载体ZrO2d带电子对Ni13催化CH4脱氢过程的影响

Unraveling the role of Ni13 catalyst supported on ZrO2 for CH4 dehydrogenation: The d-band electron reservoir

  • 摘要: C−H键活化是甲烷转化的关键,分散于ZrO2(111)表面的活性Ni13微粒能实现这一过程。密度泛函理论结果表明,相比Ni13催化过程,Ni13-ZrO2(111)更能活化CH4逐步脱氢并稳定其解离物种;且在载体ZrO2存在下,C−H键长增加,C−H断键活化能降低,放热量增多,达过渡态时,解离H与残留CHx间距减小,因此,负载催化剂Ni13-ZrO2(111)具有更好的催化性。究其原因,对于Ni−C−H,ZrO2丰富的d带电子使得Ni 3d电子密度增强,C 2p与Ni 3d轨道重叠增多,Ni−C键增强,C−H键减弱,基于此,CHx吸附增强,C−H键活性亦增强。因此,载体ZrO2d带为Ni13活化CH4促进C−H键解离提供着电子。

     

    Abstract: The activation of C−H bonds of CH4 is a key step for the conversion of methane to chemical commodities. Loading Ni onto ZrO2 is regarded as a relatively efficient way to harness the beneficial electronic property and the fine dispersion of the Ni catalyst for CH4 dissociation. Herein we demonstrate the crucial role of Ni13 catalyst supported on ZrO2 for the dissociation of CH4. The density functional theory (DFT) results show that the ZrO2 supported Ni13 stabilizes all species better and facilitates CH4 activation. The stepwise dehydrogenations of CH4 on Ni13-ZrO2(111) exhibits longer C−H bond lengths of ISs , lower Ea, and smaller displacements between the detaching H and the remaining CHx fragment in TSs . In addition, they are also thermodynamically more feasible. However, without the ZrO2 support on Ni13, the opposite results are obtained. Consequently, the ZrO2 modified Ni13 is more superior to the original Ni13 in CH4 dehydrogenation. The electronic analysis combining DFT calculations confirmed that the larger overlap between C 2p and Ni 3d, and the electron transfer of Ni→C cause the weaker C 2p−H 1s hybridization. In addition, the reduction of electron transfer of H→C leads to a stronger interaction between Ni and C along with a weak C−H bond. Hence, the ZrO2 support serves as the d-band electron reservoir at Ni13 and it is benefit to the activation of C−H bonds in CH4 dehydrogenation.

     

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