Stanisław Kowalak

Structure and dynamics of S3− radicals in ultramarine-type pigment based on zeolite A: Electron spin resonance and electron spin echo studies

X-band electron spin resonance (ESR) spectra of S(3)(-) radicals in ultramarine analog (pigment) prepared from zeolite A and maintaining the original structure of parent zeolite were recorded in the temperature range of 4.2-380 K. Electron spin echo experiments (echo detected ESR, electron spin-lattice relaxation, and spin echo dephasing) were performed in the temperature range of 4.2-50 K. The rigid lattice g factors are g(x) = 2.0016, g(y) = 2.0505, and g(z) = 2.0355, and they are gradually averaged with temperature to the final collapse into a single line with g = 2.028 above 300 K. This is due to reorientations of S(3)(-) molecule between 12 possible orientations in the sodalite cage through the energy barrier of 2.4 kJ/mol. The low-lying orbital states of the open form of S(3)(-) molecule having C(2v) symmetry are considered and molecular orbital (MO) theory of the g factors is presented. The orbital mixing coefficients were calculated from experimental g factors and available theoretical orbital splitting. They indicate that the unpaired electron spin density in the ground state is localized mainly (about 50%) on the central sulfur atom of S(3)(-) anion radical, whereas in the excited electronic state the density is localized mainly on the lateral sulfur atoms (90%). A strong broadening of the ESR lines in directions around the twofold symmetry axis of the radical S(3)(-) molecule (z-axis) is discovered below 10 K. It is due to a distribution of the S-S-S bond angle value influencing mainly the energy of the (2)B(2)-symmetry MO. This effect is smeared out by molecular dynamics at higher temperatures. A distribution of the g factors is confirmed by the recovery of the spin system magnetization during spin-lattice relaxation measurements, which is described by a stretched exponential function. Both the spin-lattice relaxation and electron spin echo dephasing are governed by localized phonon mode of energy of about 40 cm(-1). Thus, the anion-radical S(3)(-) molecules are weakly bonded to the zeolite framework, and they do not participate in the phonon motion of the host lattice because of their own local dynamics.

Influence of various synthesis parameters on the morphology and crystal size of zeolite Zn-MFI

The use of the zinc-phosphate complex in the hydrothermal synthesis has been proven to be a good way for obtaining zinc-zeolite materials, especially in the case of the zeolite Zn-MFI that can be prepared in a large range of Si/Zn ratios [1, 2]. Moreover, the pH values of the starting hydrogel play an important role on the nature of the crystalline phases obtained. For that reason the first step in the synthesis optimization is the definition of the pH range that is specific for each zoelite type. The crystal size and morphology can be varied by altering the chemical synthesis parameters (zinc, organic and water content as the main ones) as well as the source of silica. Moreover, the isopropanol decomposition is carried out with the purpose to valuate the acidity of the prepared Zn-MFI samples.

04-P-14-Preparation of zinc containing zeolite catalysts

Publisher Summary This chapter discusses the preparation of zinc (Zn)-containing zeolite catalysts by direct synthesis from hydrogels. The postsynthesis introduction of copper (Cu) is also presented. The samples are characterized by X-ray diffraction (XRD), atomic absorption spectroscopy (AAS), thermal analysis, scanning electron microscopy (SEM), and 29 silicon (Si)-nuclear magnetic resonance (NMR) spectroscopy. The catalytic results on the cumene conversion are described.

Oxygen scavengers for packing system based on zeolite adsorbed organic compounds

Zeolites (mostly faujasites) with adsorbed terpenes or phenol derivatives have been applied as effective oxygen scavengers of oxygen in packing bags. Their efficiency depends on type of zeolite and on cation modification. Na- and Cu-forms of zeolites X and Y accelerate the oxidation of terpenes greatly, whereas the H-forms retard the reaction with oxygen. The reactivity of phenol derivatives with oxygen is also affected by the zeolite support markedly. Although the reactivity of phenols does not increase after adsorption on zeolites, the oxidation products remain adsorbed and do not affect the packing system.

Preparation and properties of MFI zincosilicate

The following study demonstrates a possibility to synthesize zincosilicate MFI by hydrothermal crystallization using sodium zincate as zinc source. It reminds the conventional method of hydrothermal zeolite synthesis. The earlier syntheses involved mostly complexed Zn cations. This way relatively high Zn loading (Si/Zn=33) can be attained. The properties of the resulting samples depend on the origin of sodium zincate and on zinc content. The resulting products (particularly after ion-exchange modification) show remarkable catalytic activity for cumene cracking, 2-propanol decomposition and cyclohexane transformation towards benzene.

Cesium Bearing Ultramarine Prepared From Zeolites

Abstract Pigments analogous to ultramarine with various colors including pink have been prepared mainly from zeolites A and also from X by a thermal treatment with sulfur and various amounts of Cs 2 CO 3 . The bulky Cs + cations introduced into zeolites reduce markedly a size of their pore openings and that of inner voids and subsequently affect the type and distribution of generated sulfur chromophores. It is likely that the chromophores in cesium-rich samples occupy rather the shrunken voids of α-cavities but not the sodalite units.

Spontaneous crystallization of zincophosphate sodalite and its modifications

The following study is a continuation of our research on spontaneous synthesis of sodium zincophosphate sodalite by a simple grinding of the substrate components ( e.g. , ZnCl 2 or Zn(NO 3 ) 2 , Na 2 HPO 4 , Na 2 CO 3 ). Rapid crystallization was used for the encapsulation of some substances (elemental sulphur, CdS, KBr, pyridine, hydroquinone) during sodalite structure formation. Attempts to increase the thermal stability of the resulting sodalite by adding some silicon or tin to the starting mixture brought about only a moderate improvement. The synthesis of potassium or ammonium derivatives of zincophosphate did not result in a sodalite structure.

Zeolite Catalysts Modified with Fluorine

Incorporation of some fluorine atoms into the H-forms of high-silica zeolites or into faujasite modified with polyvalent cations (e.g. Al 3+ cations) results in a significant increase in their acidity and catalytic activity. Deep fluorination, on the other hand, reduces both acidity and activity. There is no convincing correlation between acidity of the fluorinated zeolites and their Sanderson electronegativity. Possible pathways of the fluorination of zeolites are proposed.

Synthesis and characterization of metal-benzene-tricarboxylate oxidation catalysts

The MOFs materials containing copper, zinc or both metals together combined with benzenetricarboxilate linkers have been prepared in solvothermal process and characterized. The products were tested as catalysts for low temperature oxidation of cyclohexene. They showed considerable activity and selectivity which depended markedly on kind of metal contributing in the structure. The samples containing copper and zinc together are more active than that with the only copper, whereas the latter one shows higher selectivity to cyclohexenone.

22-P-19-Application of the molecular sieves as matrices for the pigments

Publisher Summary This chapter discusses the application of the molecular sieves as matrices for the pigments. The uniform intracrystalline voids of the molecular sieves can be employed for the encapsulation of molecules containing chromophore groups and they can result in forming pigments. Natural lazurite is a good example of zeolite (sodalite)-containing sulfur anion radicals encapsulated in β-cages. The above radical can also be introduced into aluminum phosphate (AlPO 4 ) sodalite (AlPO 4 -20), but the attempts to encapsulate it to zincophosphate sodalite are unsuccessful. The latter structure, however, could accommodate cadmium sulfide (CdS) molecules, when they are encapsulated during the dry crystallization of superoxide dismutase (SOD). The organic cation radicals generated in the MFI structure channels (HZSM-5, H-ferrosilicalite, and H-zincosilicalite) as a result of the oligomerization of styrene and its derivatives form very stable pigments of various colors.