Abstract
The ability of Cl 2 to redisperse large palladium particles in NaY and HY is investigated. The mechanism of redispersion is significantly different from that reported for the Cl 2 induced redispersion of platinum in zeolites. It has been found that exposure of Pd/NaY and Pd/HY to a Cl 2 flow at 350°C leads to the formation of mobile PdCl 2, which, upon reduction at 350°C is converted to HCl and highly dispersed Pd particles in supercages. Thermal activation of the chlorinated Pd/NaY and Pd/HY leads to ion exchange of the PdCl 2 with zeolitic protons forming HCl and Pd 2+ ions in sodalite cages. Chlorination and reduction of physical mixtures of Pd with NaY and HY also produces highly dispersed Pd particles. The transport of Pd from the external surface to the interior of the Y zeolite is proposed to occur through vapor phase transport of volatile PdCl 2.
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