Bifunctional Cu/ZSM-5 for Medium-Temperature VOCs Adsorption and In Situ Catalytic Oxidation: Promoting Effect of Pretreatments and Cu Loading

The development of bifunctional materials integrating adsorption and catalytic oxidation functionalities is essential for efficient volatile organic compounds (VOCs) abatement under medium-temperature conditions. In this work, Cu-loaded ZSM-5 zeolites modified via acid–base surface pretreatments were synthesized to synergistically regulate pore structures, surface acidity, and active Cu species distribution. Acid (HNO3) etching selectively generated hierarchical mesoporosity while preserving microporous frameworks, whereas alkaline (NaOH) treatment enhanced mesopore volume but neutralized Brønsted acidity, thereby limiting redox activity. Combined with Cu loading, the optimized catalyst (5Cu/ZSM-5-A) exhibited a high specific surface area (514.6 m2/g), abundant Lewis acid sites, and highly dispersed Cu2+ species. Notably, this dual functionality resulted in a toluene adsorption capacity of 23.3 mg/g at 150 °C, while this value was only 10.4 mg/g over pure ZSM-5-O. Moreover, near-complete suppression of toluene desorption and 89.2% COx yield can be achieved during the in situ oxidation process of 5Cu/ZSM-5-A with captured toluene, while above 80.0% adsorbed toluene was released over blank ZSM-5-O without conversion. This work not only provides a strategic approach for designing zeolite-based bifunctional materials through pore engineering and chemical modulation but also offers a practical solution for energy-efficient purification of medium-temperature VOC emissions.