Assessment of copper-vanadium oxide on mixed alumina-titania supports as sulphur dioxide sorbents and as catalysts for the selective catalytic reduction of NO_x by ammonia

A series of materials featuring copper oxide and/or vanadium oxide supported on titanium oxide, aluminium oxide or a composite alumina-titania carrier were tested for suitability as sorbents/catalysts for the simultaneous removal of SO₂ and NO_x from flue gases. Sulphur dioxide sorption at 300°C was associated with the formation of copper sulphate and some aluminium sulphate, the latter via a bridging Cu-SO₄-Al surface species. Only part of the sorption capacity could be regenerated by reduction in hydrogen at 450°C. Selective catalytic reduction of nitric oxide by ammonia over CuO/TiO₂, CuO/Al₂O₃-TiO₂ and CuO/Al₂O₃ was lessened following exposure of the catalysts to SO₂ and this feature was assigned to competition for ammonia between nitric oxide and surface sulphate species, the latter involving formation of (NH₄)₂SO₄. Vanadia supported on a composite support featuring 20 wt.-% alumina, balance titania, was as active as V/TiO₂ for nitric oxide reduction by ammonia and the Al₂O₃ component rendered the catalyst resistant to SO₂ poisoning because sulphate formed on vanadia could be transferred to Al₂O₃ where it did not interfere with the activity. Catalysts with copper and vanadium oxides supported on alumina-titania were not resistant to SO₂ poisoning during selective catalytic reduction of nitric oxide because the copper component attracted too much SO₂ onto the support, thus exceeding the protective capacity of the alumina component.