Tof-SIMS: A Versatile Method for Zeolite Structure Detection

Microporous crystalline aluminosilicate zeolites are widely studied for their applications in catalysis, adsorption, purification and separation.  Throughout the history of zeolite material development, its characterization mainly relies on X-ray diffraction (XRD).  The XRD technique not only qualititavely identifies the zeolite crystaline structure, but also quantitatively estimates a reliable  zeolite phase purity. XRD can also be used to predict the chemical bonds and the position of atoms inside the zeolite crystal. Despite its advantages, XRD is incapable of verifying  zeolite crystalline structures with less than 4-5 unit cells in size and less than 1 percent of zeolite content from the mixed phases. Other characterizetion tools including magic angle spinning  NMR, neutron diffraction, Raman specstroscopy and electron microscopy have been developed to bridge the gap left by XRD.

 

This work investigates the potential use of the Time-of-Flight Secondary Ion Mass Spectrum (ToF-SIMS), a surface-sensitive and non-destructive method, to detect zeolite structures. Zeolites secondary building units have been successfully detected by using the technique. Here, Principle Component Analysis (PCA analysis), is employed to summarize the main characteristics of zeolite in order to make predictive models. Utilizing the data obtained from ToF-SIMS, PCA analysis can identify secondary building units in zeolite samples. MFI type, ZSM-5 with exchangeable cations (H⁺, NH₄⁺, Na⁺, K⁺), varied concentrations (from 0% to 100%), and Si/Al ratios (15 to ∞) has been analyzed and the 5-1 ring structure of MFI has been consistently detected.