A systematic comparative study of granular activated carbons and catalysts for ozone removal

Abstract

Ozone is one of the critical air pollutants having direct and indirect adverse health effects. The occupational safety and health administration (OSHA) set 100 ppb as the ozone's permissible exposure limit, highlighting the need for an ozone removal mechanism in many indoor settings. Activated carbon (AC) and metal oxide catalyst based ozone removal are two widely-used technologies for ozone mitigation; however, currently, little insight exists for choosing the best technology based on the application requirements. AC tests were typically limited to low ozone concentration (e.g., ppb level) making it difficult to obtain a broad picture of the link between their performance and properties. Additionally, the ozone removal by ACs and catalysts lacked a complete assessment of performance degradation over time. To fill this gap, this study involves a systematic evaluation of the ozone removal by various granular ACs and granular manganese oxide-cuprous oxide catalysts. The testing methodology was initially based on ASHRAE 145.1 standard; however, test conditions were later made more challenging to better capture the performance decline. It was surprisingly found that, among ACs, the coconut shell-based one have a substantial capacity to remove ozone at moderate and mild concentration levels (<200 ppm), even higher than catalyst, although all ACs get considerably deactivated at high concentration (>99% efficiency at 1 ppm down to <40% efficiency at 900 ppm). By contrast, catalysts feature a slow steady decrease of active sites over time (99% efficiency at 1 ppm down to >70% efficiency at 900 ppm). Subsequent analysis of the material properties demonstrated a strong link between material's type and its physical and chemical characteristics with its ozone removal capacity. The knowledge is envisioned to be of significant utility for numerous applications where ozone contamination is a challenging problem.