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Nanocrystalline TiO2 was synthesized by the solution combustion method using titanyl nitrate and various fuels such as glycine, hexamethylenetetramine, and oxalyldihydrazide. These catalysts are active under visible light, have optical absorption wavelengths below 600 nm, and show superior photocatalytic activity for the degradation of methylene blue and phenol under UV and solar conditions compared to commercial TiO2, Degussa P-25. The higher photocatalytic activity is attributed to the structure of the catalyst. Various studies such as X-ray diffraction, Raman spectroscopy, Brunauer-Emmett-Teller surface area, thermogravimetric-differential thermal analysis, FT-IR spectroscopy, NMR, UV-vis spectroscopy, and surface acidity measurements were conducted. It was concluded that the primary factor for the enhanced activity of combustion-synthesized catalyst is a larger amount of surface hydroxyl groups and a lowered band gap. The lower band gap can be attributed to the carbon inclusion into the TiO2 giving TiO(2-2x)C(x) VO2**.

The W, V, Ce, Zr, Fe, and Cu metal ion substituted nanocrystalline anatase TiO2 was prepared by solution combustion method and characterized by XRD, Raman, BET, EPR, XPS, IR TGA, UV absorption, and photoluminescence measurements. The structural studies indicate that the solid solution formation was limited to a narrow range of concentrations of the dopant ions. The photocatalytic degradation of 4-nitrophenol under UV and solar exposure was investigated with Ti1 - x M x O2 ± δ. The degradation rates of 4-nitrophenol with these catalysts were lesser than the degradation rates of 4-nitrophenol with undoped TiO2 both with UV exposure and solar radiation. However, the photocatalytic activities of most metal ion doped TiO2 are higher than the activity of the commercial TiO2, Degussa P25. The decrease in photocatalytic activity is correlated with decrease in photoluminescence due to electron states of metal ions within the band gap of TiO2.

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The structure and chemical nature of Pt in combustion-synthesized Pt/CeO2 catalysts have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS), and temperature-programmed reaction (TPR). Catalytic oxidation of CO over Pt/CeO2 is correlated with its structure. High-resolution XRD studies show that the structure could be refined for the composition of Ce1 - x Pt x O2 - δ in the fluorite structure with 6% oxide ion vacancy. TEM images show very few Pt particles on the CeO2 crystallite surface in as-prepared samples and a decrease in the density of Pt metal particles is observed on heating. XPS studies demonstrate that Pt is dispersed mostly in +2 (72%) and +4 (21%) oxidation states on CeO2, whereas only 7% is present as Pt metal particles. On heat treatment, Pt2+ species increase at the cost of Pt4+ ions. EXAFS studies show the average coordination number of 1.3 around the platinum ion in the first shell of 1% Pt/CeO2 at a distance of 1.98 Å, indicating oxide ion vacancy around the platinum ion. On heating, the average oxygen coordination of Pt and oxygen increases to 2.3. The second shell at 2.97 Å is due to Pt−Pt coordination, which is absent in PtO2 and PtO. The third shell at 3.28 Å is not observed either in Pt metal or any of the platinum oxides, which could be attributed to Pt2+−Ce4+ correlation. Thus, Pt/CeO2 forms a Ce1 - x Pt x O2 - δ type of solid solution having −□−Pt2+−O−Ce4+− kinds of linkages.

The structure and chemical environment of Cu in Cu/CeO 2 catalysts synthesized by the solution combustion method have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and extended X-ray fine structure (EXAFS) spectroscopy. High-resolution XRD studies of 3 and 5 atom % Cu/CeO 2 do not show CuO lines in their respective patterns. The structure could be refined for the composition Ce 1-x Cu x O 2-δ (x ) 0.03 and 0.05; δ ∼ 0.13 and 0.16) in the fluorite structure with 5-8% oxide ion vacancy. High-resolution TEM did not show CuO particles in 5 atom % Cu/CeO 2 . EPR as well as XPS studies confirm the presence of Cu 2+ species in the CeO 2 matrix. Redox potentials of Cu species in the CeO 2 matrix are lower than those in CuO. EXAFS investigations of these catalysts show an average coordination number of 3 around the Cu 2+ ion in the first shell at a distance of 1.96 Å, indicating the O 2ion vacancy around the Cu 2+ ion. The Cu-O bond length also decreases compared to that in CuO. The second and third shell around the Cu 2+ ion in the catalysts are attributed to -Cu 2+ -O 2--Cu 2+ -at 2.92 Å and -Cu 2+ -O 2--Ce 4+ -at the distance of 3.15 Å, respectively. The present results provide direct evidence for the formation of a Ce 1-x Cu x O 2-δ type of solid solution phase having -0-Cu 2+ -O-Ce 4+ -kind of linkages.

A 1% Pt/CeO2 catalyst prepared by the solution combustion method shows a higher catalytic activity for CO oxidation by O2 compared to Pt metal particles. At least six hydrogen atoms are taken up per Pt at −25 °C. The structure of 1% Pt/CeO2 catalyst has been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. Rietveld refinement shows that Pt ions are incorporated into the CeO2 matrix in the form of Ce1 - x Pt x O2 - δ solid solution. A decrease in oxygen content in 1% Pt/CeO2 is seen in relation to pure CeO2. TEM studies show that Pt is dispersed as atoms or ions and only a small amount as Pt metal particles. The Pt(4f) core level region in XPS shows that Pt is present mostly in the Pt2+ ionic state on CeO2 surface. FTIR of 1% Pt/CeO2 shows a strongly adsorbed CO peak at 2082 cm-1 corresponding to oxidized Pt. These structural studies show that Pt ions in the catalyst are substituted for Ce4+ ions in the form of Ce1 - x Pt x O2 - δ, creating oxide ion vacancies leading to a strong Pt2+−CeO2 interaction that is responsible for higher catalytic activity.

Oxidative precipitation in an aqueous medium of highly self-compacted crystallized Co3O4 dense nanoparticles (4−5 nm) leads to the formation of porous micrometric agglomerates exhibiting a well-defined porosity distribution. Postannealing of these powders induces drastic reorganizations first because of the fast removal of trapped water and then because of the particles sintering, resulting in larger inter-particle voids. Electrochemical behavior of this nanometric material precipitated at moderate temperature is found to be extremely dependent on the way the mixing with the SP conducting carbon is performed; the better performances being obtained by a soft mixing in an organic solvent. This textural effect provides a stable capacity over the first cycles (800 mA·h/g) and reveals a first cycle capacity loss of the same extent as for bulk Co3O4, implying that the nanotexturation undergone by bulk oxide particles during their first formatting cycle is not responsible for the corresponding initial loss. Through chemical analysis of the electrolyte we found that the long-term capacity fading of our materials can be mainly attributed to the dissolution of the active material within the organic electrolyte.