Pt and Pd black

IINS is less widely used because it requires a source of thermal neutrons, but its advantage lies in hydrogen s very high incoherent inelastic cross-section it has however been mainly applied to metal powders (Raney Pt and Pd blacks), but the adsorption of hydrogen on Ru/C and Pt/C " catalysts has been studied. Adsorption sites were determined by comparison with known structures (e.g. hydridocarbonyls ). HREELS cannot be used with supported metals. 

Our results clearly show that the behaviour of the same modifier-substrate system strongly depends on the catalyst used (the same metals on different supports or Adams Pt or Pd black), indicating that the catalyst-modifier-substrate interaction on the catalyst surface is a crucial factor in the process of enantioselection and the observed rate acceleration of pyruvate hydrogenation. On the other hand, it has been shown by CD and NMR measurements that the... 

Figure 63. Compensation plot of Arrhenius parameters for ethane total exchange with deuterium (see Table 6.2) O foils, films, Pt(l 11) blacks, powders A supported Pt. The enclosed points are fa- Pt and Pd (see text).

Figure 1. Current-potential profiles at some noble metals obtained by the potential sweep technique. Potential h is referred to the reversible hydrogen electrode potential, (a) Pt, Rh, and Pd black electrodes deposited on Au in H2SO4 (pH = 1) (Chevillot et (b) Smooth Pt...

In the electromotive force series of the elements, silver is less noble than only Pd, Hg, Pt, and Au. AH provide high corrosion resistance. Silver caimot form oxides under ambient conditions. Its highly reactive character, however, results in the formation of black sulfides on exposure to sulfur-containing atmospheres. 

Niu(Pc), Pd (Pc) and Pt"(Pc) are prepared by the condensation method with metallic Ni or NiCl2 6H20, Pd black and PtCl2 respectively.197 PdCl2 causes Pc ring chlorination and metallic Pt catalyzes H2(Pc) formation. 

It has been reported [45] that supported Pd is substantially less thermally stable than other noble metals in reducing environments. Data of Baker et al. [46] for titania-supported Pd and Pt in hydrogen show Pd to be Jess thermally stable over a wide range of temperatures. These results are consistent with those of Sermon [47] showing that neck formation starts at about 60°C in Pd black compared to >200°C in Pt black [39). 

Pd-C in both ethanol and DMF, little, if any, selectivity was obtained product ratios were 50 50 in ethanol and 60 40 in DMF. Palladium black in ethanol, which afforded 4-amino-5-nitroveratrole in 70-75% yield from 4,5-dinitroveratrole, provided no selectivity with 2,4-dinitroaniline, as well as with o- and m-dinitrobenzenes both nitro groups were hydrogenated.140 Reduction by sodium borohydride and Pd-C in methanol also does not appear to be selective, as 1,2,4-triaminobenzene is formed.141 It is of interest that over Pt-C in acidic alcohol 2,4-dinitroaniline is selectively hydrogenated at the 4-nitro group to give 4-amino-2-nitroaniline in 70% yield.142... 

Amorphous carbons, carbon black, soot, charcoals, and so on, are forms of graphite or fullerenes. The physical properties depend on the nature and magnitude of the surface area. They show electrical conductivity, have high chemical reactivity due to oxygenated groups on the surface, and readily intercalate other molecules (see later). Graphite and amorphous carbons as supports for Pd, Pt, and other metals are widely used in catalysis and for the preparation of diamond films.18... 

The difference between Pd films and powders is notable. Some of the H retained by the powders may be situated at surface imperfections. However, it is also possible that some of the hydrogen is incorporated within the defect structure of the powders, in much the same way as suggested earlier for Pt blacks. Indeed, Aben and Frieske and Wicke have noted that very high temperatures (> 700 K) are required to desorb all the H from Pd blacks. As with Pt blacks the agreement between surface areas derived from H chemisorption and Kr adsorption may be fortuitous. In any case it is apparent that evacuation at T 300 K causes the desorption of some H from the adsorbed monolayer. Consequently, at these temperatures the excess adsorption may actually correspond to readsorption into the original monolayer. 

Type of catalyst noble metals are usually supported on a carrier sometimes they are used as fine powders (Pd black and Pt black, Pt02), Ni is most often applied as skeletal Raney nickel or supported on sUica Cu is used as Cu-chromite. 

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