Effects of cerium incorporation on the catalytic oxidation of benzene over flame-made perovskite La1−xCexMnO3 catalysts

Perovskite-type La_1−xCe_xMnO₃ (x = 0–10%) catalysts were prepared by flame spray pyrolysis and their activities during the catalytic oxidation of benzene were examined over the temperature range of 100–450 °C. The structural properties and reducibility of these materials were also characterized by X-ray diffraction (XRD), N₂ adsorption/desorption, H₂ temperature-programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The incorporation of Ce was found to improve the benzene oxidation activity, and the perovskite in which x was 0.1 exhibited the highest activity. Phase composition and surface elemental analyses indicated that non-stoichiometric compounds were present. The incorporation of Ce had a negligible effect on the specific surface area of the perovskites and hence this factor has little impact on the catalytic activity. Introduction of Ce⁴⁺ resulted in modification of the chemical states of both B-site ions and oxygen species and facilitated the reducibility of the perovskite. The surface Mn⁴⁺/Mn³⁺ ratio was increased as a result of Ce⁴⁺ substitution, while a decrease in the surface-adsorbed O/lattice O (O_ads/O_latt) ratio was observed. The relationship between the surface elemental ratios and catalytic activity was established to allow a better understanding of the process by which benzene is oxidized over perovskites.     

Effect of glycine–starch mixing ratio on the structural characteristics of MgAl2O4 nano-particles synthesized by sol–gel combustion

Sol–gel auto-ignition was used to prepare nano-scale magnesium aluminate spinel, using nitrate salts as an oxidizer and glycine–starch mixtures as the fuel. The glycine–starch mixture was varied to understand the effect of fuel mixing ratio on the structural characteristics of the resulting magnesium aluminate. The products were characterized by thermogravimetric-differential thermal analyses, Fourier-transform infrared spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller surface area measurements, and transmission electron microscopy. The phase purity and crystallite size of the powder products depended on the fuel mixing ratio. The presence of starch in the fuel facilitated the preparation of pure nano-particles. To prepare nano-particles of uniform spherical morphology and diameter of <13 nm, the starch content should be optimized to avoid agglomeration.     

Effect of calcining temperature and time on the characteristics of Sb-doped SnO2 nanoparticles synthesized by the sol–gel method

Spherical Sb-doped SnO₂ (ATO) nanoparticles were synthesized by the sol–gel route, employing SnCl₄·5H₂O and SbCl₃ as precursors in an ethanol solution. The influences of the calcining temperature and calcining time on the crystallite size, crystallinity, lattice parameters, lattice distortion ratio and the resistivity of the ATO nanoparticles were synthetically investigated. The results suggested that the ATO nanoparticles were crystallized in a tetragonal cassiterite structure of SnO₂ with a highly (1 1 0)-plane-preferred orientation. The calcining temperature had a dominating effect on the crystallite size, crystallinity, lattice distortion ratios and resistivity of the ATO. As the calcining temperature increased, the average crystallite size increased, the crystallinity was promoted accompanied by a decrease in the lattice distortion ratio and a corresponding decrease in the resistivity of the ATO. X-ray diffraction (XRD) and Fourier transform infrared spectrophotometer (FTIR) analysis revealed that Sb ions could not entirely supplant the Sn ions in the SnO₂ lattice for a calcining time of less than 0.5 h, even at a calcining temperature of 1000 °C. The ATO nanoparticles calcined at 1000 °C for 3.0 h possessed the lowest resistivity of 10.18 Ω cm.