Hydrodechlorination of CCl2F2 (CFC-12) over silica-supported palladium-gold catalysts

Two series of well-mixed Pd-Au/SiO2 catalysts prepared by direct redox meth od were tested in the reaction of CCl2F2 (CFC-12) hydrodechlorination. A mo derate selectivity for CH2F2 exhibited by monometallic Pd/SiO2 (similar to 40%) is significantly increased, up to similar to 95%, with Au addition. Pr oper Pd-Au alloying is essential to obtain such a selectivity enhancement. Poorly mixed Pd-Au/SiO2 catalysts show the catalytic behaviour not very muc h different from that of Pd/SiO2, producing a lot of methane. Changes in th e apparent activation energy are also associated with the degree of Pd-Au a lloying. After reaction, the Pd/SiO2 and Pd-Au/SiO2 catalysts contain dissolved carb on. Hydrogen treatment of carbonized Pd-Au/SiO2 catalysts removes this carb on. XRD study of the regenerated samples shows no change in the structure a nd composition of Pd-Au phase, compared to freshly prereduced bimetallic ca talysts. (C) 2001 Elsevier Science B.V. All rights reserved.