Reversible NOxstorage over Ru/Na–Y zeolite

Abstract

Ruthenium loaded Na–Y zeolite was found to be an efficient adsorbent for achieving NO_x adsorption–desorption cycles comprising adsorption under oxidizing and desorption under reducing conditions. The speciation of ruthenium was investigated using TEM, EXAFS, ⁹⁹Ru Mossbauer spectroscopy and XRD in combination with Rietveld refinement. The sodium cation siting was monitored using ²³Na MAS NMR. Characterization of the Ru/Na–Y adsorbent in NO_x saturated and regenerated state revealed a unique cooperation of supported ruthenium nano metal particles and isolated Ru atoms in framework cavities affecting the sodium cations. Supported ruthenium nanoparticles assume a catalytic role in NO oxidation. Ruthenium atoms in framework cavities undergo switching of oxidation state during adsorption–desorption cycles. It triggers reversible sodium cation migrations from coordination with the framework in the regenerated state to coordination in sodium–water networks in supercages providing adsorption sites for NO_x during adsorption. The peculiar ruthenium organization is naturally obtained upon lean–rich cycling. Ru/Na–Y adsorbent is insensitive to SO_x and to the presence of CO during reductive regeneration.