Noble metal coatings metals

Jung et al. investigated the partial oxidation of methane on noble metal coated metallic monoliths heated by electricity [484]. Over a palladium catalyst supported by alumina, auto-ignition of the reaction took place at 270 °C and an O/C ratio of 1.1. However a high O/C ratio of 1.4 was required to achieve 98.9% methane conversion. 

Table 7-3 Composition and properties of noble metals with metal oxide coatings...

The term pyrophoric has usually been applied to the ignition of very fine sizes of metal particles. Except for the noble metals, most metals when refined and exposed to air form an oxide coat. Generally this coating thickness is of the order of 25 A. If the oxide coat formed is of greater size than that of the pure metal consumed, then the coat scales and the nascent metal is prone to continuously oxidize. Iron is a case in point and is the reason pure iron rusts. 

Noble metal coatings (e.g., nickel) can be effective, but only if they remain unbroken and are of sufficient density and thickness. Electrolytic deposits of tin, lead, copper or silver on steel are also considered as protectors and probably do not modify the normal features of fatigue because they suppress contact with the surrounding environment. Observations made on the use of deposits of nickel or chromium are contradictory.7... 

Incoloy, Inconel Bare—2-4 mg/cm2 in 1000 h 900°C Aluminide coatings— approximately 1 mg/cm2 in 1,000 h 900 C Intergranular corrosion observed for 800H Noble metal coatings may provide corrosion protection... 

Pt coating may serve function of catalyst and reduce corrosion Corrosion benefits of noble metal coatings must be demonstrated... 

Huff, M.P. Tornianen, P.M. Schmidt, L.D. Partial oxidation of alkanes over noble metal coated monoliths. Catal. Today 1994, 21 (1), 113-128. 

Zn-Al LDHs can be prepared by electrodeposition from aqueous solutions of the nitrates of such metals (Yarger et al., 2008). Cathodic depositions, conducted at room temperature without stirring over noble metal-coated electrodes, were achieved by reducing nitrate ions to generate hydroxide ions on the working electrode, the optimal potential being -1.65 V vs. AgCl/Ag in 4 M KCl. The overall reactions involved are... 

The Krebscosmo Bipolar Cell Electrolyzer BMZ 7.5 which is basically made from steel and titanium. The partition wall of the bipolar electrode is a PTFE foil. Anodes are expanded titanium sheet with noble metal coatings and the cathode structure is a perforated steel sheet. The cell units can be arranged in parallel groups of bipolar elements. Each cell element has 2.5 m of membrane area that operate at a nominal amperage of 7.5 KA. The cell block of the BMZ 7.5/64 electrolyzer consists of 64 elements with 16 series elements with 4 current paths with a nominal block amperage of 30 KA. Electrolytic performance is not disclosed (74). 

Due to the known limitations of the world oil reserves, methane oxidation under fuel rich conditions will become increasingly important for the production of synthesis gas. which through methanol synthesis and Fischer-Tropsch reactions is the basis of many important petrochemical synthesis routes. Therefore, catalytic oxidation of methane has again become the focus of much basic and applied catalysis research in recent years. In this context, Schmidt and coworkers were able to show recently, that catalytic direct oxidation of methane over noble metal coated monoliths can yield CO and H2 with very high conversions and selectivities at the desired 1 2 CO H2 ratio (Hickman and Schmidt. 1992 and 1993a Torniainen and Schmidt. 1994 Bharadwaj and Schmidt. 1995). 

The typical metals in this category are silver, gold, and the platinum metals rhodium, palladium, platinum, and ruthenium. The demands for corrosion protection by noble metal coatings are a pore- and crack-free deposit and a layer thickness that is able to protect the substrate for the expected lifetime of the plated parts. 

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