High-resolution solid-state 29Si and 27Al n.m.r. of aluminosilicate intermediates in zeolite A synthesis

Electrochemically controlled ion exchange: proton ion exchange with sodium zeolite X and A

“…the sample is less crystalline) [25]. The broadening of 29 Si lines of less crystalline samples has been previously observed by Lippmaa et al [28]. The Si/ Al ratio for the electrochemical sample is calculated as 1.54 (again the spectral profile agrees with published spectra [26,27] which is equivalent to a 5 % loss in aluminium.…”

“…Additionally no evidence of proton exchange was observed by 1 H-MASNMR. 29 Si-MASNMR data suggest that the crystalline and amorphous phases of the exchange zeolites are distinct.…”

“…It has been observed that the destruction of the zeolite A framework occurs preferentially at the surface of the zeolite particles [11]; this could account for the two distinct phases. A uniform loss in crystallinity would be identified by peak broadening as observed for aluminosilicate gels formed as intermediates in zeolite A synthesis [29]. …”

“…To investigate this effect, silicon magnetic resonance was conducted on a number of the samples. 29 Si-MASNMR of zeolites typically gives a fivepeak profile; each peak corresponds to a silicon-atom bound via bridging oxygens to either four, three, two, one or zero aluminium atoms. Figure 8 shows the 29 Si-MASNMR spectra of fresh NaX and NaA and corresponding electrochemical samples.…”

“…The aluminium content of the samples was examined indirectly by 29 Si-MASNMR. Samples were prepared by heating under vacuum at a rate of 50 K h −1 to 573 K. The samples were held under these conditions (573 K, 0.1 mbar) for a further 24 h before sealing, under vacuum, in a glass ampoule [18,19].…”