Platinum metals synthesis catalysts

Plasticizers, copolymerizable type, 264 Platinum metal hydrogenation catalyst, 42 Pleiadiene, MA in synthesis, 182 Polarographic reduction fumarates, 42 fumaric acid, 42 maleates, 42 maleic acid, 42 MA monomer, 42 Polarography... 

Another synthesis of pyrogaHol is hydrolysis of cyclohexane-l,2,3-trione-l,3-dioxime derived from cyclohexanone and sodium nitrite (16). The dehydrogenation of cyclohexane-1,2,3-triol over platinum-group metal catalysts has been reported (17) (see Platinum-GROUP metals). Other catalysts, such as nickel, rhenium, and silver, have also been claimed for this reaction (18). 

Oxides of Platinum Metals Anodes of platinum (and more rarely of other platinum metals) are used in the laboratory for studies of oxygen and chlorine evolution and in industry for the synthesis of peroxo compounds (such as persulfuric acid, H2S2O8) and organic additive dimerization products (such as sebacic acid see Section 15.6). The selectivity of the catalyst is important for all these reactions. It governs the fraction of the current consumed for chlorine evolution relative to that consumed in oxygen evolution as a possible parallel reaction it also governs the current yields and chemical yields in synthetic electrochemical reactions. 

The high selectivity shown by the platinum-tin catalysts and the importance of the industrial synthesis of normal aldehydes suggests that further study will be most rewarding. A review on hydroformylation by the platinum metals is available.359... 

Cadmium chromium(III) selenide can be prepared by the direct combination of the elements or by the reaction of cadmium selenide with chromium(III) selenide. Crystals of cadmium chro-mium(III) selenide have been prepared by flux growth1 in cadmium chloride, by vapor transport,2 and by a liquid-transport method3 with a platinum metal catalyst. The synthesis given... 

In contrast, stepwise substitution reactions on M(CO)6 (M = Cr, Mo, W) have been achieved with a series of heterogeneous catalysts including co-balt(ll) chloride (27), activated charcoal (159), and platinum metals dispersed on oxide or carbon supports (31), to give mono-, di-, tri-, and complete substitution (124) in yields > 90%. Representative reaction times are given in Table II (159). The efficiency of the method was further demonstrated by the stepwise synthesis of the mixed isocyanide complexes m-Mo(CO)4(CNMe)(CNBu ) and /ac-Mo(CO)3(CNMeXCNBu )2 from Mo(CO)6 in <25 min in 85 and 95% yields, respectively (159). 

The hydrogenation of a,/ -unsaturatcd aldehydes to saturated aldehydes is readily achieved over most platinum metal catalysts under mild conditions. The selective synthesis of unsaturated alcohols is, however, much more difficult to perform and several attempts have been made to develop a suitable catalytic system. 

With regard to the electro-catalyst the main research issue is to identify a platinum-based catalyst, i.e. a binary, ternary or quaternary catalyst composed of platinum and one or more transition metals that will be more active (and thereby further reducing the applied potential), exhibit an improved lifespan, and have reduced platinum loadings to reduce the cost. The NWU, located in the North-West province of South Africa where the majority of the world s platinum is mined and produced, is currently setting itself up for the synthesis, characterisation and testing of platinum-based electro-catalysts specifically for normal water electrolysis as well as for S02 electrolysis. 

In some cases a catalyst consists of minute particles of an active material dispersed over a less active substance called a support. The active material is frequently a pure metal or metal alloy. Such catalysts are called supported catalysts, as distinguished from unsupported catalysts, whose active ingredients are major amounts of other substances called promoters, which increase the activity. Examples of supported catalysts are the automobile-muffler catalysts mentioned above, the platinum-on-alumina catalyst used in petroleum reforming, and the vanadium pentoxide on silica used to oxidize sulfur dioxide in manufacturing sulfuric acid. On the other hand, the platinum gauze for ammonia oxidation, the promoted iron for ammonia synthesis, and the silica-alumina dehydrogenation catalyst used in butadiene manufacture typify unsupported catalysts. 

In the presence of CS the reaction did not begin at 25,40, 50, 60, or 70 °C. At 80 - 85 °C instant catalyst conversion from yellow insoluble salt to brown solution, evidently of a Pt(0) complex, takes place. On this catalyst, ethylene was adsorbed to frill tiiethoxysilane conversion. The catalyst proved to be stable in the presence of ethylene, thus testifying to the combined character of the compound. The next day, when a new portion of triethoxysilane was added to the previous synthesis, the reaction proceeded quantitatively, but a little more slowly (lower platinum concentration). In the absence of ethylene on the next day a black residue of platinum metal precipitated where synthesis did not proceed. 

A new method of synthesis of selective platinum catalysts for the hydrogenation of unsaturated carbonyl compounds is presented. Platinum was deposited on the supports tailored with the monolayer of transition metal oxide. Selectivity of these catalysts strongly depended on the type of inorganic support as well as on the type of transition metal in the monolayer. Catalysts were tested in the hydrogenation of furfural, crotonaldehyde and cinnamaldehyde. Selectivity of the synthesis of the appropriate unsaturated alcohols was enhanced when compared with the reactions performed over classical Pt-metal oxide catalysts. 

The complex composition of the systems using O2/H2 oxidant gives evidence that pure metal catalysts do not operate effectively without promoter, which can be halide ions and/or transition metal oxides. Our idea was to bring into contact platinum metal ions with probable promoter by means of synthesis of metal ion containing heteropolytungstates. 

The driving force for tlie development of non-platinum exliaust emission catalysts is the price, strategic importance and low availability of the platinum group metals. Our studies have shown that catalysts based on tin(IV) oxide (Sn02) promoted with chromium and/or copper (Cr-Sn02 and Cu-Cr-Sn02 catalysts) which exhibit excellent three-way catalytic activity - activity which is comparable to that shown by noble metals dispersed on ahunina. This family of materials offers tremendous promise as cheap and efficient catalyst systems for the catalytic conversion of noxious emissions from a variety of sources. In tliis paper we describe tliree aspects of this family of environmental catalysts (1) the synthesis, (2) tlieir characterisation, and (3) their catalytic activity. 

The study was performed with model and commercially important supports and catalysts gamma alumina, which is among the most popular supports in the synthesis of supported metal catalysts for oil refining, petrochemistry, and gas emissions neutralization supported platinum and palladium catalysts containing sulfated zirconia (Pt/SZ, Pd/SZ) or alumina-... 

A more radical approach is to use unwanted stocks of CFCs to prepare useful reagents and an example of this is provided by the catalytic synthesis of HCN from CCI2F2 (CFC-12) and NH3. Nickel titanate, Ni, Fe or Co metals, platinum metals or gold supported on LaFa, AIF3 or activated charcoal, are all possible catalysts, conversion and selectivity for HCN depending on the catalyst used [84]. Reactions occur in the temperature range 600-800 K. 

In spite of a very significant progress achieved with heat-treated macrocyclic compounds as ORR catalysts since the early 1970s, the activity and durability of that family of catalysts are stiU insufficient for replacing platinum at the fuel cell cathode and in other applications. Furthermore, the complex structure of macrocyclic compounds makes their synthesis expensive and potentially noncompetitive with precious-metal-based catalysts also from the materials cost point of view. For those reasons, much effort has been invested by the electrocatalysis research community in recent years into finding less expensive and catalytically more active non-precious metal ORR catalysts that would not rely on macrocylic compounds as either catalysts or catalyst precursors. In the past decade, there has been a significant improvement both in the activity and of non-macrocyclic catalysts, expected to be manufactured at a fraction of the cost of their macrocyclic counterparts. In this section, we review the precursors, synthesis routes, and applications of this relatively new family of catalysts. 

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