Sulfur Poisoning and Regeneration Behavior of Perovskite-Based NO Oxidation Catalysts

Abstract

SO x uptake and release properties of LaMnO 3 , Pd/LaMnO 3 , LaCoO 3 and Pd/LaCoO 3 perovskites were investigated via in situ Fourier transform infrared (FTIR) spectroscopy, temperature programmed desorption and X-ray photoelectron spectroscopy. Sulfation of the perovskite leads to the formation of surface sulfite/sulfate and bulk-like sulfate species. Pd addition to LaMnO 3 and LaCoO 3 significantly increases the sulfur adsorption capacity. Pd/LaMnO 3 sample accumulates significantly more sulfur than LaMnO 3 ; however it can also release a larger fraction of the accumulated SO x species in a reversible fashion at elevated temperatures in vacuum. This is not the case for Co-based materials, where thermal regeneration of bulk sulfates on poisoned LaCoO 3 and Pd/ LaCoO 3 is extremely ineffective under similar conditions. However, in the presence of an external reducing agent such as H 2 (g), Pd/LaMnO 3 requires much lower temperature (873 K) for complete sulfur regeneration as compared to that of Pd/LaCoO 3 (973 K). Sequential CO and SO x adsorption experiments performed via in situ FTIR indicate that in the presence of carbonyls and/or carbonates, Pd adsorption sites may have a stronger affinity for SO x as compared to that of the perovskite surface, particularly in the early stages of sulfur poisoning.

Effect of Particulate Matter Mineral Composition on Environmentally Persistent Free Radical (EPFR) Formation

“…There is a close relationship between EPFR and PCDD/F emissions as EPFRs are direct intermediates to PCDD/Fs in their surface mediated formation in the cool zone of incinerators. − Considering the mechanism of EPFR formation, where the organic precursor chemisorbs on the metal site, one can speculate that the presence of sulfur dioxide can result in the adsorption of SO 2 on the metal centers forming surface sulfate species. Indeed, SO 2 is a known catalytic poison for metal oxide catalysts by surface sulfidation. , …”

“…Indeed, SO 2 is a known catalytic poison for metal oxide catalysts by surface sulfidation. 44,45 To analyze the role of sulfur in EPFR suppression, XANES studies were performed at the S K-edge (Figure 3). The XANES spectra could not be analyzed by LCF due to the high disorder in the noncrystalline phase of the amorphous surrogates 46 which could not be represented by linear combinations of the available crystalline structure reference compounds.…”

Perovskites as Geo-inspired Oxygen Storage Materials for Chemical Looping and Three-Way Catalysis: A Perspective

“…For instance, Co- and Mn-containing perovskite catalysts exhibit high activity for CO/HC oxidation in a reducing environment and superior activity for the reduction of NO x in an oxidizing environment. , In addition to being standalone OSM/catalysts, perovskite oxides also show excellent performance in stabilizing PGMs (e.g., Pt, Pd, Rh, and Ru). The PGMs, in turn, can improve the resistance of perovskties to sulfur poisoning. ,,, Although perovskite-based OSMs have yet to be widely utilized in commercial TWCs, because of the relatively low sulfur resistance, difficulty for preparing structured catalysts, and the possible reactions with other components in the TWC converters, ,− their unique properties make them promising next-generation OSMs, which is a topic that is being actively investigated. Tables and summarize some of the most commonly investigated perovskite OSM/catalysts both without and with PGMs.…”

“…Under realistic conditions, La 1– x Sr x CoO 3 displayed higher NO-to-NO 2 conversions than a commercial Pt-based diesel oxidation (DOC) catalyst . Historical concerns about the stability of perovskite TWCs in SO 2 are generally related to Co-based perovskites, but both PGM-doped perovskite and the large design space of non-PGM-containing perovskite materials show promise in addressing this issue . With the promising performance, large design space, and evolving environmental challenges, perovskites offer excellent opportunities for future development of commercially viable TWCs/OSMs.…”