(755c) High Loadings of Atomically Dispersed Pd in Small-Pore SSZ-13: Superior Low Temperature Passive NOx Adsorber
The majority of harmful atmospheric CO and NOx emissions comes from vehiclesâ exhaust. Although there has been success addressing NOx emissions at temperatures above 250 ÂºC with the aid of selective catalytic reduction technology that relies on the Cu/SSZ-13 material and sacrificial urea source, emissions during vehicle cold start (when the temperature is below 150 ÂºC), are a major challenge. Herein, we show we can completely eliminate both CO and NOx emissions simultaneously under realistic exhaust flow, using a highly-loaded (2 wt %) atomically dispersed palladium in the extra-framework positions of the small-pore chabazite material as a CO and passive NOx adsorber. Until now, atomically dispersed highly loaded (> 0.3 wt%) transition metal/SSZ-13 materials have not been known: we therefore devised a general simple and scalable route to prepare such materials for Pt(II) and Pd(II) via systematic investigation of synthetic methods; this also allowed us to explain the discrepancies in the available metal/zeolite literature that stem from the lack of systematic knowledge on the synthesis of such materials. With the aid of spectroscopy and materials testing with various specifications of Pd, we show that both CO and NOx can be simultaneously completely abated with 100% efficiency (NO/Pd and CO/Pd ratio 1 which is the maximum theoretical limit) even in the presence of significant water amounts, due to the formation of mixed carbonyl-nitrosyl palladium complex in chabazite micropore.