The relationship between the structural and catalytic properties of lithiated spinel manganese oxides was investigated by means of X-ray diffraction, Infrared and Xanes spectroscopies, thermogravimetric analysis, and by evaluating two catalytic oxidation tests, namely the carbon black combustion and the toluene conversion. Li-Mn-O catalysts were prepared from stoichiometric (Li2O + MnO2) mixtures, either by the classical high temperature ceramic method or by mechanochemistry. For both catalytic tests, some spectacular temperature reductions were measured as a function of grinding. A remarkable decrease of 210 °C (from 650 °C to 440 °C) in the carbon black combustion temperature was obtained when using mechanosynthesized Li-Mn-O spinel prepared from a mixture of Li2O and MnO2 ground for 3 hours, whereas a 100 % toluene conversion rate was achieved for a temperature lower than 200 °C for the 5 hours milled ceramic LiMn2O4 while the as-made ceramic was inactive. The enhancement of the performances (i.e. decrease in carbon black combustion temperature Tc and decrease in toluene conversion temperature T95%) is due both to an increase in grain boundaries and in specific BET surface area and to the nano-crystallite size nature of the material. Besides, the spinel stoichiometry (both in oxygen or in cations) reflected by the lattice parameter variation plays a significant role in the catalytic reaction mechanism.

The influence of grinding on the structure and catalytic performances of two families of oxides, namely the perovskite-type La0.8Sr0.2MnO3 +/- lambda and the spinel-type Li-Mn-O, was investigated. Ball-milling of the well-known La0.8Sr0.2MnO3 (+/- lambda) prepared either by a solid state reaction or by a sol-gel method led to (i) a decrease in carbon black combustion temperature of 100 degreesC (T-C = 540 degreesC and of 40 degreesC (TC = 505 degreesC for ceramic and sol-gel ground 5-h samples, respectively, and (ii) to faster kinetics and higher rates of toluene conversion. A greater enhancement of the catalytic performances was obtained by using mechanical milled lithiated manganese oxides that are reported as promising catalyst candidates for the first time. Li-Mn-O catalysts were synthesized by room temperature mechanochemistry of a stoichiometric mixture of Li2O and MnO2 using various milling times (0 < t(milling) < 15 h). The nonstoichiometry, large surface area and disorder nature of the ground samples were of great benefit regarding catalytic applications. A remarkable decrease in the carbon black combustion temperature of 200 degreesC (from 650 to 450 degreesC was obtained when using a mixture of Li2O and MnO2 ground for 3 or 4 h. This low Tc value favorably compares with the Tc of 500 degreesC of ceramic LiMn2O4, which shows, however, better catalytic performances than most of the perovskite-type oxides. The grinding proves to be efficient as well for volatile organic compounds (VOCs) combustion. The inactive ceramic LiMn2O4 exhibits a 100% toluene conversion rate for a temperature lower than 200 degreesC when ground 5 h. (C) 2002 Published by Elsevier Science B.V.

Li-Mn-O oxides were synthesized by mechanochemistry from a stoichiometric mixture of Li2O and MnO2 using various grinding times (0 < t(milling) < 15 h). X-ray diffraction patterns of the ground samples (t(milling) < 10h) exhibit the same features as LiMn2O4 spinel structure (SG: Fd3m) with, however, a slight discrepancy in the lattice parameter (a(cub)) suggesting a non-stoichiometry of the Li-Mn-O oxides. a(cub) increases with milling time to reach for 8 h of grinding a value of 8.24 Angstrom similar to stoichiometric LiMn2O4. As a matter of fact, after 8 h of milling, mechanosynthesized Li-Mn-O spinel-type oxide shows quasi-identical electrochemical performances as high temperature LiMn2O4 ground for 1 h. (C) 2001 Elsevier Science B.V. All rights reserved.

The effect of grinding on the catalytic properties of La0.8Sr0.2MnO3±λ powders prepared via a ceramic or sol–gel process was studied with respect to the carbon black combustion temperature (TC). For the ceramic process, a milling time of 5 h led to a decrease of 77°C in the TC (from 615 to 538°C) in relation with increasing BET surface area. Regarding the sol–gel process, the TC decreased from 535 to 505°C after 1 h of grinding. Nevertheless, upon further milling (10 h), the benefit of the grinding effect disappeared due to a continuous decrease in the BET surface area. Finally, grinding (when well controlled) enabled one to obtain ceramic powders showing performances as good as sol–gel materials (TC≈540°C).