Disproportionation and coordination driven high-efficient NO adsorption on FAU-and LTA-type zeolites

High efficient NO adsorption on zeolites not only accelerates catalytic NO to N₂ by concentrating, but also figures out the difficulty of removing NO with low temperature and low concentration. This study evaluates the dynamic NO adsorption–desorption behaviors on 12 commercial zeolites, demonstrating 13X and 5A zeolites as excellent adsorbents with high NO adsorption capacity and low regeneration temperature. Based on extensive characterizations including N₂-physisorption, NH₃-TPD, CO₂-TPD, on-line MS and in-situ DRIFTS, the pore structure-performance relationship, acidity-performance relationship and basicity-performance relationship have been thoroughly investigated and discussed upon NO adsorption–desorption behaviors, together with the gaseous and surface species. NO directly coordinates to the strong Lewis acid sites and strong base sites (i.e., strong Lewis acid-base pairs), leading to coordinately bonded NO^δ+ and NO^δ- species, respectively. Besides, NO also directly disproportionates to N₂O and NO₂, followed by in-situ conversion of NO₂ into nitrate species. Thus, the coordination and disproportionation mechanisms have been identified for high-efficient NO adsorption on 13X and 5A zeolites, which supplements the current understandings of NO adsorption on zeolites and provides a new strategy to strengthen NO adsorption on zeolites with strong Lewis acid-base pairs.