ENHANCEMENT OF TOTAL OXIDATION OF ISOBUTENE ON BISMUTH-PROMOTED TIN OXIDE CATALYSTS

The influence of the incorporation mode of Bi2O3 to SnO2 on the total oxidation of isobutene has been investigated. The catalysts have been characterized by XRD and XPS. Although the pure oxides do not exhibit any individual catalytic activity, certain bimetallic systems display substantial catalytic properties. The observed promoting effect of bis muth depends on the nature of the precursor but not on the incorporati on medium. Bismuth oxide obtained from bismuth citrate, bismuth nitrat e and the complexes with ethylenediaminetetraacetic acid or nitrilotri acetic acid enhances catalytic activity, whereas pure Bi2O3 and bismut h acetate do not increase catalytic properties. The formation of the t ernary phase, Bi2Sn2O7, during the degradation step or during the cata lytic test, cannot be excluded although it has never been detected whe n the calcination temperature did not exceed 803 K. This pure phase di splays a very low activity but the catalysts containing at the same ti me Bi2Sn2O7 and SnO2 show appreciable catalytic performances. The poss ible intrinsic catalytic influence of highly dispersed Bi2O3 in these catalysts is discussed. In addition, several hypotheses are put forwar d to explain the synergy between SnO2 and Bi2O3: (i) a remote control mechanism based on the cooperation between separate Bi2O3 and SnO2 pha ses; (ii) the generation, during the reaction, of a highly dispersed t ernary Bi(2)Sn(2)O(7)phase which cannot be detected, and could either display important catalytic activity itself, or act synergetically wit h SnO2.