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

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