Thermal Decomposition of Co-Doped Calcium Tartrate and Use of the Products for Catalytic Chemical Vapor Deposition Synthesis of Carbon Nanotubes.

Thermal decomposition of Co-doped calcium tartrate in an inert atmosphere or air was studied using thermogravimetric analysis and X-ray absorption fine structure (XAFS) spectroscopy. It was shown that the powder substance containing 4 at.% of cobalt completely decomposes within 650-730 °C, depending on the environment, and the formation of Co clusters does not proceed before 470 °C. The products of decomposition were characterized by transmission electron microscopy, XAFS, and X-ray photoelectron spectroscopy. Surfaceoxidized Co metal nanoparticles as large as ∼5.6 ( 1.2 nm were found to form in an inert atmosphere, while the annealing in air led to a wide distribution of diameters of the nanoparticles, with the largest nanoparticles (30-50 nm) mainly present as a Co3O4 phase. It was found that the former nanoparticles catalyze the growth of CNTs from alcohol while a reducing atmosphere is required for activation of the latter nanoparticles. We propose the scheme of formation of CaO-supported catalyst from Co-doped tartrate, depending on the thermal decomposition conditions

Exothermal effects in the thermal decomposition of [IrCl 6 ] 2− -containing salts with [M(NH 3 ) 5 Cl] 2+ cations: [M(NH 3 ) 5 Cl][IrCl 6 ] (M = Co, Cr, Ru, Rh, Ir)

International audienceCo, Cr, Ru, Rh, Ir, were proposed as single-source precursors for bimetallic alloys. Their thermal decomposition in inert and reductive atmosphere below 700°C results in the formation of nanostructured porous Ir0.5M0.5 alloys. Salts decompose with significant exothermal effect during the first stage of their thermal breakdown in inert atmosphere above 200°C. The exothermal effect gradually decreases in the series: [Co(NH3)5Cl][IrCl6] > [Cr(NH3)5Cl][IrCl6] > [Ru(NH3)5Cl][IrCl6] > [Rh(NH3)5Cl][IrCl6]; [Ir(NH3)5Cl][IrCl6] does not exhibit any thermal effects and decomposes at much higher temperatures. To shed light on their thermal decomposition and the nature of the exothermal effect, DSC-EGA, in situ and ex situ IR, Raman, XPS and XAFS studies were performed. A combination of complementary techniques suggests a simultaneous ligand exchange and a reduction of central atoms as key processes. In [Co(NH3)5Cl][IrCl6], Co(III) and Ir(IV) simultaneously oxidase coordinated ammonia, which can be detected as a significant exothermal effect and the presence of Co(II) and Ir(III) in the intermediate product. The appearance of Ir-N frequencies demonstrate a ligand exchange between cations and the [IrCl6] 2anion. Salts with Cr(III), Ru(III), and Rh(III) show much lower exothermal effect due to the stability of their oxidation states. Salts with Rh(III) and Ir(III) demonstrate high thermal stability and a low tendency for ligand exchange as well as decomposition with exothermic effect