Pentasil zeolites, synthesis

One of the earliest direct bonuses of imaging zeolitic catalysts by HRTEM was the discovery (10) that the nominally phase-pure ZSM-5 (structure code MFI) contained sub-unit-cell coherent intergrowths of ZSM-11 (MEL). It soon became apparent (46) that, depending on the mode of synthesis of these and other pentasil (zeolitic) catalysts, some specimens of ZSM-5 contained recurrent (regular) intergrowths of ZSM-11. It also emerged that intergrowths of offretite and erionite are features of both nominally phase-pure erionite and of pure offretite and of many members of the so-called ABC-6 family of zeolites (47). 

Table VIII. Characteristics of some pentasil zeolites obtained from synthesis B using various organic bases or cations (adapted from ref (25), by permission).

The first in situ MAS NMR investigation of the synthesis of MTBE on acidic zeolites was performed by Mildner et al. (228) under batch reaction conditions. In this investigation, the temperature-jump MAS NMR technique (stop-and-go experiment, see Section III.A) was applied to characterize the reaction dynamics under non-equilibrium conditions on a boron-modified pentasil zeolite ( si/... 

Synthesis of Pentasil Zeolites With and Without Organic Templates... 

The synthesis of pentasil zeolites is supported by organic cations. Argauer et al. (1) first described syntheses with tetraalkylammonium and tetraalkylphosphonium compounds. The organic cations may not only initiate and sustain a certain crystallization process but also may lead to products of a new structure. This "templating" behaviour is explained by the structure-directing effect of the organic cations in the process of crystallization (2,3). 

Figure 1. Yield of pentasil zeolites (percentage crystallization) as a function of time. Abbreviations are C, for mono-n-butylair ne, CU for mono-n-propylamine, C2 for mono-n-ethylamine, C. for mono-n-methylamine, di-C, for di-n-propylamine, di-C, for di-n-propylamine,+di-C2 for di-n-ethylamine, di-n-C.. for di-n-methylamine, TPA Al-free for the aluminium-free synthesis with the tetrapr pylammonium cation, TPA for tetrapropylammonium cation, TEA Al-free for the+aluminium-free synthesis with the tetraethylammonium cation, TEA for tetraethylammonium cation and tri-C for tri-n-propylamine.

In the course of pentasil zeolite ZSM-5 synthesis, the gel mixture obtained from starting aqueous solution is a low density precipitate, which is different from the hydrogelatinous state in ZSM-34 synthesis it can be easily separated from the supernatant fluid by centrifuge. 

The product is a valuable intermediate for the production of fragrances. This compound is hardly obtainable by known synthesis routes (Rosemund reduction). Using Al- or B-pentasil zeolite at 300°C the 4-formyltetrahydropyrans can be synthesized in an easy manner and high yields over 97% (18, 19, 20). This reaction was also carried out in the gas phase in a fixed bed reactor (5) with a WHSV = 2 h 1 and a ratio of substrate/solvent (THF) = 50/50. Using SiC>2 as solid catalyst gave an additional yield of 96.5% (9). 

Other shapes of organocations do not produce SSZ-13 and, instead, give a slower synthesis of pentasil zeolites (mordenite, ZSM-5, beta) or no conversion product at all. Hiis was observed for linear substituents on charged nitrogen. Two groups were considered (1) homologous tetraalkyl ammonium compounds and... 

The objective of the present paper was to investigate the most favorable synthesis conditions for the 2MN and to study the methylation mechanism of the aromatic ring on the hydrogen form of pentasil zeolites. 

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