R-134a is processed by waste gas treatment companies according to relevant laws and is mainly treated through combustion and plasma methods. However, combustion generates secondary pollutants such as nitrogen oxides, and high-temperature decomposition using plasma requires significant energy and equipment costs. Additionally, as the reactor size increases, efficiency decreases. Therefore, there is a need for technology that can stably eliminate refrigerants at low temperatures with minimal pollutant generation. 

To overcome these limitations, the research team developed a catalytic decomposition technology that can operate at lower temperatures compared to combustion and plasma methods. They focused on the fact that the various metal components in red mud, such as iron and aluminum, can interact to form a powerful and stable catalyst for refrigerant decomposition. 

Red mud has a porous structure with a large surface area per unit mass and high thermal stability, allowing reactants to flow efficiently and inhibiting the physical and chemical degradation of the catalyst. Additionally, it creates an optimal environment for interfacial phenomena such as adsorption and electro-migration, which are essential for catalytic reactions, thereby enhancing the durability and activity of the catalyst. 

To further enhance the decomposition performance, the research team employed a simple heat treatment process to induce interactions among calcium (Ca), silicon (Si), and aluminum (Al) components, forming a composite material of tricalcium aluminate (C3A) and gehlenite (C2S). These materials, which are used to increase the strength of cement, strengthen the binding of catalyst particles, and increase the reaction surface area, thereby improving decomposition performance. 

Additionally, the hydrogen fluoride (HF) produced during the decomposition of R-134a reacts with calcium oxide (CaO) to form calcium fluoride (CaF2). Chemically stable calcium fluoride forms a thin film on the catalyst surface, acting as a protective shield to prevent the deactivation and protect the catalyst. 

The catalyst developed by the research team demonstrated excellent refrigerant decomposition performance, maintaining a high decomposition rate of over 99% for 100 hours. Additionally, it can be produced at a rate of 1 kg per hour through simple drying and grinding processes at the lab scale, making it suitable for mass production at full scale. Since it is made by recycling industrial waste, there are no raw material costs, and it can reduce waste disposal costs while potentially generating additional revenue. 

"Red mud is a strongly alkaline substance that can cause severe environmental pollution if it enters the surrounding environment, but there have been no suitable technologies to process and recycle it,” said Dr. Shin-Kun Ryi. “The developed catalyst manufacturing technology not only recycles waste to reduce environmental pollution but also effectively decomposes refrigerants, which have a strong greenhouse gas effect, with excellent performance." 

This research was conducted with the support of KIER’s R&D project, and the findings were published in the international Journal of Industrial and Engineering Chemistry.