Zeolite syntheses using diamines: evidence for in situ directing agent modification

ZSM-22 (TON) can be produced from a potassium based 1,6 hexamethylenediamin e (1,6 HDM) synthesis mixture. However, ZSM-34 (an OFF/ERI intergrowth) is synthesized from the same synthesis mixture with the addition of a source o f sodium either from colloidal silica combined with sodium hydroxide or fro m sodium silicate. NMR analyses of the as-synthesized zeolite samples deter mined the presence of a carbonyl species for all of the ZSM-34 samples, but not for any preparations that produced ZSM-22. The carbonyl species was pr esent in all ZSM-34 preparations regardless of the diamine used (NH2CnH2nNH 2 for n = 4, 6, 8, or 10) and was present only after the synthesis mixture was heated above the ambient temperature (even though the gel was still amo rphous). The source of the carbonyl may be obtained from the reaction of ca rbon dioxide preadsorbed in the basic sodium solution with the diamine to f orm a carbamic acid. Molecular modeling studies, based on pore filling, cal culated a favorable fit of the carbamic species within the pore system of t he Erionite suggesting a reason for the formation of the OFF/ERI intergrowt h. (C) 2000 Elsevier Science B.V. All rights reserved.