Methods of synthesizing chabazite zeolites with controlled aluminum distribution and structures made therefrom
A method of synthesizing chabazite zeolites with aluminum distribution. The method utilizes a source of an organic structure-directing agent, a source of an inorganic structure-directing agent, a source of aluminum and a source of silicon to create a synthesis gel which is subjected to a crystallization process to crystallize a chabazite zeolite with controlled aluminum distribution. A chabazite zeolite structure with aluminum distribution. The structure includes zeolite crystal lattice framework comprising aluminum, silicon, and oxygenand extra-framework positions comprising non-divalent chemical species like each aluminum atom in the zeolite crystal lattice framework is in an isolated configuration. Another version of the structure wherein a fraction of the aluminum atoms in the zeolite crystal lattice framework positions are not in an isolated configuration and hence oxygen molecules connected with aluminum atoms in the portion can bind together with the non-aluminum cations from the extra-framework positions.
To view all patent detail click here
This section introduces aspects that may help facilitate a better comprehension of the disclosure. Thus, these statements must be read in this light and are not to be known as admissions concerning what is or isn’t prior art.
Zeolites are a category of crystalline, microporous, silica-based molecular sieves of varying topology (micropore size and interconnectivity). They’re pure-silica (SiO.sub.2) materials containing some portion of their Si atoms replaced withAl, which create ion-exchange sites and catalytic sites. Zeolites are used in adsorption, ion-exchange and catalytic applications, and particularly in the chemical and petrochemical industry as acid catalysts. Current synthesis routes only arespecified to prepare a particular crystal structure and bulk elemental composition (Si/Al ratio).
Bronsted acidic zeolites are silica-based molecular sieve frameworks that have a portion of the Si atoms replaced with Al atoms, which create anionic charges balanced by protons that differ in intrazeolite location among known crystaltopologies and in density with changes in bulk composition (Si/Al ratio). Nevertheless, even a specified zeolite at fixed article contains catalytic diversity equaled by gaps in the arrangement and distribution of its framework Al atoms, becausereactive intermediates and transition countries shaped in their attendant Bronsted acid sites are stabilized by van der Waals interactions with surrounding oxide cavities. One type of Al arrangement describes the location of Al atoms one of differentpores of a certain zeolite, as in the case of ferrierite (FER) zeolites (Si/Al=10-20) that comprise higher fractions of Al within 8-membered rings (8-MR) when crystallized with smaller pyrrolidine (.about.0.46 nm kinetic diameter) organicstructure-directing agents (SDAs) than with bigger SDAs (e.g., benzylmethylpyrrolidinium, hexamethyleneimine), which catalyze dimethyl ether carbonylation into methyl acetate with higher mortality rates (per total Al; 473 K) because this response occurswith high specificity within 8-MR voids that solvate carbonylation transition countries more effectively than 10-MR and bigger voids. Another type of Al arrangement describes the closeness of Al atoms within the framework, ranging from the limitation of Al siteisolation (Al–O(–Si–O).sub. X–Al, x.gtoreq.3 to higher densities of proximal or”paired” Al atoms (Al–O(–Si–O).sub. X Al, x=1, 2), which was recognized, but not controlled during zeolite synthesis. For purposes of this disclosure,is structure-directing agent is a compound that is present through crystallization of the zeolite and helps guide the formation of the desired crystal structure.
The Al supply in zeolites has been associated with structural stability, deactivation and coking in acid catalysis with hydrocarbons and alcohols, so manipulating this supply may reap those technologies. Aluminum supply inzeolites has also been linked to the amounts and constructions of extraframework metal ions (e.g., Cu.sup.2+, (CuOH). sup. +) that can be exchanged onto the zeolite, and since those ions are catalytic sites in NOx (x=1,2) selective catalytic reduction withammonia, manipulating this distribution may reap those technologies.
The issue of how to restrain Al supply in zeolites is currently being addressed by changing various zeolite synthesis factors, including the Si source, Al source, Na source, counteranion (OH, Cl, PO.sub.4, NO.sub.3), the organic andinorganic additives utilized, etc.. These changes have yet to be systematically made, and also have been studied for additional zeolite structures including MFI (or ZSM-5), and haven’t led to systematic changes in the Al distribution.
An International Patent application, No.
PCT/CZ2010/000113 by Oleg Bortnovsky et. Al, titled”Method of manufacture of zeolites with pentasil structure with controlled supply of aluminium atoms from the horns” (Novel NumberWO2011095140 A1), whose contents are incorporated herein by reference in their entirety within this revelation, a method of manufacture of microporous zeolites using pentasil structure with controlled supply of aluminium atoms in an aluminosilicatetetrahedrally unified skeleton at”Al pairs” in (Al-O–(Si–O).sub. N =1,2-Al) sequences localized at one ring and in various rings in Al-O–(Si–O).sub. N p 2-Al sequences.
Chabazite (CHA) zeolites do not own a pentasil structure (i.e., composed of 5-membered rings), and belong to a different category of zeolites made up of 6-membered ring construction components. While the previously reported methods, which change therelative amounts and ratios of compound ingredients to synthesize a zeolite, may be applied to chabazite zeolites, it’s unclear how these changes could affect the Al distribution. Pentasil zeolites have over 1crystallographically-unique tetrahedral website (T-site) in the lattice, while CHA zeolites only have 1 crystallographically-unique T-site in the lattice. As a result, since the underlying mechanisms controlling Al distributions in pentasil zeolites areunknown, the specific strategies utilized to control Al distribution in pentasil zeolites wouldn’t use to CHA zeolites, since they simply contain 1 possible lattice T-site place for Al substitution.
Hence, there is unmet need for artificial processes which right and systematically control the Al distribution in chabazite zeolites in a fixed Si/Al ratio, by only manipulating the type and amount of structure-directing agents used. Further,it is desirable to change the amounts and types of inorganic and organic cations used as structure-directing agents, which contributes to clear and orderly changes in the Al distribution in CHA (SSZ-13). Meeting these needs will benefit structuralstability, deactivation and coking in acid catalysis with hydrocarbons and alcohols, and will reap the structural stability and catalytic degrees of redox catalysis that happens on metal ions exchanged onto acid zeolites, such as Cu or Fe ions exchangedonto CHA zeolites for NOx selective catalytic reduction (SCR) with ammonia.
IP reviewed by Plant-Grow agriculture technology news