Roles of bulk γ(L)-Bi2MoO6 and surface β-Bi2Mo2O9 in the selective catalytic oxidation of C3H6

γ(L)-Bi2MoO6 (L: low temperature phase) catalysts, whose surface compositions have a Mo/Bi ratio above = 0.5, exhibited high selectivity in the partial oxidation of C3H6, while catalysts with Mo/Bi surface ratios near or below = 0.5 exhibited low selectivity. γ(L)-phase catalysts which have Mo/Bi surface ratios greater than = 0.5, were demonstrated to form β-Bi2Mo2O9 on their surface. An interaction between the β- and γ(L)-phases was observed in these catalysts’ UV–vis spectra at 430 nm. The new β-phase material seems to grow along b-axis of γ(L)-phase, i.e., perpendicular to MoO2–Bi2O2 layers. Structure visualizations revealed that the α-Bi2Mo3O12, β-, and γ(H)-phases, which are selective catalysts, contain twin Mo tetrahedral structures, and that their Mo and Bi ions lie on the same plane. The pure γ(L)-phase does not contain this structure. A model for the very rapid transfer of oxygen between the γ(L)- and β-phases is discussed in relation to the kinetics of C3H6 oxidation.

Graphical abstract(1 0 1) plane of β-Bi2Mo2O9 formed on γ(L)-Bi2MoO6 seems to be active and selective sites for partial oxidation of C3H6. The acrolein formation from C3H6 takes place at β-phase sites and the incorporation of oxygen from gaseous O2 at the anion vacancies of γ(L)-phase. Bi (), Mo (), O ().Figure optionsDownload full-size imageDownload high-quality image (10 K)Download as PowerPoint slideFigure optionsDownload full-size imageDownload high-quality image (10 K)Download as PowerPoint slideFigure optionsDownload full-size imageDownload high-quality image (10 K)Download as PowerPoint slideFigure optionsDownload full-size imageDownload high-quality image (183 K)Download as PowerPoint slide