Dealumination of HZSM-5 Zeolites

Solid-state MAS NMR studies on the hydrothermal stability of the zeolite catalysts for residual oil selective catalytic cracking

“…1a), which has been well recognized as the amorphous Si species [25]. The remaining signal became narrowed owing to a marked decrease in intensity of the signal at −107.4 ppm, which indicated dealumination of the zeolite [26]. Compared with the parent sample, more aluminum species were still maintained in the framework of the modified zeolites after hydrothermal treatment, as illustrated in the 29 Si MAS NMR spectra (see Fig.…”

“…These findings can be explained by the invisibility of the aluminum species in the NMR spectrum due to larger quadrupole couplings [22,[34][35][36][37]. A new broad resonance centered around 30 ppm is also observed in the 27 Al MAS NMR spectra of the par- ent zeolite after hydrothermal treatment, which is assigned to penta-coordinated or disordered tetrahedral coordinated extraframework Al species.…”

C2–C4 light olefins from bioethanol catalyzed by Ce-modified nanocrystalline HZSM-5 zeolite catalysts

“…It can be calculated that compared with nano-HZSM-5 after calcination at 520 • C, the amount of acid sites on nano-HZSM-5 after calcinations at 620 • C remained 62.4%, and that was only 32.8% at 720 • C; while compared with 5.0 Ce-nano-HZSM-5 calcined at the 520 • C, the amount of acid sites on 5.0 Ce-nano-HZSM-5 after calcinations at 620 • C remained 81.9%, and that was 50.7% at 720 • C. This indicates that cerium modification could enhance thermal stability of HZSM-5 zeolite catalyst comparatively. The loss of acid sites could be attributed to dealumination in the HZSM-5 framework and dehydroxylation of Brönsted sites arising from the higher calcination temperature [25,37]. Furthermore, from Fig.…”

Transformation of ethylbenzene-m-xylene feed over MCM-22 zeolites with different acidities

“…The particular structure of the zeolite MCM-22 holds out interesting opportunities for modification by different methods like dealumination [13][14][15][16], change in the Si/Al ratio [17,18], etc. In the present work modified MCM-22 zeolites with varying composition of the building lattice elements and diverse number and strength of the acid sites were used for the selective transformation of EB in presence of m-xylene at high temperature and atmospheric pressure.…”