Theoretical study on the chemisorption of a hydrogen molecule on palladium
Theoretical study on the chemisorption of a hydrogen molecule on palladium
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氢分子对钯化学吸附的理论研究
DOI：
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发表时间：
1987
期刊：
影响因子：
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通讯作者：
T. Yonezawa
中科院分区：
文献类型：
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作者：
H. Nakatsuji;M. Hada;T. Yonezawa
从理论上研究了Pd/sub 2/和Pd/sub 2/-H/sub 2/体系中氢分子与钯的相互作用，作为金属表面化学吸附和催化作用的模型。复杂的从头算理论，包括电子相关（CAS-MC-SCF，SAC和SAC-CI理论）用于计算相互作用系统的基态和激发态。虽然单个Pd原子在基态显示出对氢分子的亲和力，但它不催化H-H键的裂解，并且三角加合物形式是Pd-H/sub 2/系统的稳定几何形状。Pd原子的低激发态都是排斥态。另一方面，Pd/sub 2/系统清楚地显示出对氢化学吸附的催化活性。H/sub 2/ molecule在约1.5 A下从金属上吸附，并在分子和解离吸附形式之间建立平衡，后者比前者稳定几千卡/摩尔。Pd-Pd键在此过程中没有减弱，这与催化表面的稳定性有关。Pd表面的悬挂键和电子关联在这种催化活性中起着非常重要的作用。主要涉及Pdmore »的4d轨道，外部5s轨道起次要作用。没有电子关联，解离吸附甚至不能定性地解释。激发态几乎没有机会参与Pd的催化过程。这种机制不同于Ni表面的建议。最后，对氢-钯体系的光电子能谱进行了理论计算，解释了光电子能谱的一些相互作用特征。«少
Interaction of a hydrogen molecule with palladium in the Pd-H/sub 2/ and Pd/sub 2/-H/sub 2/ systems is studied theoretically as a model for chemisorption and catalytic action of a metal surface. Sophisticated ab initio theories including electron correlations (CAS-MC-SCF, SAC and SAC-CI theories) are used for calculations of ground and excited states of the interacting systems. While a single Pd atom in the ground state shows affinity for the hydrogen molecule, it does not catalyze cleavage of the H-H bond, and a triangular adduct form is the stable geometry of the Pd-H/sub 2/ system. The lower lying excited states of the Pd atom are all repulsive. On the other hand, the Pd/sub 2/ system clearly shows catalytic activity toward hydrogen chemisorption. The H/sub 2/ molecule is adsorbed at about 1.5 A from the metal, and an equilibrium between molecular and dissociated adsorption forms is established, with the latter being more stable than the former by a few kilocalories/mole. The Pd-Pd bond is not weakened in this process, a fact related to the stability of the catalytic surface. The dangling bonds of the Pd surface and electron correlations play very important roles in this catalytic activity. The 4d orbitals of Pdmore » are mainly involved, with the outer 5s orbital playing a secondary role. Without electron correlations, the dissociative adsorption is not explained even qualitatively. There is almost no chance for the excited states to participate in the catalytic process on Pd. This mechanism differs from that proposed for a Ni surface. Lastly, photoelectron spectra are theoretically calculated to explain some interacting features of the observed spectra for the hydrogen-palladium system.« less