Jean-Paul Schoebrechts

Pd-Ag/SiO2 sol-gel catalysts designed for selective conversion of chlorinated alkanes into alkenes

Aerogel-like Pd-Ag/SiO 2 catalysts were prepared in a one-step sol–gel process by using Pd and Ag complexes containing an alkoxide moiety with ensuing ordinary drying under vacuum. Although they are trapped inside microporous silica particles which makes them sinter-proof, the resulting bimetallic particles are completely accessible. The formation of Pd-Ag alloy crystallites allows to obtain a very high selectivity in ethylene during hydrodechlorination of 1,2-dichloroethane to the detriment of ethane which is the main product when pure Pd is used.

Dispersed Pd-Ag alloys for selective production of olefins from chlorinated alkanes

A kinetic model is derived to describe experimental rates of selective hydrodechlorination of 1,2-dichlorethane into ethylene over a Pd-Ag/SiO 2 catalyst. The role of each metal in Pd-Ag alloy particles is examined. A mechanism is proposed in which ethylene is produced by dissociative adsorption of 1,2-dichloroethane on silver which is subsequently dechlorinated thanks to recombination of adsorbed chlorine atoms with hydrogen dissociatively adsorbed on palladium.

Deactivation mechanisms and regeneration of a bimetallic hydrodechlorination catalyst

The temporal evolution of the activity and selectivity of a 1.9%Pd-3.7%Ag/SiO 2 catalyst during selective hydrodechlorination of 1,2-dichloroethane into ethylene is examined. A comparison between the physico-chemical properties of the fresh catalyst and of the deactivated one suggests a deactivation mechanism by poisoning or coking of Ag sites at the surface of the active Pd−Ag particles. A regeneration treatment is proposed which allows to restore the initial properties of the fresh catalyst.