Preparation of Coimpregnated Cu−Zn/SiO2Catalysts: Influence of the Drying Step on Metallic Particle Size and on Cu0−ZnIIInteractions

Abstract

Mixed copper−zinc catalysts supported on silica were prepared by incipient wetness impregnation of nitrate salt solution. The influence of the drying temperature on the properties of the final calcined and/or reduced material was investigated. It was shown that, as in the case of monometallic Cu or Zn systems, after a drying step performed at 25 °C, the nitrates are still present as an amorphous compound, whereas the drying step at 90 °C led to the formation of a poorly crystallized hydroxynitrate compound. From XRD and DTG measurements, it was concluded that the hydroxynitrate compound in the mixed systems is a copper−zinc hydroxynitrate [Cu2−xZnx(OH)3(NO3)] in which the two cations are closely associated. After reduction at 350 °C, a “memory effect” of the drying step was observed, and the intermediate formation of the mixed hydroxynitrate led to a better interdispersion of Cu0 and ZnII in the reduced material than when drying was performed at room temperature. This is attested by the higher selectivity...