On the Role of Small Amines in Zeolite Synthesis

Abstract

A crystallization study was undertaken to relate the structure of small amines to the zeolite product obtained. At SiO2/Al2O3 = 200, certain noncyclic amines (some not previously recognized) were specific for the formation of 10-ring zeolites, e.g., ZSM-22 and ZSM-23. For example, ethylmethylamine and diethylamine yielded highly crystalline ZSM-22, while ethylamine and isopropylamine yielded ZSM-23. Consistent with their larger size, cyclic amines such as piperazine produced the 12-ring pore system, ZSM-12. At lower SiO2/Al2O3 ratios (40), a different set of zeolites was obtained, as expected, ZSM-35 and MCM-22. Again, a specific relationship was observed between the amine employed and the zeolite obtained. In both SiO2/Al2O3 regimes, several amines played non-structure-specific pore- and pH-stabilizing roles and yielded ZSM-5. With relatively few exceptions, the zeolite products were fully porefilled with amine and low in Na (Na/Al < 1). Computer simulations confirmed a pore-stabilizing role for both structure-specific and non-structure-specific amines. At the same time, among structure-specific (“structure-directing”) amines, they showed that the interaction energy differences between alternative amine−pore combinations were often quite small (0.5−2.0 kcal/mol, for example). Nevertheless, the changes in amine−pore interaction energies for this group of amines consistently tracked the changes in zeolite products observed.

Synthesis and characterization of H-ZSM-5 zeolites and their catalytic performance in CH3Br conversion to aromatics

“…The impact of the batch SiO 2 / Al 2 O 3 ratio on the obtained zeolites is mainly manifested in two aspects [44]. On the one hand, the higher the aluminum content in the mother liquid, the higher aluminum content in the obtained zeolite.…”

Vapor phase transport synthesis of zeolites from sol–gel precursors

“…the decreased flexibility of the gel framework) and to a lesser extent by the organocations [7,19], which may lead to both decreased crystallinity and crystallization of products with diminished structural complexity [19]. We did not find any systematic relationship between adsorption of organic molecules from the vapor phase and the presence of aluminum in the gels; therefore it is possible that differences in the results between the NaSiAl and NaSi systems are also due to the \ aluminosilicate gel chemistry.…”

“…Differences in morphology due to the use of different organic structure directing + agents in hydrothermal synthesis has been attributed to the relative basicity of the organic molecules used and their effect on the pH of the synthesis solution [2,18,19]. In the vapor .…”

Selective catalytic cracking of n-hexane to propylene over hierarchical MTT zeolite

“…The following chemicals were used for zeolite syntheses as reactants: colloidal silica (40 wt.% of SiO 2 , Snowtex-40, ST-40, and 0.5 wt.% Na 2 O, Nissan Chemicals), aluminum sulfate (Al 2 (SO 4 ) 3 Á18H 2 O), isopropyl amine (IPA), sodium hydroxide (NaOH) and de-ionized water (H 2 O). Instead of pyrrolidine, a common organic structure directing agent (OSDA) for ZSM-23, IPA, a less explored OSDA, was used [19,20]. MTT crystals were synthesized with the molar ratio of 1SiO 2 :0.006Al 2-O 3 :0.125NaOH:1.68IPA:45H 2 O.…”