Fluorite phase La–M–O (M = Zr and Ce) composite oxides for oxidative dehydrogenation of ethane at low or high temperatures: redox sites vs. lattice oxygen

Abstract

La_0.5Zr_0.5O_1.75 (LZ) without redox sites and La_0.5Ce_0.5O_1.75 (LC) with redox sites, both possessing disordered defect fluorite phases, were successfully synthesized using a glycine nitrate combustion method. As oxidative dehydrogenation of ethane (ODHE) catalysts, LC and LZ exhibit good reaction performance at low and high temperatures, respectively. LC can achieve a C₂H₄ yield of 18.1% at 500 °C, while LZ can achieve a C₂H₄ yield of 39.4% at 700 °C. While both have intrinsic disordered oxygen vacancies, the Ce³⁺/Ce⁴⁺ oxygen storage cycle on the LC surface promotes oxygen mobility, thereby reducing the exchange temperature between gas-phase oxygen and binuclear reactive oxygen species O₂⁻ and O₂²⁻. The lattice oxygen of LZ is less active than that of LC, so it exhibits good high-temperature reaction performance. When designing and preparing A₂B₂O₇-type catalysts for ODHE, the presence of redox sites in the fluorite phase is beneficial for low-temperature reaction performance, while the less active lattice oxygen in the fluorite phase enhances high-temperature reaction performance.