S. Mintova

The effect of the metal substrate composition on the crystallization of zeolite coatings

Abstract Zeolite Y and ZSM-5 were grown on different type of metals and alloys. The influence of chemical composition and surface imperfections of substrates on zeolite film formation was investigated. The results show that the characteristics of metal support determine the zeolite film properties, the size of the zeolite crystals, and the thickness of the coating. The chemical and plastic pretreatment of some types of substrate leads to modification of zeolite features.

Vibrational spectra of ETS-4 and ETS-10

Raman and i.r. absorption spectra of ETS-4 and ETS-10 were measured at room temperature in the frequency range 200–1,400 cm −1 . The peaks observed in the spectra were identified through model calculations of the internal modes of vibration for clusters typical of the structure of these materials.

Deposition of zeolite A on vegetal fibers

In situ deposition of zeolite A on various vegetal fibers is studied. It is found that the chemical composition and the structure of the fibers determine the degree of coverage. The effect of the content of cellulose, lignin, and waxy materials in the fibers on the process of the formation of zeolite coating is studied. The role of chemical and mechanical pretreatment of the support on the process of zeolite crystallization is discussed. It is shown that the amount of the deposited zeolite may be controlled by suitable fiber pretreatment.

Synthesis of nanosized FAU-type zeolite

This study is dedicated to crystallization of discrete faujasite particles from tetramethylammonium-containing clear homogeneous solutions. The effect of sodium, aluminium, 15-crown-5 and aging of the synthesis solution on the ultimate size of FAU- nanoparticles is investigated. Highly crystalline colloidal FAU-type zeolites with an average particle size between 40 and 80 nm and a narrow particle size distribution are synthesized. The samples are analyzed by DLS, XRD, TEM, N2 adsorption and combined TG/DSC techniques.

Tribochemical activation of seeds for rapid crystallization of zeolite Y

Abstract The influence of tribochemical activation of seeds on the crystallization of zeolite Y mas studied. Two conditions are discussed: pretreatment of the seeds alone and pretreating them simultaneously with the gel. It is shown that the latter procedure is much more effective than the former. The results obtained indicate that the duration of the tribochemical treatment is the dominant parameter in determining seed activity.

Comparison of physicochemical properties of zorite and ETS-4

On the basis of X-ray diffraction, Raman and IR spectroscopy and TG/DTA analysis a comparative study of zorite and its synthetic titanium silicate analogue ETS-4 was performed. It is shown that the observed differences between ETS-4 and zorite are due to the differing chemical compositions of these materials and to the isomorphous substitutions in zorite.

Zeolite crystallization on mullite fibers

Publisher Summary This chapter describes zeolite crystallization on mullite fibers. In industry, zeolites have been usually used in the form either of granules with adhesive additives, or as pallets and blocks of bulk particles. Neither the use of zeolites as bulk material nor as a part of a composite has been fully utilized so far. This is due to the obvious disadvantage that in the bulk usage a large part of the zeolite consists of material, which is not available in the interior, but in other instances, when the zeolite is embedded within the matrix material, the effective surface-substantially decreases. A combined usage of the whole zeolite surface can be achieved through deposition of the zeolite on a supporting substrate. Suitable substrates for this purpose are fibrous materials, due to their flexibility and the ability to use them for forming matrices of various shape and size. Therefore, the synthesis of zeolite-containing fibers of high thermal and acid stability is of a considerable technological importance.

Kinetics of zeolite ZSM-5 crystallization; template effect of propyl-substituted amines

Zeolite ZSM-5 was synthesized from the initial gel: 33Na2O: 44R: Al2O3: 1000SiO2:4000H2O: 25H2SO4, were R is tetrapropylammonium bromide (TPA. Br), tripropylamine (Tp), dipropylamine (Dp) and propylamine (Pr). The nucleation and crystallization processes were subjected to a detailed kinetic analysis. Values of nucleation and crystallization energies as well as corresponding pre-exponential factors are calculated. Throughout the crystallization a kinetic compensation effect relationship is observed between the resulting kinetic characteristics for ZSM-5 with TPA, Tp, Dp and Pr. The effect of templates is estimated on the basis of the calculated kinetic parameters. The templates used are ordered for effectiveness as: n nTPA.Br>> Pr> Dp> Tp

Structure-controlled effect of organic templates on zeolite crystallization

The effect of organic templates on the synthesis of molecular sieves is considered on the basis of quantum-chemical calculations. The ionization potential, dipole moment and geometric configuration are calculated for diamines, heterocyclic nitrogen-containing substances, and alkyl-substituted amines. The ability of these molecules to form microporous structures is discussed. It is shown that the small-sized molecules with high dipole moment are effective templates for a great number of zeolite structures. Molecules with a complicated configuration exhibit high stereospecificity in the zeolite formation.

Analysis of zeolite crystallization by using the kinetic compensation effect

Abstract Zeolite ZSM-5 was synthesized from aluminosilicate gels with different Si/Al ratio in the presence of organic templates-tetrapropylammonium bromide(TPA.Br) and pyrrolidine(Py) at temperatures of 423, 438 and 453 K. Kinetics parameters for regions of nucleation and crystal growth were obtained. A kinetic compensation effect (KCE) were established between activation energy and preexponential factor for nucleation and crystallization processes. The crystallization mechanism was discussed on the basis of the kinetic features and observed correlations.