Titania-Supported Cobalt and Cobalt-Phosphorus Catalysts:Characterization and Performances in Ethane Oxidative Dehydrogenation

摘要

TiO_2-supported Cobalt and cobalt-phosphorus catalysts pre-pared by impregnation are characterized by XRD, XPS, Laser Raman Spectroscopy (LRS), and Diffuse Reflectance Spectroscopy (DRS) and investigated in ethane oxidative dehydrogenation (ODH). At low cobalt loadings, the carrier is essentially covered by octahedral CO~(2+) ions, whereas at concentrations superior to 3.7 wt% formation of the Co_3O_4 spinel is observed. The best per-formance in ethane ODH is achieved at 550degC with the sample containing 7.6 wt% Co. The reaction begins with a conversion of 33% and a selectivity around 75%, then it decreases to reach after 150 min on stream a stationary state at 22% of conversion and 60% selectivity. This loss of 30% of the initial activity may be as-sociated with a decrease of the specific surface area and the con- comitant formation of CoTiO_3 and Co_2TiO_4, as revealed by LRS, in situ DRS, and XPS analysis. The activity in ethane ODH seems to be mainly related to the presence of Co~(2+) ions octahedral sites. Addition of phosphorus to Co(7.6)/TiO_2 catalysts results in the re-duction of Co~(3+) ions and a growth of amorphous cobalt-phosphorus compounds which provoke a severe decrease of the catalyst performance.