Platinum tetraammine

Platinum, hexachloro-ammonium salt structure, 1,16 Platinum, tetraammine-amminctrichloroplatinate polymerization isomerism, 1,187 dichloride structure, l, 16... 

For example, Pt/Si02 catalysts are conveniently made by impregnating a silica support vith a basic solution (pH 8-9) of platinum tetraammine ions, Pt(NH3)4 (dissolved as chloride). As the silica surface is negatively charged, the Pt-containing ions attach to the SiO entities and disperse over the surface. The pH should be kept belo v 9 because other vise the silica surface starts to dissolve. 

Magnus s green salt — see Platinum, tetraammine-, tetrachloroplatinate... 

The seminal paper of Brunelle (1978) outlined the rational method of catalyst synthesis whereby charged metal coordination complexes such as hexachloroplatinate ([RCy ) or platinum tetraammine ([(NH3)4Pt] ) can be electrostatically adsorbed onto oxide surfaces which contain naturally occurring hydroxyl groups (-OH) that are either protonated and positively charged (-OH2 ) or deprotonated or negatively charged (-0 ), depending on the solution pH. 

A 1 %-wt platinum supported on alumina catalyst was used throughout this study. This catalyst was prepared by a proprietary incipient wetness method with tetraammine platinum (II) hydroxide, Pt(NH3)4(OH)2, as precursor. After drying in air at 393 K for 2 hours the catalyst was calcined in air for 3 hours at 623 K and reduced at 803 K in flowing hydrogen for 3 hours. The average platinum particle diameter, measured by both CO-chemisorption and TEM, amounted to 2 nm. The total exposed surface area of the platinum amounts to 1.4 m /g. The BET surface area of the used AI2O3 was 92 m /g. 

Table 1 presents the n-hexane conversion, selectivity to isomers and coke deposited after reaction for catalysts prepared by using two different platinum precursors tetraammine platinum nitrate and hexachloroplatinic acid. Both materials were calcined at different temperatures after platinum addition. For both platinum precursors, run under standard operational conditions, the optimum calcination temperature for catalytic activity was 500 °C. The amount of coke is small and the TPO profiles of the coked samples (not shown) are similar for all catalysts. Coke is completely burnt off at temperatures below that at which the catalyst was calcined after the metal addition. This is an important feature, because regeneration procedures would not affect the metal function. 

Pt precursor (tetraammine platinum nitrate or hexachloroplatinic acid) does not affect significantly the amount and nature of coke. Under the same operational conditions, the presence of platinum decreases the amount of coke and the maximum temperature of coke burning. The absence of platinum Influences the degree of coke polymerization more than the absence of hydrogen in the feed. 

The most straightforward case of electrostatic adsorption occurs with the most stable metal complexes such as platinum or palladium tetraammines, [(NH3)4Pt]+ and [(NH3)4Pd]+ or PTA and PdTAs, respectively. Over the wide pH and concentration ranges that can be employed during syntheses from the lab to the industrial scale, the relatively strongly bound ammine ligands of these coordination complexes remain intact. This has been most directly confirmed in the case of Pt by extended X-ray absorption fine structure (EXAFS) analysis of PTA solutions and adsorbed species [23], and for PdTAs less directly by XPS [24]. 

Similar Pt catalysts with three different dispersions as in Section 17.3, supported on silica and alumina and the homolog containing ceria, were prepared by incipient wetness impregnation of tetraammine-platinum nitrate of the support. In the case of the ceria-containing catalysts, a solution of Ce(N03)3-6H20 in 15.5 ml HjO was added to the silica or alumina supports, followed by drying in air overnight and calcinations at 300°C in air. Specific conditions used in the preparation of these materials are reported elsewhere. Table 17.4 summarizes the various catalysts studied in this case as well as their dispersion. 

N4CI3H12RU, Ruthenium(III), tetraammine-dichloro-, cis-, chloride, 26 66 N4Cl4PtC4H,4, Platinum(IV), dichlorobis-... 

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