Regulating NO2 adsorption at ambient temperature by manipulating copper species as binding sites in copper-modified SSZ-13 zeolites

Abstract

Atmospheric NO2 pollution poses significant risks to human health and the environment even at low concentrations, necessitating the development of efficient technologies for its removal under ambient conditions. In this study copper (Cu)-modified SSZ-13 zeolites (referred to as Cun+SSZ-13 where n represents the valence state of Cu) were developed for NO2 removal by adsorption. Cun+SSZ-13 zeolites containing Cu species with different valence states and proportions were prepared by reducing a Cu2+-exchanged SSZ-13 zeolite (Cu2+SSZ-13) using H2 at different temperatures. The Cun+SSZ-13 reduced at 190 °C showed the highest NO2 removal capacity (1.79 mmol g−1), outperforming pristine SSZ-13 and Cu2+SSZ-13 by 52.3% and 19.4%, respectively. The improvement was due to the increased amount of adsorption sites (Cu+ and H+) and the stronger affinity of Cu+ than Cu2+ for NO2, as confirmed by density functional theory (DFT) calculations. The generation of Cu0 nanoparticles and moisture in zeolites during reduction was undesirable for NO2 adsorption. However, this could be eliminated by lowering the reduction temperature and performing thermal activation, respectively. This work provides systematic methods for designing zeolite adsorbents for ambient NO2 removal and offers insights into the burgeoning field of air pollution control.