Catalytic Performances of Co/TiO2 Catalysts in the Oxidative Dehydrogenation of Ethane to Ethylene: Effect of CoTiO3 and Co2TiO4 Phase Formation

Co/TiO2 catalysts with different cobalt loadings (3.8, 7.5 and 15 wt%) were prepared by impregnation method of Co(NO3)(2) 6H(2)O over titania. Samples containing Co(NO3)2 center dot 6H2O and TiO2 in stoichiometric proportions in order to obtain CoTiO3 and Co(2 )TiO4 phases were also synthesized. The effect of the calcination treatment at two different temperatures, 550 and 1150 degrees C, was investigated. Characterizations by several techniques, such as XRD, UV-vis-NIR, DRS, Raman and XPS, were carried out. XRD showed the coexistence of three phases: CoTiO3; Co2TiO4 and Co3O4 after calcination at 550 degrees C, while calcination at high temperature (1150 degrees C) led to single-phase systems (CoTiO3 or Co2TiO4). Diffuse reflection and XPS spectroscopy showed that divalent cobalt occupies octahedral sites in the ilmenite phase, and both tetrahedral and octahedral sites in the spinel phase. The catalytic performances of the prepared catalysts were evaluated in the oxidative dehydrogenation reaction (ODH) of ethane to ethylene, as a function of the Co content for Co/TiO2 catalysts and as a function of the calcination temperatures for the CoTiO3 and Co2TiO4 phases. Co(7.5)/TiO2 was the most active, although the conversion of ethane decreased in the first 150 min of the reaction, reaching values comparable to those of Co2TiO4 and CoTiO3; however, Co(7.5)/TiO2 was confirmed as having the best selectivity to ethylene in comparison with the bulk phases, CoTiO3 and Co2TiO4. The influence of the reaction mixture composition, specifically the presence of water, at different percentages, was investigated. There is a decrease in the overall ethane conversion and an increase in the ethylene selectivity when the percentage of water increases. This behavior can likely be attributed to an increase in the surface concentration of hydroxyl species (OH), resulting in heightened surface acidity.

Automated summary

Co/TiO2 catalysts with different cobalt loadings were prepared and the effect of calcination temperature on catalytic performance was investigated. Co(7.5)/TiO2 exhibited the highest selectivity to ethylene, and the presence of water in the reaction mixture influenced the overall conversion and selectivity. Characterizations by various techniques were carried out to analyze the catalysts.