Increasing Al-Pair Abundance in SSZ-13 Zeolite via Zeolite Synthesis in the Presence of Alkaline Earth Metal Hydroxide Produces Hydro-Thermally Stable Cobalt and Pd-SSZ-13 Materials for Pollutant Abatement Applications

Abstract

\n\nWe show that replacing alkaline (NaOH) for alkaline-earth\nmetal (Sr(OH)2 as an example) in the synthesis of SSZ-13 zeolite\nwith Si/Al~10 produces SSZ-13 zeolite material with novel, advantageous\nproperties. Its NH4-form ion-exchanges higher amount of Co(II) ions\nthan the conventional one: this is the consequence of increased number of Al pairs\nin the structure induced by the +2 charge of Sr(II) cations in the synthesis\ngel that force two charge-compensating AlO4- motives to\nbe closer together. We characterize the +2 state of Co(II) ions in these\nmaterials with infra-red spectroscopy and XANES measurements. They can be used\nfor NOx pollutant adsorption from ambient air: the ones derived from SSZ-13\nwith higher Al pair content contain more cobalt(II) and thus, perform better as\nambient-air NOx adsorbers before reaching full saturation capacity. Notably,\nCo(II)/SSZ-13 material with increased number of Al pairs is significantly more\nhydrothermally stable than its NaOH-derived analogue. Loading 1.7 wt% Pd into\nCo-SSZ-13 synthesized in the presence of Sr(II) produces a passive NOx\nadsorber (PNA) material that can be used for NOx adsorption from simulated\ndiesel engine exhaust. The critical issue for these applications is\nhydrothermal stability of Pd-zeolites. Pd/SSZ-13 synthesized in NaOH media\nloses most of its PNA capacity after ~800 ⁰C\nhydrothermal aging in the flow of air and steam (10 hours in 10% H2O/air\nflow). The 1.7 wt% Pd/Co/SSZ-13 material with Si/Al ~10 does not lose its PNA\ncapacity after extremely harsh aging at 850 and 900 ⁰C (10 hours in 10% H2O/Air flow)\nand loses only ~55% capacity after hydrothermal aging at 930 ⁰C. It shows considerably enhanced stability\ncompared with previous record for Pd/FER, Pd/SSZ-39 and Pd/BEA materials that\ncould survive hydrothermal aging no higher than 820 ⁰C. We herein reveal a new, simple, and\nscalable strategy for making remarkably (hydro)thermally stable metal-zeolite\nmaterials/catalysts with a number of useful applications. \n\n