Catalytic Behavior in Internal Steam Reforming of Methane in SOFC Conditions over LaXSr2-XMnO4 Materials

CATALYTIC BEHAVIOR IN INTERNAL STEAM REFORMING OF METHANE IN SOFC CONDITIONS OVER La_XSr_2-XMnO₄ MATERIALS

Karen Silva¹, Sebastian Vecino^1*, Monica Sandoval¹, Patrick Gèlin², Paola Gauthier-Maradei¹, Gilles Gauthier¹

1: INTERFASE, Escuela de Ingeniería Química, Universidad Industrial de Santander, Carrera 27, Calle 9 Ciudadela Universitaria, Bucaramanga, COLOMBIA

2: Université Lyon 1, CNRS, UMR 5256, IRCELYON, Institut de recherches sur la catalyse et l’environnement de Lyon, 2 avenue Albert Einstein, F-69626 Villeurbanne, France.

*e-mail: jusevema13@hotmail.com

ABSTRACT

Nowadays, solid oxide fuel cells (SOFC) are one of the most attracting and interesting energy conversion devices. They can convert the chemical energy directly to electrical energy with high efficiency (>60%) and low environmental pollution, employing several types of fuels such as hydrogen, coal gas, natural gas (methane) or another hydrocarbons fuels. These electrochemical systems operate at high temperatures (600-1000°C) using oxygen from the air as oxidant, and hydrogen directly or by internal steam reforming (ISR) of some compounds present in the fuels to produce heat as well as water and electricity. The ISR is a highly endothermic process that takes place, catalytically, at the anode of the SOFC. However, during this process and employing state of art anode material Ni/YSZ, the hydrocarbons decompose into hydrogen and additionally in an undesired compound: solid carbon (coke). This coke tends to deposit on the anode surface causing a rapid deterioration of the cell due to the deactivation of catalytic activity and the inhibition of hydrogen diffusion into the anode to continue with the electrochemical reaction. In order to overcome this limitation, it is necessary to develop new anode materials that catalyse the ISR and reduce significantly the problem described above. According to literature, single-phase oxide materials have been studied with excellent results. In this work, La0.5Sr1.5MnO4 was studied as potential new anodic material for SOFC directly fed with methane, operating at high temperature and under water deficient conditions. The material was synthesized by Pechini method and characterized by XRD. Measurements of catalytic activity in steam reforming of methane were carried out using 40 mg of catalyst at 900°C during 40h in a U-shaped quartz reactor. Different methane/water ratios (0.66≤CH4/H2O≤10) were employed to determine kinetic parameters. Coke formation during catalytic testing was measured by temperature programmed oxidation (TPO). The catalytic activity was compared with a reference material CGO (Ce0.9Gd0.1O2-d). Finally, the material was characterized again by XRD to evidence any damage or changes in the catalyst structure. This catalyst was found very active (high hydrogen production 9000ppmv) and resistant to coke formation (<69µmol/gcat), close to CGO catalyst (13000 ppmv hydrogen and 50.2µmol/gcat). The materials present an excellent stability during the test run; no structural change was found after the reaction. The small increase in the lattice parameters was attributed to the manganese reduction during the catalytic reaction (Mn+4/Mn+3 to Mn+3/Mn+2).

Key Words: Solid oxide fuel cell, Internal steam reforming, Methane, Manganite, Energy.