Květuše Jirátová

NiMo/γ-Al2O3 Catalysts from Ni Heteropolyoxomolybdate and Effect of Alumina Modification by B, Co, or Ni

A hydrotreating NiMo/γ-Al2O3 catalyst (12 wt% Mo and 1.1 wt% Ni) was prepared by impregnation of the support with the Anderson-type heteropolyoxomolybdate (NH4)4Ni(OH)6Mo6O18. Before impregnation of the support, it was modified with an aqueous solution of H3BO3, Co(NO3)2, or Ni(NO3)2. The catalysts were investigated using N2 adsorption, O2 chemisorption, X-ray diffraction, UV-Vis spectroscopy, Fourier transform infrared spectroscopy, temperature-programmed reduction, temperature-programmed desorption, and X-ray photoelectron spectroscopy. The addition of Co, Ni, or B influenced the Al2O3 phase composition and gave increased catalytic activity for 1-benzothiophene hydrodesulfurization (HDS). X-ray photoelectron spectroscopy confirmed that the prior loading of Ni, Co or B increased the degree of sulfidation of the NiMo/γ-Al2O3 catalysts. The highest HDS activity was observed with the NiMo/γ-Al2O3 catalyst with prior loaded Ni.

Thiophene conversion and ethanol oxidation on SiO2-supported 12-PMoV-mixed heteropoly compounds

Abstract Surface properties of supported MoV heteropoly compounds and their activities in hydrodesulfurization of thiophene and oxidation of ethanol were studied. Vanadium incorporated into the phosphomolybdic acid anion increased extent of oxidative dehydrogenation of ethanol to acetaldehyde, whereas the catalyst with (VO)2+ increased complete ethanol oxidation to CO2. The catalysts with (VO)2+ or one V atom in the anion showed an increase in HDS activity. Vanadium in anion of phosphomolybdic acid also increased hydrogenation ability. Acidic sites of medium strength were proved to be the most suitable for ethanol oxidation. Such explicit dependence of thiophene hydrodesulfurization on any type of acidic sites was not confirmed. Activity order of supported MoV heteropoly compounds in HDS of thiophene correlated well with the amount of hydrogen consumed during TPR.

The effect of nickel on the component state and HDS activity of alumina-supported heteropolytungstates

Hydrotreating Ni heteropolytungstate catalysts have been prepared by impregnation of γ-Al2O3-alumina with solutions of H3PW12O40 acid and its Ni salt. The nickel content is varied by adding Ni(NO3)2 salt. The calcined samples are characterized by BET, IR, TPR, and XPS techniques. The catalytic activity is tested for HDS of thiophene. It is shown that the initial heteropolyanion, its lacunary analog, and nickel substituted heteropolyanion are present on the surface as a result of the interaction between the active component and the alumina support. The mixed NiWS phase formed after sulfidation determines the HDS activity of the catalysts.

Calcined Ni—Al layered double hydroxide as a catalyst for total oxidation of volatile organic compounds: Effect of precursor crystallinity

The effect of hydrothermal treatment on properties (crystallinity, porous structure, reducibility, acidity, basicity, and catalytic activity and selectivity in toluene and ethanol total oxidation) of Ni—Al layered double hydroxide precursors and related mixed oxides was examined. The hydrothermal treatment increased considerably both the content of crystalline phase and LDH crystallite size. On the other hand, only a slight effect of the precursor hydrothermal treatment on crystallinity of the related Ni—Al mixed oxides obtained by calcination at 450°C was observed. The reducibility of NiO particles appeared to be hindered considerably compared to the reducibility of pure NiO. Catalytic activity of the Ni—Al mixed oxides prepared from the precursors hydrothermally treated for a short time (4 h) was the highest. The highest amount of acetaldehyde formed during the total oxidation of ethanol, i.e. the worst selectivity was found for the calcined Ni—Al LDH without hydrothermal treatment.

Simulation of N2O Abatement in Waste Gases by Its Decomposition over a K-Promoted Co-Mn-Al Mixed Oxide Catalyst

Abstract Intrinsic data of N 2 O catalytic decomposition over a K-promoted Co-Mn-Al mixed oxide prepared by the thermal treatment of a layered double hydroxide was used for the design of a pilot reactor for the abatement of N 2 O emissions from the off-gases in HNO 3 production. A pseudo-homogeneous one-dimensional model of an ideal plug flow reactor under an isothermal regime (450°C) was used for reactor design. A catalyst particle diameter of 3 mm is a compromise size because increasing the size of the catalyst particle leads to a decrease in the reaction rate because of an internal diffusion limitation, and particles with a smaller diameter cause a large pressure drop. A catalyst bed of 11.5 m 3 was estimated for the target N 2 O conversion of 90% upon the treatment of 30000 m 3 /h of exhaust gas (0.1 mol% N 2 O, 0.005 mol% NO, 0.9 mol% H 2 O, 5 mol% O 2 ) at 450°C and 130 kPa.

N2O catalytic decomposition — effect of pelleting pressure on activity of Co-Mn-Al mixed oxide catalysts

The effect of pelleting pressure (0–10 MPa) during the preparation of Co-Mn-Al mixed oxide catalyst on its texture and activity for N2O catalytic decomposition was examined for small grain sizes used in laboratory experiments, and for model industry catalyst particles. Adsorption/desorption measurements of nitrogen, mercury porosimetry and helium pycnometry were used for detail characterization of porous structure. A volume of micropores of about 20 mm3 g−1 was evaluated using modified BET equation. This value did practically not change with the increasing pelletization pressure except that of the sample formed at the pressure of 10 MPa. Although an increase of pelleting pressure caused an increase in bulk density and a decrease in pore size and pore volume of the prepared catalyst (resulting in lower values of N2O effective diffusion coefficient), no direct correlation between pelleting pressure used and catalyst activity has been found. In contrary, estimation of the internal diffusion limitation according to the Weisz-Prater criterion indicated that even laboratory experimental data obtained for catalyst grains with particle size lower than 0.315 mm pelletized at higher pressures could be influenced by internal diffusion. Estimation of the internal mass transfer limitation in industrial catalyst particles described by the effectiveness factor showed that effectiveness factor of about 0.07 and 0.2 can be obtained for spheres with the radius of 1.5 mm and 0.5 mm, respectively, if pelleting pressure of about 6 MPa was used for the catalyst preparation.

Heteroatom effect on hydrodesulphurization activity of TiO2-supported molybdenum heteropolyoxometalates of Anderson type

The properties of the Mo-containing samples (6 wt % Mo) prepared by mechanochemical mixing of Fe, Co, or Ni heteropolymolybdates of Andersen type and the TiO2 support are reported. A detailed characterization of the surface properties has been performed by BET scanning electron microscopy, IR, XPS and thermo programmed reaction methods and by testing of catalysts in the thiophene conversion. The effects of the mixing time and the nature of heteroatom on the properties of the samples are shown. The nanosized particles are formed when mechanochemical synthesis is running 30 min. The Ni-containing catalyst reveals the highest and the most stable activity compared to Co- and Fe-containing catalysts. Their hydrodesulphurization activity is compared to those of alumina and titania catalysts synthesized by the conventional impregnation method.

Cobalt oxides supported over ceria-zirconia coated cordierite monoliths as catalysts for deep oxidation of ethanol and N2O decomposition

Cordierite monoliths coated with ceria–zirconia supporting cobalt oxide were prepared, examined in the deep oxidation of ethanol and N2O decomposition, and compared with pelletized commercial cobalt oxide catalyst. Interaction of Co3O4 with ceria–zirconia washcoat led to formation of Co3O4 particles with slightly worse structure ordering resulting in better reducibility than that observed for the commercial Co3O4 catalyst. In oxidation of ethanol, activity of the Co3O4-containing monoliths was comparable with that of pelletized cobalt oxide catalyst with nearly seven times higher content of active components. However, conversions of N2O over the monolith catalysts were lower. Nevertheless, incorporation of Co3O4 onto ZrO2–CeO2 washcoat increased rate of both catalytic reactions, i.e., N2O decomposition and deep ethanol oxidation.Graphical Abstract