THE IMPACT OF AQUEOUS IMPREGNATION ON THE PROPERTIES OF PREREDUCED VS PRECALCINED CO/SIO2

One of the methods of preparing model supported metal catalysts for fundamental studies of promoter effects is by sequential impregnation of reduced catalysts. In general, such promotion has been found not to alter the metal particle size distribution. However, the promotion process itself may possibly result in chemical and/or structural modifications of certain catalysts. In order to better understand how the process of promotion may itself modify a Co catalyst, the effect of water impregnation and drying at various temperatures (25-110 degrees C) of reduced or calcined 20% Co/SiO2 was investigated. The results show that water impregnation and subsequent drying had a significant effect on the structure of the reduced and passivated Co catalysts. The Co oxide phase declined in favor of a Co silicate/hydrosilicate phase which reduced completely only above 800 degrees C. Steady-state isotopic transient kinetic studies of ethane hydrogenolysis revealed that the surface concentration of reaction intermediates declined following water impregnation, which suggests that the Co silicate/hydrosilicate formed was inactive. Aqueous impregnation and drying of calcined Co/SiO2, on the other hand, did not appear to modify the catalyst in any significant way. (C) 1995 Academic Press, Inc.