FUNDAMENTACIÓN DEL USO DE MATRIZ DE IMPORTANCIA AL

5.4.2.1 Synthesis of SDA

The SDA 1-butyl-3-methylimidazolium bromide (was synthesised by a previous member in the group) was converted to the hydroxide form with the use of ion-exchange resin.

5.4.2.2 Synthesis of ITQ-33

The synthesis of ITQ-33 was attempted according to the procedure already reported by Liu et al.13 _{Germanium dioxide was placed in the stirring SDA solution, after half an hour}

TEOS was added and the gel stirred until homogeneous. Finally, NH4F was added and the

gel stirred until it had reached the desired water content and the final gel ratio was obtained 0.25 SDAOH: 0.5 SiO2 : 0.5 GeO2 : 0.05 NH4F: 3 H2O. The gel was then placed

in a Teflon liner and steel lined autoclave and heated at 175 °C for 6 days. The Si/Ge ratio was also varied while maintaining the ratio of T atoms with the other components of the synthesis remaining constant.

5.4.3 Results and Discussion

5.4.3.1 Synthesis of the Zeolite

The synthesis of ITQ-33 (ITT) was conducted in a similar manner to NUD-1, whereby the Si/Ge ratio was varied, to incorporate less Ge into the structure (Table 5.2). In doing so it was hoped that the germanosilicate would be more robust under hydrolysis conditions.

Table 5.2 Shows the samples and synthesis conditions used to vary the Ge content of the ITT framework.

Name Si/Ge Ratio

ITT-Si1 ITT-Si2 ITT-Si3 ITT-Si4 1 2 3 4

The resultant PXRD patterns of the materials seemed to follow that of NUD-1 compared to those reported by Liu et al.13 _{It seemed that formation of ITT followed a similar if not}

even worse trend compared to that seen for the formation of the NUD-1 framework (Figure 5.11).

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Figure 5.11 Shows the Expected PXRD pattern for ITT (black) and the experimental PXRD patterns obtained for ITT-Si1 (red), ITT-Si2 (blue), ITT-Si3 (green) and ITT-Si4 (cyan). The increasing loss of crystallinity with higher

Si-content seemed to confirm that ITT could only be obtained within a specific Si/Ge ratio.

The ITT structure seemed to only form well at the Si/Ge ratio of 1. Even when the material was formed at higher Si/Ge ratios (Si/Ge = 2) the quality of the material was particularly substandard and would most likely be unsuitable for the ADOR process. The results of Liu

et al. indicated that it was possible to form ITQ-33 with a Si/Ge ratio of 5. However, the quality of the material that they reported under SEM and EDX analysis was very different depending on the Si/Ge ratio used and without the PXRD patterns it is hard to discern the quality of the materials that they reported. SEM and EDX analysis (Figure 5.12) of the two samples ITT-Si1 and ITT-Si2 did seem to reflect the results seen by Liu et al.13

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Figure 5.12 Shows the SEM and EDX analysis for ITT-Si1 (left) and ITT-Si2 (right). Both showed Si/Ge close to the expected values. However, there was a noticeable difference in the morphology of the crystals.

Both samples seemed to show some of the characteristic hexagonal crystal morphology associated with the ITT structure. However, the sample ITT-Si2 was clearly less well formed compared with the ITT-Si1. It is clear that the best sample attained was for ITT- Si1, with the highest Ge content. Even ITT-Si2 with a Si/Ge ratio within the range reported by Liu et al, lost a significant amount of crystallinity. Such results clearly showed the limited success of changing the ITT Ge content by increasing the Si/Ge ratio of the synthesis. It was decided that the best sample to use for investigations into the disassembly was ITT-Si1 as it showed the most crystalline behaviour.

5.4.3.2 Disassembly of ITQ-33 (ITT)

By applying hydrolysis conditions on a calcined sample of ITT-Si1 a significant change was seen in the PXRD pattern of the material (Figure 5.13).

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Figure 5.13 Shows the PXRD pattern for ITT-Si1 before (black) and after various hydrolysis conditions including (from bottom to top): 0.1 M HCl at 95 °C for 16hrs, 0.1 M HCl at RT for 16 hrs, 12 M HCl at 50 °C for 16 hrs, 12 M HCl

at RT for 16 hrs, 0.1 M HCl/EtOH at 95 °C for 16 hrs, 0.1 M HCl/EtOH at RT for 16 hrs, Ethanol at 95 °C for 16 hrs, 12 M HCl at RT for 5 mins, water at RT for 5 mins and 0.1 M HCl/EtOH at RT for 5 mins.

The results of the hydrolysis confirmed the initial suspicions discussed earlier. Clearly the ITT structure was completely lost within a short period of time under standard hydrolysis conditions. Even after 5 mins at room temperature the structure was completely lost whether in 0.1 M HCl, 12 M HCl, water or 0.1MHCl/EtOH. The Ge content of ITT-Si1 is clearly too high. Even the lack of d3r in the structure was not enough to prevent the loss of the structure. The high concentration of d4r/d3r in multiple directions and the 3- dimensional channel system makes the framework extremely susceptible to any form of hydrolysis conditions and resulted in compete dissolution of the material.