| 1. |
- 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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| 2. |
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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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
-
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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| 6. |
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| 7. |
- 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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| 8. |
- 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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| 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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| 11. |
- Acke, Filip, 1968, et al.
(författare)
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Selective reduction of NO by HNCO over Pt promoted Al2O3
- 1998
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 179:2, s. 528-536
-
Tidskriftsartikel (refereegranskat)abstract
- The activity of Pt supported on gamma-Al2O3 towards HNCO oxidation and reduction of NO by HNCO under oxygen excess is examined under transient conditions (temperature ramps between 100 and 500 degrees C). Formation of N-2, N2O, NO, and NO2 is observed. Isotope labelled (NO)-N-15 is used to show the scrambling of nitrogens in N-2 ((NN)-N-14-N-15) and N2O ((NNO)-N-14-N-15). Adsorbed species on the surface are characterised by in-situ FTIR spectroscopy in order to obtain information on reaction intermediates. Adsorbed NNx species are discussed as important intermediates in the N-2 and N2O formation. The absence of Pt results in a delay in HNCO ignition and only a small N2O formation is observed.
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| 12. |
- Acke, Filip, 1968, et al.
(författare)
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Zeolite supported Pt catalysts for reduction of NO under oxygen excess: a comparison of C3H6, HNCO and NH3 as reducing agents
- 1999
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 20:3, s. 235-242
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the zeolite SiO2/Al2O3 ratio of ZSM-5 supported Pt catalysts on the reduction of NO under oxygen excess has been investigated. The activity and selectivity of three reducing agents were compared, i.e. C3H6, HNCO and NH3. The maximum NO reduction with both C3H6 and HNCO as the reducing agent was affected by the SiO2/Al2O3 ratio of the support. Although no effect was observed on the maximum NO reduction for NH3, the yields of Nz and N2O were affected. The results are put in perspective of reaction mechanisms proposed in the literature.
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| 13. |
- Adams, Emma, 1989, et al.
(författare)
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Ammonia formation from nitric oxide over Pd-based catalysts in multicomponent feed gas compositions
- 2017
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Ingår i: Catalysis Communications. - : Elsevier BV. - 1566-7367. ; 95, s. 26-30
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Tidskriftsartikel (refereegranskat)abstract
- Using multicomponent gas feeds, the formation of ammonia from nitric oxide over Pd/Al2O3 and Pd/Ce/Al2O3 model catalysts was compared to that of a commercially-available three-way catalyst. Steady- state oxygen-sweep experiments show that the highest activity for ammonia formation is obtained over the Pd/Ce/Al2O3 catalyst whilst the lowest activity is observed for the three-way catalyst. The latter is consid- ered to be linked to the incorporation of rhodium, a component that promotes the NOx reduction selectivity towards N2. Also, lean/rich cycling experiments were carried out to simulate the cycling conditions that passive-SCR after treatment systems depend upon. High activity is again seen over the Pd/Ce/Al2O3 cata- lyst during short periodic switches. For the three-way catalyst, longer periodic switches are required for the onset of ammonia formation due to the high oxygen storage capacity of this sample as compared to the other two. Hence, a future direction of investigation could be to develop materials with equivalent water- gas shift properties of ceria, but with reduced oxygen storage capacity so as to provide hydrogen for reaction without incurring a significant delay in ammonia formation.
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| 14. |
- Adams, Emma, 1989, et al.
(författare)
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Ammonia formation over Pd/Al2O3 modified with cerium and barium
- 2016
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 267, s. 210-216
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Tidskriftsartikel (refereegranskat)abstract
- We report experimental results for ammonia formation from nitric oxide and either a direct source of hydrogen or from a mixture of carbon monoxide and water over palladium based catalysts. Specifically, the addition of barium or cerium into an alumina supported palladium sample was studied. Static and transient flow reactor experiments were performed in order to identify the effects of temperature and the presence of oxygen on the activity for ammonia formation. Modification of Pd/Al2O3 with cerium proved to be beneficial for the activity due mainly to its enhancement of the water-gas-shift reaction, thus providing a higher availability of hydrogen for ammonia formation, but also because it remains active in the presence of slightly oxidizing global conditions when hydrogen is provided directly to the feed. Although the modification of Pd/Al2O3 with barium did not affect the ammonia formation during static conditions, the activity during lean/rich cycling increased. This is important for applications of passive selective catalytic reduction.
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| 15. |
- Adams, Emma, 1989, et al.
(författare)
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Ammonia formation over supported platinum and palladium catalysts
- 2015
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 165, s. 10-19
-
Tidskriftsartikel (refereegranskat)abstract
- We report experimental results for the formation of ammonia from nitric oxide and hydrogen, and from nitric oxide, water and carbon monoxide over silica, alumina and titania supported platinum and palladium catalysts. Temperature programmed reaction experiments in gas flow reactor show a considerable formation of ammonia in the temperature range 200-450 C, which is suppressed by the presence of excess oxygen. However, oxygen sweep experiments show that for the titania supported catalysts minor amounts of oxygen promotes the ammonia formation at low temperatures. In situ DRIFT spectroscopy measurements indicate that cyanate species on the support play an important role in the ammonia formation mechanism. This work shows that aluminasupported palladium is a promising system for passive selective catalytic reduction applications, exhibiting low-temperature activity during the water-gas-shift assisted ammonia formation reaction. Conversely, titania supported samples are less active for ammonia formation as a result of the poor thermal stability of the titania support.
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| 16. |
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| 17. |
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| 18. |
- Adams, Emma, 1989, et al.
(författare)
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Passive SCR: The effect of H2 to NO ratio on the formation of NH3 over alumina supported platinum and palladium catalysts
- 2016
-
Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 59:10-12, s. 970-975
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the relationship between the H2:NO ratio and NH3 formation over alumina supported Pt and Pd catalysts. By kinetic studies and in situ infrared spectroscopy, we report that NH3 formation is not only sensitive to the catalyst formulation but equally dependent on the feed gas composition and tem- perature. Specifically, we identify that hydrogen plays an important role in the dissociation of NO at low tem- perature. We also show that the support material itself plays a vital role in the ammonia formation mechanism due to the redox behaviour of NO adsorption at low temperature. This was unexpected as the noble metal is generally considered to be the active phase for the reaction of NO and H2.
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| 19. |
- Adams, Emma, 1989, et al.
(författare)
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Structure-function relationship for alumina supported platinum during formation of ammonia from nitrogen oxide and hydrogen in presence of oxygen
- 2016
-
Ingår i: Physical Chemistry Chemical Physics. - 1463-9084 .- 1463-9076. ; 18:16, s. 10850-10855
-
Tidskriftsartikel (refereegranskat)abstract
- We study the structure-function relationship of alumina supported platinum during forma- tion of ammonia from nitrogen oxide and dihydrogen by employing in situ X-ray absorption and Fourier transformed infrared spectroscopy. Particular focus is directed towards the effect of increased levels of oxygen on the reaction as a model system for emerging technologies for passive selective catalytic reduction of nitrogen oxides. The suppressed formation of ammo- nia observed as the feed becomes net-oxidizing is accompanied by a considerable increase in the oxidation state of platinum as well as enhanced formation of surface nitrates and loss of NH-containing surface species. In the presence of (excess) oxygen, the ammonia formation is proposed to be limited by the weak interaction between nitrogen oxide and the oxidized platinum surface. This leads to slow dissociation rate of nitrogen oxide and thus low abun- dance of atomic nitrogen surface species that can react with adsorbed hydrogen atoms. In this case the consumption of hydrogen through the competing water formation reaction and decomposition/oxidation of ammonia are of less importance for the net ammonia formation.
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| 20. |
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| 21. |
- Adams, Emma, 1989, et al.
(författare)
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The chemistry of the palladium phase in Pd/Ce/Al2O3 during ammonia formation
- 2016
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The formation of NH3 from NO is a crucial reaction for passive-selective catalytic reduction applications. In this application, an in situ supply of NH3 is formed in oxygen-lean conditions, which can subsequently be used to reduce NO to N2 in the presence of excess O2 [1]. On the fundamental level, producing NH3 from NO through heterogeneous catalytic processes involves fascinating surface chemistry that is not yet well understood. In the presence of stoichiometric and excess oxygen concentrations, NH3 formation is suppressed. However, we have previously shown that Pd/Ce/Al2O3 is a promising formulation, able to temporarily facilitate the formation of ammonia under globally slightly-oxidizing but locally rich conditions [2].This work uses in situ X-ray absorption spectroscopy (XAS) to identify how the oxidation state of the catalytically active phase is affected during transient pulses of O2 in the presence of either pure NO or a combination of NO, CO and H2.
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| 22. |
- Adams, Emma, 1989, et al.
(författare)
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Water–gas-shift assisted ammonia formation over Pd/Ce/alumina
- 2018
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 307, s. 169-174
-
Tidskriftsartikel (refereegranskat)abstract
- We report experimental results for the water–gas-shift assisted formation of ammonia from nitric oxide over alumina supported palladium, modified with various amounts (0–38 wt.%) of cerium. Static and transient flow reactor experiments were performed in order to identify the effects of temperature and the presence of oxygen on the activity for ammonia formation over the catalysts. The water–gas-shift reaction is enhanced with increasing cerium content, thus providing more hydrogen for ammonia formation. During transient operation at temperatures above 350 °C, a slight delay in ammonia formation is observed over the sample containing the highest cerium loading due to its (relatively) high dynamic oxygen storage capacity. At temperatures below 175 °C, N2O formation is preferred over NH3 formation. This work highlights the importance of balancing the effects that ceria influences when choosing the ceria loading for ammonia formation in passive-SCR applications.
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| 23. |
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| 24. |
- Amberntsson, Annika, 1974, et al.
(författare)
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Influence of platinum and rhodium composition on the NOx storage and sulphur tolerance of a barium based NOx storage catalyst
- 2003
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 46:3, s. 429-439
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Tidskriftsartikel (refereegranskat)abstract
- In the present work the influence of the type of noble metals present in barium oxide based NOx storage catalysts was investigated, regarding the NOx storage performance, NO oxidation, NO reduction, sulphur deactivation and sulphur regenerability. Monolith samples with combinations of platinum and rhodium, were prepared, tested in a flow-reactor, and characterised by XPS measurements. The flow-reactor experiments simulated NOx storage and reduction cycles at 400 degrees C in synthetic gas mixtures with oxygen, propene and nitric oxide. For the sulphur deactivation and regenerability investigations 25 ppm (v/v) SO2 was added to the feed gas stream. From the experiments, it was concluded that a combination of platinum and rhodium is required to achieve good NOx storage and reduction performance. The NOx storage capacity was, however, found higher for catalysts containing only platinum compared to catalysts including rhodium. When exposed to SO2 the NOx storage capacity also seemed to deactivate faster for the samples containing rhodium than for samples with platinum as the sole noble metal. Additionally, it was observed that platinum gives high NO oxidation activity during the lean periods both with and without SO2 present in the gas feed. During the rich periods, rhodium showed high activity for NO reduction in sulphur free gas feed as well as in the presence of SO2. Finally, the results implied that to provide good sulphur regeneration ability of the NOx storage catalyst, a combination of platinum and rhodium is necessary.
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| 25. |
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| 26. |
- Amberntsson, Annika, 1974, et al.
(författare)
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Investigations of sulphur deactivation of NOx storage catalysts: influence of sulphur carrier and exposure conditions
- 2002
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Ingår i: Catalysis Today. - 0920-5861. ; 73:3-4, s. 279-286
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Tidskriftsartikel (refereegranskat)abstract
- The influence of SO2, H2S and COS in low concentrations on the deactivation of PURh/BaO/Al2O3 NOx storage catalysts was investigated. Different samples of the catalyst were exposed to synthetic gas mixtures mimicking lean/rich engine cycling in a mixed lean application at 400degreesC. The lean gas mixture contained 8 vol.% O2, 500 vol-ppm C3H6 and 400 vol-ppm NO balanced to 100 vol.% with Ar. The rich excursions were performed by switching off the oxygen supply. Sulphur, 25 vol-ppm of either SO2, H2S or COS, was added to the gas flow either during the lean, the rich or both periods. This procedure aimed at investigating the influence of the exposure conditions and therefore the lean and rich periods were kept equally long (5 min). In addition, thermodynamical calculations for the prevailing conditions were performed.
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| 27. |
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| 28. |
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| 29. |
- Amberntsson, Annika, 1974, et al.
(författare)
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Sulphur deactivation of NOx storage catalysts; Influence exposure conditions and noble metal
- 2003
-
Ingår i: Journal of Catalysis. - 0021-9517 .- 1090-2694. ; 217:2, s. 253-263
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, barium-based NOx, storage catalysts containing platinum, rhodium, or both noble metals were investigated. The influence of SO2 exposure conditions on the performance of NOx storage catalysts was studied using flow reactor measurements, FTIR, and XPS where the samples were exposed to lean and/or rich SO2-containing gas mixtures, simulating the conditions in a mixed lean application. The main results show that all samples are sensitive to sulfur and that deactivation is faster when SO2 is present in the feed under rich conditions than under lean or continuous SO2 exposure. It was also found that SO2 affects the performance of noble metals strongly and that noble metal deactivation most likely occurs during the rich period of a NOx storage cycle. Additionally, the influence of the noble metals present in the catalysts was investigated with respect to sulfur sensitivity and it was found that a combination of platinum and rhodium seems to be preferable for retaining high performance (high NO oxidation and reduction activity) of the catalyst under SO2 exposure and subsequent regeneration.
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| 30. |
- Amberntsson, Annika, 1974, et al.
(författare)
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Sulphur dioxide deactivation of NOx storage catalysts
- 1999
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 126, s. 317-324
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Tidskriftsartikel (refereegranskat)abstract
- The influence of sulphur dioxide on the NOx storage performance of a Pt-Rh/BaO/Al2O3 model catalyst has been investigated. Addition of 2.5-25 vol.-ppm SO2 to a synthetic lean-burn exhaust, containing NO, C3H6, O2 and Ar, caused deactivation of the NOx storage function of the catalyst. The rate of deactivation was found to be proportional to the exposure of SO2. This effect is seen for temperatures between 250 and 450 degrees C. Together with in situ FTIR measurements, this leads to the conclusion that sulphur accumulates in the NOx storage component of the catalyst during the exposure. Furthermore, SO2 also inhibits the oxidation capacity of the catalyst during lean periods as is observed by a decreased NO oxidation activity. The presence of SO2 also reduces the reduction capacity of the catalyst under rich periods, which leads to an increased N2O formation and a decreased NO conversion.
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| 31. |
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| 32. |
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| 33. |
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| 34. |
- Arnby, Karl, 1974, et al.
(författare)
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Characterization of Pt/γ-Al2O3 catalysts deactivated by hexamethyldisiloxane
- 2004
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 54:1, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- The deactivation of alumina supported platinum and iron catalysts by hexamethyldisiloxane (HMDS) exposure has been investigated. Three catalysts (Pt/Al2O3, Fe/Al2O3 and Fe/Pt/Al2O3) were prepared and the influence of short- and long-term deactivation on the activity for oxidation of ethyl acetate was studied. The catalysts were characterized using BET, ICP-AES, XPS, SEM and CO chemisorption. The deactivation was found to proceed by deposition of silicon-species in form of silicate (SixOy) that block the active sites on the surface of the catalysts. The silicon seems to rather attach to platinum and iron sites than to the alumina surface. The Pt/Al2O3 catalyst was moderately deactivated by HMDS even though the silicate was blocking almost the entire platinum surface. Adding iron to the catalyst increased the tolerance towards HMDS as fewer Pt sites were blocked for the Fe/Pt/Al2O3 sample. The deactivation of the two platinum containing samples was reversible since the silicate could partly be removed from the Pt sites by regeneration whereby most of the activity was restored. However, for the Fe/Al2O3 sample the deactivation was more severe and irreversible.
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| 35. |
- Arnby, Karl, 1974, et al.
(författare)
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Influence of ammonia on CO and methanol oxidation over Pt/γ-Al2O3 catalysts modified by Mg
- 2004
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 49:1, s. 51-59
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the effect of modifying Pt/γ-Al2O3 catalysts with magnesium on the oxidation of methanol and carbon monoxide in presence of ammonia. The purpose for adding magnesium to the catalysts was to enhance the low-temperature activity and to make catalysts more resistant towards ammonia inhibition. The catalysts were prepared by wet-impregnation using platinum nitrate and magnesium nitrate solutions. The platinum content was constant for all catalysts, while the magnesium content ranged from 0 to 5 wt.%. The catalysts were characterized by CO chemisorption, AAS, XRD, XPS and BET. The addition of magnesium resulted in the formation of both MgAl2O4 spinel and MgO, and did slightly improve the low-temperature activity for carbon monoxide oxidation, while the activity for methanol oxidation decreased compared to an unpromoted Pt/γ-Al2O3 catalyst. The inhibition by ammonia for carbon monoxide oxidation was low for all catalysts, while the methanol oxidation was substantially inhibited by ammonia. Adding magnesium to Pt/γ-Al2O3 catalysts did not make the catalysts more resistant to ammonia inhibition.
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| 36. |
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| 37. |
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| 38. |
- Arnby, Karl, 1974, et al.
(författare)
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Investigation of Pt/γ-Al2O3 catalysts with locally high Pt concentrations for oxidation of CO at low temperatures
- 2004
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 221:1, s. 252-261
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Tidskriftsartikel (refereegranskat)abstract
- A new method for preparing supported catalysts, in which Pt was distributed in locally high concentrations on the γ-Al2O3 support, was studied. These catalysts were compared with a conventionally prepared Pt/γ-Al2O3 catalyst in which Pt was deposited evenly on the support. The object was to ascertain whether it is possible to prepare catalysts that retain heat released from exothermic reactions to a higher extent and thereby become more low-temperature active than a conventionally prepared catalyst. A significant improvement of the activity was observed for the catalysts prepared with locally high Pt concentrations when CO (1%, 1000 and 100 ppm) was oxidized at a constant O2 concentration (10%). The improved activity is discussed in terms of heat transfer, mass transfer, and structure sensitivity. Differences in heat transfer appear to be the least probable reason for the enhanced activity for the catalysts with locally higher Pt concentrations, whereas structural effects also seem to be an unlikely explanation. Differences in mass transfer seem, however, to be a more likely reason for the improved activity.
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| 39. |
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| 40. |
- Arnby, Karl, 1974, et al.
(författare)
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The effect of platinum distribution in monolithic catalysts on the oxidation of CO and hydrocarbons
- 2005
-
Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 233:1, s. 176-185
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Tidskriftsartikel (refereegranskat)abstract
- Monolithic Pt/gamma-Al2O3 catalysts were prepd. by depositing of the platinum phase, either homogeneously or heterogeneously (i.e., local high platinum concn.), in the washcoat. The influence of the platinum distribution on the ignition and extinction processes for oxidn. of CO, propene, and propane, resp., was investigated by both temp.-programmed and oxygen step-response flow-reactor expts. In addn., in situ XANES spectroscopy was used to follow changes in the chem. state of platinum during propane oxidn. For samples with heterogeneous platinum distribution, the results show an improved low-temp. activity for CO oxidn., whereas no clear improvement is obsd. for oxidn. of propene or propane. Comparison of the results for CO and hydrocarbon oxidn. shows that the improved activity cannot be explained by thermal effects. Moreover, calcns. indicate that the enhanced activity for CO oxidn. can be due to mass-transfer phenomena. This could not be confirmed by our expts., however. Instead, the improved activity for CO oxidn. can be due to varying platinum particle size between the samples. Furthermore, the oxidn. of propane is shown to be highly influenced by the oxygen concn., showing an activity max. for gas compositions close to the stoichiometric. High oxygen levels result most probably in a predominantly oxygen-covered surface, which inhibits the reaction and, as supported by the in situ XANES experiments, passivates the surface by forming platinum oxide.
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| 41. |
- Arve, Kalle, et al.
(författare)
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Did Chemisorption Become an Obsolete Method With Advent of Tem? Comparison of Mean Particle Size and Distribution of Silver on Alumina
- 2011
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Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 141:5, s. 665-669
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Tidskriftsartikel (refereegranskat)abstract
- Silver particle size and dispersion on a Ag/Al2O3 for HC-SCR were examined by means of chemisorption and TEM. Experimental results showed that determination of the accurate mean particle size (mps) is challenging and that the both applied methods have specific characteristics increasing the inaccuracy in the results which has to be taken into account in evaluation of catalytic activity. The results from TEM imaging were found to depend highly on the mode in which the surface was scanned (bright field versus dark field). Generally the point resolution was higher in dark field but the obtained mps did not increased along with the increasing silver loading. The main limitation with the O-2-chemisorption was related to the choice of the stoichiometric factor between the adsorbent and silver atoms. However, together these techniques support each other and help to give a more realistic picture of the mean silver particle size, distribution and indications of the oxidation states on the alumina support.
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| 42. |
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| 43. |
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| 44. |
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| 45. |
- Becker, Elin, 1981, et al.
(författare)
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In situ DRIFT study of hydrogen and CO adsorption on Pt/SiO2 model sensors
- 2007
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Ingår i: 2007 IEEE Sensors. - 1930-0395. - 9781424412617 ; 1-3, s. 1028-1031
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Konferensbidrag (refereegranskat)abstract
- The sensing mechanism towards carbon monoxide of Metal Insulator Silicon Carbide (MISiC) Field Effect devices used as sensors, has been studied by in situ FTIR spectroscopy in diffuse reflectance mode (DRIFT). The infrared studies were performed using a model sensor, where adsorption of CO in presence of oxygen and hydrogen has been studied. The results show that the CO adsorption on Pt varies with varying oxygen concentration, CO concentration, hydrogen exposure and temperature. When correlating the DRIFT spectroscopy with sensor signal measurements, the CO response or MISiC field effect devices appears to be connected to the CO coverage of the sensor surface.
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| 46. |
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| 47. |
- Becker, Elin, 1981, et al.
(författare)
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In Situ Spectroscopic Investigation of Low-Temperature Oxidation of Methane over Alumina-Supported Platinum during Periodic Operation
- 2011
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:4, s. 944-951
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Tidskriftsartikel (refereegranskat)abstract
- Methane oxidation over Pt/Al2O3 at transient inlet-gas conditions was studied in situ using synchronous energy dispersive X-ray absorption spectroscopy, Fourier transform infrared spectroscopy, and mass spectrometry. The employed combination of experimental techniques allows for simultaneous analysis of the electronic state of platinum, surface coverage of reaction intermediates/products, and catalytic activity/selectivity, respectively. By cycling of the feed gas composition between net-oxidizing and net-reducing conditions, the activity for methane oxidation can be increased as compared to continuous net-oxidizing conditions. Using the white-line area of time-resolved X-ray absorption near-edge structure spectra, a quantitative estimation of the surface O/Pt ratio indicates the formation of an inhomogeneous surface oxide on the platinum crystallites during reaction. The obtained temporary high activity can be explained through Langmuir-Hinshelwood kinetics and may result either from the formation of a partially oxidized platinum surface that is more effective for methane dissociation or, more likely, from a period with more reactive chemisorbed oxygen prior to oxide formation.
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| 48. |
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| 49. |
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| 50. |
- Becker, Elin, 1981, et al.
(författare)
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Methane oxidation over alumina and ceria supported platinum
- 2009
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Ingår i: Topics in Catalysis. - : Springer Science and Business Media LLC. - 1572-9028 .- 1022-5528. ; 52:13-20, s. 1957-1961
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation of methane over Pt/Al(2)O(3) and Pt/CeO(2) catalysts was studied by transient gas-flow reactor and in situ FTIR spectroscopy experiments. The Pt/CeO(2) catalyst is generally more active, indicating more efficient CH(4) dissociation, especially during oxygen pulsing, which likely is connected to the higher oxygen storage capacity/mobility of ceria.
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