Tamara Krieger

Cobalt–aluminum co-precipitated catalysts and their performance in the Fischer–Tropsch synthesis

Cobalt–aluminum catalysts were prepared using either Co2+ precipitation onto freshly prepared Mg–Al or Zn–Al hydrotalcite (promoted samples) or co-precipitation of Co2+ and Al3+ (non-promoted samples). The evolution of initial hydrotalcite structure was monitored during its calcination and reductive treatment. It has been shown that, at moderate temperatures, hydrotalcites results decomposition yields a Co oxide phase supported by a highly defective inverted spinel-like structure. Cations Co2+ enter the support structure, and occupy both tetrahedral and octahedral positions. Octahedron coordinated Co species are reduced at 580–620°C. After the reduction at 470–480°C catalyst phase composition shows Co0 supported on inverted spinel-like structure, which contains Co2+ in the octahedral coordination. Further reduction at 600°C transforms the support to ‘ideal’ spinel, which contains no octahedron coordinated Co2+. Chemical properties of the Co–Al catalysts, including their performance in the Fischer–Tropsch synthesis (FTS), were found to depend on the catalyst reduction temperature, and thus on the support structure. Metal-support interaction is supposed to explain the observed properties of metallic cobalt.

Mechanisms for hydrogenation of acetone to isopropanol and of carbon oxides to methanol over copper-containing oxide catalysts

Abstract Mechanisms for the synthesis of methanol from CO and CO2 and for the hydrogenation of acetone to isopropanol are discussed based on the recent experimental results obtained by the authors. The state of copper-containing compounds in a hydrogen medium at 200–400°C and the nature of their interaction with the reaction components were studied. Hydrogenation of carbon oxides and acetone was proposed to be the result of the ability of copper ions to reversible transformations to generate copper metal and protons. Activation of acetone and CO2 can be achieved through their interaction with Cu0, and activation of CO through its interaction with oxygen-containing sites of Cu+1OCu+1 type which are formed after oxidation of a portion of Cu0 with carbon dioxide.

The relation between reduction temperature and activity in copper catalysed ester hydrogenolysis and methanol synthesis.

Zinc and manganese promoted silica supported copper catalysts show an activity increase in methyl acetate hydrogenolysis and methanol synthesis after high temperature reductive treatments. The effect of reduction can largely be reversed by applying a treatment in an inert atmosphere at reduction temperature, which results in a decrease in copper surface area as measured by N2O chemisorption and which is accompanied by distinct changes in the XRD pattern of the catalyst. These phenomena could be explained with a model assuming the reversible formation of epitaxial, two-dimensional, copper particles on top of a mixed oxide phase.

The nature of hydrogen stabilization in the reduced copper chromites

Abstract In situ powder X-ray and neutron diffraction showed that copper chromite retains its spinel structure (space group Fd 3 m , a = 8.348(3) A ) in hydrogen at 320°C. The spinel has a copper ion deficiency and is stabilized by the dissolved hydrogen. Two hydrogen states are observed in the spinel structure: as specific hydrogen species H (16c interstitial position) and as OH groups with covalent bounding (32e crystallographic position). The hydrogen species bonded to the lattice oxygen is formed as a result of the exchange interaction between hydrogen atoms and Cu 2+ ions. In this case a portion of copper ions are reduced to Cu 0 as flat particles onto the surface; another portion is reduced to Cu 1+ and transferred towards the 16c positions.

Non-hydrothermal synthesis of copper-, zinc- and copper-zinc hydrosilicates

Abstract Cu/SiO2, Zn/SiO2 and Cu-Zn/SiO2 samples have been prepared by the homogeneous deposition-precipitation method. The samples were analyzed by thermal analysis, X-ray diffraction and infrared spectroscopy after various heat treatments and compared with data obtained for several minerals. It has been shown that interaction between the components occurs through formation of hydrosilicates. Copper-silica system at a Cu:Si ratio ≤ 1, gives rise to a hydrosilicate stable up to a calcination temperature of 930 K resembling the mineral Chrisocolla; at higher ratios a hydroxonitrate (gerhardite type) is also formed. Zinc-silica interaction produces two hydrosilicates such as a well crystallized Hemimorphite at Zn:Si = 2 and highly dispersed Zincsilite at Zn:Si ≤ 0.75, both stable up to 1073 K. The Zincsilite structure consists of three layered sheets (an octahedral layer sandwiched by two tetrahedral ones) like the Stevensite mineral group. For the copper-zinc-silica system no copper hydrosilicate is formed. Copper merely enters the Zincsilite structure independenly of the applied (Cu + Zn):Si ratio. Resulting layered copper-zinc hydrosilicate may be described by formulaZnx-yCuy(Zn3-x–zCuz–y▪x)[Si4O10](OH)2.nH2O,where Zn3-x-zCuz-y– ions are located in octahedral sites, Znx-yCuy–ions in the interlayer; ▪x are vacancies in the layers. Copper and zinc in excess of the Zincsilite ratio of Me:Si = 0.75, gives rise to copper and copper-zinc hydroxonitrates.

Copper-cobalt catalysts for higher alcohols synthesis from syngas

Publisher Summary This chapter describes the synthesis of higher alcohols from syngas with the help of copper-cobalt (Cu–Co) catalysts and the active state of Cu–Co based catalysts with the help of in situ high temperature x-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The catalyst is prepared by coprecipitation of metal nitrates with sodium carbonate at pH 7. A dried sample is calcined at 4900C for 10 hours in flowing helium. XRD studies are carried out using a diffractometer D-500 (Siemens) with CuKα radiation (a graphite monochromator with a reflected beam). Electron microscopic studies, including TEM and selected area diffraction (SAD), are carried out using an electron microscope JEM-100 CX. Cu–Co based catalysts are known as selective toward alcohols in CO hydrogenation. Cu–Co surface alloy is also an active state for higher alcohol formation. Higher alcohols, along with hydrocarbons, are seen to be synthesized within the temperature range of 300–370° C.

Evolution of the structure of Co stevensite during its treatment in the air, inert gas flow and flowing hydrogen

Abstract Synthetic TOT (2 tetrahedron layers,1 octahedron layer) trioctahedral hydrosilicates (stevensites) of Zn, Mg, Co and Co-Zn were prepared by the deposition–precipitation technique. The evolution of both the structure and spectral properties of the silicates were studied during their treatment in various media. The position of the ν(OH) absorption band and the temperature of crystallization of the anhydrous silicate were found to be useful indicators of the cationic composition of stevensites. The data obtained are used to analyze and to review the earlier data on Co/SiO2 catalysts. It is concluded that the formation of Co stevensite occurs in the majority of cases when the pH of the maternal solution during the preparation of a catalyst is above four.

Nanocomposite Catalysts for Steam Reforming of Methane and Biofuels: Design and Performance

Vladislav Sadykov, Natalia Mezentseva, Galina Alikina, Rimma Bunina, Vladimir Pelipenko, Anton Lukashevich, Zakhar Vostrikov, Vladimir Rogov, Tamara Krieger, Arkady Ishchenko, Vladimir Zaikovsky, Lyudmila Bobrova, Julian Ross, Oleg Smorygo, Alevtina Smirnova, Bert Rietveld and Frans van Berkel, 1Boreskov Institute of Catalysis, Novosibirsk State University, 2University of Limerick, 3Powder Metallurgy Institute, 4Eastern Connecticut State University, 5Energy Research Center of the Netherlands, 1Russia 2Ireland 3Belarus 4USA 5Netherlands

Copper ions distribution in synthetic copper-zinc hydrosilicate

Abstract Copper ions distribution in the structure of synthetic copper-zinc hydrosilicate of zincsilite structure, obtained non-hydrothermal synthesis have been studied. Zinesilite is referred to the layered silicates of smectite group and is described by the formula Znx (Zn3-x▪x) [Si4O10](OH)2.nH2O, where Zn3-x – are the ions located in the octahedral positions of layers, formed by two sheets of [Si4O10] tetrahedrons; Znx are zinc ions in the interlayer; ▪x are the cation vacancies. Two types of copper ions were distinguished in accordance with the character of their interaction with hydrogen: (1) – substituting zinc ions in the octahedral positions of layers; (2) – substituting zinc ions in the interlayer. These two types of copper ions display the following properties when reacting with hydrogen: (1) – copper ions in octahedral positions start to be reduced at temperatures 553–573 K, and at 723 K reduction degree is 50% ; (2) – copper ions from interlayer start to be reduced at 503–533 K with a constant energy of activation, and their reduction may be complete at this temperature.

Doping Magnesium Hydroxide with Sodium Nitrate: A New Approach to Tune the Dehydration Reactivity of Heat-Storage Materials

Thermochemical energy storage (TES) provides a challenging approach for improving the efficiency of various energy systems. Magnesium hydroxide, Mg(OH)2, is known as a suitable material for TES at temperature T>300 °C. In this work, the thermal decomposition of Mg(OH)2 in the absence and presence of sodium nitrate (NaNO3) is investigated to adapt this material for TES at T<300 °C. The most notable observations described for the doped Mg(OH)2 are (1) a significant reduction of the decomposition temperature Td that allows tuning the dehydration reactivity by varying the NaNO3 content. The Td decrease by 25 °C is revealed at a salt content Y≤2.0 wt %. The maximum Td depression of some 50 °C is observed at Y=15-20 wt %; (2) the NaNO3-doped Mg(OH)2 decomposes considerably faster under conditions typical for closed TES cycles (at T>300 °C in vapor atmosphere) than a pure Mg(OH)2; (3) the morphology of the dehydration product (MgO) dramatically changes. Differential scanning calorimetry, high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and vibrational spectroscopy (IR and Raman) are used to study the observed effects and to elucidate possible ways the NaNO3 influences the Mg(OH)2 dehydration and morphology of the dehydration product. The mechanism involving a chemical interaction between the salt and the hydroxide accompanied by nitrate embedding into brucite layers is discussed.