CIT-5: a high-silica zeolite with 14-ring pores

Abstract

The synthesis and structure of a new zeolite, CIT-5 (California Institute of Technology Number Five), is described, which possesses one-dimensional pores comprised of 14 T-atoms (tetrahedrally coordinated silicon or aluminium atoms).Zeolites with pores comprised of larger than 12 T-atoms (extralarge pores) are much in demand 1-4 and have been so for many years. [4][5][6][7] The reason for this is the desire to perform catalysis/ adsorption on molecules > 8 Å in size.The first molecular sieve with extra-large pores was VPI-5 that is an aluminophosphate material with 18-ring pores. 8 Subsequently, other phosphate-based extra-large pore materials have been reported, e.g. cloverite. 2 All of the phosphate-based molecular sieves lack the desired properties of combined high acidity and thermal/hydrothermal stability and thus limit the practical potential. Recently, the first extra-large pore zeolite, UTD-1, was reported and shown to possess good acidity and thermal/hydrothermal stability. 9,10 Additionally, there have been numerous disclosures of ordered, aluminosilicate mesoporous materials with pore sizes of 20-100 Å. 11,12 Because the inorganic portions of the mesoporous materials are not crystalline, they lack the acidity and thermal/hydrothermal stability of high-silica zeolites. 13 Here, we report a new extra-large pore zeolite denoted CIT-5. CIT-5 is synthesized under hydrothermal conditions. A reaction mixture of composition 0.2 ROH : 0.1 LiOH : 0.02 Al 2 O 3 : 1 SiO 2 : 40 H 2 O is heated to 175 °C at autogenous pressure for ca. 12 d in order to produce CIT-5. In the absence of aluminium, pure-silica CIT-5 can be prepared in 5 d. The organic structuredirecting agent (SDA), R, is N(16)-methylsparteinium I and is prepared as previously reported. 14 In the absence of lithium, I can form pure-silica or borosilicate SSZ-24. 13,14 Thus, the key to the successful preparation of CIT-5 is both the SDA I and the inclusion of lithium. Further synthetic details are forthcoming. 15 Indexation 16 of the synchrotron powder X-ray diffraction (SPXRD) data from the pure-silica sample of CIT-5 revealed the presence of a small amount of an impurity phase together with the predominant CIT-5 phase. The CIT-5 material indexed in the orthorhombic crystal class with refined lattice constants a = 13.694(2), b = 5.0213(5), and c = 25.4970(3) Å (U = 1753.2 Å 3 ). The lattice constants for the impurity hexagonal phase were found to be a = 13.63 and c = 8.30 Å. The unit cell parameters and scanning electron micrographs helpd to identify the impurity phase as SSZ-24 (International Zeolite Association Code AFI). 17 Systematic absences for the orthorhombic CIT-5 phase indicate body-centering consistent with six possible space groups.The starting model for Rietveld refinement of CIT-5 was obtained by an iterative process of model building, distanceleast squares (DLS) 18 refinement of the atomic positions for the model, and comparison of the simulated powder X-ray pattern (CERIUS 19 ) to the experimental pattern. The model with the closest ma...

Evaluation of a New Force Field for Describing the Adsorption Behavior of Alkanes in Various Pure Silica Zeolites

“…In the simulations, zeolites were constructed by using the atomic coordinates reported, [15][16][17][18][19][20] and some details of these structures are summarized in Table 1. The zeolite lattices were assumed to be rigid in the simulations, because the flexibility of the framework has a negligible influence on the adsorption of alkanes.…”

Supra-molecular assembly of aromatic proton sponges to direct the crystallization of extra-large-pore zeotypes

“…Using large and rigid OSDAs, different extra-large-pore zeolites presenting mono-directional 14-ring channels [3][4][5], multi-dimensional extra-large channels [6,7] and even mesoporous zeolites [8,9] have been synthesized. In these cases, the zeolite crystallization occurs through the interaction of single organic molecular units with the inorganic sources present in the synthesis gel.…”

Catalytic Properties of Hierarchical Mesoporous Zeolites Templated with a Mixture of Small Organic Ammonium Salts and Mesoscale Cationic Polymers

“…However, relatively small individual micropores in zeolites such as Beta, ZSM-5, and Y strongly influence mass transport to and from the active sites located within them, severely limiting the performance of industrial catalysts. [1,2] To overcome this problem, various strategies have been successfully pursued, such as the synthesis of nanosized zeolites, [3] ultralarge-pore zeolites and zeolite analogues (VPI-5, [4] JDF-20, [5] UTD-1, [6,7] CIT-5, [8] SSZ-53, [9] ECR-34, [10] UCSB, [11] ITQ-21, [12] IM-12, [13] and SU-M, [14,15] among others), and ordered mesoporous materials (e.g. MCM-41, [17] SBA-15, [18] and FSM-16, [19]).…”

“…[1,2] [19]). However, the use of these materials is rather limited owing to the difficult separation of nanosized zeolite crystals from the reaction mixture,[3] the complexity of the templates used for the synthesis of ultralarge-pore zeolites, [6][7][8][9] and the relatively low thermal and hydrothermal stability of ordered mesoporous materials. [17][18][19][20][21][22][23][24][25][26][27][28] More recently, mesoporous zeolites from nanosized carbon templates have also been successfully synthesized, [29][30][31][32] but their industrial applications are still limited by the complexity of the synthetic procedure involved and the hydrophobicity of the carbon templates.…”