Dehydration performance of a hydrophobic DD3R zeolite membrane

Facile synthesis of the DD3R zeolite: performance in the adsorptive separation of buta-1,3-diene and but-2-ene isomers

“…25 At the same time, 19 F MAS NMR revealed the absence of fluoride species in the assynthesized as well as in the calcined DD3R crystals. This indicates that fluoride does not act as structure directing agent in the Si MAS NMR analysis revealed the absence of structural defects in the DD3R samples, also suggested by Fyfe et al 50 However, we cannot discard that the absence of Si-O defects promotes the formation of the DD3R framework.…”

“…High DD3R purities are obtained when KOH is used as a cleaning agent of the PTFE autoclave liners, and when KF is added to the synthesis mixture. By means of 13 C, 19 F and 29 Si (MAS) NMR it is shown that the crystals produced are defect free, and that fluoride addition induces neither a templating effect nor protonation of the template. The presence of KF in the synthesis medium enables better solubilisation of ADA, eliminating the need of autoclave rotation to induce mixing, and suppresses the formation of lattice defects.…”

“…Rest of the MAS NMR spectra were recorded on a Bruker DMX 500 spectrometer operating at 1 H, 19 29 Si MAS NMR spectra were recorded by use of a 4 mm MAS probe head and a sample-rotation rate of 5 kHz. To suppress baseline artefacts arising from probe ringing, directexcitation 29 Si NMR spectra were recorded using a Hahn-echo pulse sequence 90 -s-180 -s, two pulse sequence with a 90 pulse of 5 ms, and a delay s ¼ 2.5 ms. One-dimensional 1 H- 29 Si crosspolarization spectra were recorded with a ramp-shaped proton pulse combined with a rectangular 29 Si pulse of 10 ms and an interscan delay of 5 s. Two-dimensional 1 H- 29 Si correlation spectra were recorded with a rectangular pulse of 3 ms with carefully matched amplitudes on both channels.…”

“…5), whereas the protonated ammonium state would give rise to a signal at approximately 55 ppm. 19 F NMR spectra were collected from both as synthesized and calcined DD3R samples as given in Fig. 6.…”

“…The observed chemical shift, À134 ppm, is close to the values À132 and À133 ppm, previously reported shifts of KF. 47,48 Neither by recording 192 19 F NMR scans of as-prepared DD3R with an interscan delay of 600 s during 32 hours, nor by accumulating 1024 scans with an interscan delay of 30 s, any 19 F NMR signal was detected. No signal from, e.g., residual KF at À134 ppm, nor from F À anions within the cages around À180 ppm 49 have been observed.…”