PARTIAL OXIDATION OF METHANE OVER POTASSIUM-CERIUM MOLTEN CARBONATES

1. G. Lopes, A. Ferreira, A. P. Gonçalves and J. B. Branco Instituto Tecnológico e Nuclear, Estrada Nacional 10, 2686-953 Sacavém, Portugal Unidade de Ciências Químicas e Radiofarmacêuticas Introduction and Objective The applications of molten salts have been well recognized for more than a century. In spite of the use of high temperature corrosive liquids, molten salts offer unique opportunities. Low temperature multi component molten salts, as well as room temperature ionic liquids have been developed for materials processing. Currently, molten salts are finding applications in fuel cell technology, in the field of separation processes of minor actinides from the rest of the fission products that are contained in the irradiated nuclear fuel, for the direct catalytic conversion of methane under mild conditions and the partial oxidation of methane to synthesis gas [1]. Here, we report the synthesis, characterization and behaviour for the partial oxidation of methane of potassium-cerium (K-Ce) molten carbonates. Experimental All experiments were carried out using an K2CO3-Li2CO3 (50:50 wt.%) eutectic mixture (T=600 ºC) as solvent and the cerium molten carbonates prepared by the addition to this mixture of an appropriate amounts of Ce2(CO3)3 (5 and 15 wt.%). The molten salts were characterized by Differential Scanning Calorimetry (PAC-ATD ADI prototype, DSC recorded under argon-50 mL/min, 20 oC (hold 15 min) until 1000 oC at a 10 oC/ min heating rate), X-Ray Powder Diffraction (XRD, reflection geometry with a PANalitycalX’Pert Pro diffractometer using Cu, ka monochromatic radiation l=1.5406 Å), Infrared Spectroscopy (IR, recorded on a Bruker spectrometer with samples mounted as Nujol mulls) as well as Elemental Analysis (C,H,N, S and O, performed on a CE instrument EA1110 automatic analyzer). PARTIAL OXIDATION OF METHANE OVER POTASSIUM-CERIUM MOLTEN CARBONATES Catalysts Characterization DSC tests before catalytic test XRD patterns for the molten salts • XRD tests were performed before and after the catalytic tests. • The melting of the salts leads to the CeO2formation. Phase diagram for the eutectic mixture • Melting temperatures between 484 ºC and 506 ºC; • The addition and increase of cerium % decreases the transition temperature IR results for the molten salts DSC tests after catalytic test • New features are not seen before and after the catalytic reaction. • Slight contraction of the CeO2 lattice is observed. • Characteristic bands of CO3. Catalytic Results The study of the Gas Hourly Space Velocity (GHSV, mL of CH4 / g of catalyst. h) and CH4 / O2 molar ratio was undertaken. The outlet gas composition was analyzed on-line by gas chromatography (GC) with a thermal conductivity detector (TCD). Catalyst activity was defined as the number of mL of methane converted per g of catalyst and per hour (mLCH4/g.h), m≈25 g. • New features are not seen before and after the catalytic reaction. • Slight contraction of the CeO2 lattice is observed. Effect of GHSV at CH4/O2 molar ratio = 2 Effect of CH4/O2 molar ratio at GHSV= 8520 Selectivity results for GHSV = 2863 and CH4/O2 molar ratio = 2 • Lower GHSV and CH4/O2 molar ratio influences the catalyst • activity. CO2 is the only product of the reaction. • Conversion of methane increases with the increase • of the cerium amount. • Molten carbonate with 15% Ce is the only that • shows selectivities to hydrocarbons References Acknowledgements [1] a) B. Mishraet al., Journal of Physics and Chemistry of Solids, 2005, 66, 396; b) T.R. Griffiths et al., Journal of Alloys and Compounds, 2006, 418, 116; c) J.J.Peng, et al., Applied Catalysis A: General, 2000, 201, L55; d) Y.G. Wei, et al., Journal of Natural Gas Chemistry, 2007, 16, 6. This work was supported by FCT, under contract number PTDC/QUI/72290/2006