Metals platinum-group

Platinum electrodes do not give products continuously in CO2 reduction in aqueous media under 1 atm as shown in Table 3. Platinum electrodes initially reduce CO2 to reduced 002 . The entity of the reduced CO2 is CO strongly adsorbed on the Pt electrode, as revealed by Beden et al. by means of infrared spectroscopy. Tills fact is later confirmed by other workers. In addition to linearly bonded CO as the major adsorbed species, small amounts of bridged and multibonded CO, COH and HCOO species are also detected on Pt electrode surface. The presence of reduced CO2 on Pt electrode practically inhibits further reduction of CO2 in aqueous media. The formation of reduced CO2 proceeds as below in the potential region in which adsorbed hydrogen is stably present. 

Formation of reduced CO2 , or adsorbed CO, on Pt electrodes has been studied using Pt single crystal electrodes. Yeager and his coworkers reported reduction of CO2 at Pt(ll 1), Pt(lOO) and Pt(llO) in HCIO4 solution. They showed by voltammetry and infrared spectroscopy that Pt(llO) electrode is the most active in 

CO2 reduction, whereas Pt(lll) is inert. Later Aramata et at, Rodes et al. and Hoshi et al. confirmed this fact. Fig. 17 gives time courses of adsorbed CO formation on Pt(lll), Pt(lOO) and Pt(llO) in HCIO4 solution published by Aramata et al The amount of CO was determined by anode stripping. Rodes et al. showed in their study using a Pt(llO) electrode that adsorbed hydrogen consumed is regenerated during the reaction as above. 

The Vt=o for = 2, 3, 4 and 6 gives a peak at 0.2 V, where the amount of adsorbed hydrogen is less than at 0.1 V. This apparently strange feature is rationalized by involvement of vacant sites of the Pt surface in the activation of CO2 reduction. Other series of Pt single crystals are studied for CO2 reduction in addition to Pt(s)-[Z7(111) X (111)], i.e., Pt(S)-[w(100) X (111)], Pt(S)-[w(l 11) X (100)], and kinked stepped surfaces Pt(S)-[ 7(100) x (110)] and Pt(S)-[/7(l 10) X (100)]. Among all these crystal orientations, kinked surfaces are the most active in CO2 reduction. E/=o depends linearly on the density of step or kink atoms as shown in Fig. 19. This fact shows that the kink or step structure is closely connected with the active sites for the CO2 reduction. 

As previously mentioned, high pressure electrolysis is effective in activation of CO2 reduction at Pt electrode. Hara et al. reported that CO2 can be reduced in aqueous 0.1-M KHCO3 under 30 atm mainly to HCOO and CO with the faradaic efficiency of 50.4% and 6.1% respectively at the current density 163 mA cm .  

The platinum-group metals (PGMs), which consist of six elements in Groups 8— 10 (VIII) of the Periodic Table, are often found collectively in nature. They are mthenium, Ru rhodium, Rh and palladium, Pd, atomic numbers 44 to 46, and osmium. Os indium, Ir and platinum, Pt, atomic numbers 76 to 78. Corresponding members of each triad have similar properties, eg, palladium and platinum are both ductile metals and form active catalysts. Rhodium and iridium are both characterized by resistance to oxidation and chemical attack (see Platinum-GROUP metals, compounds). 

Platinum was found in conjunction with gold after the Spanish conquest of South America. It was referred to as platina, or Htde silver. It was regarded as an unwanted impurity in the silver and gold, and was often discarded. However, scientific interest in platinum gradually grew and in 1741 the first samples of New World platinum were brought to England for scientific examination. 

At the start of the nineteenth century, platinum was refined in a scientific manner by William Hyde WoUaston, resulting in the successful production of malleable platinum on a commercial scale. During the course of the analytical work, WoUaston discovered paUadium, rhodium, indium, and osmium. Ruthenium was not discovered until 1844, when work was conducted on the composition of platinum ores from the Ural Mountains. 

The relative abundance of the stable isotopes of the PGMs and their CAS Registry Numbers are shown in Table 1. 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

See Vinyl polymers, vinyl chloride polymers Vinyl cm,ORiDE. 

Institut fur Anorganische Chemie Johann Wolfgang Goethe-Universitat Marie-Curie-Strasse II D-60439 FranIfurtIMain, Germany 

Institut fiir Anorganische Chemie Technische Universitat Munchen Lichtenbergstrasse 4 D-85747 Garching, Germany 

Implements for Trace Analysis of Platinum Group Metals 

The elements ruthenium, rhodium, palladium, osmium, iridium, and platinum form the so-called platinum group metals (PGM) of the periodic table. According to the new lUPAC rules, they are located in the groups 8, 9, and 10 (formerly called subgroup VIII). 

PGM tend to form complexes that often serve as starting materials for the synthesis of other PGM compounds [3] as well as for technical uses, e.g., in catalysis (see Sec. 1.1). PGM complexes also play an important role as anticancer drugs (see Sec. 1.2). 

---

The mechanism for CO oxidation over platinum group metals has been established from a wealth of data, the analysis of which is beyond the scope of this chapter. It is quite evident that surface science provided the foundation for this mechanism by directly showing that CO adsorbs molecularly and O2 adsorbs... 

With osmium tetroxide catalyst [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19)... 

CARBON - CARBON AND ARTIFICIALGRAPHITE - APPLICATIONS OF BAKED AND GRAPHITIZED CARBON] (Vol 4) -With osmium tetroxide catalyst [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19)... 

---