Browsing by Author "Olsson, L."

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Open Access
Chemical deactivation by phosphorous under lean hydrothermal conditions over Cu/BEA NH3-SCR catalysts
(Elsevier, 2014-04-05) Andonova, S.; Vovk, E.; Sjöblom, J.; Ozensoy, E.; Olsson, L.
To obtain a better understanding of the deactivation of SCR catalysts that may be encountered due to the presence of P-containing impurities in diesel exhausts, the effects induced by P over Cu/BEA NH3- SCR catalysts were studied as functions of the temperature of poisoning and P concentration in the feed. Cu/BEA catalysts with different Cu loadings (4 and 1.3 wt% Cu) were exposed to P by controlled evaporation of H3PO4 in the presence of 8% O2 and 5% H2O at 573 and 773K. The reaction studies were performed by NH3-storage/TPD, NH3/NO oxidation and standard NH3-SCR. In addition, a combination of several characterisation techniques (ICP–AES, BET surface area, pore size distribution, H2-TPR and XPS) was applied to provide useful information regarding the mechanism of P deactivation. Pore condensation of H3PO4 in combination with pore blocking was observed. However, the measured overall deactivation was found to occur mostly by chemical deactivation reducing the number of the active Cu species and hence deteriorating the redox properties of the Cu/BEA catalysts. The process of P accumulation on the surface preferentially occurs on the “over exchanged” Cu active sites with the formation of phosphate species. This is likely the reason for the more severe deactivation of the 4% Cu/BEA compared to 1.3% Cu/BEA. Further, the higher NOx reduction performance at 773K of the P-poisoned Cu/BEA catalysts was found to originate from the lower selectivity towards NH3 oxidation, which occurs predominately on the “over-exchanged” sites.
Open Access
Sulfur-tolerant BaO/ZrO2/TiO2/Al2O3 quaternary mixed oxides for deNOX catalysis
(Royal Society of Chemistry, 2017) Say, Z.; Mihai, O.; Tohumeken, M.; Ercan, K. E.; Olsson, L.; Ozensoy, E.
Advanced quaternary mixed oxide materials in the form of BaO/Al2O3/ZrO2/TiO2 functionalized with Pt active sites (i.e. Pt/BaO/AZT) were synthesized and structurally characterized via XRD and BET in comparison to a conventional Pt/20BaO/Al benchmark NSR/LNT catalyst. The interactions of these catalysts' surfaces with SOx and NOx gases were monitored via in situ FTIR and TPD. There exists a delicate trade-off between NOx storage capacity (NSC) and sulfur uptake/poisoning which is strongly governed by the BaO loading/ dispersion as well as the surface structure and acidity of the support material. Flow reactor measurements performed under realistic catalytic conditions show the high NOx activity for the Pt/20BaO/AZT catalyst at 573 K. After sulfur poisoning and subsequent regeneration at 773 and 973 K, Pt/20BaO/AZT surpassed the NOx catalytic performance at 573 K of all other investigated materials including the conventional Pt/ 20BaO/Al benchmark catalyst.
Open Access
Trade-off between NOx storage capacity and sulfur tolerance on Al2O3/ZrO2/TiO2–based DeNOx catalysts
(Elsevier, 2019) Say, Zafer; Mihai, O.; Kurt, Merve; Olsson, L.; Özensoy, Emrah
Al2O3/ZrO2/TiO2 (AZT) ternary mixed oxides functionalized with Pt and BaO were synthesized in powder and monolithic forms and were utilized in NOx Storage Reduction/Lean NOx Trap (NSR/LNT) catalysis as novel catalytic materials. Adsorption of NOx and SOx species and their interactions with the catalyst surfaces were systematically investigated via in-situ FTIR technique revealing different NOx coordination geometries governed by the presence and the loading of BaO in the powder catalyst formulation. While BaO-free Pt/AZT stored NOx as surface nitrates, BaO incorporation also led to the formation of bulk-like ionic nitrate species. NOx adsorption results obtained from the current Temperature Programmed Desorption (TPD) data indicated that NOx Storage Capacity (NSC) was enhanced due to BaO incorporation into the powder catalyst and NSC was found to increase in the following order: Pt/AZT < Pt/8BaO/AZT < Pt/20BaO/Al2O3 < Pt/20BaO/AZT. Increase in the NSC with increasing BaO loading was found to be at the expense of the formation of bulk-like sulfates after SOx exposures. These bulk-like sulfates were observed to require higher temperatures for complete regeneration with H2(g). Catalytic activity results at 473 K and 573 K obtained via flow reactor tests with monolithic catalysts suggested that Pt/AZT and Pt/8BaO/AZT catalysts with stronger surface acidity also revealed higher resistance against sulfur poisoning and superior SOx regeneration in spite of their relatively lower NSC. Monolithic Pt/ 20BaO/AZT catalyst revealed superior NSC with respect to the conventional Pt/20BaO/Al2O3 benchmark catalyst at 573 K after sulfur regeneration. On the other hand, this trend was reversed at high-temperatures (i.e. 673 K). Preliminary results were presented demonstrating the enhancement of the high-temperature NSC of AZTbased materials by exploiting multiple NOx-storage components where BaO functioned as the low/mid-temperature NOx-storage domain and K2O served as the high-temperature NOx storage domain. Enhancement in the high-temperature NOx-storage in the BaO-K2O multiple storage domain systems was attributed to the formation of additional thermally stable bulk-like nitrates upon K2O incorporation.