A Density Functional Theory Modeling on the Framework Stability of Al-Rich Cu-SSZ-13 Zeolite Modified by Metal Ions

The metal ion-modified aluminum-rich Cu-SSZ-13 zeolite possesses high hydrothermal stability (especially with modifications using yttrium). In this study, DFT was used to model the location of Cu2+, Cu+, Ca2+, and Y3+ on Al-rich SSZ-13. The Al distribution in the framework of SSZ-13 zeolite affects the locations of metal ions. The isolated Cu+, Cu2+, Ca2+, and Y(OH)2+ ions are most stable in the six-membered ring, and the easiest site for Cu(OH)+ or Y(OH)2+ is in the eight-membered ring. When Cu2+ and Y(OH)2+ or Cu2+ and Ca2+ are in the same cage, Cu2+ is located in the six-membered ring and Y(OH)2+ or Ca2+ migrates to the eight-membered ring of the zeolite. The Y3+ exhibits the strongest effect on stabilizing the framework Al followed by Ca2+. In addition, metal ions could form multiple coordination bonds with the zeolite framework O, which further stabilizes the framework Al and enhances the hydrothermal stability of SSZ-13 zeolite.