An ultrafast approach for the syntheses of defective nanosized lanthanide perovskites for catalytic toluene oxidation

Abstract

In this article, Sr²⁺ and/or Fe³⁺-doped LaMnO₃ perovskites were rapidly synthesized using supercritical water (sc-H₂O) in a continuous hydrothermal flow reactor. Nanosized perovskites (6–45 nm) with defective structures were obtained, which led to high surface areas (28–67 m² g⁻¹) and enriched defects. After being subjected to catalytic toluene oxidation, La_0.9Sr_0.1Mn_0.9Fe_0.1O₃ exhibited superior activity with T₅₀ (i.e., the temperature of 50% toluene conversion) at approximately 213 °C, T₉₀ (i.e., the temperature of 90% toluene conversion) at approximately 236 °C, and the reaction rate constant, k, at 1.47 mL g⁻¹ s⁻¹ (at 180 °C). Such activity was even comparable to that of some noble metal catalysts. H₂-TPR, O₂-TPD and ¹⁸O₂-TPSR analyses suggested that both the Langmuir–Hinshelwood and Mars–van Krevelen mechanisms are involved in such a toluene oxidation process, where the dissociation of gaseous oxygen (via the surface oxygen vacancies) and the diffusion of mobile lattice oxygen (to the catalyst surface) in the lanthanide perovskites played a crucial role in determining their toluene oxidation efficiencies. This explained why La_0.9Sr_0.1Mn_0.9Fe_0.1O₃ that has enriched surface oxygen vacancies and high lattice oxygen mobility (both originating from the structural distortion in sc-H₂O reaction) could yield a remarkable performance in catalytic toluene oxidation.