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

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

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

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

The Superior Hydrothermal Stability of Pd/SSZ-39 in Low Temperature Passive NOx Adsorption (PNA) and Methane Combustion

We successfully synthesized uniform SSZ-39 with an average crystal size of about a micron. Pd (0.7 - 3 wt%) was supported on SSZ-39 with Si/Al ratio ~12. The as-synthesized materials were characterized by FTIR, XRD, Helium Ion Microscopy, HAADF-STEM imaging, 27Al, 29Si and H solid state NMR spectroscopic techniques. <br>FTIR studies with CO and NO probe molecules reveal that the 0.7 wt% Pd/SSZ-39 material with Si/Al ~12 has the majority of Pd dispersed atomically as isolated Pd(II) and Pd(II)-OH centers, and thus can be used as a low-temperature passive NOx adsorber. Pd(II)-NO, Pd(II)(OH)(NO) and Pd(II)(CO)(NO) complexes form during PNA in this material. We compare this PNA material directly with the Pd/SSZ-13 system (with Si/Al ratio ~12) and show its superior hydrothermal stability. Remarkably, Pd/SSZ-39 with Si/Al ratio ~12 survives hydrothermal aging up to 815 ºC in 10% H2O/Air vapor for 16 hours without significant loss in activity. The SSZ-39 crystal structure remains intact during hydrothermal aging up to 1,000 ºC as we elucidate it with XRD and HAADF-STEM imaging/EDS mapping. However, changes to the framework during such harsh hydrothermal treatment significantly change the NOx release profiles during PNA as evidenced by high-field 27Al NMR on fresh and aged Pd/SSZ-39 samples as well as PNA performance measurements. <br>Besides PNA application, these hydrothermally very stable materials (3 wt% Pd on SSZ-39 with Si/Al ratio ~12) can be used as a robust methane combustion catalyst under industrially relevant conditions (GHSV~600,000hr-1). This catalyst shows minimal deactivation after both harsh hydrothermal aging at 750 and 800 ºC, and prolonged time on stream (105 hrs) at 425 ⁰C. In contrast, both 3wt% Pd/alumina and 3wt% SSZ-13 supported samples lose a significant portion of their activity.<br>

The Superior Hydrothermal Stability of Pd/SSZ-39 in Low Temperature Passive NOx Adsorption (PNA) and Methane Combustion

We successfully synthesized uniform SSZ-39 with an average crystal size of about a micron. Pd (0.7 - 3 wt%) was supported on SSZ-39 with Si/Al ratio ~12. The as-synthesized materials were characterized by FTIR, XRD, Helium Ion Microscopy, HAADF-STEM imaging, 27Al, 29Si and H solid state NMR spectroscopic techniques. <br>FTIR studies with CO and NO probe molecules reveal that the 0.7 wt% Pd/SSZ-39 material with Si/Al ~12 has the majority of Pd dispersed atomically as isolated Pd(II) and Pd(II)-OH centers, and thus can be used as a low-temperature passive NOx adsorber. Pd(II)-NO, Pd(II)(OH)(NO) and Pd(II)(CO)(NO) complexes form during PNA in this material. We compare this PNA material directly with the Pd/SSZ-13 system (with Si/Al ratio ~12) and show its superior hydrothermal stability. Remarkably, Pd/SSZ-39 with Si/Al ratio ~12 survives hydrothermal aging up to 815 ºC in 10% H2O/Air vapor for 16 hours without significant loss in activity. The SSZ-39 crystal structure remains intact during hydrothermal aging up to 1,000 ºC as we elucidate it with XRD and HAADF-STEM imaging/EDS mapping. However, changes to the framework during such harsh hydrothermal treatment significantly change the NOx release profiles during PNA as evidenced by high-field 27Al NMR on fresh and aged Pd/SSZ-39 samples as well as PNA performance measurements. <br>Besides PNA application, these hydrothermally very stable materials (3 wt% Pd on SSZ-39 with Si/Al ratio ~12) can be used as a robust methane combustion catalyst under industrially relevant conditions (GHSV~600,000hr-1). This catalyst shows minimal deactivation after both harsh hydrothermal aging at 750 and 800 ºC, and prolonged time on stream (105 hrs) at 425 ⁰C. In contrast, both 3wt% Pd/alumina and 3wt% SSZ-13 supported samples lose a significant portion of their activity.<br>