J. Wrzyszcz

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.

Physicochemical properties and structure of MgMoO4-MoO3 catalysts

Abstract An attempt was made to elucidate the properties of the MgMoO 4 -MoO 3 system containing various amounts of MoO 3 which is active in the oxidizing dehydrogenation reaction converting ethylbenzene into styrene. By applying ir, Ra, ESR spectroscopy and the DTA and DTG methods, the samples containing an octahedral phase on the tetrahedral MgMoO 4 base were found to have catalytic activity. Besides, the active centers include the Mo(V) ion, most probably in the MoO 5 5− type polyhedra with a distorted pyramid structure.

Homogeneous and alumina supported rhodium complex catalysed hydrogenation

Abstract The complex Rh (OH) (CO) (PPh3)in homogeneous as well as in γ-Al2O3 supported system was used as catalyst precursor for hex-1-ene and benzene hydrogenation at 80°C and 6.5 atm of H2. The hydride complexes, HRh (CO) (PPh3)3 and HRh (CO) (PPh3), identified by 1H and 31p NMR studies, were found to be the active forms in the homogeneous system. γ-Al2O3 supported Rh (OH) (CO) (PPh3)2 complex, activated for 2 h in hydrogen atmosphere does not change its catalytic activity for four weeks. X-ray diffraction spectra show that hydrogenation proceeds with participation of rhodium complexes rather than rhodium metal catalytic centers.

Reactions of normal alcohols in the presence of a dehydrogenating iron catalyst

A oxidizing condensation of normal alcohols C4 to C12 in the gas phase over Fe3O4 catalyst containing Cr, Si and K oxides was studied. The reactions were carried out in a continuous process at atmospheric pressure. Initially the alcohols undergo dehydrogenation to aldehydes and esters, and at higher temperatures symmetric ketones containing 2n - 1 atoms of carbon in a molecule are formed. A mechanism for the reaction is proposed.

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.

C-alkylation of m-cresol with n- and iso-propanol over iron catalyst

The gas-phase alkylation of m-cresol (3-methylphenol) with n-and iso-propanol was investigated. The reactions were carried out in a continuous process at atmospheric pressure over an iron catalyst that contains Cr, Si and K oxides. It is possible to obtain n and iso-propyl derivatives of m-cresol with satisfactory selectivity.