Platinum sulfides

In past years, metals in dilute sulfuric acid were used to produce the nascent hydrogen reductant (42). Today, the reducing agent is hydrogen in the presence of a catalyst. Nickel, preferably Raney nickel (34), chromium or molybdenum promoted nickel (43), or supported precious metals such as platinum or palladium (35,44) on activated carbon, or the oxides of these metals (36,45), are used as catalysts. Other catalysts have been suggested such as molybdenum and platinum sulfide (46,47), or a platinum—nithenium mixture (48). 

Rufus IB, Viswanathan B, Ramakrishnan V, Kuriacose JC (1995) Cadmium sulfide with iridium sulfide and platinum sulfide deposits as a photocatalyst for the decomposition of aqueous sulfide. J Photochem Photobiol A 91 63-66... 

Procedure The irradiated molybdenum is dissolved in cone, sulfuric acid and technetium is distilled with the acid. The distillate obtained is diluted to 4 M H2SO4, heated to boiling and treated with bromic water. A platinum salt (1 mg of Pt/200 ml solution) is added to the solution as collector, and technetiiun is coprecipitated with the platinum sulfide. The precipitate is dissolved in NH OH/ HjOj mixture and the solution evaporated to dryness. The residue is dissolved in cone. HjSO or HCIO4 and technetium separated from platimun by distillation. The solution is diluted and the sulfide precipitated. 

Co-precipitation of Re S with platinum sulfide from cone, hydrochloric acid solutions of microamounts of technetium and rhenium is suitable for the separation of technetium from rhenium , since technetium is only slightly co-precipitat-ed under these conditions (Fig. 7). At concentrations of 9 M HCl and above, virtually no technetium is co-precipitated with platinum sulfide at 90 °C, whereas rhenium is removed quantitatively even up to 10 M HCl. The reduction of pertechnetate at high chloride concentration may be the reason for this different behavior, because complete co-precipitation of technetiiun from sulfuric acid solutions up to 12 M has been observed. However, the separation of weighable amounts of technetium from rhenium by precipitation with hydrogen sulfide in a medium of 9-10 M HCl is not quantitative, since several percent of technetiiun coprecipitate with rhenium and measurable amounts of rhenium remain in solu-tion . Multiple reprecipitation of Re S is therefore necessary. 

Fig. 7. Co-precipitation of microamounts of technetium and rhenium with platinum sulfide at 90 °C as a function of hydrochloric acid concentration ...

The dissociation also is rapid helow this temperature (between 450°C to 850°C), however, only in the presence of a catalyst, such as sdica, platinum sulfide or cohalt molybdate. Other sulfur species are also produced in the reaction. 

Platinum sulfide appeared superior to palladium for the reductive alkylation of piperidine with acetone. A more carefully controlled comparison of platinum sulfide with palladium and with platinum is shown in Table 2 for the reaction of N-ethylcyclohexylamine with cyclohexanone. Platinum gave a very poor conversion of the starting secondary amine (27%) and a correspondingly low yield of the tertiary amine product (22%), although the yield based on conversion was good (81%). The... 

These results illustrate the practicality of preparing trialkylamines by the reductive alkylation of dialkylamines with aliphatic ketones. Excellent yields are obtained, particularly with the more reactive and less hindered ketones, such as cyclohexanone and acetone, and with the less hindered secondary amines. Platinum sulfide, or other platinum metal sulfides, are the catalysts of choice when more hindered reagents require more severe operating conditions. 

Platinum catalysts have been shown to be highly selective for the hydrogenation of halonitrobenzenes to haloanilines. A number of effective platinum catalysts or catalyst systems have been described in the literature, mostly in patents.96 Dovell and Greenfield found that the sulfides of the platinum metals and cobalt were highly selective in the hydrogenation of halo-substituted nitrobenzenes.117-119 There was no detectable dechlorination with the sulfides of palladium, platinum, rhodium, ruthenium, and cobalt no detectable debromination occurred with platinum sulfide trace debromination occurred with rhodium sulfide and cobalt sulfide and appreciable debromination occurred with palladium sulfide. Typical hydrogenations with 5% platinum sulfide on carbon catalyst are given in eqs. 9.52 and 9.53 with 2,5-dichloronitrobenzene and p-bromobenzene, respectively.118... 

Malz, Jr. et al. found platinum sulfide supported on carbon to be superior to any of other nonsulfided and sulfided catalysts in the selective hydrogenation of 6-chloro-2(l//)-quinoxalinone-4-oxide to 6-chloro-2(l//)-quinoxalinone.230 The hydrogenation was performed in an aqueous potassium hydroxide solution at 60°C and 0.69-1.38 MPa H2 to give the product containing 92% of the desired compound in 90% isolated yield (eq. 9.79). 

The Tc activity is separated from the bombarded Mo Isotopes by means of a volatility separation method and then the Tc Is prepared as a thin sample for counting by co-pptn. with platinum sulfide. 

We selectively hydrogenated 6-chloro-2(IH)-hydroxyquinoxaline-4-oxides to 6-chloro-2(IH)-quinoxalinone, using sulfided and non-sulfided catalysts. The catalyst of choice is platinum sulfide. Our catalyst studies included sulfided and non-sulfided platinum, palladium, rhodium, ruthenium, sulfided nickel, Raney nickel, and cobalt. 

Another unique example of the use of sulfided catalysts is in the production of 6-chloro-2(lH)-quinoxalinone (5) from 6-chloro-2(lH)-quinoxaline-4-oxide (4) on platinum sulfide (Malz et al., 1993). 

PuAl20gy Pt-asbestosy Pt-Cy Pt-silk PtyFe-C Pt02, Platinum rhodium oxide Platinum sulfide-carbon H tClg... 

Platinum sulfide-carbon Sec. from prim, amines and 0x0 compounds... 

With platinum sulfide-on-carbon, a catalyst not sensitive to poisons, reductions can be performed with retention of halogen and sulfur-carbon bonds... 

Ramasubramanian N. Anodic behavior of platinum electrodes in sulfide solutions, the formation of platinum sulfide. J Electroanal Chem 1975 64 21-37. 

The dissociative adsorption of hydrogen sulfide has been shown to occur in the gas phase according to the above reactions at elevated temperatures [49]. Although the conductivity of the solid electrolyte membrane can increase due to oxidation of the adsorbed SH and H2S (i.e., reaction (5.16)), the formation of a stable platinum sulfide film can lead to fuel cell failure [38]. 

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