Catalyst sputter coating

For this micro reactor version, the catalyst was coated on the AlMg3 platelet as a thin silver layer by sputtering [43,44], A further set of platelets was covered with an a-alumina layer by sol-gel technique and impregnated by a three-step procedure with silver lactate. 

This process is conducted under vacuum and deposition is line-of-sight. It is expensive and best suited to planar surfaces having relatively small areas. Impediments to commercial applications are aids to fundamental research. Catalysts can be prepared, studied, and tested under UHV conditions and in the absence of chemical contaminants. Most of our detailed understanding of gold nanoparticle catalysts comes from work on sputter-coated model catalysts. 

Catalyst bed formation by physical etching involves depositing a catalyst layer (<100nm) by either evaporation or sputter coating and bombarding it with energetic... 

Fig. 14.15 SEM views of the catalyst coated whiskers on a microstructiired substrate after sputter coating with a PtCoMn alloy. Reproduced from [54] with permission of the Electrochemical Society...

In our study 2 ml of Silfo was mixed with 2 drops of the catalyst and applied to the skin surface. It was peeled off after 1-2 minutes when dry and subsequently covered with a thin smear of DPX (R. A. Lamb, London) — a styrene based slide mounting medium, and placed in a desiccator for 6 hours. The surface replicas were then removed from the rubber base. These were then sputter coated with gold in a Polaron, E 5000 coater and viewed in a Cambridge scanning electron microscope (SEM) stereoscan, Mark II. Replicas of S.C. from patients with dominant ichthyosis, a patient with Refsum s syndrome and normal controls were studied. 

A Pt catalyst was applied by dry and wet techniques. By means of sputtering using a mask process protecting parts of the microstructure, the micro channel bottom was coated selectively. In addition, an y-alumina layer was applied by the sol-gel technique. Initially, the whole micro structure was covered by such a layer. Then, photoresist was applied and patterned so that only the channel part remained covered. After removal of the exposed photoresist and unprotected y-alumina, only the channel bottom was coated with y-alumina. 

For comparison, a 20wt% Pt/XC72 catalysts prepared commercially by E-TEK had an average diameter of 2.6 nm. The sputter deposited Pt had a standard deviation between 0.42 and 0.49 nm, whereas the commercial E-TEK catalyst has a standard deviation of 0.79 nm. Thus, the sputtering technique creates smaller and more uniformly dispersed Pt particles than those prepared chemically. It should be noted that the Pt/C samples having low loadings prepared via sputtering did not uniformly coat... 

Usually the nanotube arrays have been made from a titanium thick film or foil, in which case the resulting nanotubes rest upon an underlying Ti substrate as separated by a barrier layer. The nanotube arrays have also been fabricated from a titanium thin film sputtered onto a variety of substrates, such as silicon and fluorine doped tin oxide (FTO) coated conductive glass. This extends the possibility for preparing technical catalysts by deposing a thin Ti layer over a substrate (a foam, for example) and then inducing the formation of the nanostructured titania film by anodic oxidation. ... 

Sputtering technologies offer an even faster procedure at the cost of the versatility of the catalysts produced. Sputtering produces catalysts with a dense surface layer. These catalysts are different from industrially used catalysts, which usually have a larger surface area. The BET surface area of sputtered catalysts is below 1 m2 g 1 and thus much lower than the surface area of the wash-coated catalysts (usually above 60 m2 g1). However, if catalysts for a fast reaction have to be screened, the gas components will mainly react at the surface of the catalyst and the porosity of the catalyst is not important. 

The homogeneity of this binary layer composition was examined using secondary neutral particles mass spectrometry (SNMS) [37]. This procedure removes the catalyst coat stepwise and delivers the amount of the catalyst components in the respective layer depending on the sputtering time. One second of sputtering time corresponds here to a layer removal of approximately 1 nm. Hence the sputtering time is also a measure of the layer thickness. The maximum layer thickness was 500 nm. 

The methods proposed in the literature to do so, e.g. spin-coating [9], thermal evaporation [10], chemical vapor deposition [11], flash evaporation [12], laser deposition [13] and r.f. reactive sputtering [14], are rather scarce and complex. Moreover, they are often more dedicated to the deposition of active phase on flat and/or monolithic supports (to produce model catalysts for surface science purposes) than on powder supports. These methods thus usually only allow the production of samples at a small scale, so that they are often inadequate for the production of pulverulent real catalysts in large amounts. 

---