Operando Identification of the Active Phase in Sr-Promoted Lanthanum Cobaltite Perovskite-Derived Catalysts for Ammonia Decomposition.

Abstract

Storing energy in molecular form, particularly hydrogen in carbon-free carriers such as ammonia, is considered a key strategy for future energy systems. The release of hydrogen via ammonia decomposition is a critical step in this context that requires scalable and economically viable catalysts. In this work, spray-flame synthesis (SFS) was employed to prepare La1- xSrxCoO3- δ (0≤ x ≤ 1) nanoparticles (≈ 10 nm), which serve as precursors for SrO-promoted Co/La2O3 catalysts prepared by exsolution. ESR, operando XRD, and ambient pressure photoelectron spectroscopy (APXPS) provide insights into dynamic interfacial restructuring of the catalysts under the harsh ammonia decomposition conditions. The catalysts contain 25 wt% Co and achieve a maximum hydrogen productivity of 108 mmo l H 2 ·gCo -1·min-1 at 500°C for the La0.75Sr0.25CoO3- δ-derived material. The coverage of La2O3 with SrO/Sr─OH species under reaction conditions inhibits the migration of La-based species, which block active Co sites in the absence of the promoter. An excess of Sr, however, promotes the growth of Co particles and reduces the exposed Co surface area. Beyond its structural role, operando APXPS reveals that SrO also influences reaction kinetics by facilitating NHx decomposition and weakening the binding strength of nitrogen, which is consistent with an electrostatic effect of SrO.