Platinum ions experiment

CAT 1 = platinum ion-exchanged zeolites without salen CAT 2 = sublimation of salen into platinum ion-exchanged zeolites CAT 3 = zeolite USY impregnated with platinum salen complexes CAT 4 = AljOi impregnated with platinum salen complexes CAT 5 = SiOa impregnated with platinum salen complexes CAT 6 = homogeneous experiment without zeolite... 

It follows from the proposed mechanism of chloride ion exchange in this system that platinum exchange between the platinum(ii)-platinum(iv) species should proceed at the same rate as does the chloride ion exchange. Another way of observing the same thing would be to start with Pt in one of the complexes and follow the rate at which it is distributed between the two different oxidation states of platinum. These experiments have been done and support the proposed mechanism. 

We have undertaken a series of experiments Involving thin film models of such powdered transition metal catalysts (13,14). In this paper we present a brief review of the results we have obtained to date Involving platinum and rhodium deposited on thin films of tltanla, the latter prepared by oxidation of a tltanliua single crystal. These systems are prepared and characterized under well-controlled conditions. We have used thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and static secondary Ion mass spectrometry (SSIMS). Our results Illustrate the power of SSIMS In understanding the processes that take place during thermal treatment of these thin films. Thermal desorption spectroscopy Is used to characterize the adsorption and desorption of small molecules, In particular, carbon monoxide. AES confirms the SSIMS results and was used to verify the surface cleanliness of the films as they were prepared. 

Experiments by Freund and Spiro/ with the ferricyanide-iodide system showed that the additivity principle held within experimental error for both the catalytic rate and potential when the platinum disk had been anodically preconditioned, but not when it had been preconditioned cathodically. In the latter case the catalytic rate was ca 25% less than the value predicted from adding the current-potential curves of reactions (15) and (16). This difference in behavior was traced to the fact that iodide ions chemisorb only on reduced platinum surfaces. Small amounts of adsorbed iodide were found to decrease the currents of cathodic Fe(CN)6 voltam-mograms over a wide potential range. The presence of the iodine couple (16) therefore affected the electrochemical behavior of the hexacyanofer-rate (II, III) couple (15). 

Platinum catalysts were prepared by ion-exchange of activated charcoal. A powdered support was used for batch experiments (CECA SOS) and a granular form (Norit Rox 0.8) was employed in the continuous reactor. Oxidised sites on the surface of the support were created by treatment with aqueous sodium hypochlorite (3%) and ion-exchange of the associated protons with Pt(NH3)42+ ions was performed as described previously [13,14]. The palladium catalyst mentioned in section 3.1 was prepared by impregnation, as described in [8]. Bimetallic PtBi/C catalysts were prepared by two methods (1) bismuth was deposited onto a platinum catalyst, previously prepared by the exchange method outlined above, using the surface redox reaction ... 

If a voltage is applied across two platinum electrodes (usually platinum sheets coated with platinum black) placed in an electrolytic solution, an electric current will be transferred to an extent that is in accordance with the amounts and the mobilities of the free positive and negative ions present in the solution. Under the precautions required (see Section 2.1.1.2), the experiment obeys Ohm s law, which here can be described by... 

However, in our experiments the complex of platinum (IV) with KI, K2[PtIg], was not affected by 1 h of sonication, probably because of the low concentration and inert nature of the metal ion involved and the relatively weak power of the ultrasound (20 kHz, 6 W/cm2). 

Table 11 summarizes results of spin trapping experiments where PBN-Nu and other ST-Nu" systems have been oxidized anodically at platinum. Originally, all the reactions were suggested to proceed via Nu radicals (Janzen et al., 1980 Walter et al., 1982), but the fact that PBN is oxidized at a lower potential than Cl-, CNO and CN- (Tables 1 and 5) clearly shows that the faster electrochemical process must be PBN— PBN + at the potentials employed. On the other hand, azide ion is oxidized in a faster reaction than any of the spin traps used and thus azide radical is implicated as being trapped. The Cr 4MePyPBN [17] system is a case where possibly Cl is involved in view of the high pa of this spin trap. 

Photolytic. Water containing 2,000 ng/pL of dibromochloromethane and colloidal platinum catalyst was irradiated with UV light. After 20 h, dibromochloromethane degraded to 80 ng/pL bromochloromethane, 22 ng/pL methyl chloride, and 1,050 ng/pL methane. A duplicate experiment was performed but 1 g zinc was added. After about 1 h, total degradation was achieved. Presumed transformation products include methane, bromide, and chloride ions (Wang and Tan, 1988). 

Such electrochemical experiments have been used to generate and study the reactivity of anionic species [(R4)- = NCCH2 ]112. In another application, electrogenerated extra radical anions or dianions were used in the determination of pKA values for common phosphonium ions, via double potential step chronoamperometry at a platinum cathode180. 

Halogenated Hydrocarbons. A few halogenated hydrocarbons were studied by the usual procedure, using mixtures in air over the platinum filament. Neither dichlorodifluoromethane (CC12F2) nor 1,1-dichloro-ethene yielded a measurable ion current at temperatures up to 900°C. 1,1,1-Trichloroethane yielded a modest ion current, but the results were erratic and not reproducible. There was some indication that the halogen compounds changed the behavior of the filament. Consequently, no further experiments with halogenated compounds were conducted. This erratic behavior was in contrast with the very reproducible results with hydrocarbons. 

In these experiments, synthetic zeolites of the faujasite-type without binding substance were used. Calcium and nickel-calcium samples in ionic form were obtained by ion exchange under conditions ensuring stability of the crystal structure (5). Platinum addition was carried out by ion exchange with Pt(NH3)6Cl4 (6). 

The results obtained clearly demonstrate that sulfate ions promote the consolidation of titania morphology in nanometer scales and the formation of a crystalline, anatase phase in aerogels dried using supercritical carbon dioxide. This trend is consistently demonstrated by adsorption experiments as well as SAXS and XRD studies. The presence of platinum promotes the formation of a fine polymeric structure of titania in nanometric scales. After calcination all samples exhibit a similar morphology, yet with a notable difference in texture parameters. 

The activation of the normally inert methylene group of glycine by coordination to a transition ion has been recognized for many years. The substantial increase in the acidity of the methylene hydrogens has been directly confirmed by deuterium labelling experiments,451 and has also been shown to occur in other a-aminocarboxylate complexes of cobalt(III)451 456 and platinum(II).457... 

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