REV.CHIM.(Bucharest)♦68♦No. 9 ♦2017 http://www.revistadechimie.ro 2039 Study of Co-Cr Mixed Oxides for Different Applications VASILE GEORGESCU 1 , GABRIEL VASILIEVICI 2 *, MIHAELA BOMBOS 2 , CASEN PANAITESCU 3 1 Ilie Murgulescu Institute of Physical Chemistry, Romanian Academy, Spl.Independentei 202, 77208 Bucharest, Romania 2 National Research Institute for Chemistry and Petrochemistry, ICECHIM, Spl. Independentei 202, 060021, Bucharest, Romania 3 Petroleum - Gas University of Ploiesti, 39 Calea Bucuresti, 100520, Ploiesti, Romania Mixture metal oxide system Co-Cr were prepared by decomposition of the precursor complexes obtained from a mixture Co-Cr nitrates with tartaric acid. The samples were subsequently submitted to chemical analysis, magnetic measurements, IR spectrometry, UV-Vis, thermal analysis, XRD, EXAFS and TPR. At 600 o C was identificated a solid solution of CoCr 2 O 4 with Co 3 O 4 . With Cu-CrK-edge EXAFS the local structure of samples calcinated of 420 o C and 600 o C was obtained. By theirs analysis was calculated: the lengths of M- O bounds, number of coordination (N), Debye-Waller factor (A 1 ) and x metallic cations fraction in tetrahedral structures (spinelic centers). The TPR measurements were emphasized the existence of two reduction cycles. Keywords : mixed oxides, spinelic compounds, thermoprogrammed reduction Mixed oxide materials are widely used as catalysts [1- 5], different composites [6-9], nanomaterials templated by egg-shell membranes [10], preparation of polyamides composite nanofibres [11], preparation of ceramic and inorganic fibres [12-15], mixed oxide materials for development of integrated gas sensors [16-20], composite type multi-component metal oxide-based sensors [21-24]. Transition metal oxides are widely used as catalysts for complete oxidation of CO from exhaust gases and of VOCs (volatile organic compounds). The catalytic oxidation is the most attractive way to eliminate VOCs at low concentration in industrial gaseous effluent. For practical applications, the catalyst should be supported on a structurated support to a treat large gas flows with low pressure drop. Several studies have investigated the catalytic oxidation as an alternative to the incineration process for the destruction of VOCs. The catalytic oxidation can be highly efficient for the total oxidation avoiding the formation of harmful byproducts. The catalytic reaction is an energy- efficient low cost process and can be carried out at much lower temperatures avoiding the formation of NOx. There have been numerous studies on the catalytic oxidation of several organic compounds using different materials based on transition metal oxides, bulky and supported, as catalysts [25-28]. This basic chemical equation of oxidation of organic molecule (HC) is: (1) The temperature needed for the catalytic oxidation process depends on the type of the organic compounds, space velocity (i.e. volumetric flow rate of gas per catalyst volume in given time) and concentration. Transition metal oxides have shown very good achievements with respect to NO reduction. Most of the reported catalysts require o high working temperature 673- 773 K, to get reasonably high NO reduction [29-32]. In the some works is presented simultaneous removal of VOCs and NOx by mixed oxides catalysts [33-36]. The aim of the present paper is to check a mixed oxides material with stability of structure, starting from complexes of Co-Cr with tartaric acid. Experimental part The precursor complexes were obtained by precipitation of Cu-Cr nitrates in aqueous solution with tartaric acid at p H 7, in a solution of ethanol and ammonium hydroxide 10% in a ratio 1:1. After precipitation, the resulted compound was dried in vacuum at 90 o C and calcined at 600 o C. The sample were subsequently submitted to chemical analysis, magnetic measurements, IR spectrometry, UV-VIS, thermal analysis, XRD, EXAFS and TPR. Magnetic measurements ESR was carried out with JEOL spectrometer and EPR with Varian spectrometer [29]. Thermal analysis were achieved with Setaram Set Sys DSC- TG/DTA Equipment and UV-Vis measurements with Perkin Elmer Lamda 35 spectrometer [29]. The structure and crystalline lens parameters of the samples were determined by EXAFS method with pHi QUANTERA SXM 2010 and XRD spectra were obtained with Rigaku last IV apparatus. The IR investigation was carried out in the spectral range 4000-400 cm -1 with M-80 Carl Zeiss Jena spectrometer. Thermoprogrammed reduction (TPR) measurements was carried out with CHEMBET 3000 apparatus by determining the hydrogen consumption from a flowing gas mixture of argon with 3% hydrogen. The gas flow rate was kept at 6 cm 3 s -1 . A linear heating program of temperature increasing was achieved in the range 20-500 o C. The samples were pretreated in flowing argon at 500 o C. After cooling them in flowing argon to room temperature, the carrier gas was switched to the mixture argon with 3% H 2 and baseline was stabilized; the system was then heated at 10 K/ min -1 to 500 o C while the hydrogen consumption from the carrier gas was recorded (curve HCR 1 , heating cycle record). The sample was kept at 500 o C until the baseline was stable and then cooled in argon to room temperature. After switching on the gas mixture and baseline stabilization, the heating program was again applied and the curve HCR 2 was recorded. Results and discussions The corroboration of the results concerning chemical analysis, magnetic measurements [29] and IR-spectra to the following formula for the precursor: [Cr Co 4 Ta 6 ] . 5H 2 O( where Ta is the tartaric anion). * email: gabi.vasilievici@gmail.com