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We combine experiment and theory to investigate the cooperation or competition between organic and inorganic structure-directing agents (SDAs) for occupancy within microporous voids of chabazite (CHA) zeolites, and to rationalize the effects of SDA siting on biasing the framework Al arrangement (Al-O(-Si-O)-Al, x = 1-3) among CHA zeolites of essentially fixed composition (Si/Al = 15). CHA zeolites crystallized using mixtures of TMAda and Na contain one TMAda occluded per cage and Na co-occluded in an amount linearly proportional to the number of 6-MR paired Al sites, quantified by Co titration. In contrast, CHA zeolites crystallized using mixtures of TMAda and K provide evidence that three K cations, on average, displace one TMAda from occupying a cage and contain predominantly 6-MR isolated Al sites. Moreover, CHA crystallizes from synthesis media containing more than ten-fold higher inorganic-to-organic ratios with K than with Na before competing crystalline phases form, providing a route to decrease the amount of organic SDA needed to crystallize high-silica CHA. Density functional theory calculations show that differences in the ionic radii of Na and K determine their preferences for siting in different CHA rings, which influences their energy to co-occlude with TMAda and stabilize different Al configurations. Monte Carlo models confirm that energy differences resulting from Na or K co-occlusion promote the formation of 6-MR and 8-MR paired Al arrangements, respectively. These results highlight opportunities to exploit using mixtures of organic and inorganic SDAs during zeolite crystallization in order to more efficiently use organic SDAs and influence framework Al arrangements.
This article was published in the following journal.
Name: Journal of the American Chemical Society
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Compounds derived from organic or inorganic acids in which at least one hydroxyl group is replaced by an –O-alkyl or other organic group. They can be represented by the structure formula RCOOR’ and are usually formed by the reaction between an acid and an alcohol with elimination of water.
Inorganic derivatives of ammonia by substitution of one or more hydrogen atoms with chlorine atoms or organic compounds with the general formulas R2NCl and RNCl2 (where R is an organic group).
Agents employed in the preparation of histologic or pathologic specimens for the purpose of maintaining the existing form and structure of all of the constituent elements. Great numbers of different agents are used; some are also decalcifying and hardening agents. They must quickly kill and coagulate living tissue.
An occlusion resulting in overstrain and injury to teeth, periodontal tissue, or other oral structures.
Organic compounds that have a tetrahydronaphthacenedione ring structure attached by a glycosidic linkage to the amino sugar daunosamine.