Platinum ions reduction

The Pt4f signal obtained with samples with high platinum loading (1 and S%) shows us that despite the low heating rate [0. Scc/min] used during the calcination of the san le, the deconqrosition of the tetramin platinum ion provoked the reduction ofthe ion at sqrerfdal level TPR results (Fig. 6) ow that this did not occur in the bulk... 

The inefficiency of the platinum/hydrogen reduction system and the dangers involved with the combination of molecular oxygen and molecular hydrogen led to a search for alternatives for the reduction of the manganese porphyrin. It was, for example, found that a rhodium complex in combination with formate ions could be used as a reductant and, at the same time, as a phase-transfer catalyst in a biphasic system, with the formate ions dissolved in the aqueous layer and the manganese porphyrin and the alkene substrate in the organic layer [28]. 

It has recently been recognized that crystal structure and particle size can also influence photoelectrochemical activity. For example, titanium dioxide crystals exist in the anatase phase in samples which have been calcined at temperatures below 500 °C, as rutile at calcination temperatures above 600 °C, and as a mixture of the two phases at intermediate temperature ranges. When a range of such samples were examined for photocatalytic oxidation of 2-propanol and reduction of silver sulfate, anatase samples were found to be active for both systems, with increased efficiency observed with crystal growth. The activity for alcohol oxidation, but not silver ion reduction, was observed when the catalyst was partially covered with platinum black. On rutile, comparable activity was observed for Ag, but the activity towards alcohol oxidation was negligibly small . Photoinduced activity could also be correlated with particle size. 

Treatment of some mesylated N,N-diallylamino sugars with triethylamine tnhydrofluoride results m the fluorination and regioselective transfer of the mtro gen atom to give, after platinum-catalyzed reductive deallylation, 2,3-ammo-fluorodeoxysugars A mechanism involving aziridimum ions has been proposed [44] (equation 32)... 

Fig. 3.19 Cathodic polarization curves for 100 and 10,000 ppm Fe3+ (as FeCI3) on platinum in nitrogen-deaerated solution. The increase in current density at 400 mV (SHE) is due to a velocity effect in introducing nitrogen sparging into the solution. The limiting current density is increased by a factor of about 100 on increasing the concentration from 100 to 10,000 ppm. The increase in current density near-100 mV (SHE) is due to hydrogen ion reduction resulting from a decrease in pH dueto Fe3+ hydrolysis.

Platinum ions reduce to metallic Pt by injecting holes into the Si valence band. Thus Pt ions act as an oxidizing agent for silicon, and result in the simultaneous formation of photoluminescent porous silicon under certain conditions. Nickel ions may exchange charge with both the conduction and the valence band. The reduction of Ni ions competes with hydrogen evolution, and the deposition of Ni can only be achieved at high pH where it is kinetically faster. The role of silicon surface states as reaction intermediates is discussed. 

When the sensor is exposed to a test gas environment, the oxygen molecules get adsorbed onto the porous eleetrode, commonly made of platinum, and dissociate into atomic oxygen. Then the oxygen atoms diffuse into the boundary of the eleetrode (Pt), eleetrolyte (YSZ), and the gas called the triple phase boundary (TPB), where electron transfer takes place from the electrode to the atomic oxygen forming O " ions (reduction). The overall electrode reaetions are as follows (Robertson and Michaels 1990 Mitterdorfer and Gauckler 1999) ... 

Another metallization chemistry [9-11] involves the formation of a covalent bond between palladium and platinum ions and the amine groups of DNA bases. A solution of palladium acetate is mixed with a solution of DNA and the palladium ions become associated with DNA by forming covalent bonds with the amine groups of the DNA bases. Subsequent reduction of the palladium ions allows them to form autocatalytic sites for the deposition of a palladium metal coating on the surface of the DNA. Reduction of the palladium bonded to the DNA results in very small metal deposits of palladium. However, there may not be enough metal to form a continuous conducting wire after a single treatment with the palladium... 

The standard potential for the anodic reaction is 1.19 V, close to that of 1.228 V for water oxidation. In order to minimize the oxygen production from water oxidation, the cell is operated at a high potential that requires either platinum-coated or lead dioxide anodes. Various mechanisms have been proposed for the formation of perchlorates at the anode, including the discharge of chlorate ion to chlorate radical (87—89), the formation of active oxygen and subsequent formation of perchlorate (90), and the mass-transfer-controUed reaction of chlorate with adsorbed oxygen at the anode (91—93). Sodium dichromate is added to the electrolyte ia platinum anode cells to inhibit the reduction of perchlorates at the cathode. Sodium fluoride is used in the lead dioxide anode cells to improve current efficiency. 

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