Metals reacting with gases studied

One major reason for the great interest in the processes of thin metal-containing films is that reactions on the surface of small metal clusters can be studied. Indeed, prior to the development of thin-film chemistry, reactions of similar particles were studied only in the gas phase at rather high temperatures. Under these conditions, most of the primary products are unstable and decompose in the course of further reaction, which is non-selective. As a result, the information obtained on the routes and mechanisms of reactions of disperse metals appears to be scarce, while the use of such reactions in synthesis is inexpedient. Conversely, low-temperature reactions in the films of co-condensates are very promising from the standpoint of determining the detailed reaction mechanism, as well as for synthesis of previously unknown complexes and organometallic compounds. It is important that atoms of only a few metals react with organic compounds immediately at the instant of their contact on the cooled substrate. Rather often, atoms and/or small (molecular) clusters are first stabilized in the film, and then their transformations are observed. 

Analysis of the halohydrocarbons, halocarbons, and sulfur hexafluoride is usually achieved by gas chromatography that is equipped with an electron capture detector. Complex metal anions, such as cobalt hexacyanide, are used as nonradioactive tracers in reservoir studies. The cobalt in the tracer compound must be in the complex anion portion of the molecule, because cationic cobalt tends to react with materials in the reservoir, leading to inaccurate analytic information [1226]. 

Considerable interest in the subject of C-H bond activation at transition-metal centers has developed in the past several years (2), stimulated by the observation that even saturated hydrocarbons can react with little or no activation energy under appropriate conditions. Interestingly, gas phase studies of the reactions of saturated hydrocarbons at transition-metal centers were reported as early as 1973 (3). More recently, ion cyclotron resonance and ion beam experiments have provided many examples of the activation of both C-H and C-C bonds of alkanes by transition-metal ions in the gas phase (4). These gas phase studies have provided a plethora of highly speculative reaction mechanisms. Conventional mechanistic probes, such as isotopic labeling, have served mainly to indicate the complexity of "simple" processes such as the dehydrogenation of alkanes (5). More sophisticated techniques, such as multiphoton infrared laser activation (6) and the determination of kinetic energy release distributions (7), have revealed important features of the potential energy surfaces associated with the reactions of small molecules at transition metal centers. 

The reactivity of metal phosphide cations [MPJ+, and anions [MPJ , may also be studied in the gas phase. Laser ablation of mixtures of cobalt or nickel metal powders with red phosphorus gave a range of anions M PJ and cations [MPJ+ (185). The anions were unreactive, but the cations have been reacted with several neutral molecules. The ions [MPJ+, where M = Co, Ni and x = 2,4, 8, undergo five types of reactions. 

Other Compounds Experimental studies indicate that 1 ppm As from gaseous AsHs in fuel gas does not affect cell performance, but when the level is increased to 9 ppm As, the cell voltage drops rapidly by about 120 mV at 160 mA/cm (71). Trace metals, such as Pb, Cd, Hg, and Sn in the fuel gas, are of concern because they can deposit on the electrode surface or react with the electrolyte (15). Table 6-3 addresses limits of these trace metals. 

Because chemists have defined oxidation in terms of electron transfer, it is quite unnecessary for redox reactions to have oxygen as the oxidizing agent. Study the next example of metallic zinc reacting with chlorine gas to form zinc chloride ... 

In 1825, however, he studied the chemical action of the voltaic current, and tried to isolate chemically the metal believed to be present m alumina. He first prepared liquid aluminum chloride by passing a current of chlorine gas over a mixture of charcoal and alumina heated to redness. By allowing potassium amalgam to react with the aluminum chloride, he prepared an aluminum amalgam, and by distilling off the mercury out of contact with the air, he obtained a metal that looked like tin (11). 

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