Oxidative dehydrogenation of ethane to ethene over BaO- and BaBr₂-modified Ho₂O₃ catalysts

The addition of BaBr₂ (<70 mol%) to Ho₂O₃ could improve considerably both the C₂H₆ conversion and C₂H₄ selectivity of the ODE (oxidative dehydrogenation of ethane) reaction. The use of BaO as a modifier was not suitable because the catalyst degraded rapidly due to BaCO₃ formation. At 640°C, C₂H₆ : O₂ : N₂ = 2 : 1 : 4, and space velocity = 6000 mL h^-1 g^-1, C₂H₆ conversion of 70.6%, C₂H₄ selectivity of 80.2%, and C₂H₄ yield of 56.6% were observed over the 50 mol% BaBr₂/Ho₂O₃ catalyst after a reaction time of 1 h. We conclude that the addition of BaBr₂ to Ho₂O₃ can (i) enhance oxygen activation, (ii) protect a certain amount of active basic sites from CO₂ poisoning, and (iii) suppress C₂H₄ deep oxidation. It is possible that the presence of Br ions could have induced the formation of new active sites suitable for C₂H₄ generation. However, we observed continuous leaching of bromine during the ODE reaction, and the 50 mol% BaBr₂/Ho₂O₃ catalyst gradually degenerated to a somewhat aged BaO/Ho₂O₃ catalyst. After 40 h of reaction, the C₂H₆ conversion, C₂H₄ selectivity, and C₂H₄ yield diminished to 51.8, 63.8, and 33.0%, respectively.