Mordenite steam-acid leaching

Fig. 34. NH -mordenite. Si MAS NMR spectra at (sample 1) 811 K and steamed acid leach, and (sample 2) calcinated and steamed at 811 K. (a, b) Upper spectra are without and (c, d) lower spectra with cross-polarization [84H3].

Figure 5. J9Si-NMR spectra of mordenite dealuminated by acid leaching and subsequent steaming. (Reproduced from ref. 19. Copyright 1986 American Chemical Society.)...

The steamed and acid-leached mordenite samples were examined by high-resolution solid-state H, Si, Al MAS and H/ Si CP NMR spectroscopic techniques in order to study the aluminum species and evaluate the dealumi-nation process during steaming and leaching. 

Fig.1. Relative intensities of the (150) XRD reflection of 1 parent Na-mordenite (Si/Al = 5.9), 2 after acid leaching (Si/Al = 35) and 3 after subsequent steaming at 600°C for 2 h [23]...

In some instances the materials were also repeatedly subjected to this two-step treatment to enhance the degree of dealumination, e.g., in [89]. In the case of zeolites resistant to acids due to high framework Si/Al ratios, e.g.,mordenite and ZSM-5, acid leaching may also precede the hydrothermal treatment [ 10,23]. In this case, healing of framework hydroxyl nests left by aluminum release is the lattice-stabilizing process. The hydrothermal stability of steamed Y zeolites was found to increase upon removal of extra-framework aluminum by extraction with acids [94]. 

---