What are the disadvantages of ozone decomposition catalysts?

While ozone decomposition catalysts play a vital role in air purification and industrial waste gas treatment, their practical limitations cannot be ignored. These shortcomings do not exist in isolation; rather, they are interconnected and mutually reinforcing, collectively constituting bottlenecks in their technological expansion and performance optimization.

First, the core disadvantage of catalysts lies in their environmental sensitivity and stability, which directly determine their service life and efficiency. The most prominent challenge comes from water vapor (humidity) in the environment. Most highly effective non-precious metal catalysts, such as transition metal oxides represented by manganese dioxide (MnO₂), possess numerous unsaturated bonds on their surfaces, which serve as active sites for ozone decomposition. However, water molecules (H₂O), being more polar than ozone molecules, compete more strongly for these active sites, forming a "water film" that physically blocks contact between ozone and the catalyst, resulting in a sharp drop in catalytic efficiency in high-humidity environments. Besides water vapor, other impurities in the environment are also catalyst poisons. Sulfur dioxide (SO₂), in particular, can undergo irreversible chemical reactions with active catalyst components, forming stable sulfates or sulfites that permanently cover or destroy active sites, causing "sulfur poisoning." Similarly, chlorine compounds, volatile organic compounds (VOCs), and dust particles can deactivate catalysts through chemical poisoning or physical blocking (clogging catalyst pores). Furthermore, under long-term operation or localized overheating, catalyst nanoparticles are prone to migration and aggregation (sintering), resulting in a reduction in specific surface area and a sharp decrease in the number of active sites. This is a form of structural deactivation.

Secondly, balancing cost and performance remains a major challenge, from the material itself to engineering applications. To overcome these stability issues, researchers have developed precious metal catalysts, such as platinum (Pt) and palladium (Pd), which generally exhibit superior low-temperature activity and stronger resistance to poisoning. However, their prohibitive prices significantly increase the cost of application, making them difficult to deploy on a large scale in high-volume, low-value scenarios, such as general building ventilation systems. Although non-precious metal catalysts are relatively low-cost, their performance often suffers from shortcomings. Many catalysts perform well under ambient temperature and dry conditions, but their lack of low-temperature activity becomes apparent when exposed to low temperatures or high humidity. This necessitates additional heating to maintain efficiency, further increasing system energy consumption and complexity. Engineering design often requires a low gas space velocity (i.e., a slower air velocity or a larger catalyst loading) to ensure sufficient contact time between ozone molecules and the catalyst. This means that when processing large air volumes, a large and substantial catalyst bed is required. This not only increases the initial equipment investment but also significantly increases the system's airflow resistance (pressure drop), requiring higher blower power and creating a continuous energy burden.

Finally, these limitations in materials science and reaction engineering ultimately converge into a limited service life and complex maintenance requirements. Because poisoning, sintering, and pulverization are inevitable and gradual processes, catalyst activity gradually decreases over time, necessitating replacement. This means users face ongoing maintenance costs and the disposal of spent catalysts, rather than a "set-it-and-forget-it" solution. In practical applications, protecting the expensive catalyst requires the addition of complex pretreatment systems, such as precision filters for dust removal and chemical scrubbers for SO₂ and NOx removal. This further increases the complexity, footprint, and overall cost of the entire system.

In summary, the shortcomings of ozone decomposition catalysts present a complex chain of challenges: the inherent environmental sensitivity of the materials (fear of water and poisoning) limits their stability; the use of precious metals to enhance stability or activity encounters cost bottlenecks; and both low-cost conventional catalysts and expensive precious metal catalysts face the difficult trade-off between efficiency, energy consumption, and lifespan in engineering applications. Current research is focusing on overcoming these limitations through nanostructure design, surface hydrophobic modification, and the development of novel non-precious metal composite materials, aiming to develop next-generation ozone decomposition catalysts that combine high activity, stability, long life, and affordability.