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- Carlsson, Per-Anders, 1972, et al.
(författare)
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A transient in situ FTIR and XANES study of CO oxidation over Pt/Al2O3 catalysts
- 2004
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 226:2, s. 422-434
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Tidskriftsartikel (refereegranskat)abstract
- We report experimental results for the oxidation of CO over supported Pt/Al2O3 catalysts operating in oxygen excess at atmospheric pressure. To study the reaction kinetics under transient conditions we have employed step changes of the O2 concentration by intermittently switching off the O2 supply at various temperatures ranging from 523 to 623 K. Detailed in situ FTIR and XANES data for CO coverage and the chemical state of Pt, respectively, are presented together with the CO conversion, which in both cases was monitored by mass spectrometry. A red-shift of the vibrational frequency of linearly bonded CO which correlates with a blue-shift of the Pt LIII binding energy indicates that the Pt catalyst initially is partially oxidised and gradually reduced when the O2 supply is switched off. Control experiments with a NO2 oxidised Pt/Al2O3 catalyst support these findings. A hysteresis in the catalytic activity due to the different rates whereby Pt is oxidised and reduced as a function of gas-phase composition is observed. The activation energy for the Pt oxide reduction (decomposition) process is estimated to be about 50 kJ/mol. The results further emphasise that the conventional three-step Langmuir-Hinshelwood (LH) scheme used to interpret CO oxidation on Pt surfaces must be complemented by a Pt oxidation and reduction mechanism during transient conditions. Moreover, FTIR data suggest that during the extinction, the partially oxidised platinum surface is reduced by chemisorbed CO which should be explicitly accounted for in the modeling of the reaction mechanism.
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| 3. |
- Gustafsson, Fredrik, et al.
(författare)
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Particle Filters for Positioning, Navigation and Tracking
- 2002
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Ingår i: IEEE Transactions on Signal Processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1053-587X .- 1941-0476. ; 50:2, s. 425-437
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Tidskriftsartikel (refereegranskat)abstract
- A framework for positioning, navigation and tracking problems using particle filters (sequential Monte Carlo methods) is developed. It consists of a class of motion models and a general non-linear measurement equation in position. A general algorithm is presented, which is parsimonious with the particle dimension. It is based on marginalization, enabling a Kalman filter to estimate all position derivatives, and the particle filter becomes low-dimensional. This is of utmost importance for high-performance real-time applications. Automotive and airborne applications illustrate numerically the advantage over classical Kalman filter based algorithms. Here the use of non-linear models and non-Gaussian noise is the main explanation for the improvement in accuracy. More specifically, we describe how the technique of map matching is used to match an aircraft's elevation profile to a digital elevation map, and a car's horizontal driven path to a street map. In both cases, real-time implementations are available, and tests have shown that the accuracy in both cases is comparable to satellite navigation (as GPS), but with higher integrity. Based on simulations, we also argue how the particle filter can be used for positioning based on cellular phone measurements, for integrated navigation in aircraft, and for target tracking in aircraft and cars. Finally, the particle filter enables a promising solution to the combined task of navigation and tracking, with possible application to airborne hunting and collision avoidance systems in cars.
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| 4. |
- Jansson, Jonas, 1973, et al.
(författare)
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A mechanistic study of low temperature CO oxidation over cobalt oxide
- 2001
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 16-17:1-4, s. 385-389
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Tidskriftsartikel (refereegranskat)abstract
- The CO oxidation over Co3O4 and Co3O4/Al2O3 has been investigated using flow reactor and in situ FTIR studies. Cobalt oxide shows very high activity even at room temperature. However, a gradual deactivation takes place during reaction. The deactivated catalyst shows the presence of two different carbonate species and one graphite-like species. A possible mechanism for the deactivation is discussed.
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| 9. |
- Jansson, Jonas, 1973, et al.
(författare)
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On the catalytic activity of Co3O4 in low-temperature CO oxidation
- 2002
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 211:2, s. 387-397
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation of CO over Co3O4 at ambient temperature was studied with flow reactor experiments, and in-situ spectroscopic and structural methods. The catalyst deactivates during the reaction. The rate of deactivation increased with increasing CO or CO2 gas-phase concentration but decreased with increased 02 concentration or increased temperature. Regeneration of the catalyst in 10% O-2/Ar was more efficient than regeneration in Ar alone. The presence of carbonates and surface carbon on the deactivated catalyst was concluded from TPO experiments. None of these species could, however, be correlated with the deactivation of the catalyst. In-situ FTIR showed the presence of surface carbonates, carbonyl, and oxygen species. The change in structure and oxidation state of the catalyst was studied by in-situ XRD, in-situ XANES, XPS, and flow reactor experiments. One possible explanation for the deactivation of the catalyst is a surface reconstruction hindering the redox cycle of the reaction. (C) 2002 Elsevier Science (USA).
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| 10. |
- Jansson, Jonas, 1973
(författare)
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Studies of Catalytic Low-Temperature CO Oxidation over Cobalt Oxide and Related Transition Metal Oxides
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The catalytic oxidation of carbon monoxide at low temperatures is important in many applications. The use of a low temperature active catalyst may lower the emissions during the cold-start of a car, and volatile organic compounds in exhaust gases from stationary sources might be treated without the need of preheating the gas. In this thesis the catalytic oxidation of carbon monoxide (CO) over metal oxides (MnO2, Fe2O3, Co3O4, NiO, CuO, ZnO and CeO2) has been studied. Of these metal oxides cobalt oxide is the most active for CO oxidation at low temperatures and can oxidise CO at room temperature. NiO, CuO and MnO2 are also active for CO oxidation at moderate temperatures. The main focus in this thesis has been on cobalt oxide which was studied with flow reactor experiments, in-situ FTIR, in-situ XRD, in-situ XANES and XPS. NiO, CuO and MnO2 were studied with flow reactor experiments and in-situ FTIR. The activity of all these catalysts when preoxidised decreased slowly with time during CO oxidation at constant temperature. The rate of deactivation could be decreased by increasing the stoichiometric ratio S = 2·[O2]/[CO], increasing the temperature or decreasing the CO or CO2 concentration. Different types of carbonate species were detected at the surfaces of the Co3O4 and NiO catalysts both upon CO or CO2 adsorption and during CO oxidation. Carbonyls and surface carbon were detected on Co3O4. Three main hypotheses for the deactivation of the catalysts during CO oxidation at constant temperature are discussed: Blocking of the active sites by carbonates, carbonyls or hydroxyl groups, a slow reduction of the oxidation state of the active metal ions, and a surface reconstruction leading to deactivation. For cobalt oxide the most probable explanation for the deactivation was a slow gradual surface reconstruction. Microkinetic modelling is an important tool in studying catalytic reactions. Some of the models proposed for the surface reactions involved in the CO oxidation over cobalt oxide were fitted with non-linear regression. The most common practical problems encountered in non-linear regression and different strategies for how these could be solved are discussed and a general strategy regarding non-linear regression is suggested.
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