Synthesis and characterization of perovskite catalysts

Lanthanum-strontium transition metal based perovskites represent a technologically important class of materials. A new process based on spray-freezing/freeze drying for production of such perovskite powders is described. The process makes use of reactive aqueous slurries of lanthanum (or other rare earth metal) hydroxides and of metal nitrate solution as the starting material. Addition of the hydroxide slurry to the nitrate solution results in a partial precipitation of the transition metal which can further be adjusted with ammonia. The resulting well-homogenized suspension is spray-frozen, freeze-dried and calcined to form the perovskite phase. For several perovskites temperatures of 900 K are sufficient to produce nearly phase pure material consisting of soft agglomerates which are easily reduced to submicron particles. Examples of activity in methane and propane combustion and of thermal stability of nickel cobalt based perovskite catalysts prepared by the new method are presented. (C) 1999 Elsevier Science B.V. All rights reserved.