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 bismuth depends on the nature of the precursor but not on the incorporation medium. Bismuth oxide obtained from bismuth citrate, bismuth nitrate and the complexes with ethylenediaminetetraacetic acid or nitrilotriacetic acid enhances catalytic activity, whereas pure Bi2O3 and bismuth acetate do not increase catalytic properties. The formation of the ternary phase, Bi2Sn2O7, during the degradation step or during the catalytic test, cannot be excluded although it has never been detected when the calcination temperature did not exceed 803 K. This pure phase displays a very low activity but the catalysts containing at the same time Bi2Sn2O7 and SnO2 show appreciable catalytic performances. The possible intrinsic catalytic influence of highly dispersed Bi2O3 in these catalysts is discussed. In addition, several hypotheses are put forward to explain the synergy between SnO2 and Bi2O3: (i) a remote control mechanism based on the cooperation between separate Bi2O3 and SnO2 phases;(ii) the generation, during the reaction, of a highly dispersed ternary Bi2Sn2O7phase which cannot be detected, and could either display important catalytic activity itself, or act synergetically with SnO2.