Catalyst continued silver

The loss of the catalytically active surface of Raney nickel due to recrystallization is a continuously progressing process that can be retarded to some extent in Raney-nickel anodes by dispersing oxide ceramic materials like Zr02 and Ti03 in the nickel matrix. More serious is anodic oxidation for some metals additionally accompanied by dissolution of the catalyst to which even platinum is subject but which is an even more serious hazard for the less noble catalysts as silver and Raney nickel. 

Sato and Seo [277] demonstrated that a silver catalyst continuously emits low-energy electrons. This emission is chemically stimulated when the catalyst produces ethylene oxide. There is a strong correlation between the production rate and the emission rate. The emitting layer is continuously renewed and is apparently silver oxide. 

Electroless reactions must be autocatalytic. Some metals are autocatalytic, such as iron, in electroless nickel. The initial deposition site on other surfaces serves as a catalyst, usually palladium on noncatalytic metals or a palladium—tin mixture on dielectrics, which is a good hydrogenation catalyst (20,21). The catalyst is quickly covered by a monolayer of electroless metal film which as a fresh, continuously renewed clean metal surface continues to function as a dehydrogenation catalyst. Silver is a borderline material, being so weakly catalytic that only very thin films form unless the surface is repeatedly cataly2ed newly developed baths are truly autocatalytic (22). In contrast, electroless copper is relatively easy to maintain in an active state commercial film thicknesses vary from <0.25 to 35 p.m or more. 

Electrochemical Process. Several patents claim that ethylene oxide is produced ia good yields ia addition to faradic quantities of substantially pure hydrogen when water and ethylene react ia an electrochemical cell to form ethylene oxide and hydrogen (206—208). The only raw materials that are utilized ia the ethylene oxide formation are ethylene, water, and electrical energy. The electrolyte is regenerated in situ ie, within the electrolytic cell. The addition of oxygen to the ethylene is activated by a catalyst such as elemental silver or its compounds at the anode or its vicinity (206). The common electrolytes used are water-soluble alkah metal phosphates, borates, sulfates, or chromates at ca 22—25°C (207). The process can be either batch or continuous (see Electrochemicalprocessing). 

This study relates to a continuous process for the preparation of perfluoroalkyl iodides over nanosized metal catalysts in gas phase. The water-alcohol method provided more dispersed catalysts than the impregnation method. The Cu particles of about 20 nm showed enhanced stability and higher activity than the particles larger than 40 nm. This was correlated with the distribution of copper particle sizes shown by XRD and TEM. Compared with silver and zinc, copper is better active and stable metal. 

Eranen, K., Lindfors, L.E., Klingdted, F. et al. (2003) Continuous reduction of NO with octane over a silver/alumina catalyst in oxygen-rich exhaust gases combined heterogeneous and surface-mediated homogeneous reactions, J. Catal. 219, 25. 

The commercial success of the indirect oxidation route has dampened enthusiasm for continuing the search for the silver bullet catalyst that will facilitate direct oxidation, a la EO. Further activity in that area seems more and more like the quest for that Philosophers Stone that turns lead into gold. 

In 1986, a process to produce 1 by the continuous, vapor phase oxidation of 1,3-butadiene over a silver on alumina catalyst was discovered by Monnier and Muehlbauer of the Kodak Corporate Research Laboratories (10). The process was further developed and commercialized by Eastman Chemical Company at its Longview, Texas plant (11). Following this discovery of an economical process for 1, the production of 2,5-DHF was once again of commercial interest. 

The uniqueness of silver as an epoxidation catalyst has continuously attracted interest and several valuable articles have appeared since the... 

This reaction is accompanied by complete combustion into water and carbon dioxide. The only selective catalyst known is based on silver. This catalyst was known as early as the 1930s and has been continuously improved since then in a rather empirical way. It has been discovered that the catalyst may be promoted by the addition of alkali metal ions. Moreover, the presence of chlorine has a beneficial effect (cf. Fig. 5.11) [94]. Chlorine has to be added continuously because it disappears from the surface by reacting to give chlorinated ethane. It is sufficient to mix 10-40 ppm chlorine with the feed. The feed consists of a mixture of... 

Successful examples of selective oxidation catalysis in industry include the conversions of ethylene to ethylene oxide and of methanol to formaldehyde, both on silver catalysts. Ethylene oxide, with an annual worldwide production capacity over 11 million tons, is an important intermediate for the production of glycols (antifreeze agents), ethoxylates (additives in washing powder), cosmetics, polyester fibers, and pharmaceuticals. The partial oxidation of ethylene to ethylene oxide is carried out on silver metal particles supported on o -Al203 or SiC and promoted by alkaline earth or alkali metals. Trace amounts of ethylene dichloride are also fed continuously into the reactor to suppress deep oxidation. Selectivities of about 75-85% are typical nowadays for this process. Formaldehyde, with a production capacity of... 

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