Cobalt nanoparticles prepared in faujasite zeolites by borohydride reduction
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Metallic cobalt nanoparticles have been prepared in the faujasite zeolite by the reduction of the Co2+-exchanged zeolite with sodium borchydride aqueous solutions. The influences of the temperature used for treating the Co2+-faujasite zeolite before reduction and the concentration of NaBH4 Solution on the degree of reduction and the size of cobalt particles have been investigated. Although the treatment of the Co2+-exchanged faujasite zeolite at a higher temperature before reduction leads to a lower degree of reduction, an appropriate treatment temperature is needed for obtaining cobalt nanoparticles with sizes less than 5 run. Cobalt particles with a maximum size distribution at 1-2 nm, which are probably located inside the supercages of faujasite zeolite, can be obtained by using a higher concentration of NaBH4 aqueous solution (10 M), while lower NaBH4 concentrations lead to the formation of larger cobalt particles (>10 nm) mainly located outside the cages of the zeolite. The smaller cobalt nanoparticles located inside the supercages of faujasite zeolite exhibit higher CO conversions in Fischer-Tropsch synthesis than the larger cobalt particles outside the supercages or the cobalt on the surface of non-porous silica. Unique product distributions are observed in the catalysis over the smaller cobalt nanoparticles in the supercages of faujasite zeolite. (c) 2005 Elsevier Inc. All rights reserved.
CitationMICROPOROUS AND MESOPOROUS MATERIALS，2005,86（1-3）：38-49