title: DRIFT study on cerium-tungsten/titania catalyst for selective catalytic reduction of NOx with NH3.
abstract: CeO(2)/TiO(2) and CeO(2)-WO(3)/TiO(2) catalysts prepared by impregnation method assisted with ultrasonic energy were investigated on the selective catalytic reduction (SCR) of NO(x) (NO and NO(2)) by NH(3). The catalytic activity of 10% CeO(2)/TiO(2) (CeTi) was greatly enhanced by the addition of 6% WO(3) in the broad temperature range of 200-500 °C, the promotion mechanism was proposed on basis of the results of in situ diffuse reflectance infrared transform spectroscopy (DRIFT). When NH(3) was introduced into both catalysts preadsorbed with NO + O(2), SCR would not proceed except for the reaction between NO(2) and ammonia. For CeO(2)/TiO(2) catalysts, coordinated NH(3) linked to Lewis acid sites were the main adsorbed ammonia species. When NO + O(2) was introduced, all the ammonia species consumed rapidly, indicating that these species could react with NO(x) effectively. Two different reaction routes, L-H mechanism at low temperature (<200 °C) and E-R mechanism at high temperatures (>200 °C), were presented for SCR reaction over CeO(2)/TiO(2) catalyst. For CeO(2)-WO(3)/TiO(2) catalysts, the Lewis acid sites on Ce(4+) state could be converted to Brønsted acid sites due to the unsaturated coordination of Ce(n+) and W(n+) ions. When NO + O(2) was introduced, the reaction proceeded more quickly than that on CeO(2)/TiO(2). The reaction route mainly followed E-R mechanism in the temperature range investigated (150-350 °C) over CeO(2)-WO(3)/TiO(2) catalysts. Tungstation was beneficial for the formation of Ce(3+), which would influence the active sites of the catalyst and further change the mechanisms of SCR reaction. In this way, the cooperation of tungstation and the presence of Ce(3+) state resulted in the better activity of CeO(2)-WO(3)/TiO(2) compared to that of CeO(2)/TiO(2).
authors.affiliation: Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, PR China.
authors.forename: Liang
authors.initials: L
authors.lastname: Chen
authors.forename: Junhua
authors.initials: J
authors.lastname: Li
authors.forename: Maofa
authors.initials: M
authors.lastname: Ge
mesh_terms: D000397:Air Pollution / Q000517:prevention & control; D000641:Ammonia / Q000737:chemistry*; D002384:Catalysis; D002563:Cerium / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D014025:Titanium / Q000737:chemistry*; D014414:Tungsten / Q000737:chemistry*
chemical_list: D010087:Oxides; C009495:titanium dioxide; D002563:Cerium; D009569:Nitric Oxide; C030583:ceric oxide; D000641:Ammonia; C511604:tungsten oxide; D014025:Titanium; D014414:Tungsten