Novel hybrid perovskite catalysts for DE-NOx applications

Abstract

The main purpose of this study is to identify the nature of hybrid perovskites in the form of LaCoxMn1-xO3 (x=0.0-1.0) for catalytic De-NOx applications. Characteristic structure, thermal stability and NOx/SOx adsorption/release properties of perovskites were studied by XRD, BET, XPS, in-situ FTIR, ex-situ FTIR, TEM, BET, TPD and TPR. LaCo0.8Mn0.2 and LaCo0.7Mn0.3O3 were found to yield the highest NOx storage Capacity (NSC) among other investigated perovskites due to their optimized B-site composition. NOx and SOx adsorption experiments pointed out that B-site substitution did not have a significant alteration on adsorption geometries of corresponding adsorbates. NOx uptakes of the investigated perovskites were observed to be enhanced via H2 reduction as verified by IR results. Furthermore, N2 (28 a.m.u) release monitored by QMS during NOx TPD revealed direct N-O bond activation and complete reduction of NOx species under certain conditions. SOx adsorption and reduction experiments suggested that SOx reduction via H2 is more effective for Mn-enrich perovskites, since Co-enriched materials formed irreversible sulfate species. It was observed that adsorbed NOx species can be readily replaced by SOx species in the co-presence of NOx and SOx. It was also demonstrated that the oxygen-defect density and the surface oxygen concentration of hybrid perovskites can be modified by fine-tuning the substitution at the B-site. Based on ex-situ FTIR results, it was established that Co-O linkages could be gradually replaced with Mn-O linkages by increasing the Mn loading in the perovskite composition. Furthermore, specific surface areas (SSA) of hybrid perovskites were found to be enhanced by increasing the Mn loading. Current results suggest that hybrid perovskites are promising novel catalytic architectures for De-NOx applications due to their high NSC and versatile chemical structure which can be fine-tuned to enhance SOx tolerance, redox properties and thermal stability.