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 (TCM's) have been prepared and tested in the direct synthesis of H2O2. Such TCM's 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 CAM's to obtain an even Pd particles distribution inside the membrane pore network, whereas electroless plating deposition (EPD) was successfully applied to AAM's 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 CAM's and AAM's 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.