Květa Jirátová

Characterization of activated Cu/Mg/Al hydrotalcites and their catalytic activity in toluene combustion

Five hydrotalcite-type compounds containing different amounts of Cu2+ and Mg2+ cations were prepared by coprecipitation method (the molar ratio Cu2+:Mg2+:Al3+ in brucite-like layers varied as follows: 0:4:2, 1:3:2, 2:2:2, 3:1:2, and 4:0:2). The products were characterized by XRD, TG and DTA measurements. The increasing content of Cu2+ decreased both the dehydration and decomposition temperatures. Extrudates prepared from the solids were calcined at different temperatures and the properties of the resulting materials (surface area, pore volume, TPR, surface basicity and acidity) were examined. Maximum of the Mg/Al hydrotalcite surface area was observed at 400°C, basicity at 450°C and acidity at 550°C. Incorporation of Cu2+ into brucite-like layers caused a substantial decrease in both basicity and acidity. Acidity rose with increasing amounts of copper in the layers and basicity went through a local minimum. An increase in the amount of magnesium in the precursors manifested itself in a decreased reducibility of the Cu2+ component. The oxidation activity in the toluene combustion increased with increasing amounts of Cu2+ in the solids and corresponded with the amount of easily reducible copper component.

Hydrodesulfurization activities of NiMo catalysts supported on mechanochemically prepared Al-Ce mixed oxides

Abstract Al2O3-CeO2 supports containing 1-10 wt% Ce were prepared mechanochemically by milling aluminum and/or cerium nitrates with NH4HCO3. Heteropolymolybdate, (NH4)4NiMo6O24, was used as the precursor of the Ni and Mo to prepare NiMo6/Al2O3-CeO2 components in catalysts by impregnation method. The physicochemical properties of the catalysts were determined using chemical analysis, X-ray diffraction, temperature-programmed H2 reduction, temperature-programmed NH3 desorption, X-ray photoelectron spectroscopy (XPS), and the Brunauer-Emmett-Teller method. The catalyst acidity decreased with increasing Ce concentration in the support. XPS showed that the NiS/MoS ratio decreased two-fold for the Ce-modified alumina support. NiMo6/Al2O3, which had the highest acidity, showed the highest activity in hydrodesulfurization of 1-benzothiophene (normalized per weight of catalyst). The concentration of surface MoOxSy species (which is equal to the concentration of Mo5+) gradually decreased to zero for catalysts with Ce concentrations ( 10 wt%. However, the activities of all the catalysts prepared mechanochemically from Al2O3 and Al2O3-CeO2 supports significantly exceeded that of a reference NiMo6/Al2O3 catalyst prepared by impregnation method using the same precursor and with the same composition.

Mixed oxides of transition metals as catalysts for total ethanol oxidation

Oxides of transition metals could be suitable alternatives to catalysts based on noble metals in the oxidation processes used for the abatement of volatile organic compounds. Mixed oxides of transition metals can exhibit good efficiency and thermal stability, as well as being inexpensive. In this work, oxide catalysts containing various combinations of Cu, Co, Ni, Mn, and Al, grained or supported on oxidised aluminium foil Al2O3/Al, were studied in terms of their chemical and physical properties, including their chemical composition, porous structure, phase composition, reducibility, and activity in total ethanol oxidation. Ternary co-precipitated catalysts in the form of grains obtained from layered double hydroxide-like precursors were highly active, especially those containing manganese. Deposition of the selected precursors on an anodised aluminium foil-support afforded less active catalysts, mainly because the required metal molar ratios were not achieved, and insufficient amounts of metals were deposited. However, by controlling the preparation conditions (pH), higher loading of active components and higher catalytic activity were obtained.

Role of the support of the nickel catalyst in the synthesis of morpholine from diethylene glycol and ammonia

Abstract The strong effect of the support on the physical properties and catalytic activity and selectivity of high-loaded nickel catalysts (about 55 wt.% Ni) used in reductive amination of diethylene glycol (DEG) and diethylene glycol amine (DEGA) to form morpholine was confirmed. In DEG amination, catalytic activity was proportional to the dispersion of metallic nickel only, while in DEGA amination catalytic activity depended on the acidity of the catalysts.

THE FORMATION OF LAYERED DOUBLE HYDROXIDES ON ALUMINA SURFACE IN AQUEOUS SOLUTIONS CONTAINING DIVALENT METAL CATIONS

Layered double hydroxides (LDHs) are often used as precursors for mixed-oxide catalysts and the deposition of a LDH layer on supporting materials would be advantageous because of better utilization of active components. The purpose of the present study was to investigate the formation of LDHs on Al2O3/Al supports prepared by the anodic oxidation of aluminum foil in dilute aqueous solutions of Co, Mn, and/or Ni nitrates. The LDH deposition was carried out under hydrothermal conditions at 80–180°C for periods ranging from 8 h to 7 days. In the initial stages of the reaction, a surface alumina hydration was observed. The LDH phase was detected after long-term deposition (3–7 days) at 120–160°C and only a small amount of Mn was incorporated in the LDHs deposited. In solutions containing only Co and Mn cations, scanning electron microscopy (SEM) images show a gradual growth of platy crystals resulting in the formation of discrete bulky aggregates with sizes up to several tens of micrometers. The adhesion of aggregates to the support probably decreased with increasing size and oversized aggregates fell away; none was found in SEM images of the samples obtained after prolonged reaction times. When Ni cations were present in the solution, they were incorporated preferentially into the LDH phase; an homogeneous layer was formed, with single platy crystals oriented perpendicular to the support. After calcination at 500°C, the products formed on Al2O3/Al support exhibited a shift of reduction maxima to higher temperatures in comparison with mixed oxides obtained by thermal decomposition of coprecipitated LDHs.