*Article* **Improvement of Alkali Metal Resistance for NH3-SCR Catalyst Cu/SSZ-13: Tune the Crystal Size**

**Zexiang Chen <sup>1</sup> , Meiqing Shen 1,2, Chen Wang 1,3, Jianqiang Wang <sup>1</sup> , Jun Wang 1,\* and Gurong Shen 4,\***


**Abstract:** To improve the alkali metal resistance of commercial catalyst Cu/SSZ-13 for ammonia selective catalytic reduction (NH<sup>3</sup> -SCR) reaction, a simple method to synthesize Cu/SSZ-13 with a core–shell like structure was developed. Compared with smaller-sized counterparts, Cu/SSZ-13 with a crystal size of 2.3 µm exhibited excellent resistance to Na poisoning. To reveal the influence of the crystal size on Cu/SSZ-13, physical structure characterization (XRD, BET, SEM, NMR) and chemical acidic distribution (H<sup>2</sup> -TPR, UV-Vis, Diethylamine-TPD, pyridine-DRIFTs, EDS) were investigated. It was found that the larger the crystal size of the molecular sieve, the more Cu is distributed in the crystal core, and the less likely it was to be replaced by Na to generate CuO. Therefore, a 2.3 µm sized Cu/SSZ-13 well-controlled the reactivity of the side reaction NH<sup>3</sup> oxidation and the generation of N2O. The result was helpful to guide the extension of the service life of Cu/SSZ-13.

**Keywords:** alkali metal poison; Cu/SSZ-13; crystal size; NH<sup>3</sup> -SCR
