Chemisorption properties of iridium on alumina catalysts
Chemisorption properties of iridium on alumina catalysts
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DOI：
10.1016/0021-9517(80)90295-x
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发表时间：
1980-09
影响因子：
7.3
通讯作者：
G. Mcvicker;R. Baker;R. L. Garten;E. L. Kugler
中科院分区：
文献类型：
--
作者：
G. Mcvicker;R. Baker;R. L. Garten;E. L. Kugler
摘要 对于这些吸附物的强结合部分，高度分散的 0.3% 至 1.0% 铱在氧化铝催化剂上的 H Ir 和 CO Ir 比率接近 2。此类催化剂中的铱颗粒无法通过高分辨率 TEM 检测到，其尺寸上限为 0.6 nm。增加金属浓度或氧化煅烧导致平均铱颗粒尺寸的增加和吸附物/金属比率的相应降低。对于部分团聚的催化剂，根据化学吸附数据计算出的平均微晶尺寸与通过 TEM 直接观察到的平均微晶尺寸非常一致。观察到吸附的一氧化碳的红外光谱取决于铱微晶尺寸和表面覆盖率。在饱和覆盖条件下（CO Ir> 1），高度分散的催化剂在 2060 cm−1 处显示出主要的羰基带。相比之下，团聚催化剂（CO Ir< 1）则显示出以 2020–2025 cm−1 区域为中心的带最大值。化学吸附、TEM 和红外数据综合表明，孤立的铱原子最多可以吸附两个吸附原子，而铱簇 (> 0.6 nm) 在每个暴露的金属位点吸附单个吸附原子。
Abstract Highly dispersed 0.3 to 1.0% iridium on alumina catalysts exhibit H Ir and CO Ir ratios near two for the strongly bound fraction of these adsorbates. Iridium particles in such catalysts are not detectable by high-resolution TEM which places an upper limit of 0.6 nm on their size. Increasing the metal concentration or oxidative calcination resulted in an increase in the average iridium particle size and a corresponding decrease in adsorbate/metal ratios. Average crystallite sizes calculated from chemisorption data and observed directly by TEM for partially agglomerated catalysts were found to be in good agreement. Infrared spectra of adsorbed carbon monoxide were observed to be dependent upon both iridium crystallite size and surface coverage. Under saturation coverage conditions (CO Ir> 1), highly dispersed catalysts displayed a major carbonyl band at 2060 cm− 1. Agglomerated catalysts (CO Ir< 1), in contrast, exhibit a band maxima centered in the 2020–2025 cm− 1 region. Taken together the chemisorption, TEM, and infrared data indicate that isolated iridium atoms can adsorb up to two adatoms while iridium clusters (> 0.6 nm) adsorb a single adatom per exposed metal site.