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The first step towards obtaining crystallization intermediates was to determine the correct amount of water to be added to the bottom cup of the autoclave for the three synthesis methods under study. As the incorporation of silicon into an AFI framework was the main topic of study in this work, the crystallinity of samples was important to optimize. Literature reports have variously used low and high relative amounts of water17,

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to varying degrees of success in synthesizing AFI sieves, and so ranges of added water were used. The products of these experiments were studied using XRD and 29Si NMR to investigate the effect water content made on the crystallinity and silicon content in the SAPO-5 sieve.

The results of the SAC optimization based on added volume of water are shown in Figure 3.2. According to previously reported studies, the resonances centered around - 90, -95, -100, -105, and -110 ppm have been assigned to Si(OAl)4, Si(OAl)3(OSi),

Si(OAl)2(OSi)2, Si(OAl)1(OSi)3 and Si(OSi)4 respectively.33, 43, 44 This work will refer to

these silicon sites in the common notation: Q0 for Si(OAl)4, Q4 for Si(OSi)4, etc. A range

of added amounts of water from 0.3 g to 1.8 g per gram of dry-gel were tested. The spectra clearly indicate the amount of water added has a marked effect on the degree of silicon incorporation for this synthesis method. Simultaneously, it is clear that the amount of added water had little to no effect on the crystallinity of the sieves as observed by XRD.

After three days reaction under SAC conditions, in all cases a peak centered around -91.5 ppm is present. This peak can be assigned to Q0 nuclei, i.e. silicon atoms with only aluminum in their second coordination spheres, Si-(OAl)4. Increasing the

Figure 3.2:29Si MAS spectra and X-ray diffractograms for the added water optimization of the SAC synthesis of SAPO-5.

relative amount of these kinds of silicon nuclei in the sieve is desirable, as they represent homogeneously incorporated silicon nuclei that act as acid sites. The other main feature of the spectra is a broader, asymmetric peak centered around -110 ppm (Q4) but with significant intensity between -100 and -115 ppm. This resonance represents Q2-4 nuclei, which could either be unreacted silica left over from the added reagents or may represent silica islands within the sieve. The relative size of the Q0 peak compared with dense silica phase peaks of any kind (specifically Q4, though not exclusively) was used to determine which amount of water was able to yield the highest amount of silicon incorporation. A clear difference can be seen between the 0.3 g and 1.2 g samples: more silicon is incorporated as Q0 nuclei when using more added water. From 1.2 g to 1.8 g of added water, the relative sizes of the incorporated Q0 silicon peak at -90 ppm versus the dense phase peaks do not change significantly,. Based on these data, the optimized amount of added water at this temperature was set at 1.2 g per gram of dry-gel, and this amount was used to obtain crystalline intermediates with significant silicon incorporation.

An optimization of the added amount of water in the VPT synthesis method based on XRD results can be seen in Figure 3.3. The crystallinity of all samples, ranging from 0.4 g to 2.0 g added water per gram of added dry-gel precursor are comparable. The minor amorphous halo seen in the 1.6 g of water added sample excluded it from usage. The other samples would have to be compared based on their silicon uptake, as studied using 29Si NMR. For the water optimization of the VPT syntheses the same NMR parameters were used as for the SAC samples. Figure 3.3 shows the results of these experiments, with accompanying X-ray diffractograms. The diffractograms all show highly crystalline AFI frameworks developed after the three-day reaction time. Only a

very slight difference in crystallinity can be observed between the samples. The 29Si NMR results are also similar to the SAC results, with the finished crystals showing well- resolved Q0 nuclei peaks at ca. -90 ppm and the presence of leftover dense silica starting material present as signified by the peak centered ca. -110 ppm. There is no pattern noted for better silicon incorporation with increasing or decreasing water added, as was the case in the SAC method. Incorporation does change depending on how much water was used, but not in a predictable fashion. Based on the relative sizes of the incorporated and non- incorporated silicon sites, as well as the aforementioned slight differences in crystallinity

Figure 3.3: 29Si MAS spectra and X-ray diffractograms for the added water optimization of the VPT synthesis of SAPO-5.

notable via XRD, the added amount to be used in the crystallization runs was set at 1.2 g of water per 1.00 g dry-gel.

The results of water volume optimization in the VPSU method looking at XRD and 29Si NMR are shown in Figure 3.4. Aside from the 1.6 g added water sample, which shows a significant presence of co-crystalline SAPO-1845, all the samples are well crystalline AFI frameworks when looking at XRD after the three-day reaction time. The

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Si one pulse MAS NMR spectra of the crystallized samples show only one sharp peak at ca. -90 ppm. This peak can be assigned to Q0 well incorporated framework silicon nuclei. No other peaks were visible, indicating little, if any, silicon was present that had Figure 3.4: 29Si MAS spectra and X-ray diffractograms for the added water optimization of the VPSU synthesis of SAPO-5. Impurities are marked with an asterisk.

other silicon atoms as its next closest neighbours, i.e. no silica was present in the finished product. Without another peak for comparison, this made selection of the optimized synthesis parameters difficult. Based on crystallinity and the symmetry and resolution of the Q0 peak, the 0.8 g of water sample was chosen for the crystallization run.