CO2在金属表面活化的UBI-QEP方法研究

应用UBI-QEP方法估算了金属表面上形成的活化吸附态CO₂^-在Cu(111),Pd(111),Fe(111)和Ni(111)表面上的吸附热,计算了各种相关反应的活化能垒.结果表明,CO₂^-在4种过渡金属表面的相对稳定性的顺序为Fe>Ni>Cu>Pd;在Fe和Ni表面上CO₂^-较易生成,且容易进一步发生解离反应,在Fe表面会解离成C和O吸附原子,而在Ni表面上解离的最终产物为CO和O;在Cu表面上,CO₂^-虽较难形成,但其加氢反应的活化能比解离反应低,因此加氢反应是其进一步活化的有效模式;在Pd表面上,CO₂^-吸附态在能量上很不稳定,所以CO₂在Pd表面上不容易活化.

The UBI-QEP Study of CO2 Activation on the Metal Surfaces

The conversion and utilization of CO 2 are not only an important research subject in C 1 chemistry, but also of great significance in pollution control. It is generally accepted that CO - 2 adspecies on metal surfaces as an activated adsorption state of CO 2 is a pivotal intermediate in the process of CO 2 activation. The adsorption energy of CO - 2 and the energy barrier of various pathways of CO 2 activation on Cu(111), Pd(111), Fe(111) and Ni(111) surfaces have been predicted by using the UBI QEP(Unity bond index quadratic exponential potential) method. The theoretical results show that the stability of CO - 2 adsorbed on the above four transition metal surfaces follows the order: Fe(111)>Ni(111)>Cu(111)>Pd(111). CO - 2 surface species can be readily formed on the Fe and Ni surfaces and is liable to dissociate, giving rise to \{C(a)\} and O(a) on the Fe surface and CO(a) and O(a) on the Ni surface, respectively. On the Cu surface, though the formation of CO - 2 is less favorable, the hydrogenation of the as formed CO - 2 would be favorable over its direct dissociation which can lead to CO and O adspecies. On the Pd surface, the activation of CO 2 is rather difficult, as the formation of CO - 2 adspecies is thermodynamically quite unfavorable from the view point of activation enthalpies.