Direct synthesis of hydrogen peroxide is conducted using a palladium membrane reactor. The palladium membrane is prepared on the external surface of the porous a-alumina tubing, by electroless plating (ELP) or chemical vapor deposition (CVD). Thus prepared membrane is immersed into aqueous reaction solution. Hydrogen is supplied from inside of the palladium membrane, while oxygen was bubbled in the reaction solution. Both reacted at the surface of the membrane to produce hydrogen peroxide. Hydrogen peroxide is produced steadily for more than 80 h and the selectivity based on the amount of reacted hydrogen was estimated to be ca. 50%. The reactor performance is investigated in correlation with membrane properties and the hydrogen/oxygen supply pressures. (C) 2009 Elsevier Ltd. All rights reserved.