Platinum metals, definition

Electrodeposition could be a pseudo-S-L type process, although definitive proof is lacking. The element to be ionized, uranium [16] or plutonium [17], is coelec-trodeposited with a platinum metal layer, then covered with an additional layer of platinum. The U or Pu is believed to be electrodeposited as an oxide, and platinum is electrodeposited as the metal. Hence there is thought to be a U or Pu oxide buried in the metal matrix. When this deposit is heated, after a sufficient length of time atomic cations of U or Pu begin to sublime from the surface without measurable metal oxide ions. Metal oxide ions should be readily observable if they are present in the matrix. Thermodynamic calculations indicate that the hot platinum matrix will not reduce the U and Pu oxides to the metallic state, and yet the observed species are atomic ions and not oxide molecular ions. 

These generalized approaches have been applied specifically to the NMR spectra of EDTA, DTPA, MIDA, and NTA and the metal chelates formed by these ligands. Included are the chelates of the ions of the alkali metals, the alkaline earths, zinc, mercury, lead, molybdenum, zirconium, and some of the platinum metals. For the four chelating agents studied the nitrogen atoms within the ligands are definitely protonated before the carboxylate... 

Such binary borides (p. 145), carbides (p. 297) and nitrides (p. 417) as are formed have been referred to already. The ability of the metals to absorb molecular hydrogen has also been alluded to above. While the existence of definite hydrides of nickel and platinum is in doubt the... 

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

A definite decomposition voltage occurs for the following reason. As soon as there is a potential difference between the electrodes, H+ ions move to the cathode and Cl ions to the anode. The ions are discharged, forming layers of adsorbed gas on the inert metal surfaces. This essentially amounts to having a hydrogen electrode and a chlorine electrode in place of the two platinum electrodes. The outcome is a typical chemical cell ... 

Cg Dehydrocyclization. Arguments have been put forward that primary ring closure produces six-membered rings over three important catalyst types oxides, supported platinum, and bimetallic catalysts (107). The postulation of metal catalyzed Cg ring closure does not involve any definite suggestion whether its mechanism is direct or stepwise. ... 

Less than half a century after Balboa had stood silent on a peak in Darien, facing the unknown ocean, a famous Italian scholar and poet, Julius Caesar Scaliger, or della Scala, recorded the presence there of an unknown noble metal. In 1557 he made what is probably the first definite allusion to platinum. Girolamo Cardano (1501—1576), in his well-known work On Subtlety, had defined a metal as a substance which... 

Thus, a more appropriate question to ask is Is it possible to measure the absolute potential of the hydrogen reaction, /H+(abs) Actually it is possible. Remembering the definition of a standard hydrogen electrode potential (see Section 6.3.4), this was defined as the potential obtained when a metal comes in contact with a solution containing H+ under thermodynamically reversible conditions at unit activity, and H2 at 1 atm, at 298 K. As to the identity of the metal base, it can in principle be any metal at which it is possible to observe the reaction H2 H+ + e taking place at equilibrium. In practice, the metals used as substrates can only be noble metals because most other metals enter into equilibria with their own species in solution. Usually platinum is the metal chosen. 

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