Co/AlPO_4—5催化剂中Co的状态及其作用

STATES AND ACTION OF COBALT IN Co/AlPO_4-5CATALYST

本文用IR,TEM,FABMS,ESCA,XRD以及还原度的测定等方法,描述了Co/AlPO_4-5上Co_3O_4在氢作用下变成Co°,CoO以及未还原的Co_3O_4三种状态的还原过程和钴的颗粒分布的变化,并表明在还原过程中,可能有钴的簇状物生成,导致B酸形成。

The TEM ESCA has been used to study of Co3O4 in Co/ AlPO4-5 catalyst in the process of reduction by H2 and the particle size distribution of cobalt before and after reduction by H2was also studied. The results showed that the states of cobalt were presented as Co3O4 before reduction by H2 and after reduction by H2 they existed in Co, CoO and Co3O4 three states. The sequence of reduction was Co3O4-CoO-Co°. CoO-Co° is the rate determining step. The results also showed that before reduction its particle size distribution is in a wide range, andthe average particle size is -6.9nm. After reduction its particle size disribution is more homogeneous and the average particle size is -3.2nm. The FAB-MS results showed that at 773K in the process of reduction cobalt species were dislodged from the channels of catalyst to external surface and surface can become very rich in cobalt of cobalt oxide. The determination and calculation of the reduction degree give us a conclusion that the reduction process is a typic touching sphere model and the reduction degree is difficult to reach 100% under our experimental condition. From all of the former experiment results, we suggest that the cobalt clusters may be formed after reduction by H2, which induce the production of Bronsted acid site so that n-hexane cracking reaction can occur on this catalyst and carboniogenic products distribution exists. The peak of Bronsted acid is also found in the IR spectra of the reducted Co / AlPO4-5.