Otomotiv uygulamaları için platin içermeyen perovskit tabanlı oksidasyon katalizörleri

Textural properties, structural integrity and NOx/SOx adsorption/release properties of LaMnO3, Pd/LaMnO3, LaCoO3 and Pd/LaCoO3 type perovskites were studied via in-situ FTIR, ex-situ FTIR, TPD, XRD, XPS and N2 sorption. Adsorption geometries of NOx species on the synthesized samples were determined via in-situ FTIR, which revealed similar NOx adsorption types for all perovskites. The NOx adsorption capacity (NSC) of LaMnO3 is higher than that of LaCoO3, due to the higher specific surface area and the higher crystallization temperature of the Mn-based perovskite. In situ FTIR and TPD experiments showed that incorporation of Pd into the perovskite structure does neither have a significant influence on the type of adsorbed NOx species nor on the NSC. However, the surface structures of perovskites significantly change after reduction in H2 atmosphere, leading to drastic increase in the uptake of NOx. Although NOx adsorption behavior of LaCoO3 and Pd/LaCoO3 are quite similar, Pd has significant influence on preserving the structural integrity of Pd/LaCoO3 upon reduction with H2 at 623 K. Moreover, TPD measurements showed that complete reduction of surface nitrite/nitrate groups was observed for Co-based perovskites with the appearance of a N2 (28 a.m.u) signal. SOx adsorption/desorption behavior of LaMnO3, Pd/LaMnO3, LaCoO3, and Pd/LaCoO3, was also investigated via in-situ FTIR. Sulfation of the perovskite surfaces reveals the presence of surface sulfite/sulfate and bulk-like sulfate species. Pd incorporation into both LaMnO3 and LaCoO3 significantly increases the SOx storage on the surface. Investigation of the SOx release characteristics of LaMnO3 and Pd/LaMnO3 showed that although Pd-containing sample stores significantly more SOx, it can also release a large fraction of the adsorbed SOx species in a reversible fashion via thermal regeneration. However, this is not the case for Co-based materials. Sulfur poisoning is irreversible on both LaCoO3 and Pd/LaCoO3 with the formation of bulk sulfates where thermal regeneration is not effective. For investigating the reduction of sulfate/sulfite species and the regeneration of the sulfur-poisoned catalysts under reducing conditions, desulfation experiments were performed by utilizing H2. This set of experiments showed that although Pd-containing perovskites store more sulfur compared to Pd-free counterparts, they can be efficiently regenerated with H2 at significantly lower temperatures. Thus, these results suggest that Pd-promoted Mn-based perovskite systems are promising oxidation catalysts revealing high NOx oxidation capability, high NSC and enhanced sulfur tolerance. Keywords: Perovskite, NOx storage, LaMnO3, Pd/LaMnO3, LaCoO3, Pd/LaCoO3, SOx poisoning