Cu-MCM-41介孔分子筛中不同价态铜上的吸附性能研究

Adsorption Behavior of Copper with Different Valence States in Cu-MCM-41

合成了不同铜含量的Cu-MCM-41,高温还原后仍具有良好的介孔结构。孔壁中的铜容易被H2还原为Cu(0)。通过在氦气流中加热,可以导致孔壁中的Cu!还原为Cu"。MCM-41中不同价态的铜具有不同的吸附性能:Cu(0)强烈吸附O2,吸附热高达427kJ·mol-1;Cu"在室温下几乎不吸附O2,表明Cu"在室温下较稳定;而Cu"在对CO与C2H4的吸附中,除了CO的吸附热与Cu(0)的相近外,所生成的吸附热与吸附量均较高。红外光谱也表明,Cu"比Cu(0)更容易吸附CO与C2H4。C2H4仅仅以π-键键合在Cu(0)表面,而在Cu"表面上却是以di-σ和π-键键合,由于di-σ键较强,使得C2H4在Cu"上具有较高的吸附热。

Abstract： The Cu-MCM-41 mesoporous materials with different contents of Cu were synthesized, It was found that a reduction in the high temperature did not alter the mesoporous structure of the materials. The copper in walls of MCM-41 silica was easily reduced to Cu（0） in H2, and a heat treatment in flowing He resulted in the reduction of Cu（Ⅱ） to Cu（Ⅰ）. The Cu（0） strongly adsorbed O2 and the adsorption heat was up to 427 kJ.mol^-1, while Cu（Ⅰ） did not adsorb O2 at room temperature, indicating better stability of Cu（Ⅰ） at ambient temperature. However, in the cases of the adsorption of CO and ethylene on Cu（Ⅰ）, apart from the adsorption heat for CO being nearly the same as that of Cu（0）, the adsorption heat and the adsorption quantity on Cu（Ⅰ） were all higher. And the results of infrared spectra also showed that the cases of the adsorption of CO and ethylene on Cu（Ⅰ） were easier than that on Cu（0）. Adsorbed ethylene on Cu（0） was only via or-bond while that on Cu（Ⅰ） was via both di-σ and π-bonds. Due to the di-σ bond strength being larger than the strength of π-bond, the adsorption heat of ethylene on Cu（Ⅰ） is higher.