Redox behavior of transition metal ions in zeolites. I. Reversibility of the hydrogen reduction of copper Y zeolites
Redox behavior of transition metal ions in zeolites. I. Reversibility of the hydrogen reduction of copper Y zeolites
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DOI：
10.1021/j100589a009
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发表时间：
1975
期刊：
影响因子：
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通讯作者：
R. Herman;J. Lunsford;H. Beyer;P. Jacobs;J. Uytterhoeven
中科院分区：
文献类型：
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作者：
R. Herman;J. Lunsford;H. Beyer;P. Jacobs;J. Uytterhoeven
CuNaY沸石中Cu（II）离子的还原通过两步机制发生，其中Cu（I）首先形成，然后还原为金属铜。还原的第一步可以通过使用相对温和的条件进行，例如在200 ℃下用H2处理1小时，并且它是完全可逆的。在400 ℃氢中还原时，形成铜微晶，其中一些在还原20小时后生长到300 μ m的尺寸。这些较大晶体中的铜可以缓慢地再氧化成CuO。假设存在于沸石笼内的较小的金属颗粒可以容易地再氧化为位于沸石内的交换位点处的Cu（II）。大约有一半的金属铜是以较大的晶体形式存在的，另一半则是以小团簇的形式存在的。还原和再氧化过程中，通过定量观察反应中H2或O2的消耗量和H2O的生成量，并用EPR谱测定Cu（II）的含量。Cu~+-CO和Cu~+-NO络合物的IR和EPR谱分别表明了Cu（I）的存在。
The reduction of Cu (II) ions in CuNaYzeolites occurs via a two-step mechanism in which Cu (I) is first formed and then reduced to metallic copper. The first step in the reduction may be carried out by using relatively mild conditions, eg, H2 at 200 C for 1 hr, and it is completely reversible. Reduction in H2 at 400 C results in the formation of copper crystallites, some of whichgrow to a size of 300 Á after 20 hr of re-duction. The copper in these larger crystals may be reoxidized slowly to CuO. The smallermetal particles, which are postulated to reside within the zeolite cages, may be readily reoxidized to Cu (II), located at ex-change sites within the zeolite. Approximatelyhalf of the metallic copper is in the form of the larger crys-tallites and half is present in small clusters. The reduction and reoxidation was followed by quantitatively observing the H2 or O2 consumption and H2O produced in the reaction, while the amount of Cu (II) was de-termined by EPR spectroscopy. The presence of Cu (I) was detected by the ir and EPR spectra of the Cu+-CO and Cu+-NO complexes, respectively.