G. M. Alikina

Honeycomb catalysts for clean-up of diesel exhausts based upon the anodic-spark oxidized aluminum foil

Abstract The technology of the aluminum foil anodic spark oxidation in the water-based electrolytes has been applied to form strongly adhering protective alumina layer at the surface. Basic features of the oxidation were studied by SEM and XRD. Secondary supports, promoters and modifiers including rare-earth elements were used to increase the thermal stability of these composites up to 900°C. These materials were assembled as thin wall honeycomb supports loaded with a number of active components. The catalysts were tested in the reactions of CO and CHx oxidation, NOx selective reduction by hydrocarbons and demonstrated a high performance and a low pressure drop at high space velocities. City diesel buses field tests of converters equipped with those catalysts demonstrated their high and stable performance in clean-up of exhausts from SOF, CO, gaseous hydrocarbons and NOx.

Pt-Supported Nanocrystalline Ceria-Zirconia Doped with La, Pr or Gd: Factors Controlling Syngas Generation in Partial Oxidation/Autothermal Reforming of Methane or Oxygenates

Nanocrystalline CeO2-ZrO2 (Ce:Zr 1:1) samples doped with La, Pr or Gd cations (containing up to 30 at.%) were prepared via the Pechini route. Pt (1.4 wt.%) was supported via impregnation with H2PtCl6 solution followed by drying and calcination. The samples’ surface features were studied by SIMS and FTIRS of adsorbed CO. The oxygen mobility was characterized by the dynamic oxygen isotope exchange and H2 TPR. Catalytic activity was studied in the flow installation using diluted feeds (0.7% CH4 +0.5% O2 or 1% C3H6O + 0.5% O2 +0.5% H2O in He). In the selective oxidation of methane (POM), the catalytic activity correlates with Pt dispersion controlled by the oxidized sample’s ability to stabilize Pt2+ cations as precursors of small reactive Pt clusters formed under reaction conditions. This is favoured by a larger doping cation (La) and a developed network of nanodomain boundaries. At comparable Pt dispersion, the highest performance was demonstrated by a La-doped system, which correlates with the highest surface/near-surface oxygen mobility controlled by the strength of Ce-O bonds in the surface layer. In the autothermal reforming of acetone, the activity trends differ from those in POM because of the more prominent role of the oxygen mobility required to prevent surface coking.

Physicochemical and catalytic properties of La1-xCax FeO3-0.5x perovskites

The phase analysis of La1-xCaxFeO3-0.5x perovskites prepared by a ceramic process from oxides is studied by X-ray diffraction and differential dissolution methods. Atx < 0.5, the system does not form a continuous series of homogeneous solid solutions and does not consist of the members of a homological series. Atx < 0.5, the system contains two phases and calcium ferrite nanoparticles located on the surface of lanthanum ferrite. Atx > 0.5, the formation of the structures of a brownmillerite-based homological series is found. The catalytic activity of perovskites depends nonmonotonically on thex value and reaches the maximum atx = 0.6.

Real structure and catalytic activity of La1−xSrxCoO3 perovskites

Abstract Mechanoceramical synthesis of La 1− x Sr x CoO 3 (0≤ x ≤1) perovskites was made from simple oxides. Samples calcined at 900 and 1100°C for 4 h are nearly monophase and well crystallized. Sr adding was found to cause a structure rearrangement from the hexagonal (at x ≤0.4) to the cubic one (at 0.8> x >0.4) and back to the hexagonal at x >0.8. There are two maxima of the catalytic activity versus chemical composition: at x =0.3 and at x =0.8. TEM data for these samples were obtained and disordered surface layers were detected. There is a correlation between the catalytic activity and surface layers microstructure.

Cu, Co, Ag-Containing Pillared Clays as Catalysts for the Selective Reduction of NOx by Hydrocarbons in an Excess of Oxygen

Thermally stable Al- and Zr-PILC loaded with copper and cobalt cations and silver nanoparticles were synthesized. The structural and surface features of these nanosystems were studied and compared with those of bulk analogs – partially stabilized ZrO2 loaded with the same active components. Specificity of the catalytic properties of nanocomposites in SCR of NOx by propane, propylene and decane in the excess of oxygen appears to be determined both by distribution of active components on the catalytic surface and degree of their interaction with supports. Formation of ads.-NOx, nitroxyl-hydrocarbon CxHyNO2⋅ and isocyanate NCO intermediates was observed by ESR and IR spectroscopy in situ.

Study of synthesis gas production over structured catalysts based on LaNi(Pt)Ox- and Pt(LaPt)- CeO2-ZrO2 supported on corundum

Abstract Study of partial oxidation of methane (POM), steam (SR), authothermal (AR) and dry (DR) reforming of methane over catalysts containing LaNiO3 (pure or promoted by Pt) or LaPtO x /CeO 2 -ZrO 2 supported on the fragments of corundum monolith reveals that the most effective catalysts contain LaNiO 3 and LaPtO x with La excess. The reduction pretreatment as well as addition of Pt to LaNiO x facilitates the formation of syngas at a lower temperature, furthermore, Pt favors a high catalyst stability preventing catalyst coking.

Physicochemical and catalytic properties of La1-xCaxFeO3-0.5x perovskites prepared using mechanochemical activation

The phase composition of La1 – xCaxFeO3 – 0.5x perovskites synthesized from preactivated oxides was studied by powder X-ray diffraction analysis and differential dissolution. The system does not form a continuous series of homogeneous solid solutions. No intermediate samples from this series are monophasic. It was found that the synthesis under nonequilibrium conditions (mechanical activation + calcination at 900°С for 4 h) resulted in nonequilibrium microheterogeneous solid solutions with degrees of calcium substitution for lanthanum of no higher than 0.5. A longer calcination (for 16 h) or an increase in the calcination temperature of solutions up to 1100 °С decreased the calcium content of the samples down to x ∼ 0.2 because of the formation of a brownmillerite phase. The catalytic activity of the test samples in the oxidation of CO changed nonmonotonically with x, and it was maximum at x = 0.5–0.6, which correlates with the maximum density of interphase boundaries in these samples.

Design of Multilayer Ceramic MIEC Membranes

Abstract The development of multilayer mixed conducting oxide membranes on porous dead‐end tubular mineral‐based glass‐ceramic supports is presented. Nanopowders of compatible complex perovskites and fluorites as membrane materials were obtained by mechanochemical synthesis. The deposition of oxide ceramic porous and dense layers was carried out by casting of slurries in organic medium, prepared from narrow fractions of agglomerated powders. A linear dependence between the sintering temperature Ts and calculated effective melting point T*m for complex perovskites and fluorites was revealed that allowed to propose a simple rule for the synthesis of complex oxides with required Ts. Dead‐end tubular supports were produced by casting from selected kaolins with organic/inorganic additives. The misfit in sintering temperatures of porous substrate and MIEC ceramic layers was eliminated by modification of substrate and heavily doping of mixed oxides. The elimination of shrinkage misfit between the porous substrate and ceramic layers was achieved by optimization of operation conditions and compositions of both substrate and ceramics. Almost gas‐tight cost efficient catalytic membrane reactors CMRs with large operation surface ∼30 cm2 and good prospects for up‐scaling were produced and tested.

Performance of monolithic catalysts with complex active component in partial oxidation of methane into syngas: experimental studies and modeling

Publisher Summary Partial oxidation of methane (POM) on monolithic catalysts at short contact times is a promising process for designing compact syngas generators. As is demonstrated for Rh- or Pt- supported catalysts, the optimization of their performance requires process modeling based upon a detailed elementary step reaction mechanism verified for pure metals. For more complex active components such as Pt-promoted LaNiO 3 /Ce-Zr-O etc, elucidation of such detailed elementary kinetics would require too extensive research. This chapter presents a verification of more simple approach to modeling of both steady-state and start-up performance based upon using the rate constants for the reactions of methane selective oxidation and reforming reactions estimated for small separate units of monolithic catalysts in nearly isothermal conditions. Two types of honeycomb monolithic substrates based on corundum (a hexagonal prism with a side of 40 mm and triangular channels with wall thickness of 0.2–0.3 mm) or fechraloy foil (cylindrer 50 mm diameter, 200–400 cpsi, 20 μm foil thickness) were used. The metal surface is protected by a thin (∼10 μm) nonporous layer of corundum supported by the dust blasting. The active component comprised of mixed LaNiO 3 /Ce-Zr-La-O oxides (up to 15 wt%) and Pt (up to 0.5 wt.%) was supported via washcoating and/or impregnation procedures followed by drying and calcination.

La0.8Sr0.2Ni0.4Fe0.6O3–Ce0.8Gd0.2O2–δ Nanocomposite as Mixed Ionic–Electronic Conducting Material for SOFC Cathode and Oxygen Permeable Membranes: Synthesis and Properties

Mixed ionic–electronic conducting nanocomposite La0.8Sr0.2Ni0.4Fe0.6O3 (LSNF)–Ce0.8Gd0.2O2– δ (GDC) was prepared via ultrasonic dispersion of nanocrystalline powders of perovskite and fluorite oxides in water with addition of surfactant, followed by drying and sintering up to 1300°C. Analysis of the real structure of nanocomposite (studied by XRD and TEM with EDX) and its surface composition (studied by XPS) revealed moderate redistribution of elements between phases favoring their epitaxy. Results of impedance spectroscopy, oxygen isotope exchange, O2 TPD and H2 TPR experiments revealed a positive effect of composite interfaces on the oxygen mobility and reactivity agreeing with the ambipolar transport behavior of MIEC composite. Preliminary testing of button-size cell with functionally graded LSNF–GDC cathode layer supported on thin YSZ layer covering Ni/YSZ cermet demonstrated high and stable performance, which is promising for its practical application.