Hydrothermally fabricated single-crystalline strontium-substituted lanthanum manganite microcubes for the catalytic combustion of toluene

La_1-xSr_xMnO_3-δ (x = 0.4, 0.5, and 0.6) catalysts were fabricated hydrothermally from KMnO₄, MnCl₂ (KMnO₄/MnCl₂ molar ratio = 3/7), and stoichiometric amounts of lanthanum and strontium nitrates in KOH solution. The physicochemical properties of the materials were characterized by a number of analytical techniques. It was found that the La_1-xSr_xMnO_3-δ samples fabricated at 250 °C are single-crystalline perovskite-type oxides in the form of microcubes. The as-fabricated La_1-xSr_xMnO_3-δ materials display various states of oxygen nonstoichiometry. The total amount of oxygen vacancies and Mn⁴⁺ in the catalysts decreases in the order of La_0.5Sr_0.5MnO_3-δ > La_0.4Sr_0.6MnO_3-δ > La_0.6Sr_0.4MnO_3-δ. It has been found that the trends of catalyst reducibility and catalytic performance of the three catalysts follow a similar order. We observed 100% toluene conversion at 255 °C over the La_0.5Sr_0.5MnO_3-δ catalyst, 113 °C lower than that observed over a polycrystalline La_0.5Sr_0.5MnO_3-δ catalyst prepared by calcination at 950 °C. The excellent performance of the former can be related to the high Mn⁴⁺/Mn³⁺ ratio, distinct oxygen nonstoichiometry, and single-crystalline structure of the catalyst.