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.
Scopus Subject Areas
- Physical and Theoretical Chemistry