Chapter 40
Competitive Role of Organic and Inorganic Cations in Directing One-Dimensional Zeolitic Structures Downloaded by UCSF LIB CKM RSCS MGMT on November 19, 2014 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0398.ch040
ZSM-48 and EU-1 1
Girolamo Giordano , Janos B. Nagy, Eric G. Derouane, Nicole Dewaele, and Zelimir Gabelica Laboratory of Catalysis, Center for Advanced Materials Research, Facultés Universitaires Notre Dame de la Paix, Namur, 61 Rue de Bruxelles, B-5000 Namur, Belgium
The Bis-quaternary ammonium ions (e.g. hexamethonium,HM )favour the formation of two different one-dimensional zeolites, namely ZSM-48 and EU-1. The resulting structure essentially depends on the initial aluminium content in the starting hydrogel. The stability fields for both zeolites synthesized by using various reactant compositions have been established. Zeolite ZSM-48 is prepared from a silica hydrogel containing HM ions and alkali cations (Li, Na, and Κ), in presence or in absence of Al . For a higher initial Al content and increased crystallization time, zeolite EU-1 is obtained. The critical role of hexamethonium ions and inorganic cations on the crystallization rate of ZSM-48 was systematically studied. HM ions favor the ZSM-48 formation by interacting electrostatically with Al negative charges and stabilizing its structure by acting as pore fillers. ++
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The s y n t h e s i s o f pure and h i g h l y crystalline z e o l i t e s from a l l u m i n o s i l i c a t e h y d r o g e l s r e q u i r e s t h e study of the simultaneous effects of different parameters i n v o l v e d i n t h e s y n t h e s i s . Most o f t h e s e z e o l i t e s are prepared i n presence o f organic d i r e c t i n g Current address: Dipartimento di Chimica, Université della Calabria, Arcavacata di Rende, 1-87030 Rende (CS), Italy 0097-6156/89A)398-0587$06.00A) ο 1989 American Chemical Society In Zeolite Synthesis; Occelli, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
Downloaded by UCSF LIB CKM RSCS MGMT on November 19, 2014 | http://pubs.acs.org Publication Date: July 31, 1989 | doi: 10.1021/bk-1989-0398.ch040
588
ZEOLITE SYNTHESIS
a g e n t s whose r o l e c a n be d r a s t i c a l l y i n f l u e n c e d b y t h e a c t u a l composition o f the hydrogel. Recent work has p o i n t e d out t h e predominant templating role of bis-quaternary ammonium i o n s ( e . g . hexamethonium ions) i n directing one-dimensional z e o l i t i c s t r u c t u r e s namely z e o l i t e s ZSM-48 a n d EU-1, t h e f i r s t r e p r e s e n t a t i v e member o f t h e EU0 f a m i l y ( 1 - 4 . ) . Z e o l i t e s having ZSM-48 t o p o l o g y also crystallize from hydrogels c o n t a i n i n g other l i n e a r o r g a n i c s t r u c t u r e directing agents, such as diamines (UL) o r v a r i o u s (poly)alkylamines (£). Z e o l i t e ZSM-50, a n o t h e r member o f t h e EU0 f a m i l y p o s s e s s i n g t h e t o p o l o g y o f EU-1, a l s o c r y s t a l l i z e s i n presence o f dibenzyldimethylammonium ions ( 2 ) . The framework o f ZSM-48 i s composed o f f e r r i e r i t e type sheets, c o n n e c t e d i n s u c h a s p e c i f i c way a s t o g e n e r a t e l i n e a r 10-membered r i n g c h a n n e l s . The s t r u c t u r e i s a random i n t e r g r o w t h o f t h e Imma-Cmcm frameworks a n d c o n t a i n s 48-T atoms p e r u n i t c e l l ( & ) . R e c e n t l y B r i s c o e e t a l . (ϋ) d e s c r i b e d t h e framework topology of zeolite EU-1. I t c o n s i s t s of a u n i d i m e n s i o n a l 10-membered r i n g c h a n n e l s y s t e m w i t h s i d e p o c k e t s formed a t r e g u l a r i n t e r v a l s o f f t h e c h a n n e l s . The u n i t c e l l c o n t a i n s 112-T atoms a n d t h e framework symmetry i s Cmma. The aim o f t h i s work i s t o evaluate the (competitive) r o l e o f other ingredients i n s t a b i l i z i n g p r e f e r e n t i a l l y one o r t h e o t h e r s t r u c t u r e . The most i n t e r e s t i n g a r e t h e c a t i o n i c s p e c i e s , namely t h e a l k a l i + +
and H M ions, p o t e n t i a l n e u t r a l i z i n g agents t o A 1 0 ~ n e g a t i v e l y c h a r g e d framework c e n t e r s . I n d e e d , alkali c a t i o n s were shown t o p l a y an i m p o r t a n t r o l e i n t h e formation o f many zeolites, either as s t r u c t u r e directors i n t h e nucleation process (1Ω.-12.) o r as s t a b i l i z i n g m i n e r a l i z e r s d u r i n g growth ( 1 1 , 1 2 . ) , t h e r e b y a f f e c t i n g t h e f i n a l s i z e , morphology and c o m p o s i t i o n o f the c r y s t a l l i t e s . Besides t h e i r obvious r o l e as templates o r s t r u c t u r e d i r e c t i n g agents (13.) o r a s s t a b i l i z i n g p o r e fillers Qrl!) t h e o r g a n i c c a t i o n s w i l l a l s o compete w i t h a l k a l i ions f o r t h e s t a b i l i z a t i o n o f t h e n e g a t i v e l y charged framework (1Û, 11,1!) . The present approach c o n s i s t s i n examining t h e structure and composition of selected crystalline zeolites obtained by h e a t i n g under appropriate c o n d i t i o n s hydrogels having the general composition: 2
x M 0 2
y HMBr
2
ζ Al 03 2
60 S i 0
2
3000 H 0 2
by s y s t e m a t i c a l l y v a r y i n g t h e i n i t i a l c a t i o n i c , o r g a n i c and A l c o n t e n t t o d e f i n e t h e fundamental r o l e o f H M + +
ions
i n each
opecific
system,
crystallization
and t o ultimately
conditions
optimize
f o r each
the
zeolite.
In Zeolite Synthesis; Occelli, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.
40. GIORDANO ET AL.
Competitive Role ofOrganic and Inorganic Cations
589
Experimental A series composition : χ M 0 2
of hydrogels
y HMBr
2
having
ζ A1 0 2
3
the following
60 S i 0
2
3000
molar
H 0 2
(where HMBr s t a n d s f o r hexamethonium b r o m i d e ; M= L i , Na o r K; 0
