THE IMPACT OF AQUEOUS IMPREGNATION ON THE PROPERTIES OF PREREDUCED VSPRECALCINED CO SIO2/

One of the methods of preparing model supported metal catalysts for fu ndamental studies of promoter effects is by sequential impregnation of reduced catalysts. In general, such promotion has been found not to a lter the metal particle size distribution. However, the promotion proc ess itself may possibly result in chemical and/or structural modificat ions of certain catalysts. In order to better understand how the proce ss of promotion may itself modify a Co catalyst, the effect of water i mpregnation and drying at various temperatures (25-110 degrees C) of r educed 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 re duced completely only above 800 degrees C. Steady-state isotopic trans ient kinetic studies of ethane hydrogenolysis revealed that the surfac e concentration of reaction intermediates declined following water imp regnation, which suggests that the Co silicate/hydrosilicate formed wa s inactive. Aqueous impregnation and drying of calcined Co/SiO2, on th e other hand, did not appear to modify the catalyst in any significant way. (C) 1995 Academic Press, Inc.