Thermally sprayed wire-mesh catalysts for the purification of flue gases from small-scale combustion of bio-fuel - Catalyst preparation and activity studies

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).