Palladium sulfides

The effects of tin/palladium ratio, temperatnre, pressnre, and recycling were studied and correlated with catalyst characterization. The catalysts were characterized by chemisorption titrations, in situ X-Ray Diffraction (XRD), and Electron Spectroscopy for Chemical Analysis (ESCA). Chemisorption studies with hydrogen sulfide show lack of adsorption at higher Sn/Pd ratios. Carbon monoxide chemisorption indicates an increase in adsorption with increasing palladium concentration. One form of palladium is transformed to a new phase at 140°C by measurement of in situ variable temperature XRD. ESCA studies of the catalysts show that the presence of tin concentration increases the surface palladium concentration. ESCA data also indicates that recycled catalysts show no palladium sulfide formation at the surface but palladium cyanide is present. 

Schultz and Matijevic (16) prepared nanoparticles of palladium sulfide (PdS) by the continuous double-jet mixing of PdCl2 or Na2(PdCl4) and Na2S. They found that the particle size was 20-30 nm in mean diameter obtained in acidic media (pH = 2-3), but 2-5 nm in alkaline media, probably due to the high equilibrium concentration of sulfide ions S2- by dissociation of H2S and HS in the alkaline media (pH = 10-12). A cationic surfactant, cetyl trimethyl ammonium bromide (CTAB), was found to be useful for stabilizing the small particles prepared in alkaline media. 

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... 

Palladium has been recommended as an internal standard for spec-trographic analysis of precipitated heavy metals such as are involved in this procedure 15). Palladium sulfide precipitates readily and completely under both acid and ammoniacal conditions, and, therefore, it seemed satisfactory for the purpose. 

The Gibbs free energy of formation values. Figs. 10.9 and 10.10, can be used to estimate the dissociation pressure or the gas composition where surface scale formation will be thermodynamically feasible. Assuming the formation of the corrosion product follows a similar reaction as the decomposition of palladium-sulfide (Eq. 10.10), the correlation between the equilibrium constant and Gibbs free energy of formation is illustrated by Eq. 10.11. 

In another study, a poly4VP layer was grafted, which was further activated in a PdCl2 solution followed by reaction with CO or H2S to yield composite particles with metallic palladium or palladium sulfide nanoparticles in the shell. 

Converting Palladium to Palladium Sulfide. Crimson, invented by Shipley, employs a conversion step after the activator where palladium is changed to palladium sulfide, which is claimed to be more conductive for subsequent electrolytic copper plating. The enhancer stabilizes the conductive film so that it is chemically resistant to imaging steps. The stabilizer neutralizes residues from the enhancer, thereby preventing contamination of subsequent steps. The microetch selectively removes activator from copper surfaces to achieve optimum copper-to-copper bond and reliable dry film adhesion. The process works best in conveyorized horizontal equipment and can be followed by pattern or panel electroplating. (See Fig. 30.3.)... 

Recent studies show that zero-valent metals (e.g., iron, zinc, and palladium), sulfide minerals (like FeS and FeS2), and green rust can act as abiotic agents and increase the reductive dechlorination rates of chlorinated ethanes and ethenes. For example, in the presence of zero-valent iron, P-elimination is the main degradation pathway of chlorinated ethenes. In the P-elimination pathway, chlorines in vicinal carbon atoms are eliminated and a third C-C bond will be formed (Tobiszewski and Namiesnik, 2012 Brown et al., 2009 and Ma and Wu, 2008). Kara et al. (2005) reported fliat with P-elimination, TCE, c-DCE, and t-DCE reduction occmred 40, 10, 100 times faster, respectively, in comparison to hydrogenolysis (Kara et al. 2005). 

Scheme 5 Catalytic activity of palladium sulfide for hydrothiolation...

The structures of the palladium sulfides have been confirmed clearly by scanning electron microscopy (SEM) study [26]. When Pd(OAc)2 dissolved in alkyne in the presence of y-terpinene is allowed to react with cyclohexanethiol upon microwave heating, nanostructured Pd species (Pd nanobelts) is formed in 85% yield. y-Terpinene acts as an excellent radical trapper and suppresses the formation of anfi -Markovnikov addition product 3 by radical pathway. On the other hand, the addition of thiols to Pd(OAc)2 followed by addition of alkyne leads to amorphous particles in the pm-size region. The formed Pd nanobelts exhibits excellent catalytic activity toward the hydrothiolation of aUcynes. In particular, the hydrothiolation with aUcanethiols proceeds efficiently with excellent regioselectivity upon microwave heating (Scheme 6). 

---