Preparation of Pd-composite membranes

Pure Pd-composite membranes are the most popular Hj permeation membranes, whose preparation methods have been extensively studied. In what follows, some main and novel methods are summarized. 

Electroless plating, in particular, is an autocatalytic process which allows obtaining thin films with good adhesion (Basile and Gallucd, 2011c).The Pd 

The traditional activation of the substrates is usually performed by dipping the substrates first into a stannous chloride solution (sensitization) and, thereafter, in a Pd chloride solution (activation), several times. A typical composition of the sensitization and activation solutions is shown in Table 2.5 (Basile and Gallucci, 2011c). It can be noted that activation is performed at acidic pH in order to maintain a good salt solubility. The overall reaction is  

The surface modification can be done separately or combined with the activation process and has been extensively studied for the preparation of Pd and Pd-based alloy membrane on porous substrates. Except for obtaining a smooth surface, the modification can simultaneously introduce a buffer layer to avoid diffusion reaction between Pd/Pd-based alloy and substrate. Furthermore, the modification process can introduce a well-dispersed Pd-seed for the catalyst of the electroless plating Pd. 

Using Si02 colloidal suspensions, Su et al. (2005) modified the porous stainless steel tube with a nominal particle retention size of 0.2 pm. The Si02 colloids with particle sizes 70-100 nm and 20-50 nm were coated on the substrate in a clean room at 22°C and 50% relative humidity. Each of the two suspensions was prepared by mixing Snowtex and ethanol at a weight ratio of 1 5 and was coated on the outer surface of the substrate four times 

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