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This work considers effect of type and content of dopant on the real structure, state of surface Pt species and oxygen mobility of nanocrystalline Lnx(Ce0.5Zr0.5)1-xO2-δ (Ln=La3+, Gd3+, Pr3+/4+) solid solutions prepared by Pechini route. For the reactions of methane selective oxidation and dry reforming into syngas, catalytic activity correlates rather well with either surface (in diluted feeds) or bulk (in realistic feeds) oxygen mobility as well as Pt dispersion controlled by the type and content of a dopant.
This work presents the first results of synthesis of framework binary phosphates of zirconium and transition metal cations (Co, Cu, Ce) via nanocomposites of starting inorganic salts with citric acid and studies of their structure genesis. Nanoparticles of layered Zr phosphates with typical sizes in the range of 18–24 Å are formedat the mixing stage. Less basic Cu and Co cations are mainly octa-coordinated with both phosphate groups of those nanoparticles and citric acid molecules. At subsequent thermal treatment, Cu and Co cations are incorporated within Zr phosphate nanoparticles acquiring a low coordination approaching a tetrahedral one while rearranging the nuclei structure into that of a framework type. Removal of citric acid by heating under air at 200–300°C preserves the size of nanoparticles while their ordered stacking forms mesoporous structure with a narrow pore size distribution ∼ 50 Å and specific surface area up to 200 m2/g after calcination at 600°C. The binary phosphates promoted by a small amount of Pt were found to be effective catalysts of NOx selective reduction by decane in the oxygen excess not subjected to coking with a high and stable performance at high space velocities in the presence of steam.
SAXS and EXAFS were applied to study genesis of polynuclear zirconium hydroxyspecies in pillaring solutions as dependent upon the zirconium concentration, addition of alkaline-earth chlorides and aging. After the montmorillonite clay pillaring, the structure of zirconium nanopillars was characterized by applying X-ray structural analysis, UV-Vis, FTIRS of adsorbed CO and nitrogen adsorption isotherms. Main pillaring species appear to be nanorods comprised of several Zr4 tetramers. Basic structural features of the tetramers are preserved in zirconia nanoparticles fixed between alumosilicate layers in pillared clays. In calcined samples, those nanoparticles contain only bridging hydroxyls and/or oxygen anions responsible for bonding within pillars and between pillars and clay sheets.
Thermally stable alumina and zirconia pillared clays 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 zirconias and γ-alumina loaded with the same active components. Specificity of the catalytic properties of nanocomposites in the reactions of nitrogen oxides reduction by propane, propylene and decane in the excess of oxygen appears to be determined both by the degree of interaction between pillars and active components and the type of reducing agent.
The structure and surface properties of composites based upon high-surface-area framework zirconium phosphates with supported WO3, MoO3 and Pt nanoparticles were studied by using combination of structural and spectral methods. The effect of these promoters on performance of zirconium phosphates in the reaction of pentane and hexane isomerization is considered.
Mechanochemical activation of solid inorganic precursors and sol-gel routes followed by hydrothermal treatment in the presence of surfactants were used to synthesize highly dispersed NZP-type complex zirconium phosphates. Genesis of samples real structure and its impact on the surface properties and catalytic performance in the reactions of hexane isomerization and dehydroaromatization have been studied.
The relationship between the chemical composition, bulk real structure, surface properties and catalytic activity of dispersed complex framework zirconium phosphates with a NASICON-type structure is considered. For both crystalline and amorphous samples, a model of their bulk structure is suggested. The Lewis and Bröensted acidity was shown to vary broadly and be dependent upon the composition and preparation procedure, which is important for catalysts of hydro-carbons activation. Selective catalytic reduction of NOx by methane in excess oxygen appears to be one of the application areas for these systems.
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