Catalysts with Sub-Surface Active Layers Prepared by Co-Impregnation,

摘要

Catalyst supports containing a narrow band of active material,either on the surface ('egg shell'),in the center ('egg yolk'),or in between ('egg white'),can be beneficial for certain types of reactions,or for resisting poisoning. Egg white platinum distributions on alumina bead supports were successfully prepared by impregnation with chloroplatinic acid in the presence of competing citrate ions. Narrow (50micrometers) active bands were obtained provided the adsorbed platinum ions were immobilized by hydrazine vapour reduction prior to drying. The position of the sub-surface platinum layer was determined reproducibly by the citrate ion concentration,while the amount of platinum deposited increased with increasing concentration of the chloroplatinic acid. It is recommended that a mathematical model for the non-equilibrium impregnation process be constructed.