载体ZrO_(2)的d带电子对Ni_(13)催化CH_(4)脱氢过程的影响

Unraveling the role of Ni_(13) catalyst supported on ZrO_(2) for CH_(4) dehydrogenation:The d-band electron reservoir

C−H键活化是甲烷转化的关键,分散于ZrO_(2)(111)表面的活性Ni_(13)微粒能实现这一过程。密度泛函理论结果表明,相比Ni_(13)催化过程,Ni_(13)-ZrO_(2)(111)更能活化CH_(4)逐步脱氢并稳定其解离物种;且在载体ZrO_(2)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CH_(x)间距减小,因此,负载催化剂Ni_(13)-ZrO_(2)(111)具有更好的催化性。究其原因,对于Ni−C−H,ZrO_(2)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,CH_(x)吸附增强,C−H键活性亦增强。因此,载体ZrO_(2)的d带为Ni_(13)活化CH_(4)促进C−H键解离提供着电子。

The activation of C−H bonds of CH_(4) is a key step for the conversion of methane to chemical commodities.Loading Ni onto ZrO_(2) is regarded as a relatively efficient way to harness the beneficial electronic property and the fine dispersion of the Ni catalyst for CH_(4) dissociation.Herein we demonstrate the crucial role of Ni_(13) catalyst supported on ZrO_(2)for the dissociation of CH_(4).The density functional theory(DFT)results show that the ZrO_(2)supported Ni_(13)stabilizes all species better and facilitates CH_(4) activation.The stepwise dehydrogenations of CH_(4) on Ni_(13)-ZrO_(2)(111)exhibits longer C−H bond lengths of ISs,lower E_(a),and smaller displacements between the detaching H and the remaining CH_(x) fragment in TSs.In addition,they are also thermodynamically more feasible.However,without the ZrO_(2)support on Ni_(13),the opposite results are obtained.Consequently,the ZrO_(2)modified Ni_(13)is more superior to the original Ni_(13)in CH_(4) 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 ZrO_(2) support serves as the d-band electron reservoir at Ni_(13) and it is benefit to the activation of C−H bonds in CH_(4) dehydrogenation.