Clarification of acid site location in MSE-type zeolites by spectroscopic approaches combined with catalytic activity: comparison between UZM-35 and MCM-68

Abstract

MSE-type zeolites synthesized by different organic structure-directing agents (OSDAs), UZM-35 and MCM-68, were prepared. The location of Brønsted acid sites derived from the framework Al atoms and acidic properties were...

Regulation of the Si/Al ratios and Al distributions of zeolites and their impact on properties

“…Molecules such as carbon monoxide (CO), Py, and 2,6-ditert-butylpyridine (DTBPy) can be used as probes of the acid site location. 290,291 The probe molecules with different sizes could be adsorbed on the different accessible acid sites, which can be further characterized by FT-IR or 13 C NMR and thus reveal the Al distributions. 291 Moreover, certain divalent cation such as Co 2+ is practical experimental probe for paired Al in zeolite because the single Al atoms cannot accommodate the Co 2+ while the Al pairs can accommodate bare Co 2+ and hydrated Co 2+ , close unpaired Al can only accommodate hydrated Co 2+ .…”

“…290,291 The probe molecules with different sizes could be adsorbed on the different accessible acid sites, which can be further characterized by FT-IR or 13 C NMR and thus reveal the Al distributions. 291 Moreover, certain divalent cation such as Co 2+ is practical experimental probe for paired Al in zeolite because the single Al atoms cannot accommodate the Co 2+ while the Al pairs can accommodate bare Co 2+ and hydrated Co 2+ , close unpaired Al can only accommodate hydrated Co 2+ . For example, with this method, the amount of single Al atoms, Al pairs, and close unpaired Al atoms in SSZ-13 can be calculated as:…”

“…Molecules such as carbon monoxide (CO), Py, and 2,6-di-tert-butylpyridine (DTBPy) can be used as probes of the acid site location. 290,291 The probe molecules with different sizes could be adsorbed on different accessible acid sites, which can be further characterized by FT-IR or 13 C NMR and thus reveal the Al distributions. 291 For example, with this method, the amount of single Al atoms, Al pairs, and close unpaired Al atoms in SSZ-13 can be calculated as follows:…”

“… 290,291 The probe molecules with different sizes could be adsorbed on different accessible acid sites, which can be further characterized by FT-IR or 13 C NMR and thus reveal the Al distributions. 291 Moreover, certain divalent cations such as Co 2+ are practical experimental probes for paired Al in zeolites because single Al atoms cannot accommodate Co 2+ while Al pairs can accommodate bare Co 2+ and hydrated Co 2+ and close unpaired Al can only accommodate hydrated Co 2+ . For example, with this method, the amount of single Al atoms, Al pairs, and close unpaired Al atoms in SSZ-13 can be calculated as follows: [Al single ] = [Al framework ] − 2[Co max ] [Al pair ] = 2([Co bare ] − [Co D6R ]) [Al close ] = 2[Co max ] − 2([Co bare ] − [Co D6R ]) where [Co max ] is the Co concentration in the zeolite maximally exchanged by the Co 2+ hexaaqua complex, [Co bare ] is the concentration of bare Co 2+ in the maximally bare Co 2+ exchanged zeolite, and [Co D6R ] is the concentration of bare Co 2+ in the hexagonal prism.…”

The Directing Role of Aluminum in the Synthesis of PST-21 (PWO), PST-22 (PWW), and ERS-7 (ESV) Zeolites

“…Notably, Sklenak et al prepared a large number of ZSM-5 samples (Si/Al = 14–45) and were able to distinguish the Al population of the 24 different crystallographic positions using 27 Al MQ MAS NMR spectra, and periodic quantum/classic calculations. A similar strategy in the group of Yokoi and co-workers, using high-resolution 27 Al MAS NMR technique, allowed them to distinguish whether the different Al peaks belong to the different types of micropores in zeolite structures such as MFI and MSE . Further, the authors analyze samples of the same topology and same Si/Al, obtained with different organic structure directing agents (OSDAs), to demonstrate how each OSDA generates a different Al distribution.…”