Chlorine platinum chlorides

The Shilov method, discussed in Section 10.4.1, has been accomplished as a catalytic process.327 Aqueous platinum chlorides can be used as catalysts for the homogeneous catalytic chlorination of methane. The reaction is carried out at 100-125°C with chlorine to yield methyl chloride that is partially hydrolyzed to... 

Foger and Jaeger (70, 71) studied the mechanism of platinum redispersion by chlorine, finding that redispersion occurs by a four-step process. First, one of a number of platinum chloride species forms. For successful redispersion it is critical that conditions be selected such that /J-PtCb forms. This process is influenced by temperature, concentration, and support materials. Second, the volatile / -PtCl2 is transported in the vapor phase. Third, /f-PtCh is readsorbed. 

Electrophilic chlorination of methane is accomplished in water at 125 °C in presence of platinum chloride catalyst989. 

The product is a crystalline substance, hard and brittle, capable of being pounded to powder in a mortar. Density 13-8 at 18° C. Heated in chlorine, silicon chloride is formed, leaving a residue of platinum. 

However, the study failed to reveal bis(ethylene)platinum chloride in the mixture. A similar tratir-chlorine substitution should be easier with the strong trans effect of an olefin ligand. Chart and Wilkins have prepared this compound (84) and found that it rapidly releases ethylene at room temperature ... 

A low-temperature methane chlorination with aqueous platinum chlorides in the presence of chlorine has been reported by Horvath et al. [90]. The reaction of methane with chlorine in water at 398 K in the presence of platinum chlorides results in the platinum-assisted formation of methyl chloride which is partially hydrolysed in situ to methanol (Figure 19). 

Platinum(II) salts as well as the system Pt(II) + Pt(IV) have been used as catalysts in the oxidation of C-H compounds with various strong oxidants. Thus the reaction of methane with chlorine in water at 125 °C in the presence of platinum chlorides affords methyl chloride which is partially hydrolyzed in situ to methanol [17b], A combination of Pt(II) and metalhc platinum oxidized ethane in the presence of oxygen to a mixture of acetic and glycohc acids [17c,d]. 

Ammonium chloride in aqueous solution yields chlorine ions just as the platinum. chloride-ammonia compound, 2NH3.PtCl4 with 1, 2, 3, or 4 additional molecules of ammonia does. Since ionization was pointed out as a characteristic property determining in which way the ammonia had added to the platinic chloride or the influence it exerted in the compound, it is likely that the ammonia in the ammonium chloride is combined with the hydrogen chloride in the same way that the ammonia is combined with the platinic chloride when the chlorines of the latter become ionic. If, therefore, the structure of ammonium chloride is known, it is possible to assign a structure to the addition compounds of platinic chloride and ammonia as far as the ammonia molecules which cause the chlorine atoms to become ionic are concerned. 

Characters and Tests.—Colourless, rhomhoidal crystalline plates, cool saline taste, sparingly soluble in cold water. Its aqueous solution is not affected by silver nitrate or ammonium oxalate. Strongly heated, it fuses, gives off oxygen gas, and leaves a white residue (potassium chloride), which readily dissolves in water, and produces a solution which yields a white precipitate (silver chloride) with silver nitrate, indicating the presence of chlorine, and a yellow precipitate (potassium-platinic chloride) with platinum chloride, showing the presence of potassium. It explodes when triturated in a mortar with sulphur. ... 

At mixed oxide electrodes, free orbitals of the metals from the platinum group (Pt, Ir, Ru) are able to catalyze direct reactions such as the formation of chlorine. First, chloride is bound to the surface of the electrode oxidation happens in the second step. 

Treatment of impure gold is largely via the Miller process (30) in which chlorine is bubbled through the molten metal and converts the base metals to chlorides, which volatilise. Silver is converted to the chloride, which is molten and can be poured. The remaining gold is less pure (99.6%) than that produced by the WohlwiU process and may require additional treatment such as electrolysis. If platinum-group metals (qv) are present, the chlorine process is unsuitable. 

The next step of the UOP method of CCR regeneration is oxidation and chlorination. In this step, the catalyst is oxidized in air at about 510°C. A sufficient amount of chloride is usually added as an organic chloride, such as trichloroethane, to restore the chloride content and acid function of the catalyst to that of the fresh catalyst. If the platinum crystaUites ate smaller than about 10 nm, sufficient chlorine is present in the gas to completely tedispetse agglomerated platinum on the catalyst, as a result of the Deacon equUibtium ... 

Oxidation and chlorination of the catalyst are then performed to ensure complete carbon removal, restore the catalyst chloride to its proper level, and maintain full platinum dispersion on the catalyst surface. Typically, the catalyst is oxidized in sufficient oxygen at about 510°C for a period of six hours or more. Sufficient chloride is added, usually as an organic chloride, to restore the chloride content and acid function of the catalyst and to provide redispersion of any platinum agglomeration that may have occurred. The catalyst is then reduced to return the metal components to their active form. This reduction is accompHshed by using a flow of electrolytic hydrogen or recycle gas from another Platforming unit at 400 to 480°C for a period of one to two hours. 

Catalyst Deactivation. Catalyst deactivation (45) by halogen degradation is a very difficult problem particularly for platinum (PGM) catalysts, which make up about 75% of the catalysts used for VOC destmction (10). The problem may weU He with the catalyst carrier or washcoat. Alumina, for example, a common washcoat, can react with a chlorinated hydrocarbon in a gas stream to form aluminum chloride which can then interact with the metal. Fluid-bed reactors have been used to offset catalyst deactivation but these are large and cosdy (45). 

Promoters, usually present in smaU amount, which enhance activity or retard degradation for instance, rhenium slows coking of platinum reforming, and KCl retards vaporization of CuCU in oxy-chlorination for vinyl chloride. 

Turning now to the acidic situation, a report on the electrochemical behaviour of platinum exposed to 0-1m sodium bicarbonate containing oxygen up to 3970 kPa and at temperatures of 162 and 238°C is available. Anodic and cathodic polarisation curves and Tafel slopes are presented whilst limiting current densities, exchange current densities and reversible electrode potentials are tabulated. In weak acid and neutral solutions containing chloride ions, the passivity of platinum is always associated with the presence of adsorbed oxygen or oxide layer on the surface In concentrated hydrochloric acid solutions, the possible retardation of dissolution is more likely because of an adsorbed layer of atomic chlorine ... 

The relative proportions of oxygen and chlorine evolved will be dependent upon the chloride concentration, solution pH, overpotential, degree of agitation and nature of the electrode surface, with only a fraction of the current being used to maintain the passive platinum oxide film. This will result in a very low platinum consumption rate. 

Batsanov et al. 23) reacted sulfur with PtCU and PtBr2 by heating mixtures of the reactants in evacuated, sealed ampoules. At 100 -200°C after 12-24 h, sulfide chlorides PtCljS (1.70 < x < 2 0.6 s y < 3.35) and sulfide bromides PtBr S (1.87 < x 2.06 0.84 y s 1.80) were formed. The compositions depended on the initial PtX2 S ratio, and the temperature. At 320-350°C, loss of chlorine led to the compounds PtClS (1.7 y 1.9). According to their X-ray powder patterns, all of these products retained the main structural features of the original platinum halides. From considerations of molar volumes, the authors deduced the presence of polysulfide anions. 

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