INFLUENCE OF A REDUCTION PROCESS ON THE CATALYTIC PERFORMANCES OF BIXGD1-XVO4, CATALYSTS FOR THE HYDROGENATION OF CARBON-DIOXIDE

The activities for hydrogenation of carbon dioxide (syntheses of CO an d methane) of the catalysts Bi0.99Gd0.01VO4 and Bi0.50Gd0.50VO4 are co mpared at 543 K and at pressure: 2 x 10(5) Pa (after a reduction treat ment under hydrogen at four different temperatures TR and without any pre-treatment). It is shown that reduction treatment at temperatures l ower or equal to 573 K is an activation procedure leading to the decre ase of time needed to reach the steady state and to an increase of act ivities. With higher TR a decrease of the activities of the two cataly sts occurs. A spectroscopic study, carried out using XRD, IR and XPS, shows that the two samples present different behaviors during the redu ction procedure. The decrease of the catalytic performances of Bi0.99G d0.01VO4 is related to the absence of metallic Bi-0 and to the presenc e of surface hydroxyl groups. The decrease of the catalytic performanc es of Bi0.50Gd0.50VO4 is explained by the migration of Bi-0 toward the bulk or its surface agglomeration.