Silicalite-1 formation in acidic medium: Synthesis conditions and physicochemical properties

Hydrothermal crystallization of clathrasils in acidic medium: Energetic aspects

“…It is known that the zeolites obtained via the fluoride route usually contain lesspoint defects, thus possess a framework with better local orders and higher integrity [35,44]. And this effect becomes more profound in the acidic medium [25,26] 29 Si MAS NMR in Figure 3 in principle supports that this trend holds with the acidic medium synthesized clathrasils, by showing well-resolved peaks that can be attributed to different crystallographic T sites. However, materials with local structural imperfections may occur in an acidic medium as well, probably due to the not optimized recipes of individual synthetic batches.…”

“…Recently, Valtchev et al have demonstrated that high-silica and pure-silica zeolites can crystallize in strongly acidic fluoride media [25,26]. Essentially, the system pH should stay above the isoelectric point of the dissolved silicate species, which is around ca.…”

Acidic properties of Al-rich ZSM-5 crystallized in strongly acidic fluoride medium

“…The reference has similar Q 4 signals and a broader band extending in the Q 3 and Q 2 region. 41,42 The high spectral resolution for MFI-zeolites synthesized in the acidic medium that is associated with highlyordered and defect-free crystal lattices, 20,21 is not attained for the IZT products. Only slightly better than the basic reference, the structures of the IZT products still contain disorders.…”

“…20 We have recently demonstrated the synthesis and morphology control methods for silicalite-1, highsilica ZSM-5, and some other microporous silicate materials in the pH range of 2~5. [20][21][22][23] However, it is difficult to incorporate active catalytic metals whose oxo-anions have higher isoelectronic points (IEP) in the neutral and acidic fluoride medium framework. Unfortunately, Al as one of the most common framework elements in zeolites, is hardly to be incorporated under acidic conditions since the aluminate ion has pHIEP = 7.7.…”

Acidic medium synthesis of zeolites – an avenue to control the structure-directing power of organic templates

“…Recently we have demonstrated that the chemical field for the hydrothermal crystallizations of silicalite-1 21,22 and some other zeolite-type tectosilicate materials 23 can be extended from the conventional basic and near-neutral conditions to the strongly acidic region. Besides elaborating on the unique structural and surface-chemical properties of the zeolite products obtained in the acidic media, we have also predicted the possibility of discovering new OSDAs that do not work under basic conditions but become feasible in the extended chemical field.…”