Oxidative dehydrogenation of ethane over alumina-supported Pd catalysts. Effect of alumina overlayer

The effect a 45 atom-thick overlayer of aluminum oxide, deposited by atomic layer deposition, was investigated on a 2.5 wt.% Pd/Al₂O₃ catalyst in which the Pd nanoparticles were encapsulated by the support consequent to the preparation method. The overlayer suppressed the activity for oxidative dehydrogenation of ethane, but it also effectively prevented metal sintering and suppressed coking for reactions at high temperatures. On the catalyst with the alumina overlayer, a steady activity was observed even at 600 °C and above when the gaseous oxygen was completely consumed, while attaining 70% selectivity for ethene at 38% conversion, versus 10% selectivity at comparable conversions without the overlayer. The overlayer preferentially deposited on edge Pd atoms, as indicated by preferentially suppression of the CO chemisorption peak at 2056 cm^-1, which are responsible for coking. The high ethene selectivity at 675 °C could be due to coupled homogeneous and heterogeneous reactions at the high temperature, together with phase change of PdO to Pd.