Predicting the effect of drying on supported coimpregnation catalysts

In this paper, a model was developed to describe the catalyst redistributio n that occurs during drying of a coimpregnation catalyst. The model takes i nto account convective flow, catalyst and coimpregnant diffusion, adsorptio n on the support, and transport in the gas phase. For low catalyst adsorpti on capacity and low initial coimpregnant concentrations, the system behaves in a manner similar to systems without a coimpregnant. At higher coimpregn ant concentration when the coimpregnant has the higher adsorption constant, the catalyst faces strong competition for adsorption sites at the external surface. It therefore migrates toward the center where free sites are avai lable. If the catalyst has the higher adsorption constant, it adsorbs prefe rentially at the surface, and the coimpregnant hinders the back-diffusion o f the catalyst. This can lead to rather sharp egg-shell profiles. Finally, we discuss how to develop a drying strategy that will lead to a desired cat alyst profile.