Efficient nitric oxide capture and reduction on Ni-loaded CHA zeolites

Abstract

As a prominent contributor to air pollution, nitric oxide (NO) has emerged as a critical agent causing detrimental environmental and health ramifications. To mitigate emissions and facilitate downstream utilization, adsorption-based techniques offer a compelling approach for direct NO capture from both stationary and mobile sources. In this study, a comprehensive exploration of NO capture under oxygen-lean and oxygen-rich conditions was conducted, employing Ni ion-exchanged chabazite (CHA-type) zeolites as the adsorbents. Remarkably, Ni/Na-CHA zeolites, with Ni loadings ranging from 3 to 4 wt%, demonstrate remarkable dynamic uptake capacities and exhibit exceptional NO capture efficiencies (NO-to-Ni ratio) for both oxygen-lean (0.17–0.31 mmol/g, 0.32–0.43 of NO/Ni) and oxygen-rich (1.64–1.18 mmol/g) under ambient conditions. An NH₃ reduction methodology was designed for the regeneration of absorbents at a relatively low temperature of 673 K. Comprehensive insights into the NO_x adsorption mechanism were obtained through temperature-programmed desorption experiments, in situ Fourier transform infrared spectroscopy, and density functional theory calculations. It is unveiled that NO and NO₂ exhibit propensity to coordinate with Ni²⁺ via N-terminal or O-terminal, yielding thermally stable complexes and metastable species, respectively, while the low-temperature desorption substances are generated in close proximity to Na⁺. This study not only offers micro-level perspectives but imparts crucial insights for the advancement of capture and reduction technologies utilizing precious-metal-free materials.