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

<div> <p>We show that replacing alkaline (NaOH) for alkaline-earth metal (Sr(OH)<sub>2 </sub>as an example) in the synthesis of SSZ-13 zeolite with Si/Al~10 produces SSZ-13 zeolite material with novel, advantageous properties. Its NH<sub>4</sub>-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 AlO<sub>4</sub><sup>-</sup> 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% H<sub>2</sub>O/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% H<sub>2</sub>O/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>

Synthesis–Structure–Activity Relationship in Cu-MOR for Partial Methane Oxidation: Al Siting via Inorganic Structure-Directing Agents

“…To underpin our hypothesis, we performed an ionic exchange with Co 2+ ions to quantify the concentration of Al pairs. Acidic solutions of Co 2+ ions preferentially exchange on paired Al sites. ,, The Langmuir-type cobalt-ion exchange isotherm of the acidic cobalt acetate solution (pH 3–4) showed comparable cobalt uptake for both MOR zeolites and the absence of cobalt oxide nanoparticles. This was irrespective of their Al source discounting varying degrees of Al pairing as a possible explanation for the differing MeOH productivity (Figure S13a).…”