CeO_2-La_2O_3/γ-Al_2O_3催化还原SO_2反应机理的研究

Studies on Reaction Mechanism of SO_2 Reduction Catalyzed by CeO_2-La_2O_3/γ-Al_2O_3

采用浸渍法制备了负载型CeO2 /γ Al2 O3 ,La2 O3 /γ Al2 O3 和CeO2 La2 O3 /γ Al2 O3 催化剂 ,并用XRD和XPS对催化剂进行了表征 ,在n(SO2 ) /n(CO) =1/ 3,载流气体为N2 ,气体流量为 1L/min ,催化剂用量为 15 g的条件下 ,考察了催化剂催化CO还原SO2 反应的性能 ,研究了催化剂的活化过程、催化活性和反应物配比对活性的影响 .结果表明 ,CeO2 La2 O3 /γ Al2 O3 在催化还原SO2 反应中的活化温度比单组分催化剂CeO2 /γ Al2 O3 或La2 O3 /γ Al2 O3 下降了 5 0～ 10 0℃ ,而且具有更高的活性 .这可以解释为由CeO2 的redox反应与La2 O3 的COS中间物反应之间的协同作用所致 .还对SO2 还原反应机理进行了探讨 ,发现CeO2 的redox反应所生成的单质硫是整个过程中COS中间物反应的重要来源 .在此基础上 ,对CeO2 La2 O3 /γ Al2 O3 催化CO还原SO2 反应提出了redox COS叠加反应机理 .

Supported catalysts CeO 2/γ-Al 2O 3, La 2O 3/γ-Al 2O 3 and CeO 2-La 2O 3/γ-Al 2O 3 were prepared by impregnation. The studies were engaged in the catalytic reduction of SO 2 by CO over the catalysts under the following conditions: feed gas 25%SO 2-75%CO, with N 2 as a carrier gas, flow rate 1 L/min and catalyst mass 15 g. The activation process and catalytic activity of the catalysts, as well as the effect of the concentration ratio of the reactants on the catalytic reaction were investigated. The XRD and XPS were used to characterize the catalysts before and after the reaction. The result demonstrated that the activation temperature of CeO 2-La 2O 3/γ-Al 2O 3 is 50～100 ℃ lower than that of La 2O 3/γ-Al 2O 3 or CeO 2/γ-Al 2O 3, and CeO 2-La 2O 3/γ-Al 2O 3 has higher activity than La 2O 3/γ-Al 2O 3 or CeO 2/γ-Al 2O 3 for catalytic reduction of SO 2 by CO. This result revealed the synergism between redox reaction of CeO 2 and COS intermediate reaction of La 2O 3. The experimental results showed that the generation of elemental sulfur from the redox reaction of CeO 2 was an important source of COS intermediate reaction through the whole reaction, based on which a redox-COS overlapped reaction mechanism was proposed for the reduction of SO 2 by CO over CeO 2-La 2O 3/γ-Al 2O 3.