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- Carlsson, Per-Anders, 1972, et al.
(författare)
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Low-temperature CO oxidation over a Pt/Al2O3 monolith catalyst investigated by step-response experiments and simulations
- 2004
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30/31:1-4, s. 375-381
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Tidskriftsartikel (refereegranskat)abstract
- The ignitionextinction processes for CO oxidation over a Pt/Al2O3 monolith catalyst have been studied by flow-reactor experiments and simulations. The study was performed by stepwise changes of the inlet O2 concentration ranging 020 vol% while the CO concentration and the inlet gas temperature were kept constant at 1.0 vol% and 423 K, respectively. Several features observed experimentally are qualitatively simulated with our model: (i) the ignition of the CO oxidation demands 8.0vol% O2 (ii) corresponding to a catalyst ignition temperature of 433 K (due to the exothermicity of the reaction) and (iii) occurs in the rear part of the monolith where (iv) a local reaction zone is formed which (v) moves towards the reactor inlet as a function of time on stream. Additionally, the simulations show first order kinetic phase transitions, i.e. rapid adsorbate concentration changes, where the catalyst surface is predominantly CO covered in the low reactive state and almost completely oxygen covered in the high reactive state. For the ignition process the kinetic phase transition occurs after the actual catalytic ignition. However, the extinction process is more difficult to simulate dynamically without changing the model parameters for O2 adsorption in the low and high reactive state, respectively. The influence of diffusion limitations and the role of formation of a less reactive Pt state under oxidising conditions is discussed.
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| 4. |
- Carlsson, Per-Anders, 1972, et al.
(författare)
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Periodic control for improved low-temperature catalytic activity
- 2001
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 16-17:1-4, s. 343-347
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Tidskriftsartikel (refereegranskat)abstract
- The influence of transient changes in the gas composition on the low-temperature activity of a commercial three-way catalyst and a Pt/Al2O3 model catalyst has been studied. By introducing well-controlled periodic O2 pulses to simple gas mixtures of CO or C3H6 (in N2), a substantial improvement of the low temperature oxidation activity was observed for both catalysts. The reason for low activity at low temperatures is normally attributed to self-poisoning by CO or hydrocarbons. The improved catalytic performance observed here is suggested to origin from the transients causing a surface reactant composition that is favourable for the reaction rate.
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- Eriksson, Håkan, 1973, et al.
(författare)
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Potential for increased electricity production at an integrated pulp and paper mill with black liquor gasification
- 2001
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Ingår i: Proceedings of the 2001 TAPPI Engineering/Finishing and Converting Conference and Trade Fair, San Antonio, 16-20 September 2001. - 1930657838 ; , s. 411-426
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Konferensbidrag (refereegranskat)abstract
- A number of ongoing efforts aim at reducing greenhouse gas emissions from industrial energy systems. This can be achieved through increased biofuel usage. Biofuels are however a limited resource, and their usage must therefore be as efficient as possible. The objective of this study was to identify pulp and paper mill powerhouse configurations with maximal electricity production from a given limited amount of biofuel (black liquor and conventional wood fuels). The configurations investigated include black liquor gasification and conventional Tomlinson recovery boiler systems. The study is based upon a detailed model of the mill's chemical recovery island and a simplified model of the remainder of the mill. In order to satisfy the mill's heat balance, extra biofuel must be imported for most of the configurations considered. The configuration with the highest on-site electricity production (96 MW) includes biofuel gasification and firing in a gas turbine combined cycle unit. However, if biofuel is assumed a limited resource, importing biomass to the mill implies that less biofuel is available for other competing users. The net global electric power production is shown to decrease from 96 MW to 41 MW for the same powerhouse configuration when performance is evaluated in a global perspective.
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| 7. |
- Fridell, Erik, 1963, et al.
(författare)
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Model studies of NOx storage and sulphur deactivation of NOx storage catalysts
- 2001
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 16-17:1-4, s. 133-137
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Tidskriftsartikel (refereegranskat)abstract
- The storage of NOx under lean conditions in model NOx storage catalysts as well as the deactivation by sulphur have been studied. We find that NO2 plays an important role in the storage mechanism as an oxidising agent. Two different mechanisms for this are discussed: the formation of surface peroxides and the oxidation of nitrites to nitrates, FTIR studies show that NOx is stored as surface nitrates, The sulphur deactivation is found to be more severe when SO2 is added during the rich phase than when SO2 is added during the lean period. FTIR shows the formation of bulk sulphates both under lean and rich conditions.
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| 8. |
- Fridell, Erik, 1963, et al.
(författare)
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Platinum oxidation and sulphur deactivation in NOx storage catalysts
- 2004
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30-31:1-4, s. 143-146
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Tidskriftsartikel (refereegranskat)abstract
- Flow reactor experiments and X-ray photoelectron spectroscopy (XPS) measurements were used to investigate the importance of platinum oxide formation on Pt/BaO/Al2O3 NOx storage catalysts during reactions conditions. The reaction studied was NO(g) + 1/2 O-2(g) NO2 (g). During NO2 exposure of the catalyst the NO2 dissociation rate decreased during the reaction. This activity decrease with time was also studied with XPS and it was found to be due to platinum oxide formation. The influence of sulphur exposure conditions on the performance of the NOx storage catalysts was studied by exposing the samples to lean and/or rich gas mixtures, simulating the conditions in a mixed lean application, containing SO2 The main results show that all samples are sensitive to sulphur and that the deactivation proceeds faster when SO2 is present in the feed under rich conditions than under lean or continuous SO2 exposure. Additionally, the influence of the noble metals present in the catalysts was investigated regarding sulphur sensitivity and it was found that a combination of platinum and rhodium seems to be preferable to retain high performance of the catalyst under SO2 exposure and subsequent regeneration. Finally, the behaviour of micro-fabricated model NOx storage catalysts was studied as a function of temperature and gas composition with area-resolved XPS. These model catalysts consisted of a thin film of Pt deposited on one-half of a BaCO3 pellet. It was found that the combination of SO2 and O-2 resulted in migration of Pt on the BaCO3 support up to one mm away from the Pt/BaCO3 interface.
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| 9. |
- Fridell, Erik, 1963, et al.
(författare)
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The Mechanism for NOx Storage
- 2000
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Ingår i: Catalysis Letters. - 1572-879X .- 1011-372X. ; 66:1-2, s. 71-74
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms for storing of NOx in platinum-barium-alumina catalysts during lean-rich transients are investigated. Oxidation of NO to NO2 is found to be an important step. NO2 is found to be important for oxidation of the catalyst or of nitrites to form nitrates. NOx is then stored in the form of surface nitrates. FTIR studies show no formation of bulk nitrates in these experiments.
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| 10. |
- Svedberg, Pernilla, 1974, et al.
(författare)
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Influence of the storage material on the storage of NOx at low temperatures
- 2004
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30/31:1-4, s. 199-206
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Tidskriftsartikel (refereegranskat)abstract
- The NOx storage performance at low temperature (100-200°C) has been studied for model NOx storage catalysts. The catalysts were prepared by sequentially depositing support, metal oxide and platinum on ceramic monoliths. The support material consisted of acidic aluminium silicate, alumina or basic aluminium magnesium oxide, and the added metal oxide was either ceria or barium oxide. The NOx conversion was evaluated under net-oxidising conditions with transients between lean and rich gas composition and the NOx storage performance was studied by isothermal adsorption of NO2 followed by temperature programmed desorption of adsorbed species. The maximum in NOx storage capacity was observed at 100°C for all samples studied. The Pt/BaO/Al2O3 catalyst stored about twice the amount of NO x compared with the Pt/Al2O3 and Pt/CeO2/Al2O3 samples. The storage capacity increased with increasing basicity of the support material, i.e. Pt/Al2O3·SiO2
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