| 1. |
- 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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Influence of the type of reducing agent (H2, CO, C3H6 and C3H8) on the reduction of stored NOX in a Pt/BaO/Al2O3 model catalyst
- 2004
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30-31:1-4, s. 161-168
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation, a comparative study for a NOx storage catalytic system was performed focusing on the parameters that affect the reduction by using different reductants (H2, CO, C3H6 and C3H8) and different temperatures (350, 250 and 150 degrees C), for a Pt/BaO/Al2O3 catalyst. Transient experiments show that H2 and CO are highly efficient reductants compared to C3H6 which is somewhat less efficient. H2 shows a significant reduction effect at relatively low temperature (150 degrees C) but with a low storage capacity. We find that C3H8 does not show any NOx reduction ability for NOx stored in Pt/BaO/Al2O3 at any of the temperatures. The formation of ammonia and nitrous oxide is also discussed.
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| 4. |
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| 5. |
- 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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| 6. |
- Acke, Filip, 1968, et al.
(författare)
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Comparison between ammonia and propene as the reducing agent in the selective catalytic reduction of NO under lean conditions over Pt black
- 1999
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 20:2, s. 133-144
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic activity of Pt black towards the reduction of NO under lean conditions is examined. Ammonia and propene are tested as reducing agents. A scrambling between nitrogens is observed in the formation of N2 and N2O for NH3. For C3H6, a reduction of NO to mainly N2O is found. A minor formation of N2 is only observed for high C3H6 concentrations. The role of NO2 as an intermediate in the reduction of NO is examined by using a feed gas mixture containing NO2, as well as by studying the catalytic activity of Pt black towards the NO-O2 and NO2-O2 reactions. No effect is observed in the maximum NOx conversion for C3H6 whereas for NH3 a decreased activity is found. The presented results are put in perspective of the reaction mechanisms proposed in the literature.
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| 7. |
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| 8. |
- Acke, Filip, 1968, et al.
(författare)
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Influence of the platinum-support interaction on the direct reduction of NOx under lean conditions
- 1998
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 116, s. 285-294
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Tidskriftsartikel (refereegranskat)abstract
- Catalysts containing Pt supported on SiC, Al2O3 and ZSM-5 were prepared and studied for NOx reduction by C3H6 in Oz excess under transient (temperature ramps) and steady-state conditions. The maximum NOx reduction activity in the heating ramp experiments was similar for Pt/SiC and Pt/ZSM-5, while Pt/Al2O3 showed higher maximum activity. Both N-2 and N2O formation was observed for all catalysts, although the respective amounts varied with the investigated system. Highest Nz selectivity was observed for Pt/Al2O3. When the NOx reduction activity was studied under steady-state conditions the activity of Pt/Al2O3 decreased substantially (mainly due to a loss in N-2 production). Pt/ZSM-5 became somewhat more selective towards Na production whereas the activity and selectivity of Pt/SiC remained at about the same values as far the heating ramp experiments. Adsorbed species on the surface of the different catalysts were investigated using in-situ FTIR in order to obtain information about the reaction mechanisms. The adsorption of species on Pt/SiC was negligible, while a number of absorption bands were observed for Pt/Al2O3 (N and C containing species, and -NCO) and Pt/ZSM-5 (HC).
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| 9. |
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| 10. |
- Acke, Filip, 1968, et al.
(författare)
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Role of adsorbed surface oxygen in the adsorption of NO on alkaline earth oxides and Pt-promoted CaO surfaces
- 1999
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Ingår i: Journal of Physical Chemistry B Materials. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 103:6, s. 972-978
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Tidskriftsartikel (refereegranskat)abstract
- Adsorbed surface oxygens are formed on CaO, SrO, and BaO during exposure to N2O, and their presence is shown to affect the room-temperature NO adsorption. Information about the adsorbed intermediates is contained in the desorption products and in the desorption temperatures during the subsequent heating ramp in Ar. The presence of adsorbed oxygen species increases the total amount of adsorbed NO for CaO and BaO substrates, whereas for SrO the adsorbed intermediate is stabilized. Two NO desorption peaks are found for CaO and SrO, one at low and one at high temperature. The former is assigned to adsorbed NO, whereas the latter is assigned to adsorbed -NO2 and/or -NO3 species. NO adsorption as -NO2 and/or -NO3 species finds evidence in the corresponding O2 desorption. Only one NO desorption peak is found for BaO. This NO desorption peak disappears in the absence of preadsorbed surface oxygens. O2 desorption is observed, even in the absence of any preadsorbed surface oxygens, for CaO and SrO substrates. This suggests NO bond dissociation upon NO adsorption. The effect of the promotion of CaO by Pt has also been investigated. The respective desorption profiles are similar to those for the unpromoted CaO with preadsorbed surface oxygens, although the amounts are significantly increased.
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