| The art of modern technology and growing demand for durable and portable energy storage has turned batteries into an essential companion to most portable electronic devices. Rechargeable lithium ion battery is one of the most energy dense and lightest of all the competing battery types. LiMn2O 4 spinel is known as an active cathode material for lithium-ion batteries because of its low cost, abundant precursors, non-toxicity and environmental benignness. In addition, it shows good structural and chemical stability and high charge-discharge rate capability. Its charge storage capacity of 145 mAh/g is comparable to that of layered LixCoO2 oxide (140 mAh/g). Thus, LiMn2O4 is a preferable candidate for transportation applications in spite of its few minor shortcomings. The progress of LiMn2O4 by industry around the world has made it a leading candidate for vehicle applications such as in Chevy Volt. Recent developments in LiMn2O4-based cathodes for lithium ion batteries are centered at the preparation of thin films, substitution of a small fraction of manganese ions with other metal cations (e.g., Cr, Al, Co, etc.), and surface modifications. Our recent research project is focused on developing new synthetic approaches to cathode materials that can be used in the rechargeable lithium ion and, especially, thin film batteries. The first single-source molecular precursor for the lithium-manganese cathode material is reported. Heterometallic beta-diketonate LiMn2(thd) 5 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) has been obtained in high yield by simple one-step solid state redox reaction employing commercially available reagents. Substantial scale-up preparation of complex is feasible using a solution approach. The crystal structure of precursor contains discrete Li:Mn = 1:2 trinuclear molecules held together by bridging diketonate ligands. Complex is relatively stable in open air, highly volatile, and soluble in all common solvents. It was confirmed to retain its heterometallic structure in solutions of non-coordinating solvents. The heterometallic diketonate was shown to exhibit clean, low-temperature decomposition in air/oxygen that results in pure spinel-type oxide LiMn2O4.;The promotion of noble metal-based heterogeneous catalysts by heavy post-transition elements such as Bi, Pb, Sn, and Sb was known for a long time to play a crucial role in the improvement of their overall catalytic performances (activity, sometimes selectivity) and/or their lifetime in a wide series of selective liquid-phase oxidation reactions of functionalized organic substrates. The use of such catalysts in the oxidation of carbohydrates is particularly attractive, since these processes provide an environmentally friendly route to convert the renewable resources under mild conditions into many intermediate chemicals that are of primary importance for the synthesis of high added value chemicals in the food, cosmetic, and pharmaceutical industries. In particular, carbon supported Bi-Pd catalysts were successfully employed in the partial oxidation of alcohols and aldehydes to carboxylic acids using molecular oxygen or air. The selective and almost quantitative aqueous phase conversion of glucose to gluconic acid, of glyoxal to glyoxalic acid, and of propylene glycol to lactic and pyruvic acids has been actively investigated. Silica-supported Bi-Pd catalysts were also used for the synthesis of benzylacetate by oxyacetoxylation of toluene. We proposed to use Bi-Pd heterometallic compounds as single-source precursors for the synthesis of supported Bi-Pd catalysts. The heterometallic complex [Bi2Pd2(O2CCF3)10 (HO2CCF3)2] was obtained by the solid state reaction of BiIII trifluoroacetate/trifluoroacetic acid adduct with unsolvated trinuclear PdII trifluoroacetate. The crystal structure of precursor consists of discrete tetranuclear molecules, in which two paddlewheel [BiPd(O2CCF3)4] units are connected by two chelating-bridging trifluoroacetate ligands through bismuth ends. There are no metal-metal bonds in the tetrameric structure, since both Bi˙˙˙Pd (3.0843(4) A) and Bi˙˙˙Bi (4.5074(4) A) distances are too long to be considered as bonding interactions. A study of the solution behavior revealed that not only the coordinated trifluoroacetic acid in heterometallic complex can be effectively replaced by other donor solvent molecules, but also the tetranuclear core can be cleaved in solution into discrete dinuclear Bi-Pd species. The Bi-Pd complex was used as precursor for the preparation of a bimetallic Bi-Pd carbon-supported catalyst. The preparation procedure included the modification of the carbon support in order to increase the number of oxygenated functions at its surface followed by grafting heterometallic complex via ligand exchange for surface carboxylates, before activating thermally. The resulting catalyst, consisted of small supported metallic particles, was found to be more active than the reference materials prepared from multi-source homometallic Pd and Bi precursors. |
