Effect of Particle Size and Adsorbates on the L3, L2 and L1 X-ray Absorption Near Edge Structure of Supported Pt Nanoparticles
Effect of Particle Size and Adsorbates on the L3, L2 and L1 X-ray Absorption Near Edge Structure of Supported Pt Nanoparticles
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DOI：
10.1007/s11244-011-9662-5
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发表时间：
2011-04-01
影响因子：
3.6
通讯作者：
Miller, Jeffrey
中科院分区：
文献类型：
--
作者：
Lei, Yu;Jelic, Jelena;Miller, Jeffrey
已在二氧化硅、碱-二氧化硅、氧化铝、二氧化硅-氧化铝、碳和SBA-15载体上制备了约1至10nm的Pt纳米颗粒。 He 中还原催化剂的 EXAFS 光谱显示，随着颗粒尺寸减小至 3 nm 以下，Pt-Pt 键距缩短。对于 1 nm 的 Pt 颗粒，键长减少了 0.13 埃。 CO 和 H-2 的吸附导致 Pt-Pt 键距增加到 Pt 箔附近，例如。克，2.77 埃。除了 Pt 键距随尺寸变化外，随着颗粒尺寸减小到约 5 nm 以下，XANES 在 L-3 边缘处向更高能量移动，边缘附近的强度降低，边缘以外的强度增加。我们认为这些特征对应于配位效应（边缘处的减少）和晶格收缩（边缘外的增加）。在 L-2 边缘，仅存在向边缘处的更高能量的小转变。然而，在边缘之外，随着颗粒尺寸的减小，强度大幅增加。在 L-1 边缘，XANES 光谱的位置或形状没有变化。 CO 和 H2 的吸附也会导致 L-3 和 L-2 边缘发生变化，但在 L-1 边缘没有观察到变化。密度泛函理论和 XANES 计算表明，实验 XANES 的趋势可以用边缘附近可用的状态来解释。 CO 和 H-2 吸附都会导致费米能级的态耗尽，但在费米能级以上会产生反键态，从而导致强度增加超出边缘。
Pt nano-particles from about 1 to 10 nm have been prepared on silica, alkali-silica, alumina, silica-alumina, carbon and SBA-15 supports. EXAFS spectra of the reduced catalysts in He show a contraction of the Pt-Pt bond distance as particle size is decreased below 3 nm. The bond length decreased as much as 0.13 angstrom for 1 nm Pt particles. Adsorption of CO and H-2 lead to a increase in Pt-Pt bond distance to that near Pt foil, e. g., 2.77 angstrom. In addition to changes in the Pt bond distance with size, as the particle size decreases below about 5 nm there is a shift in the XANES to higher energy at the L-3 edge, a decrease in intensity near the edge and an increase in intensity beyond the edge. We suggest these features correspond to effects of coordination (the decrease at the edge) and lattice contraction (the increase beyond the edge). At the L-2 edge, there are only small shifts to higher energy at the edge. However, beyond the edge, there are large increases in intensity with decreasing particle size. At the L-1 edge there are no changes in position or shape of the XANES spectra. Adsorption of CO and H2 also lead to changes in the L-3 and L-2 edges, however, no changes are observed at the L-1 edge. Density Functional Theory and XANES calculations show that the trends in the experimental XANES can be explained in terms of the states available near the edge. Both CO and H-2 adsorption result in a depletion of states at the Fermi level but the creation of anti-bonding states above the Fermi level which give rise to intensity increases beyond the edge.