1H MAS NMR Studies of Molecules Adsorbed on Activated Zeolites

Probing the Acid Strength of Brønsted Acidic Zeolites with Acetonitrile: Quantum Chemical Calculation of 1H, 15N, and 13C NMR Shift Parameters

“…Experimental studies on bare acid sites in zeolites find shifts of around 4−5 ppm: a review article by Hunger 1 reports the following ranges of experimental 1 H signals from bridging OH groups: 3.8−4.3 ppm in large cavities or channels of zeolites and 4.6−5.2 ppm if they are situated in small channels or cages within a zeolite. In the study of Böhlmann et al, the 1 H NMR spectrum of FAU(Si/Al = 2.5) shows peaks at about 4.4 ppm and 4.7 ppm for bridging OH in large and small cavities, respectively. In the same work, MFI(15) shows signals for the Brønsted protons at 4.3 and 4.9 ppm.…”

“…Experimentally, a range of organic molecules have been employed as microscopic probes to characterize the acid properties. NMR studies − have concentrated on investigating chemical shifts, which are connected to changes in electronic structure and, therefore, give insight into the strength of interaction. Dynamic studies have also been performed.…”

Surface characterization and catalytic evaluation of copper-promoted Al-MCM-41 toward hydroxylation of phenol

“…Typically Al atoms are incorporated into the framework of mesoporous MCM-41 by isomorphous substitution of Al for Si atoms during hydrothermal synthesis [8][9][10][11]. However, Al-containing MCM-41 has a low acidity compared to that of zeolites like HY and ZSM-5 [12].…”

Zeolites and Other Structurally Microporous Solids as Acid–Base Materials

“…1 H NMR studies allowed to assign peaks, usually in the range near 4 ppm, to the acidic protons of H-MFI. Some studies found the peak split into two 110,111 or even four components with the more intense peak at 3.8 ppm. 112 The Inelastic Neutron Scattering study of Jobic et al 113 showed that the deformation mode g-OH is split for H-MFI, suggesting that at least two well-different OH groups actually exist.…”