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- Abdulhamid, Hussam, 1974, et al.
(författare)
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A combined transient in situ FTIR and flow reactor study of NOx storage and reduction over M/BaCO3/Al2O3 (M=Pt, Pd or Rh) catalysts
- 2006
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 244:2, s. 169-182
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Tidskriftsartikel (refereegranskat)abstract
- Transient in situ DRIFTS and flow-reactor experiments were performed to study the storage and reduction of NOX over Pt/BaCO3/Al2O3, Pd/BaCO3/Al2O3, and Rh/BaCO3/Al2O3 samples using CO, H-2, C3H6, or C3H8 as the reducing agent. The DRIFTS results show that exposure of the examined samples to NO2 results in the formation of nitrite/nitrate peaks over alumina and barium and that the reduction of stored NOX is influenced by the type of precious metal and reducing agent. Using CO as the reductant results in a lower NOX reduction capacity for Pt/BaCO3/Al2O3 compared with Pd- and Rh-based samples, whereas H-2 shows a significant ability to reduce the stored NOX on all samples examined. In addition, the reduction with CO and C3H6 proceeds via the formation of isocyanate species over both barium and alumina sites. The intensity of barium-isocyanate species for Pt/BaCO3/Al2O3 is significantly lower than the corresponding intensity for the Pd- and Rh-based samples, suggesting that the interaction between barium and Pt is lower than the corresponding interaction in the Pd/BaCO3/Al2O3 and Rh/BaCO3/Al2O3 samples. (c) 2006 Elsevier Inc. All rights reserved.
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| 2. |
- Abdulhamid, Hussam, 1974, et al.
(författare)
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In situ FTIR study of SO2 interaction with Pt/BaCO3/Al2O3 NOx storage catalysts under lean and rich conditions
- 2006
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 241:1, s. 200-210
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of SO2 with Pt/BaCO3/Al2O3 NOx storage catalysts under lean and rich conditions in the absence and presence of water was investigated by means of in situ FTIR spectroscopy at 350 degrees C. For the lean condition (SO2 + O-2), surface and bulk barium sulfates were formed in addition to sulfites and surface sulfates on alumina. Pt does not appear to play an essential role in the formation of these species under lean conditions. In contrast, under reducing conditions (SO2 + H-2), Pt catalysed the reduction of SO2 with H-2 to form reduced sulfur species that accumulate on both Pt and barium sites. A subsequent treatment with NO2 resulted in the reduction of NO2 in the oxidation of these sulfur-containing species to form bulk barium sulfate instead of being stored over barium sites. Introducing water significantly affected sulfur trapping over the catalyst surface. During the lean conditions, the presence of water resulted in almost no surface barium sulfate formation. Meanwhile, the formation of bulk barium sulfate was increased, probably due to enhanced sulfate formation. However, the presence of H2O under reducing conditions resulted in significantly lower sulfur storage on both barium and alumina in comparison with humid lean exposure conditions.
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| 3. |
- Abdulhamid, Hussam, 1974, et al.
(författare)
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The reduction phase in NOx storage catalysis: Effect of type of precious metal and reducing agent
- 2006
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 62:3-4, s. 319-328
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Tidskriftsartikel (refereegranskat)abstract
- The effect of different reducing agents (H2, CO, C3H6 and C3H8) on the reduction of stored NOx over PM/BaO/Al2O3 catalysts (PM = Pt, Pd or Rh) at 350, 250 and 150 °C was studied by the use of both NO2-TPD and transient reactor experiments. With the aim of comparing the different reducing agents and precious metals, constant molar reduction capacity was used during the reduction period for samples with the same molar amount of precious metal. The results reveal that H2 and CO have a relatively high NOx reduction efficiency compared to C3H6 and especially C3H8 that does not show any NOx reduction ability except at 350 °C over Pd/BaO/Al2O3. The type of precious metals affects the NOx storage-reduction properties, where the Pd/BaO/Al2O3 catalyst shows both a high storage and a high reduction ability. The Rh/BaO/Al2O3 catalyst shows a high reduction ability but a relatively low NOx storage capacity.
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| 7. |
- Carlsson, Per-Anders, 1972, et al.
(författare)
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Methane oxidation over Pt/Al2O3 and Pd/Al2O3 catalysts under transient conditions
- 2007
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Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 115:1-2, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- We communicate experimental results for the oxidation of methane by oxygen over alumina supported Pd and Pt monolith catalysts under transient conditions. Temperature programmed reaction (TPReaction) and reactant pulse-response (PR) experiments have been performed, using a continuous gas-flow reactor equipped with a downstream mass spectrometer for gas phase analysis. Special attention was paid to the influence of gas composition changes, i.e., O 2 and H 2 pulsing, respectively, on the methane conversion. For Pt/Al 2 O 3 oxygen pulsing can significantly increase the methane conversion which can be even further improved by pulsing hydrogen instead. Such transient effects are not observed for the Pd/Al 2 O 3 catalyst for which instead constantly lean conditions is beneficial. Our results suggest that under lean conditions Pd and Pt crystallites may undergo bulk- and partial (surface oxide formation) oxidation, respectively, which for Pd results in more active surfaces, while for Pt the activity is reduced. The latter seems to connect to a lowering of the ability to dissociate methane. © 2007 Springer Science+Business Media, LLC.
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