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应用H_2吸附的程序升温脱附(TPD)和环戊烷(CP)的脉冲反应,对Pt-Ir/Al_2O_3催化剂及其参比样Al_2O_3、Pt/Al_2O_3、Ir/Al_2O_3进行氢吸附及氢解活性的测定.试验注意到:Pt/Al_2O_3,Pt-M/Al_2O_3等负载型贵金属催化剂的TPD谱图一般包括两个可区分开的波峰,即T_m在100℃附近的低温峰(α峰)和T_m在500℃附近的高温峰(β峰)。前者是非活化吸附氢的信号,与催化剂的表面性质有关;后者是吸收氢或溢流氢(spillover),与催化剂表面性质无关。Pt-Ir/Al_2O_3(3)、Ir/Al_2O_3(2)、Pt/Al_2O_3(1)的TPD谱图α峰面积是Aa(3)>Aa(2)>A_α(1),Al_2O_3无信号,表示不吸附氢。它们在CP上的氢解活性也是这样的顺序,其表观反应速度常数之比为:k_3∶k_2∶k_1=15∶8∶1.根据Aa(3)=Aa(2)+Aa(1),及240℃、280℃时k_3与k_2的比各约等于1.0和2.0的关系。认为Pt-Ir/Al_2O_3的活性中心,多数由Pt/Al_2O_3,Ir/Al_2O_3的活性中心组成,可简单表示为(Pt)_m+(Ir)_no在设定三个催化剂的金属分散度相同的基础上,从TPD谱图a峰的面积和Pt,Ir的含量,求得它们的氢吸附的化学计量相对值,表示为PtH,Ir_2H_3.结果指出:Ir在Pt-Ir/Al_2O_3中基本上是独立存在,保存Ir/A1_2O_3中原有的形态与结构.Ir是高氢解活性组分,烃类氢解是它的特征反应.
The hydrogen adsorption and hydrogenolysis activities of Pt-Ir / Al_2O_3 catalyst and its reference samples Al_2O_3, Pt / Al_2O_3 and Ir / Al_2O_3 were investigated by temperature programmed desorption (HTPD) and pulsed reaction of cyclopentane (CP) The TPD spectra of Pt / Al 2 O 3, Pt-M / Al 2 O 3 and other supported precious metal catalysts generally include two distinguishable peaks, that is, the low temperature peak (α peak) with T_m near 100 ℃ and T_m High temperature peak around 500 ° C (β peak). The former is a non-activated hydrogen adsorption signal, and the surface properties of the catalyst; the latter is to absorb hydrogen or spillover spillover, and the surface properties of the catalyst has nothing to do. The peak areas of the TPD spectrum of Pt-Ir / Al 2 O 3 (3), Ir / Al 2 O 3 (2) and Pt / Al 2 O 3 (1) are Aa (3)> Aa (2)> A_α Do not absorb hydrogen. Their hydrogenolysis activity on CP is also in this order, the apparent reaction rate constant ratio: k_3: k_2: k_1 = 15: 8: 1. According to Aa (3) = Aa (2) + Aa , And the ratio of k_3 to k_2 at 240 ℃ and 280 ℃ is about 1.0 and 2.0 respectively. The active centers of Pt-Ir / Al_2O_3 are mostly composed of active centers of Pt / Al_2O_3 and Ir / Al_2O_3 and can be expressed simply as (Pt) _m + (Ir) _no. When the metal dispersions of the three catalysts are set to be the same , The relative stoichiometric values of their hydrogen adsorption were calculated from the area of the a peak of the TPD spectrum and the contents of Pt and Ir and were expressed as PtH and Ir_2H_3.The results showed that Ir essentially existed independently in Pt-Ir / Al_2O_3 , Preserve the original form and structure of Ir / A1_2O_3.Ir is a high hydrogenolytic active component, hydrocarbon hydrogenolysis is its characteristic reaction.