Effect of hydrothermal treatment temperature on the catalytic performance of single-crystalline La0.5Sr0.5MnO3−δ microcubes for the combustion of toluene

Perovskite-type oxide La0.5Sr0.5MnO3−δ catalysts were fabricated hydrothermally at 220, 240, 250 or 270 °C for 50 h (denoted as LSMO-220, LSMO-240, LSMO-250, and LSMO-270, respectively). We characterized the materials by a number of analytical techniques. It was found that the La0.5Sr0.5MnO3−δ samples are single-crystalline cubic perovskite-type oxides in the form of microcubes. The as-fabricated samples displayed various surface and bulk compositions that can be related to the discrepancy in treatment temperature. The surface Mn/(La + Sr + Mn) ratio and the initial H2 consumption rate at low-temperatures increase according to the sequence of LSMO-240 < LSMO-270 < LSMO-220 < LSMO-250. We observed that the surface Mn4+/Mn3+ ratio and catalytic performance of the materials follow a similar order. The temperature for 100% toluene conversion over LSMO-250 was 280 °C. The excellent performance of the materials can be related to (i) Mn surface enrichment, (ii) high Mn4+/Mn3+ ratio, (iii) oxygen nonstoichiometry, and (iv) single-crystalline structure of the catalysts.