| 1. |
- Brandin, Jan, 1958-, et al.
(författare)
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Deactivation and Characterization of SCR Catalysts Used in Municipal Waste Incineration Applications
- 2018
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Ingår i: Catalysis Letters. - : Springer. - 1011-372X .- 1572-879X. ; 148:1, s. 312-327
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Tidskriftsartikel (refereegranskat)abstract
- Catalysts used for selective catalytic reduction were deactivated for various times in a slipstream from a municipal solid waste incineration plant and then characterized. The activity for NO reduction with NH3 was measured. The Brunauer–Emmett–Teller surface areas were determined by N2 adsorption from which the pore size distributions in the mesopore region were obtained. Micropore areas and volumes were also obtained. The composition of fresh and deactivated catalysts as well as fly ash was determined by atomic absorption spectroscopy and scanning electron microscopy with energy dispersive X-ray analysis. The changes in surface area (8% decrease in BET surface area over 2311 h) and pore structure were small, while the change in activity was considerable. The apparent pre-exponential factor was 1.63 × 105 (1/min) in the most deactivated catalyst, compared to 2.65 × 106 (1/min) in the fresh catalyst, i.e. a reduction of 94%. The apparent activation energy for the fresh catalyst was 40 kJ/mol, decreasing to 27 kJ/mol with increasing deactivation. Characterization showed that catalytic poisoning is mainly due to decreased acidity of the catalyst caused due to increasing amounts of Na and K.
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| 2. |
- Brandin, Jan, 1958-, et al.
(författare)
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High-temperature and high concentration SCR of NO with NH3 : application in a CCS process for removal of carbon dioxide
- 2012
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Ingår i: Chemical Engineering Journal. - : Elsevier. - 1385-8947 .- 1873-3212. ; 191, s. 218-227
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates several commercial selective catalytic reduction (SCR) catalysts (A–E) for application in a high-temperature (approximately 525 °C) and high-concentration (5000 ppm NO) system in combination with CO2 capture. The suggested process for removing high concentrations of NOx seems plausible and autothermal operation is possible for very high NO concentrations. A key property of the catalyst in this system is its thermal stability. This was tested and modelled with the general power law model using second-order decay of the BET surface area with time. Most of the materials did not have very high thermal stability. The zeolite-based materials could likely be used, but they too need improved stability. The SCR activity and the possible formation of the by-product N2O were determined by measurement in a fixed-bed reactor at 300–525 °C. All materials displayed sufficiently high activity for a designed 96% conversion in the twin-bed SCR reactor system proposed. The amount of catalyst needed varied considerably and was much higher for the zeolithic materials. The formation of N2O increased with temperature for almost all materials except the zeolithic ones. The selectivity to N2 production at 525 °C was 98.6% for the best material and 95.7% for the worst with 1000 ppm NOx in the inlet; at 5000 ppm NOx, the values were much better, i.e., 98.3 and 99.9%, respectively.
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| 3. |
- Odenbrand, C. U.Ingemar
(författare)
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Penetration of Poisons Along the Monolith Length of a V2O5/TiO2 Diesel SCR Catalyst and Its Effect on Activity
- 2019
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Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1011-372X .- 1572-879X. ; 149:12, s. 3476-3490
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: Catalysts used for selective catalytic reduction of NOx on diesel engines were deactivated for 890 and 2299 h in the exhausts from a diesel engine running on Swedish diesel fuel mark 1. The deactivated catalytic monoliths (100 mm long) were cut in 10 mm pieces along their axis and were characterized by physicochemical methods as well as by determination of the activity in the reduction of NOx by NH3 and in the oxidation of NH3 by O2.
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| 4. |
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| 5. |
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| 6. |
- Ahlstrom, AF, et al.
(författare)
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Combustion characteristics of soot deposits from diesel engines
- 1989
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223. ; 27:3, s. 475-483
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study was to investigate the combustion characteristics of soot deposits from diesel-powered engines. The soot deposits were collected in the exhaust stream from diesel engines at Volvo Truck Corporation in Gothenburg, Sweden. The combustion experiments were performed in a flow reactor in the presence of 2–10% O2 and 0 or 7% H2O. The temperature was increased at a rate of 10°C/min and the production rates of CO and CO2 were determined. The surface area of the soot deposits increased as the soot was heated in an inert gas stream. Combustion rates increased rapidly at temperatures above 400°C. Kinetic studies indicated that the reaction between oxygen and the carbon in diesel soot could be described by Langmuir-Hinshelwood kinetics in the absence of water vapour. The soot deposits were combusted more effectively when water vapour was present in the gas mixture. The selectivity for production of CO was constant in the absence of water vapour but followed the temperature dependence of the water-gas shift reaction in the presence of water vapour. Ignition temperatures of the soot deposits decreased as the oxygen content in the gas mixture increased. When water vapour was present, the soot deposits ignited at even lower temperatures. This study shows that diesel deposits can only be combusted at relatively high temperatures in the absence of a combustion catalyst.
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| 7. |
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| 8. |
- Ahlstrom Silversand, AF, et al.
(författare)
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Combustion of methane over a Pd-Al2O3/SiO2 catalyst, catalyst activity and stability
- 1997
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Ingår i: Applied Catalysis A: General. - 0926-860X. ; 153:1-2, s. 157-175
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Tidskriftsartikel (refereegranskat)abstract
- Palladium supported on Si-stabilised alumina has been demonstrated to be an active and durable catalyst for the combustion of methane. Si is more effective in stabilising alumina than La or Ba when the elements are added through an impregnation technique. Multiple stabilisation with combinations of La, Ba and Si does not increase further the stability against sintering. The stability increases logarithmically with the amount of Si added (0.5-8 atomic%). The rate of sintering is not affected by an increase of the water vapour content of the atmosphere from 1 to 20 vol.%. Doping palladium with rhodium or platinum increases the activity of the catalyst for methane combustion. The high-temperature stability of pure Pd is however superior to the stabilities of the Rh- and Pt-doped catalysts. Addition of La or Ce to the Pd-catalyst increases its stability against thermal deactivation but leads to an overall decrease in activity. The activity of the as-prepared catalysts are affected by the Pd-content below a value corresponding to 5% of the monolayer capacity. Thermally deactivated catalysts show a stronger activity dependence of the Pd-content than as-prepared catalysts. The combustion reaction is first order with respect to methane and zero-order with respect to oxygen (>2 vol.% of oxygen). Carbon dioxide has no inhibitory effects on the combustion. The activity of the Pd-catalyst is decreased by a factor of 5 through deactivation at 1473 K for 768 h. The decrease in activity is linearly correlated to the decrease in specific surface area.
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| 9. |
- Ahlstrom-Silversand, AF, et al.
(författare)
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Modelling catalytic combustion of carbon monoxide and hydrocarbons over catalytically active wire meshes
- 1999
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Ingår i: Chemical Engineering Journal. - 1385-8947. ; 73:3, s. 205-216
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Tidskriftsartikel (refereegranskat)abstract
- A new way of preparing catalytically active wire meshes through a thermal-spray technique is described. A metal substrate (e.g. Kanthal AF) was plasma-sprayed with a composite ceramic/polymer-powder. The polymer content of the sprayed layer was burnt off whereupon a well-defined macro-porosity was created. By treating the so obtained material with an alumina-sol the specific surface area could be increased by a factor of 50 or more. The ceramic layer was finally activated with precious metals through an impregnation step. A numerical model was developed to compare the performance of wire-mesh-, monolith- and pellets catalysts. The model describes the resistance to internal and external mass- and heat transfer and the effects of axial dispersion. The wire-mesh model was verified through experiments. Different evaluation parameters were derived to compare the catalyst performance relative to the catalyst volume, the geometric weight, the catalyst weight, the pressure drop and the temperature response. Wire-mesh catalysts offer the following advantages: high mass and heat transfer numbers, moderate pressure drop, insignificant effects of pore diffusion and axial dispersion, thermal and mechanical strength, geometric flexibility, excellent thermal response, simplicity in the catalyst recovery. The cost of a wire-mesh catalyst is expected to be competitive to other alternatives. (C) 1999 Elsevier Science S.A. All rights reserved.
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| 10. |
- Ahlstrom Silversand, AF, et al.
(författare)
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Thermally sprayed wire-mesh catalysts for the purification of flue gases from small-scale combustion of bio-fuel - Catalyst preparation and activity studies
- 1997
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Ingår i: Applied Catalysis A: General. - 0926-860X. ; 153:1-2, s. 177-201
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Tidskriftsartikel (refereegranskat)abstract
- Catalytically active wire meshes were used to combust different pollutants present in flue gases from bio-fuel combustion, e.g. CO, propylene, terpenes and tar. Alumina was spray-deposited onto wire meshes of Kanthal AF (8-20 Tayler mesh) with a plasma spray equipment. The specific surface area of the ceramic layer was increased through wash coating, in-situ precipitation or sol-treatment. The catalytically active materials consisted of precious metals (Pd/Pt) or metal oxides (V2O5/CuO) and were added to the ceramic matrix through an impregnation technique. The combustion was in most cases severely limited by external mass transfer. The effects of the specific surface area and the loading of catalytically active material were only significant in the reaction controlled domain. In the mass transfer controlled domain the conversion was affected only by the flow conditions and the external surface area of the wire meshes. CO and most hydrocarbons were effectively combusted at temperatures below 773 on a Pd/Pt-catalyst. The catalyst performance was not affected by the presence of water vapour or carbon dioxide or by low oxygen concentrations. Similar combustion experiments were performed with a commercial monolith and it can be concluded that the performance of the catalytically active wire meshes in the mass-transfer controlled domain was superior. Tar-residues, soot particulates and charcoal particles were effectively combusted over a Pd/Pt-doped oxide-catalyst (V2O5/CuO).
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