NICKEL-CATALYSTS FOR INTERNAL REFORMING IN MOLTEN-CARBONATE FUEL-CELLS

Natural gas may be used instead of hydrogen as fuel for the molten car bonate fuel cell (MCFC) by steam reforming the natural gas inside the MCFC, using a nickel catalyst (internal reforming). The severe conditi ons inside the MCFC, however, require that the catalyst has a very hig h stability. In order to find suitable types of nickel catalysts and t o obtain more knowledge about the deactivation mechanism(s) occurring during internal reforming, a series of nickel catalysts was prepared a nd subjected to stability tests at 973 K in an atmosphere containing s team and lithium and potassium hydroxide vapours. All the catalysts pr epared showed a significant growth of the nickel crystallites during t he test, especially one based on alpha-Al2O3 and a coprecipitated Ni/A l2O3 sample having a very high nickel content. However, this growth of nickel crystallites only partially explained the very strong deactiva tion observed in most cases. Only a coprecipitated nickel/alumina cata lyst with high alumina content and a deposition-precipitation catalyst showed satisfactory residual activities. Addition of magnesium or lan thanum oxide to a coprecipitated nickel/alumina catalyst decreased the stability. Adsorption and retention of the alkali was the most import ant factor determining the stability of a catalyst in an atmosphere co ntaining alkali hydroxides. This is because the catalyst bed may remai n active if a small part of the catalyst bed retains all the alkali.