Effect of the degree and type of the dealumination method on the structural, compositional and acidic characteristics of H-ZSM-5 zeolites
Φόρτωση...
Ημερομηνία
Τίτλος Εφημερίδας
Περιοδικό ISSN
Τίτλος τόμου
Εκδότης
Elsevier
Περίληψη
Τύπος
Είδος δημοσίευσης σε συνέδριο
Είδος περιοδικού
peer reviewed
Είδος εκπαιδευτικού υλικού
Όνομα συνεδρίου
Όνομα περιοδικού
Microporous and Mesoporous Materials
Όνομα βιβλίου
Σειρά βιβλίου
Έκδοση βιβλίου
Συμπληρωματικός/δευτερεύων τίτλος
Περιγραφή
A series of H-ZSM-5 zeolites with different framework Si/Al ratios were prepared by hydrothermal synthesis and post-synthesis dealumination by various methods, i.e., HCl, steaming, steaming/HCl and ammonium hexafluorosilicate (AHFS). The degree of framework dealumination and the amount/type of the extra-framework phases formed were greatly dependent on the method of dealumination and the severity of the experimental conditions. The hydrothermal treatment of a parent ZSM-5 sample with Si/Al similar to 27 was very effective and produced significant amounts of Si-Al extra-framework phases, while the reaction with HCl in relatively strongly acidic environments resulted in very low dealumination. Treatment with AHFS was proven to be an appropriate method for preparing moderately dealuminated H-ZSM-5 samples which are free from extra-framework Al. The relative crystallinity and the microporosity of all dealuminated H-ZSM-5 zeolites were retained to a high degree (> 80%), even for the severely steamed samples (similar to 96% dealumination). The morphology of the crystals/particles was not changed significantly; however, each dealumination method had a different effect on the partial breakdown of the crystals and on the formation of extra-framework/amorphous phases with a mesoporous character. The number of acid sites that corresponded to the high-temperature desorption peak of the ammomia-temperature programmed desorption spectra was found to be equivalent to the framework Al (FA1) content of all H-ZSM-5 samples, irrespective of the degree of dcalumination and the amount of extra-framework phases. Theses phases had a low capability of adsorbing ammonia compared to the FA1 atoms and were the main source of acidity for the severely steamed samples which had almost no FA1 (D 2001 Elsevier Science B.V. All rights reserved.
Περιγραφή
Λέξεις-κλειδιά
h-zsm-5 zeolites, dealumination, extra-framework phases, crystal morphology and porosity, acidity, temperature-programmed desorption, nuclear-magnetic-resonance, high-silica zeolites, y-type zeolites, unit-cell size, al-27 mas nmr, hzsm-5 zeolites, catalytic-activity, zsm-5 zeolite, hydrothermal treatment
Θεματική κατηγορία
Παραπομπή
Σύνδεσμος
<Go to ISI>://000171341700024
http://ac.els-cdn.com/S1387181101003997/1-s2.0-S1387181101003997-main.pdf?_tid=955c9580-356a-11e3-8130-00000aab0f6b&acdnat=1381821944_fddfa0846a37cafeac5f94a0de7d11b9
http://ac.els-cdn.com/S1387181101003997/1-s2.0-S1387181101003997-main.pdf?_tid=955c9580-356a-11e3-8130-00000aab0f6b&acdnat=1381821944_fddfa0846a37cafeac5f94a0de7d11b9
Γλώσσα
en
Εκδίδον τμήμα/τομέας
Όνομα επιβλέποντος
Εξεταστική επιτροπή
Γενική Περιγραφή / Σχόλια
Ίδρυμα και Σχολή/Τμήμα του υποβάλλοντος
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας