Effect of pyrazolium-derived compounds as templates in zeolite synthesis

Abstract

A series of diquaternary pyrazolium-derived organic templates (N,N 0 -dimethyl-N,N 0 -1,6-dihexylidenedi-pyrazolium, denoted as 6C-DMP, 6C-DEP, 6C-DPP, respectively) with methyl, ethyl and propyl groups substituted on the N atom of pyrazole ring at both terminals have been used in the synthesis of high silica MTW and MFI zeolites. Through combining the characterization results, including XRD, NMR, elemental analysis, TG, XRF, FE-SEM, N 2 sorption and FE-TEM, with molecular mechanics simulations to explore the location, orientation and the interaction energies of the three templates, we confirmed the state of templates in zeolite framework, carefully characterized their morphology/structure properties, and finally investigated their different spatial effects for the zeolite formation. The study found that 6C-DMP and 6C-DEP are able to produce MTW, while 6C-DPP is able to produce MFI. 6C-DMP, owing to a good match with the MTW framework and can be used to synthesize regular MTW zeolite with few defects. The MTW zeolite prepared by using 6C-DEP as a template presents more defects and irregular macromorphology due to a relatively poor match to the MTW framework. 6C-DPP can get MFI other than MTW due to a larger spatial hindrance, and it is located in the MFI framework with a special spatial orientation.

Engineering Fractal MTW Zeolite Mesocrystal: Particle-Based Dendritic Growth via Twinning-Plane Induced Crystallization

“…MTW zeolite possesses intergrowth of monoclinic and orthorhombic polymorphs and unidimensional 12-member-ring pore along the b -axis and is an important catalyst in various reactions involving bulky molecules . Various morphologies of it have been reported, such as shuttle-like, cubic, pseudohexagonal, and so on, whereas the reasons remains elusive. In our recent work, the crystal structure of hexagonal plate and screwed MTW zeolite has been successfully uncovered, and MTW zeolite was regarded as an excellent example to discern the crystallographic basis for superstructured zeolite thanks to its special crystalline symmetry and one-dimensional (1-D) micropore channel .…”

Alkalinity-controlled zeolite nucleation and growth: ultrafast synthesis of total-morphology zeolite L mesocrystals and adsorption evaluation

“…Meanwhile, Kumar et al modulated the size and morphology of SSZ-13 [34] , zeolite L [35] , and SAPO-34 [36] by using recyclable organic modifiers to regulate the aggregation growth of precursor particles. In our previous works, a series of ZSM-5 mesocrystals were synthesized under the seed-induced synthesis route by using inorganic cations to modulate the assembly behavior [37,38] , and ZSM-12 mesocrystals with a clustered, fractal, or finned structure were obtained by tuning the concentration-dependent crystallization kinetics [39][40][41] . However, owing to the intrinsic complexity of the zeolite synthesis system, different stages of the crystallization process -namely induction, nucleation, growth, and ripening -are often intertwined and exhibit significant interplay [30] .…”

Charge distribution and conformational stability effects of organic structure-directing agents on zeolite synthesis

“…Recently, alkylated imidazolium cations, with two nonadjacent nitrogen atoms in the five-membered aromatic ring, have been extensively used as OSDAs in zeolite synthesis and have afforded many materials with novel framework structures or compositions (e.g., zeolites ITW, STW, RTH, etc.). 3d,5 While the pyrazolium derivatives have received little attention as OSDAs, 6 their aromatic ring with two adjacent nitrogen atoms possesses the same shape, size, and chemical formula as those of the imidazolium ring but a different charge distribution. Therefore, a comparison of the structure-directing abilities of pyrazolium-based cations in zeolite synthesis with those of imidazolium-based cations will allow us to investigate in detail how the charge distribution in OSDAs can influence the phase selectivity.…”