27Al MAS NMR spectra

Diffraction patterns and FTIR spectra of skeletal vibrations of the ZSM-5 and ferrierite zeolites indicated high crystallinity of the analyzed samples. The strong band with a chemical shift of about 55 ppm in the 27Al MAS NMR spectra of hydrated zeolites indicated the presence of more than 97 % Al in the framework in tetrahedral coordination the very low intensity of the peak at 0 ppm indicated less than 3 % rel. of Al in octahedral coordination. 

The MWCNTs were purified using HF at 20 wt %. The samples were filtrated, washed with deionized water and dried at 100°C overnight. TGA analysis was carried out by heating at 10 °C/min from room temperature to 800°C. Nitrogen physisorption was used to determine BET surface area and BJH pore volume and size. 27Al MAS NMR spectra for the calcined samples were obtained. 

Solid state H and 27Al MAS NMR spectra were collected using a Broker DSX-500 spectrometer (11.7 T) and a Broker 4 mm CPMAS probe. For dehydration studies, the calcined and rehydrated zeolites were packed in a 4mm Zr02 NMR rotor, evacuated (10" 3 Torr) while heated and then held at desired temperature for 2 h. 

The 27Al MAS NMR spectra of as-synthesized Al-MCM-41 samples show a main signal of tetrahedral coordinated aluminum at ca. 53 ppm. The aluminum is nearly entirely incorporated into the framework. As generally observed, calcination leads to the formation of penta- Al[51 and octahedrally coordinated aluminum Al[61 on the expense of the tetrahedral framework Al[41. In the 27A1 MAS NMR spectra of calcined samples appear additional lines at ca 30 ppm and 0 ppm, respectively (Fig. 1). Only ca. 1/3 of the Al atoms remain in tetrahedral framework positions even after thermal treatment at 600°C. 

Figure 4.33 shows the 27Al MAS-NMR spectra of the sample HC (Figure 4.33a) and PHEU(20) (Figure 4.33b). It is evident that the peaks at about 56 and -14ppm are from tetrahedral and octahedral Al, respectively [85],...

Figure 2. 27Al MAS NMR spectra of hydrated samples A, USYA and Real A on the absolute intensity scale. 10,000 scans were acquired in each case using resonant rf pulses of 600 ns duration.

Figure 4. 29Si and 27Al MAS NMR spectra of samples derived from sample USYA by treatment with aqueous solutions of KOH of different concentrations for 24 hours. The framework Si/Al ratios of the products are indicated in the right-hand column. 

Al MAS NMR spectra were taken at aluminum frequency of 78.15 MHz. Typically, 10,000 to 25,000 transients were acquired at a spinning frequency of 12 kHz, using a 4 mm diameter rotor with a double bearing system. 

There have been a number of NMR studies of zeolite-Y systems.361 363 Other zeolites studied similarly include zeolite-HL 364 zeolite-BEA 365 zeolite-TNU-10 366 and zeolite-USY.367 27Al MAS-NMR spectra were used to probe the effects of simultaneous incorporation of Al and Ge into zeolite ZSM-5.368 Related systems for which NMR structural studies have been made include Mo-ZSM-5 369,370 and Cu-ZSM-5.371 13C CP/MAS-NMR data were used to... 

Al MAS NMR spectra of an AIPO4-8 sample in hydrated form and after dehydration in vacuum at 293 K are shown in Fig. 11. In the dehydrated sample, the aluminium resonance is at 35 ppm, characteristic of tetrahedral coordination. A trace of aluminium exhibits a chemical shift of ca. 10 ppm, typical of aluminium monohydrate. It indicates that the dehydration of this particular sample is not... 

The 27Al MAS NMR spectra (Figure 18) indicates that in the as-prepared PAA, as well as in specimens heated to <800 °C, the aluminium exists in four-, five-, and six-fold coordination, corresponding to the resonances at 55 ppm, 30 ppm, and 7 ppm, respectively (MacKenzie and Smith, 2002). Again, this is comparable to the phosphoric PAA data in Figure 14. 

MAS NMR spectra were obtained with a Bruker 400 MSL spectrometer. The experimental conditions used in the 29Si DEC, 29Si CP, 27Al, 27A1 CP and 31P DEC were as follows ... 

Figure 9. 27Al, 29Si, 29Si CP and 31P MAS NMR spectra of MCM-1 sample No.27.

The intensity of the 27Al MAS NMR spectrum of the realuminated sample R-3 (Figure 2) is greater than that of the dealuminated sample D-2. The F2 projection indicates that aluminium in the latter sample is in the tetrahedral coordination. The nutation spectra (Figure 3) clearly show that... 

Ca NMR data were reported for calcium peroxides formed in the disproportionation of EI202 catalysed by Ca(OH)2.36 19F, 27Al, 29Si and 31P MAS-NMR spectra were used to study the structures of samples in the... 

In this study, the distribution of Al atoms over the individual T sites of the ZSM-5 framework is examined by a combined experimental and computational approach. Eleven differently prepared samples of ZSM-5 were studied by 27Al 3Q MAS NMR spectroscopy. To interpret the observed NMR spectra, we calculated the isotropic shift of Al occupying all the distinguishable T sites of ZSM-5 and used the calculated isotropic shifts to assign the observed resonances to individual distinguishable T sites. 

Cerqueira and co-workers203 confirmed the appearance of the of the tetrahedral aluminium and phosphorus in AlPO-like crystalline structures both in beta (BEA) and in MOR zeolites treated with phosphoric acid. 31P MAS,27Al MAS and TQM AS NMR spectra permitted the species present in the samples to be assigned. Possibly, besides the the Altet-f species, other Al species are also taking part in the activity and selectivity of the catalysts. The formation of Alocl o P can also contribute to the increase in the activity by preventing further dealumination. Dual zeolite additives have no impact on the quality of naphtha when compared to MFI-based additives, which are used in the fluid catalytic cracking processes. 

Nuclear Magnetic Resonance Spectroscopy. The Si, 27Al, and Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) spectra were recorded on a Bruker MSL 300 spectrometer. The recording conditions are shown in Table 10-1. 

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