On the kinetic and structure sensitivity of lean reduction of NO with C3H6 over nanodispersed Pt crystals
On the kinetic and structure sensitivity of lean reduction of NO with C3H6 over nanodispersed Pt crystals
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DOI：
10.1016/j.apcatb.2005.01.006
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发表时间：
2005-07
影响因子：
22.1
通讯作者：
Balint Ioan;A. Miyazaki;K. Aika
中科院分区：
文献类型：
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作者：
Balint Ioan;A. Miyazaki;K. Aika
采用胶体法制备了平均粒径为12 nm的铂纳米晶（约52%立方晶），并将其负载于氧化铝上。首先考察了Pt的暴露量（由金属负载量或催化剂重量控制）对贫燃脱NOx反应催化性能的影响。在250°C下观察到的最佳NOx转化率峰值为56%。典型地，丙烯转化率水平在峰值NOx转化率下在85-100%范围内。无运输影响的催化数据已被确定，然后用于计算NO和C3 H6转化的动力学参数（周转频率和活化能）。在225-275°C温度范围内测定的NO和C3 H6转化的平均TOF值分别在0.04-0.27和0.05-0.50s-1之间。NO和C3 H6转化的平均活化能分别为91和108 kJmol −1。NO/O2/C3 H6反应的结构敏感性以及结构良好的铂纳米晶在反应条件下的形态演变得到了清楚的证明。脱NOx催化行为主要与Pt纳米颗粒的形状（刻面效应）有关，在较小程度上与Pt纳米颗粒的尺寸（体效应）有关。与多晶催化剂（0.1：2）相比，在统计学上富含具有低折射率小面的Pt纳米颗粒、相对无缺陷的催化剂的N2/N2 O比更高（0.1：1）。高浓度的边缘，角落，扭结，和多晶铂颗粒的表面缺陷的主要因素负责的整体催化活性的NOx转化。大的（24 nm）以及小的（2.4nm）多晶Pt颗粒显示出相同的催化NO转化行为。根据实验结果，它建议，可以预见，通过最佳的形态（尺寸和刻面）控制的负载Pt颗粒的催化活性和选择性的进一步改善，为贫脱NOx反应（在比催化活性和N2/N2 O比的增加）。
Well-defined platinum nanocrystals (≈52% cubic) with an average diameter of 12nm were prepared by colloid method and then supported on alumina. The effect of amount of the exposed Pt (controlled either by metal loading or by the catalyst weight) on the catalytic performances for lean-burn deNOxreaction was taken firstly under investigation. An optimum peak NOxconversion of ≈56% was observed at 250°C. Typically, the propylene conversion level was in the 85–100% range at peak NOxconversions. The catalytic data free of transport effects have been identified and then used to calculate kinetic parameters for NO and C3H6conversions (turnover frequencies and activation energies). The average TOF values for NO and C3H6conversions, determined in the 225–275°C temperature domain, ranged between 0.04–0.27 and 0.05–0.50s−1, respectively. The average activation energies for NO and C3H6conversions were 91 and 108kJmol−1, respectively. The structure sensitivity of NO/O2/C3H6reaction as well as the morphological evolution of the well-structured platinum nanocrystals in reaction conditions have been clearly evidenced. The deNOxcatalytic behavior was mainly related to the shape (facet effect) and to a lesser extent to the size (bulk effect) of the Pt nanoparticles. The N2/N2O ratio was higher (≈1:1) for the catalyst statistically rich in Pt nanoparticles with low index facets, relatively free of defects, compared to the polycrystalline one (≈1:2). High concentration of edges, corners, kinks, and surface defects of polycrystalline platinum particles was the main factor responsible for the overall catalytic activity for NOxconversion. Large (24nm) as well as small (2.4nm) polycrystalline Pt particles showed in great lines the same catalytic behavior for NO conversion. In light of experimental results, it is suggested that further improvement in the catalytic activity and selectivity for lean deNOxreaction (increase in the specific catalytic activity and N2/N2O ratio) can be foreseen through an optimum morphological (size and facet) control of the supported Pt particles.