Dissociation of Methane on La2O3 Surfaces Doped with Cu, Mg, or Zn

作者：Li Bo; Metiu Horia^*

来源：Journal of Physical Chemistry C, 2011, 115(37): 18239-18246.

DOI：10.1021/jp2049603

We use density functional theory to examine methane dissociative adsorption on La2O3 substitutionally doped with Cu, Mg, or Zn. We find that these dopants activate the surface oxygen atoms and make methane dissociation exothermic. Cu-doped lanthana is very active, but it loses oxygen too easily and the surface is likely to be reduced at the temperatures at which methane dissociates. The reduced surface has lower activity. The effect of Mg doping on methane activation is less than that of Zn. We focus, therefore, on Zn-doped lanthana and calculate the activation barrier for methane dissociation. We suggest that, for dissociative adsorption, the Bronsted-Evans-Polanyi rule needs to be modified to take into account not only the binding energy of the products but also the distance between the fragments formed by dissociation. We also show that an oxygen vacancy on the Zn-doped lanthana surface adsorbs oxygen from the gas and converts it into a species that should be described as O-2(-). This reacts with methane and dissociates it. Our main conclusion is that Zn-doped lanthana is a much better catalyst than lanthana, for methane activation, if one can prepare it so that the Zn dopants are in the surface layer. Unfortunately, the calculations show that the Zn atom prefers to be located in the bulk (in the absence of gases) and its influence on the chemistry of the surface, when this happens, is substantially diminished.

• 出版日期2011-9-22