Selective adsorption of NO_x from hot combustion gases by Ce-doped CuO/TiO₂

CuO/TiO₂ has been shown to be a superior sorbent for selective, reversible adsorption of NO from hot combustion gases. High NO_x adsorption capacities at 200 and 300 °C were obtained with a 5% CuO/TiO₂ sorbent, and the NO_x desorbed rapidly at 450 °C. Doping with 2% Ce on the CuO/TiO₂ sorbent further increased both uptake rates (50% increase in initial rate) and NO_x capacity (by 30%). In a direct comparison with the most promising known sorbent, MnO/ZrO₂ (1:1 molar ratio), reported by Eguchi et al. (J. Catal. 1996, 158, 420), the Ce-CuO/TiO₂ sorbent showed both higher uptake rates (by 100% in initial rate) and higher NO_x capacity (by 15%). The effects of CO₂, H₂O, and SO₂ on NO_x sorption on the Ce-CuO/TiO₂ sorbent were studied at 200 °C. CO₂ slightly decreased the initial uptake rate but increased the NO_x capacity. H₂O coadsorbed with NO_x on different sites, both reversibly (i.e. desorbed at 450 °C). SO₂ irreversibly adsorbed (likely to sulfate the surface of TiO₂) and decreased the NO_x capacity by approximately 20%. The BET surface area of the TiO₂ support was 50 m²/g. Further studies with TiO₂ of higher surface areas are in progress.