Palladium-modified catalytic membranes for the direct synthesis of H2O2: preparation and performance in aqueous solution

A series of new tubular catalytic membranes (TCMs) have been prepared and tested in the direct synthesis of H2O2. Such TCMs are carbon-coated asymmetric α-alumina mesoporous membranes supported on macroporous α-alumina. Pd was introduced by deposition-precipitation to obtain an even Pd particle distribution inside the membrane pore network. This type of membrane was active in the direct synthesis of H2O2. Catalytic tests were carried out in a semi-batch recirculating reactor under very mild conditions. Concentrations as high as 250-300 ppm H2O2 were commonly achieved after 6-7 h on stream, with a particularly high decomposition rate in the presence of H2. Important features are optimization of the metal deposition procedure and preactivation. To slow down the decomposition and favor the synthesis of H2O2, a smooth metal particle surface is needed.