Cloverite: exploring the 30-.ANG. supercage for advanced materials science applications

Abstract

The cubic network of 30 A diameter supercages in the novel gallophosphate molecular sieve cloverite receives attention in this work because of its potential as a host in innovative host-guest nanochemistry aimed at advanced materials applications.A multiprong analytical approach (PXRD, TGA/DSC/TMA/MS, 'H, ,3C, 3IP, 7lGa, l29Xe NMR, UV-Vis, FT-IR, Raman, physical adsorption) is employed to begin the exploration of the thermal and chemical properties of cloverite, as-synthesized with the quinuclidine template and following various post-synthesis treatments. The freezing out of guest motions (template/water) and/or a change in the space group of as-synthesized cloverite occurs around -57 °C. Removal of extraframework H20 occurs in two barely resolved stages at 90 °C and 110 °C. At this stage the quinuclidine template exists predominantly in the protonated form. The dehydration event is reversible and has very little effect on the integrity of the cloverite framework. Acid-base titrations of dehydrated cloverite with anhydrous NH3 and HC1 at room temperature reveal the essentially neutral nature of both the P(OH) and Ga(OH) hydroxyl groups of the interrupted framework of cloverite. This is to be contrasted with defect hydroxides in cloverite which behave as Bronsted acid sites. However, all P(OH) and Ga(OH) groups can be selectively deuterated with D2 at 240 °C and D20 at room temperature, leaving the hydrogens on the quinuclidinium template effectively untouched. Xe gas can access the larger, but not the smaller, channel of cloverite, both as-synthesized and after dehydration at 150 °C. Three thermal events occur around 350 °C, 450 °C, and 550 °C in which the occluded template (25%, 70%, 100%) and framework hydroxyls (40%, 90%, 100%) are systematically depleted from cloverite, simultaneously with the evolution of quinuclidine cracking products, framework HF, and H20. At each of these stages, Xe gas can only gain access to the supercages, being excluded from the LTA/RPA channel system of cloverite. The proton on the quinuclidinium housed in the interrupted framework of cloverite appears to play a key role in the production of dehydroxylated-dehydrofluorinated and/or partially fragmented double four-rings, through the thermally induced loss of framework HF and H20 over this temperature range. However, up until about 450-500 °C, the disruption of double four-rings appears to be localized and short-range in nature. It does not appear to significantly reduce the crystallinity of cloverite at the unit cell level or the framework microporosity of the material, the latter with respect to 02 and n-hexane adsorption. This process continues up to 800 °C, with the unit cell maintained essentially intact, at which point one observes catastrophic breakdown of the cloverite structure. The collapsed material at this stage is X-ray amorphous, but around 850 °C it recrystallizes predominantly into the dense phase tridymite form of GaP04. Between 850 and 1050 °C the evolution of CO is observed, which is considered to arise from a carb...

H → 31P, 31P → 1H, and 2H → 1H CP/MAS NMR Studies of the Large-Pore Gallophosphate Molecular Sieve Cloverite

“…The gallophosphate cloverite − has a cubic structure with the unit cell formula [Ga 768 P 768 O 2976 (OH) 192 ]·192RF (where RF stands for quinuclidinium fluoride template). This molecular sieve has the largest pore openings and cages (1.3 and 2.9 nm in diameter, respectively) found so far in microporous materials and, in this respect, can only be compared with the recently synthesized aluminophosphate JDF-20, which also has 20 T-atom rings .…”

Ionothermal Synthesis of an Aluminophosphate Molecular Sieve with 20‐Ring Pore Openings

“…[29] In situ PXRD patterns show that distinct intensity changes occur accompanied by the loss of physically adsorbed water and the organics; however, no significant shift in lattice parameter and loss of crystallinity was observed until about 950 8C, at which temperature the dense phase AlPO 4 tridymite was formed. In the TG/DTA diagrams, the first weight loss of 12 % is observed between 30 8C and 200 8C with endothermic effect which can be attributed to the removal of physically adsorbed water.…”

DRIFTS Study of the Surface Structure and Nitridation Process of Mixed Galloaluminophosphate Oxynitride (AlGaPON) Catalysts

“…In fact, two hydroxyl group bands are commonly reported in GaPO 4 solids, one at 3668 cm -1 and the other at 3700 cm -1 . Although the different authors do not agree on the assignation of the one at 3700 cm -1 to P−OH , or Ga−OH 39,40 groups, all of them assign the one at 3668 cm -1 to P−OH groups. ,,− From the results shown above, we propose the band at 3700 cm -1 as due to Ga−OH groups and the one at 3668 cm -1 as due to both P−OH and Ga−OH groups.…”