Abstract
The interzeolite conversion of faujasite (FAU-type) zeolites to chabazite (CHA-type) zeolite in the presence of N,N,N-trimethyladamantammonium and N,N,N-dimethylethylcyclohexylammonium cations was investigated over a large compositional range by carefully controlling the reaction mixture compositions. Highly crystalline CHA zeolites were also obtained by the transformation of several zeolite types including EMT, LTL, LEV, RTH, and MFI frameworks. The formation of CHA zeolite from FAU zeolite precursors was substantially faster than that from zeolite L with a similar composition. High-silica CHA zeolites were also produced successfully using a mixture of TMAda with a number of less expensive organic structure-directing agents. The CHA zeolite materials have been synthesized with high crystallinity and with a Si/Al ratio ranging from 5 to 140. Our data support the importance of structural similarity between the zeolite precursors, nucleation/crystallization processes, and the zeolite product in the interzeolite conversion compared to conventional amorphous aluminosilicate gels. Our synthetic methods could be used to prepare other 8-membered ring zeolites such as AEI and AFX frameworks, potential candidates for selective catalytic reduction of NOx, light olefin production, and CO2 abatement.
Highlights
Crystalline zeolite materials possessing uniform channel systems and molecular-sized pore windows have been widely used as catalysts and adsorbents in a variety of industrial processes, including petrochemical and fine chemical processes [1,2,3,4]
We investigated in the direct transformation of various zeolite framework types FAU, LTL, LEV, MFI, EMT, and RTH into CHA zeolites. e synthesized materials were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR), and liquid N2 physisorption. e synthesis methods provide a fast and reliable alternative to the synthesis of CHA-type zeolites with any desired Si/Al ratio larger than 5
E ion exchange of DMECHA iodide to its hydroxide form was carried out using Amberlyst A26 hydroxide exchange resin. e typical mass ratio employed for the ion exchange was 1:3:5 to the Organic Structure-Directing Agents (OSDAs) as halide: Amberlyst resins: water. e exchange was carried out overnight at room temperature. e hydroxide solution was evaporated to a desired concentration on a BUCHI Rotavapor
Summary
Crystalline zeolite materials possessing uniform channel systems and molecular-sized pore windows have been widely used as catalysts and adsorbents in a variety of industrial processes, including petrochemical and fine chemical processes [1,2,3,4]. Small pore zeolites possessing 8-membered ring (8MR) window apertures have recently been studied extensively as catalysts for efficiently reducing NOx emission from the exhaust of diesel vehicles [5,6,7], the methanol-toolefins [8,9,10], and adsorbents for gas separations such as CO2/N2 [11,12,13], CO2/CH4 [14, 15], and small hydrocarbon separations [16, 17]. Alternative methods of synthesis using zeolites as Si and Al precursors could be used to improve the zeolite properties or the synthesis process. Small pore zeolites such as LEV, CHA, AEI, SFW, ERI, and AFX have been prepared successfully from the hydrothermal transformation of crystalline
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
