Titania-supported cobalt and cobalt-phosphorus catalysts: Characterization and performances in ethane oxidative dehydrogenation

TiO2-supported Cobalt and cobalt-phosphorus catalysts prepared by impregnation are characterized by XRD, XPS, Laser Raman Spectroscopy (IRS), and Diffuse Reflectance Spectroscopy (DRS) and investigated in ethane oxidative dehydrogenation (ODH). At low cobalt loadings, the carrier is essentially covered by octahedral Co2+ ions, whereas at concentrations superior to 3.7 wt% formation of the CO3O4 spinel is observed. The best performance in ethane ODH is achieved at 550 degreesC 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 associated with a decrease of the specific surface area and the concomitant formation of CoTiO3 and Co2TiO4, as revealed by LRS, in situ DRS, and XPS analysis. The activity in ethane ODH seems to be mainly related to the presence of Co2+ ions octahedral sites. Addition of phosphorus to Co(7.6)/TiO2 catalysts results in the reduction of Co3+ ions and a growth of amorphous cobalt-phosphorus compounds which provoke a severe decrease of the catalyst performance. (C) 2001 Academic Press.