S. Pavlova

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.

The influence of solid precursors nature on structural, textural and surface properties of framework zirconium phosphates synthesized via mechanochemical activation

Abstract The framework zirconium phosphates with incorporated La 3+ and NH 4 + cations were synthesized via mechanical activation of solids followed by the hydrothermal treatment. Their phase composition, local bulk structure, surface properties and microstructure appear to be defined both by the structure of amorphous zirconium phosphates formed via mechanical activation of solids depending on precursors acidity and reactivity and by the pH-dependent mechanism of subsequent crystallization during hydrothermal treatment.

Methane dry reforming over Ni catalysts supported on Ce–Zr oxides prepared by a route involving supercritical fluids

Abstract Ce0.5Zr0.5O2 mixed oxides were prepared in a flow reactor in supercritical isopropanol with acetylacetone as a complexing agent. Variation of the nature of the Zr salt and the temperature of synthesis affected the phase composition, morphology and specific surface area of oxides. X-ray diffraction and Raman spectroscopy studies revealed formation of metastable t” and t’ phases. Oxides are comprised of agglomerates with sizes depending on the synthesis parameters. Loading NiO decreases the specific surface area without affecting X-ray particle sizes of supports. Such sintering was the most pronounced for a support with the highest specific surface area, which resulted in the lowest surface content of Ni as estimated by X-ray photoelectron spectroscopy and in the formation of flattened NiO particles partially embedded into the support. The catalytic activity and stability of these samples in the dry reforming of methane were determined by the surface concentration of Ni and the morphology of its particle controlled by the metal-support interaction, which also depends on the type of catalyst pretreatment. Samples based on ceria-zirconia oxides prepared under these conditions provide a higher specific catalytic activity as compared with the traditional Pechini route, which makes them promising for the practical application.

Ni-loaded nanocrystalline ceria-zirconia solid solutions prepared via modified Pechini route as stable to coking catalysts of CH4 dry reforming

Abstract Mixed nanocrystalline Ce-Zr-O oxides (Ce/Zr = 1 or 7/3) were prepared by modified Pechini route using ethylene glycol solutions of metal salts. Detailed characterization of their real structure and surface properties by X-ray diffraction on synchrotron radiation with the full-profile Rietveld analysis, high resolution electron microscopy with elemental analysis, Raman spectroscopy, UV-Vis and X-ray photoelectron spectroscopy revealed a high homogeneity of cations distribution in nanodomains resulting in stabilization of disordered cubic phase. This provides a high dispersion of NiO loaded on these mixed oxides by wet impregnation, a high reactivity and mobility of oxygen in these catalysts and strong interaction of Ni with support in the reduced state. This helps to achieve a high activity and coking stability of developed catalysts in CH4 dry reforming in feeds with CH4 concentration up to 15% and CH4/CO2 ratio =1.

Synthesis of mesoporous complex framework zirconium phosphates via organic- inorganic nanocomposites: genesis of structure, adsorption and catalytic properties

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 Ǻ are formed at 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 o C preserves the size of nanoparticles while their ordered stacking forms mesoporous structure with a narrow pore size distribution ~ 50 A and specific surface area up to 200 m 2 /g after calcination at 600 o 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.

Highly dispersed framework zirconium phosphates-acid catalysts for pentane and hexane isomerization

The structural features, texture and surface properties of highly dispersed partially substituted framework zirconium phosphates synthesized via sol-gel or mechanochemical activation route followed by the hydrothermal treatment in the presence of polyethylene oxide were studied and compared with catalytic properties in the pentane and hexane isomerization. The most efficient promoter was found to be Si which increases the surface density of the Broensted Zr-OH centers. Pt-supported Si-modified systems demonstrate promising activity and selectivity in propane and hexane hydroisomerization at 300–400°C.

Mechanochemical Synthesis of Complex Zirconium Phosphates

Cation- and anion-substituted zirconium phosphates of XkZrm(PO4)n−yY composition, where X = Na+, La3+, NH4+, Y = F−, WO42−, 1/3 < k < 2, 2 < m < 4, 3 < n < 6 were synthesized by the procedure, including mechanical activation of the starting salts mixture followed by annealing at 300–900°C. The interaction between components was studied by XRD, EXAFS, FT–IR, [31P-MAS] NMR. The possibility of synthesizing nonstoichiometric compounds is demonstrated and prospects for application of the mechanochemical method for synthesis of complex zirconium phosphates are outlined.

High-Surface - Area Framework Zirconium Phosphates as Catalysts of Hexane Isomerization and Dehydroaromatization: Synthesis and Properties

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.