Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Palladium coated ceramic and carbon-modified ceramic membranes (including its characterisation)

Catalytic membranes based on dispersed Palladium as the active component have been prepared. Compared to dense Palladium membranes, these catalytic membranes offer better gas transport rates, reduced costs and higher reaction rates. The catalytic membranes can be applied (besides the target reaction of hydrogen peroxide direct synthesis) to a variety of solid catalysed gas/liquid reactions, which can benefit in terms of improved safety and reduced diffusion limitation. Examples include the (selective) elimination of pollutants in water by hydrogenation or oxidation and the selective synthesis of organics by hydrogenation or oxidation.

Different methods were developed to deposite Palladium uniformly into the fine-porous surface layer of inside-coated as well as outside-coated asymmetric tubular ceramic single-tube and multi channel membranes with or without modification by carbon. Metal organic chemical vapour deposition (MOCVD) was used at DECHEMA: Two tailored batch-type MOCVD variants were developed, both based on a control of the deposition range of the active component in the membrane. One uses an organic wax to trap the sublimed metal precursor prior to (mainly thermal) decomposition; the other relies on a stoichiometric reluctant introduced in the membrane surface layer before the MOCVD by impregnation which later reacts with the precursor vapour. Both methods enable a high Palladium loading; they reach an excellent uniformity of the Palladium content over the whole surface of the membrane and a good control of the deposition depth.

The second method, which was developed, is based on precipitation-deposition, and the third method is based on electroless plating deposition. These methods allow a good and reproducible deposition and a fine control of the amount of Palladium, which is deposited, uniformly in a thin layer of the membrane.

The membranes prepared were characterized by various techniques (AAS, EPMA, SEM, TEM, CO- chemisorption) in order to assess the amount of Palladium deposited, its distribution over the cross section and along the tube axis as well as the Palladium particle size.

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