operation. Therefore, when evaluating ozone decomposition catalyst performance, it is necessary to consider not only initial activity but also reaction stability, structural changes, and long-term performance under humid conditions.
The primary function of an ozone decomposition catalyst is to reduce the activation energy of ozone decomposition, enabling ozone (O₃) to rapidly convert into oxygen (O₂). During the catalytic process, ozone molecules first adsorb onto the catalyst surface, followed by electron transfer and oxygen species conversion at active sites, ultimately completing the decomposition process.
The typical reaction can be expressed as:
O₃ → O₂ + O*
The generated active oxygen species (O*) further participate in surface oxygen cycling, allowing the catalyst to continuously promote the reaction.
However, in real operating environments, gas streams usually contain water vapor, ozone, and other trace components simultaneously. When moisture enters the catalyst system, it alters the surface adsorption state of the catalyst and affects the interaction between ozone molecules and active sites.
Therefore, the impact of humidity on ozone decomposition catalysts is not simply a matter of reduced gas flow efficiency. It involves multiple factors, including surface chemical processes, pore structure utilization, and changes in active site availability.
Catalyst surfaces contain numerous active sites capable of adsorbing ozone, including defect sites, oxygen vacancies, and active metal centers on metal oxide surfaces.
Under low-humidity conditions:
Ozone molecules can rapidly diffuse to the catalyst surface;
Active sites maintain high utilization efficiency;
The decomposition reaction proceeds continuously.
However, as humidity increases, water molecules preferentially adsorb onto certain polar regions of the catalyst surface and compete with ozone for adsorption sites.
Studies have shown that in some metal oxide catalytic systems, increasing relative humidity from 20% RH to 80% RH may reduce catalytic activity by approximately 10%–40%. The actual reduction depends on catalyst composition, pore structure, and surface hydrophilicity.
This indicates that performance data obtained under dry laboratory conditions may not accurately represent real industrial operating performance.
Ozone decomposition catalysts typically rely on surface oxygen cycling to complete the catalytic process.
For example, active oxygen species on the catalyst surface can promote ozone decomposition:
O₃ + active site → O₂ + active oxygen
The active oxygen species then participate in subsequent reaction cycles.
When moisture enters the system, hydroxyl groups (—OH) may form on the catalyst surface, altering the distribution of oxygen species.
In some cases, moderate moisture may promote certain reaction pathways because surface hydroxyl groups can participate in oxygen transfer processes. However, excessive water coverage can hinder oxygen migration and slow down the catalytic cycle.
Therefore, the influence of humidity on catalyst performance is not always negative; it depends on humidity level, material structure, and operating conditions.
Ozone is widely used in water treatment applications, including industrial wastewater treatment and advanced oxidation processes.
Because ozone is typically transferred into water through gas-liquid contact, the discharged off-gas often carries a significant amount of water vapor.
Field measurements from some engineering applications indicate:
Relative humidity in ozone off-gas streams is commonly above 70% RH;
Systems without moisture removal may reach humidity levels above 90% RH;
Continuous operation periods may extend to several thousand hours.
Under these conditions, long-term water adsorption on the catalyst can gradually affect ozone mass transfer and reaction efficiency.
For example, in an industrial wastewater ozone treatment project, the ozone outlet concentration initially met the design requirements, but gradually increased after several months of operation. Investigation showed that the catalyst had not experienced significant mechanical degradation. Instead, prolonged exposure to high humidity increased surface water adsorption and reduced active site utilization. After optimizing gas pretreatment and using catalytic materials better suited for humid conditions, the system returned to stable operation.
In addition to water treatment, ozone decomposition catalysts are also used in:
Ozone generator off-gas treatment;
Industrial air purification systems;
Laboratory gas treatment equipment;
Specialized ozone control systems.
Humidity in these applications can be affected by seasonal changes, production processes, ventilation conditions, and HVAC system operation.
Therefore, industrial users should not select catalysts based on a single humidity condition but should evaluate the actual operating range.
Traditional catalyst evaluations usually focus on:
Ozone conversion efficiency;
Reaction temperature;
Gas hourly space velocity (GHSV);
Catalyst loading amount.
These parameters reflect fundamental catalyst performance, but industrial applications require humidity-related evaluation as well.
More comprehensive evaluation methods include:
Testing under different humidity conditions: Compare ozone removal efficiency at different humidity levels, such as 20% RH, 50% RH, and 80% RH.
Long-term hydrothermal stability testing: Monitor activity changes, pressure drop variations, and structural stability after hundreds or thousands of hours of operation.
Ozone decomposition catalysts typically contain porous structures to increase gas-catalyst contact area.
However, excessively small pores may lead to:
Water retention;
Slower drying processes;
Reduced reaction pathways.
A balanced distribution of micropores and mesopores can facilitate ozone diffusion while minimizing long-term moisture accumulation.
The hydrophilicity and hydrophobicity of catalyst surfaces need to maintain an appropriate balance.
If the catalyst surface adsorbs too much water:
Water may cover active regions;
Ozone adsorption may be restricted.
If the surface completely repels water, certain oxygen transfer processes may also be affected. Therefore, ozone decomposition catalysts require surface properties optimized according to specific application environments.
For high-humidity ozone off-gas streams, the following measures can be considered:
Adding gas-liquid separation processes;
Reducing the risk of liquid water entering the catalyst bed;
Optimizing gas flow velocity;
Controlling operating temperature.
These measures can reduce long-term moisture exposure of the catalyst.
Catalyst selection should consider:
Ozone concentration;
Gas flow rate;
Operating temperature;
Humidity range;
Continuous operating duration.
minstrong has optimized ozone decomposition catalysts for different industrial humidity conditions during catalyst development, enabling catalytic materials to adapt to various gas treatment environments.
Future development of ozone decomposition catalysts will mainly focus on the following areas:
Expanding humidity tolerance range: Optimizing material composition, surface structure, and pore design to improve stability under high-humidity conditions.
Reducing humidity-induced performance degradation: Minimizing water coverage on active sites and improving long-term performance retention.
Enhancing adaptability to complex environments: Improving catalyst stability in gas streams containing dust, organic compounds, and other impurities.
Humidity is a critical factor determining the industrial performance of ozone decomposition catalysts. Water not only affects ozone adsorption on catalyst surfaces but may also alter surface oxygen cycling, active site availability, and long-term structural stability.
For industrial users, ozone decomposition catalyst selection should focus on humidity tolerance, long-term performance retention, and compatibility with actual operating conditions, rather than relying solely on initial activity measured under dry conditions.
Only by considering humidity effects can the operational performance of catalysts be predicted more accurately and maintenance and replacement costs be reduced.
author：Gloria
date:2026-07-22
Contact: Candyly
Phone: 0086-15308453884
Tel: 0086-731-84115166
Email: sales@minstrong.com
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