STUDY OF THE MIXED OXIDES BIXGD1-XVO4, CA TALYSTS FOR THE HYDROGENATION OF CARBON-DIOXIDE

The performances of catalysts belonging to the BixGd1-xVO4 are studied at two pressures (2 x 10(5) and 21 x 10(5) Pa) for the hydrogenation of CO2. They are catalysts active for the syntheses of CO and CH4. The study shows that the more active systems are mixed oxides (with high content of bismuth) which present a fergusonite-type monoclinic struct ure. A spectroscopic study, carried out using X.R.D, IR, E.S.R. and X. P.S., reveals that the most active systems are unstable in the conditi ons of the tests. In these conditions, they are mixtures of oxides whi ch contain mainly Bi3+, metallic bismuth, V2O3 and Gd2O3. The activiti es of the systems are correlated with the surface concentrations of bi smuth. It is proposed that bismuth is one component of the sites activ e for the catalytic synthesis of CO and of CH4. Literature data allow to state precisely the mechanisms which take a part in the hydrogenati on process and to propose the active sites which ton on the surface of the studied catalytic systems.