Preparation, performances and reaction mechanism for the synthesis of H2O2 from H2 and O2 based on palladium membranes

A series of new tubular catalytic membranes (TCMʹs) have been prepared and tested in the direct synthesis of H2O2. Such TCMʹs are asymmetric α-alumina mesoporous membranes supported on macroporous α-alumina, either with a subsequent carbon coating (CAM) or without (AAM). Pd was introduced by two different impregnation techniques. Deposition–precipitation (DP) was applied to CAMʹs to obtain an even Pd particles distribution inside the membrane pore network, whereas electroless plating deposition (EPD) was successfully applied to AAMʹs to give a 1–10 μm thick nearly-dense Pd layer. Both type of membranes were active in the direct synthesis of H2O2. Catalytic tests were carried out in a semi-batch re-circulating reactor under very mild conditions. Concentrations as high as 250–300 ppm H2O2 were commonly achieved with both CAMʹs and AAMʹs after 6–7 h time on stream, whereas the decomposition rate was particularly high in the presence of H2. Important features are the temperature control and pre-activation. In order to slow down the decomposition and favor the synthesis of H2O2 a smooth metal surface is needed.