Kim Jae Y, Rodriguez José A, Hanson Jonathan C, Frenkel Anatoly I, Lee Peter L
Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
J Am Chem Soc. 2003 Sep 3;125(35):10684-92. doi: 10.1021/ja0301673.
Time-resolved X-ray diffraction, X-ray absorption fine structure, and first-principles density functional calculations were used to investigate the reaction of CuO and Cu(2)O with H(2) in detail. The mechanism for the reduction of CuO is complex, involving an induction period and the embedding of H into the bulk of the oxide. The in-situ experiments show that, under a normal supply of hydrogen, CuO reduces directly to metallic Cu without formation of an intermediate or suboxide (i.e., no Cu(4)O(3) or Cu(2)O). The reduction of CuO is easier than the reduction of Cu(2)O. The apparent activation energy for the reduction of CuO is about 14.5 kcal/mol, while the value is 27.4 kcal/mol for Cu(2)O. During the reduction of CuO, the system can reach metastable states (MS) and react with hydrogen instead of forming Cu(2)O. To see the formation of Cu(2)O, one has to limit the flow of hydrogen, slowing the rate of reduction to allow a MS --> Cu(2)O transformation. These results show the importance of kinetic effects for the formation of well-defined suboxides during a reduction process and the activation of oxide catalysts.
利用时间分辨X射线衍射、X射线吸收精细结构和第一性原理密度泛函计算详细研究了CuO和Cu₂O与H₂的反应。CuO的还原机制很复杂，包括一个诱导期以及H嵌入氧化物本体。原位实验表明，在正常供氢情况下，CuO直接还原为金属Cu，不形成中间体或低价氧化物（即不存在Cu₄O₃或Cu₂O）。CuO的还原比Cu₂O的还原更容易。CuO还原的表观活化能约为14.5 kcal/mol，而Cu₂O的值为27.4 kcal/mol。在CuO还原过程中，体系可达到亚稳态（MS）并与氢反应，而不是形成Cu₂O。为了观察Cu₂O的形成，必须限制氢气流速，减缓还原速率以实现亚稳态向Cu₂O的转变。这些结果表明了动力学效应在还原过程中形成明确低价氧化物以及氧化物催化剂活化方面的重要性。
