Cu ion-exchanged copper aluminosilicate catalysts for nitric oxide removal under excess oxygen atmosphere

Abstract

The selective catalytic reduction of NO by propane in the presence of excess oxygen atmosphere was studies with Cu,Al-silicate and Cu ion-exchanges Cu,Al-silicate (Cu/Cu,Al-silicate) catalysts. The reaction was carried out in a 0.6 cm quartz tube reactor. A gas mixture containing NO (1000 ppm), C₃H₈(3000 ppm), O₂ (10 vol.%), and He balance was fed at flow rate of 50 cc/min (GHSV~4000 h-1). The catalytic activity of the catalysts was tested at the temperature range from 150-600 ℃. It was found that the activity of Cu, Al-silicate depended on the amount of copper content and form of cation (Na, NH₄ or H-form) on Cu,Al-silicate. Futhermore, it was found that Cu in Cu,Al-silicate, which Cu was in crystals, revealed high light-off temperature, but broad temperature window, which was one of the important factor for NO reduction. Thus, to apply this catalyst at lower light-off temperature, copper ion-exchanged was conducted on Cu,Al-silicate. Experimental results showed that, the resulting catalyst, Cu/Cu,Al-silicate had higher activity; however, several times of Cu ion-exchanged decreased activity, which was due to the formation of microcluster of CuxOy on surface of the catalyst and these oxides blocked active sites for the reaction. Catalytic activity testing showed that Cu/Na-Cu,Al-silicate showed high activity close to Cu/Na-ZSM-5. The light-off temperature of CU/Na-CU,Al-silicate and Cu/Na-ZSM-5 were 228 ℃ and 225 ℃, respectively. However, Cu/Na-Cu,Al-silicate revealed wider temperature window for No conversion than that of Cu/Na-ZSM-5. Therefore, Cu/Na-Cu,Al-silicate was a potential catalyst for NO removal under oxidizing condition. The activities of both catalysts, Cu/Na-Cu,Al-silicate and Cu/Na-ZSM-5, with 300 ppm SO₂ were declined almost at the same rate. The declining was ascribed to the change of oxidation state of cooper by adsorbed SO₂ or the competitive adsorption of SO₂ and NO on adsorption sites. Coated Cu/Na-Cu,Al-silicate on monolith demonstrated higher activity than the pelleted catalyst when the same amount of Cu/Na-Cu,Al-silicate was used. The light-off temperatures of the coated catalyst and the pelleted catalyst were 312 ℃, and 380 ℃, respectively. In addition, changing ratio of Cu/Na-Cu,Al-silicate to Al₂O₃ from 50 : 50 to 70 : 30 slightly affected the activity of NO removal.