1H N M R magic angle spinning (MAS) studies of heterogeneous catalysis

1H mas NMR study of OH groups in the AlPO4/SiO2 system

“…Presumably, the resonance at 0.5 ppm is due to hydroxy groups of intermediate acid-base strength. Finally, the signal at 3.3 ppm can be assigned to P-OH groups, consistent with previous results of other authors for AIPO4/A1203 systems and AIPO4 molecular sieves, which provide signals in the region of 3.0 ppm that have been ascribed to these groups [10]. Figure 2c shows the IH MAS NMR spectrum for solid S, which is similar to CRAMPS [11] and MAS spectra [12] reported by other authors.…”

“…Figure 2c shows the IH MAS NMR spectrum for solid S, which is similar to CRAMPS [11] and MAS spectra [12] reported by other authors. It exhibits an asymmetric signal that peaks at 1.8 ppm and can be assigned to isolated SiOH groups [10]. The asymmetry of this downtield signal is due to the presence of geminal OH groups in the silica, which has large line widths that can be ascribed to more closely spaced OH groups undergoing hydrogen bonding of variable strength with each other [13].…”

A study of the acidity of SAPO-34 by solid-state NMR spectroscopy

“…In Refs. [38][39][40][41], it was ascribed to hydrogen-bonded SiOH groups. To confirm their assignments of these 1 H NMR peaks, the dehydrated SAPO-34_H sample was selected to perform the Al TRAPDOR experiment, it is observed that the peaks at 3.7 and 2.6 ppm are dephased by the 27 Al irradiation, indicating that the protons associated with these peaks are in the proximity to the Al atoms in the framework, while the signal at 1.6 ppm is depressed in the TRAPDOR difference spectrum, indicating that this proton is relatively far from Al atoms.…”

Oxygen coordination of aluminum cations in dehydrated AlPW12O40 investigated by solid-state NMR spectroscopy

“…0 ppm [6,7]. In the case of internal AlOH groups interacting via hydrogen bondings with neighboring oxygen atoms, chemical shifts of the 1 H MAS NMR signals of 2.6-4.5 ppm were observed [6][7][8].…”