Catalyst coating electroless plating

Electroless Electrolytic Plating. In electroless or autocatalytic plating, no external voltage/current source is required (21). The voltage/current is suppHed by the chemical reduction of an agent at the deposit surface. The reduction reaction must be catalyzed, and often boron or phosphoms is used as the catalyst. Materials that are commonly deposited by electroless plating (qv) are Ni, Cu, Au, Pd, Pt, Ag, Co, and Ni—Fe (permalloy). In order to initiate the electroless deposition process, a catalyst must be present on the surface. A common catalyst for electroless nickel is tin. Often an accelerator is needed to remove the protective coat on the catalysis and start the reaction. 

After fixing Pd catalyst on modified nylon 12 surfaces by various methods, they were coated by electroless Ni-P alloy plating. Alumina- or silica-modified nylon 12 was well wet by electroless plating liquid, and modified nylon 12 situations in a liquid were good dispersed. Nickel metal was deposited on silica or alumina surface. Finally, it was confirmed that the formation of metal layer was depended mainly on the method of Pd catalyst fixing. 

A Fe-Co-B catalyst system on Ni foam was prepared by a modified electroless plating method. Hydrogen production rate of the system was foimd as 221 mL min g p at 30°C. Activation energy was calculated as 27 kj moTF The relatively higher catalytic activity of the catalyst is related with its porous microstructure. This enhanced the accessibility of reactants to catalyst active sites. Catalyst coating was 12.5 mg cm (Ni foam) and the composition was 56.4% Co, 38.8 wt.% Fe and 4.8 wt.% B. BET specific surface area of the catalyst system was 9.7 m g F Also in the study, it was claimed that the maximum reaction rate was not observed at the beginning of the reaction due to the pore diffusion resistance and hydrogen desorp-tion/absorption equilibrium in the catalyst was in need of time. The catalyst system lost 30% of its initial catalytic activity after 3 cycle and 46% after 6 cycle [23]. 

Co-B on Ni foam support catalyst system was produced by low temperature electroless plating method. With this approach, maximum hydrogen production rate of 24 L min g at 30°C was achieved. The catalyst system was mixture of spherical particles and a thin nanosheet-like structure of 10 nm. Layered aggregates of these nanosheet-like morphologies were seen as smooth spherical particles of size 2-10 pm. Co/B ratio in the catalyst coating was 3.67 according to EDX results and 1.45 according to XPS... 

The actual reaction is more complicated than equation (12.1) becausephosphorous and protons are also reduced. As a result, a nickel phosphorous alloy rather than pure nickel is obtained. Under appropriate conditions, the reduction reactions only take place at the metal surface, which acts as a catalyst. Electroless plating thus produces a compact coating of uniform thickness all over the substrate surface. In contrast to electrodeposition, electroless plating can also be used with insulating substrates, such as polymers, the surface of which has been previously activated by a suitable catalyst. 

Ferreira-Aparicio et al. reported the development of a laboratory-scale membrane reactor for the partial dehydrogenation of methylcyclohexane into toluene in a membrane reactor [527]. A platinum/alumina catalyst containing 0.83 wt% platinum was put into a porous stainless steel tube, which had been prior coated with a palladium membrane by electroless plating. At 350 °C reaction temperature and a pressure of 1.4 bar at the reaction side, 99% of the hydrogen product could be separated through the membrane, which had a thickness of 11 pm. However, the sweep stream required on the permeate side was more than 20 times higher than the hydrogen permeate flow rate that could be achieved. 

Most electroless silver appHcations are for silvering glass or metallizing record masters. Mirror production is the principal usage for electroless silver. The glass support is cleaned, catalyzed using a two-step catalyst, and coated on one side with an opaque silver film (46). Silver-plated nylon cloth is used as a bacteriostatic wound dressing. A tiny current appHed to the cloth causes slow silver dissolution. The silver acts as a bactericide (47). 

Surfaces can also be coated without involving electricity. Electroless nickel plating, for example, involves pretreating the surface of any material, including nonconductive materials, with a catalyst such as sodium hypophosphite. This treated surface is then immersed in a heated nickel-phosphorous or nickel-boron solution. The metal ions from the solution are reduced to metal in contact with the catalyst and form a dense alloy layer on the treated surface. 

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