Exceptionally high and reversible NO x uptake by hollow Mn-Fe composite nanocubes derived from Prussian blue analogues.

Noble metal-based catalysts are widely used as passive NO x adsorbers (PNA) for cold-start NO x emissions; however, efficient porous materials as an alternative have great development potential. Herein, porous Mn-Fe composites with hollow nanocubes derived from Prussian blue analogue (PBA) precursors were used as PNA. The effects of O 2 , the molar ratio of Mn/Fe, calcination temperature and reaction temperature on their adsorption capacity were explored. The physicochemical properties of the obtained catalysts were systematically characterized by XRD, SEM, BET surface area, TGA, XPS and DRIFT techniques. The developed Mn 1 Fe 2 -450 presented excellent NO x uptake (more than 2.16 mmol g -1 at 200 °C). Moreover, a high NO x adsorption performance was also retained in the presence of 10% water vapor. The existing Mn 3+ and Fe 2+ species could contribute to the NO x adsorption and gaseous O 2 can accelerate NO activation to form more easily adsorbed NO 2 . Surface NO 2 is further diffused and stored into the bulk of the Mn-Fe composite in the form of nitrite and nitrate. This work revealed a novel candidate for PNA catalysts, which might provide inspiration for the design of new adsorbent materials.