Probing the reactivity and structure relationship of Ln2Sn2O7 (Ln=La, Pr, Sm and Y) pyrochlore catalysts for CO oxidation

To elucidate the structure and reactivity relationship of A(2)B(2)O(7) pyrochlore compounds, a series of Ln(2)Sn(2)O(7) catalysts (Ln = La, Pr, Sm and Y) with varied rare earth cation A sites but with a fixed Sn cation B site have been synthesized and probed by CO oxidation. It is revealed that all the samples are composed of cubic pyrochlore phases. By replacing the A site with different rare earth cations, the r(A)/r(B) ratios decrease in the sequence of La2Sn2O7, Pr2Sn2O7, Sm2Sn2O7, Y2Sn2O7, which transforms the crystalline structures of the samples from well-ordered to less-ordered pyrochlore phases. As a consequence, the mobility of the lattice oxygen related to the intrinsic 8a oxygen vacancies improved evidently, thus inducing the formation of more abundant surface mobile oxygen species. Therefore, the intrinsic and overall activity of Ln(2)Sn(2O)7 catalysts can be strengthened. Due to the least ordered structure and the presence of the largest amount of surface active oxygen species, Y2Sn2O7 displays the highest activity among all the catalysts in this study.