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 degrees C, C2H6:O-2:N-2 = 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. (C) 1998 Academic Press.