丙烯在MoO3和WO3缺氧表面吸附的原子簇模型的从头算研究

本文选取原子簇模型, 用从头算UHF方法优化几何构型, 并进行二级MΦller-Plesset微扰(MP2)相关能计算, 研究了丙烯在MoO3和WO3表面的吸附态结构。优化得到的吸附前后的几何构型及计算的原子净电荷和吸附能都一致地表明,WO3对丙烯的吸附作用强于MoO3; 丙烯均用π成键电子向中心原子Mo或W配位而被吸附在MoO3的缺氧表面, 使丙烯中的碳-碳双键减弱致使容易断裂, 进而起到促进歧化反应的作用。从MP2计算的WO3对丙烯的吸附能0.934eV大于MoO3对丙烯的吸附能0.506eV及吸附过程均不必翻越能垒, 还可以定性理解用WO3作催化剂时的丙烯歧化反应的最佳温度(675K)高于用MoO3作催化剂(均以Al2O3为载体)的最佳反应温度(480K), 且WO3在675K时的催化活性高于MoO3在480K时的活性。

Ab initio study of the adsorption of propene on the surfaces of MoO3 and WO3 with the cluster model

The adsorption of propene on the surface of MO3(M=Mo and W) is studied, in this paper, by use of a cluster model and the ab initio UHF geometry optimization method followed by the energy calculation with the second-order MΦller-Plesset perturbation procedure (MP2). The optimized geometries, the calculated net atomic charges and adsorption energies all show that the adsorption of propene on the surface of WO3 is stronger than that of MoO3. The electron charge is transferred from the π bonding orbital of the propene to the central atom M. When the propene is adsorbed on the surface of MO3 so that it is easier to break the carbon-carbon double bond and easier to take the metathesis reaction of propene The adsorption energies of propene on the surfaces of MoO3 and WO3 obtained from the MP2 calculations are 0.934eV and 0.506eV, respectively, and there is no energy barrier for the adsorption process, which leads us to understand qualitatively the experimental fact that the best reaction temperature (675K) of propene metathesis for using the WO3 catalyst supported on alumina is higher than that (480K) for using the MoO3 on alumina, and that the catalytic activity of the WO3 at 675K is higher than that of the MoO3 at 480K.