Mirosław Zawadzki

Hydrothermal synthesis of nanoporous zinc aluminate with high surface area

Abstract Hydrothermal treatment at low temperatures is proposed for obtaining a nanocrystalline zinc aluminate spinel of interesting properties from catalytic point of view, including high specific surface area (up to 340 m2/g), nanoporosity, and narrow pore size distribution. The precursors for hydrothermal synthesis were basic aluminium nitrate having the empirical formula Al2(OH)6−x(NO3)x wherein x was equal or closed to 1, and hydrated zinc acetate. The proposed synthesis, in contrast to other methods, does not require a high temperature calcination to obtain the spinel phase. The properties of hydrothermally obtained zinc aluminate spinel make them an advanced material suitable for use in catalytic or high-tech ceramic applications.

Some catalytic properties of hydrothermally synthesised zinc aluminate spinel

Abstract Two samples of zinc aluminate were hydrothermally synthesised from zinc acetate and different aluminium sources: basic aluminium nitrate or aluminium hydroxide. The textural properties of the prepared ZnAl 2 O 4 samples are different from these one of the zinc aluminate prepared by conventional way. Powder XRD and TEM measurements reveal that samples are single-phase material or mixture of ZnAl 2 O 4 with small amount of γ-Al 2 O 3 , with morphology of quasi-spherical shape. Catalytic properties of the hydrothermally obtained zinc aluminate and Pt (Pd) catalysts supported on them were investigated in the reactions of cyclohexene isomerisation and combustion of trichloroethylene, respectively. It was evidenced that activity and selectivity of the investigated materials could be qualitatively correlated with the part of the strong acid centres measured by TPD of NH 3 .

Emission properties of nanostructured Eu3+ doped zinc aluminate spinels

Abstract The preparation of nanostructured ZnAl2O4 spinel powders doped with Eu3+ ions obtained by a hydrothermal method is described. XRD analyses demonstrated that the powders were single-phase spinel nanopowders with high crystallite dispersion. The averaged spinel particle size was determined to be 6 nm as prepared and it increased up to 8 nm for calcination at 500°C. The emission spectra of Eu3+ ions measured for the samples calcinated at 500°C demonstrated inhomogeneous shapes characteristic for disordered material which after heating at 1500°C changed shape into an ordered shape characteristic of the crystalline form.

Preparation and optical properties of nanocrystalline and nanoporous Tb doped alumina and zinc aluminate

Abstract Preparation and morphology of nanocrystalline and nanoporous ceramics composed of a network of alumina and zinc aluminate doped with Tb ions are reported. The pore size distributions are determined by nitrogen adsorption at 77 K. The emission spectra and lifetimes of Tb 3+ ions were measured. The effect of thermal conditions of preparation on emission properties was investigated. It is concluded that with increasing thermal heating the sizes of nanoparticles increase leading to the cluster formation of Tb 3+ ions.

Catalytic alkylation of phenol with methanol over zinc aluminate

Two samples (A and B) of zinc aluminate spinel were prepared and used as catalysts of phenol methylation. Both catalysts were synthesised at hydrothermal conditions from zinc acetate and from various aluminium precursors: aluminium isopropoxide (catalyst A) or basic aluminium nitrate (catalyst B). Catalyst A was pure ZnAl2O4 and B - besides ZnAl2O4 contained traces of γ-Al2O3. Reactions of phenol alkylation with methanol were carried out in the gas phase under atmospheric pressure in a standard flow reactor with fixed bed. Catalysts indicated different properties in dependence on the aluminium precursor used during preparation. In the presence of catalyst A higher selectivity of ortho-methylation of phenol was obtained. Catalyst B was active both in O-alkylation and C-alkylation.

Morphological and phase changes of transition aluminas during their rehydration

Transition aluminas (TA), obtained by fast (0.5–1 s) calcination of gibbsite in the temperature range 375–600°C, were rehydrated at 20, 70 and 90°C. The rehydration process was investigated using transmission electron microscopy. X-ray, and thermogravimetric-differential thermal analysis. During rehydration, the TAs react yielding aluminium hydroxides: pseudoboehmite, boehmite, and bayerite. The phase-composition changes are accompanied by changes in particle morphology. Using transmission electron microscopy, six stages of rehydration were found, with characteristic morphological changes occurring. The changes are responsible for connecting the particles into stable grains during the process of obtaining catalyst carriers or adsorbents from TA.

The role of Pd colloids as catalysts in the phosphane-free methoxycarbonylation of iodobenzene

The catalytic activity of PdCl2(cod) (1) in the methoxycarbonylation of iodobenzene (at 40–70 °C, 1–5 atm of CO, in methanol solution) increased remarkably when tetra-n-butylammonium salts [nBu4N]X (X = Br, Cl, I, BF4, PF6) were added to the system. XRD analyses confirmed that under methoxycarbonylation reaction conditions palladium was reduced to a Pd colloid of nanometer size, 2.0–5.6 nm, which was responsible for the catalytic activity. In the absence of ammonium salts fast deactivation of the colloid was observed, even when PVP (polyvinylpyrrolidone) was added as a stabilizer. Catalytic tests performed with isolated Pd colloid demonstrated its high catalytic activity in methoxycarbonylation when used together with [nBu4N]X salts. A mechanism of palladium reduction to Pd nanoparticles is proposed.

A new efficient catalytic method of naphthols ring alkylation

Abstract The attempts carried out so far concerning catalytic ring alkylation of naphthols with alcohols have, as a rule, brought about a complex mixture of products from which the separation of individual compounds with the aim of their practical utilization has been proved to be impossible. We have found that naphthols and some of their derivatives could be easily alkylated with methanol or higher alcohols in the presence of iron oxide catalyst by a gas-phase continuous process. As a result of alkylation the alkyl group enters into the ortho -position to the hydroxyl group. The yields of alkylnaphthols are approximately about 90%, which simplifies their separation and purification considerably. The advantage of the newly developed method of alkylation is that it leads to high degree of raw materials utilization: it is practically wasteless, thus it is well suited to the requirements of modern process technologies. Its application may contribute to the increase of the demand for naphthol derivatives as potential raw materials for many new syntheses of pharmaceuticals, plant protection agents, dyes, etc.

Improved properties of micronized genetically modified flax fibers.

The aim of this study was to investigate the effect of micronization on the compound content, crystalline structure and physicochemical properties of fiber from genetically modified (GM) flax. The GM flax was transformed with three bacterial (Ralstonia eutropha) genes coding for enzymes of polyhydroxybutyrate (PHB) synthesis and under the control of the vascular bundle promoter. The modification resulted in fibers containing the 3-hydroxybutyrate polymer bound to cellulose via hydrogen and ester bonds and antioxidant compounds (phenolic acids, vanillin, vitexin, etc.). The fibers appeared to have a significantly decreased particle size after 20h of ball-milling treatment. Micronized fibers showed reduced phenolic contents and antioxidant capacity compared to the results for untreated fibers. An increased level of PHB was also detected. Micronization introduces structural changes in fiber constituents (cellulose, hemicellulose, pectin, lignin, PHB) and micronized fibers exhibit more functional groups (hydroxyl, carboxyl) derived from those constituents. It is thus concluded that micronization treatments improve the functional properties of the fiber components.

Thermal stability improvement of hopcalite catalyst

The properties of hopcalite in alumina matrix formed by rehydration of transition aluminas have been investigated in comparison with conventional hopcalite catalyst. By using X-ray diffraction, thermal analysis and activity measurements in combustion ofn-butane and air mixture it was found that the presence of alumina matrix leads to improvement of thermal stability at elevated temperatures and to limitation of spinel phase recrystallization. The modified catalyst was found to show much higher activity after thermal treatment at temperatures above 773 K than pure hopcalite at the same conditions.