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- 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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| 2. |
- 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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| 3. |
- 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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