Pt-group metals

The most important quality of the pzc is that it contains information about the structural details of the metal/solution interface. In the absence of surface-active electrolytes, the pzc depends only on the nature of the metal and the solvent.3,4,5 Conversely, the pztc is not exclusively relevant to the structure of the interface this is truer the larger the value of in Eq. (8) (or of At where i is the species to which the electrode is reversible e.g., H+ for the Pt group metals in the H adsorption region). 

Pt and Pt-group metals (poly- and single crystals) have long been among the most intensively studied systems in electrochemistry6 8,io,ii,i4,25,140,186,188,206,412,752-7%. nevertheless reliable ff=0 values... 

Potentials of Zero Charge of Polycrystalline Pt-Group Metals In Aqueous Solutions... 

Experiments at present are concentrated on sd-metals and Pt-group metals. The sp-metals, on which theories of the double layer have been based, are somewhat disregarded. In some cases the most recent results date back more than 10 years. It would be welcome if double-layer studies could be repeated for some sp-metals, with samples prepared using actual surface procedures. For instance, in the case of Pb, the existing data manifest a discrepancy between the crystalline system and the crystal face sequence of other cases (e.g., Sn and Zn) the determination of EgaQ is still doubtful. For most of sp-metals, there are no recent data on the electron work function. 

In addition to the establishment and understanding of activity trends on nanosegregated surfaces, it has been anticipated that finding relationships between chemical and electronic properties of thin metal films of Pt group metals deposited over 3d and 5d elements has the potential to open up new opportunities in the quest to... 

A review28 describes compounds of the Pt-group metals including halide, oxide, sulfide, coordination compounds, organometallic compounds, and metal cluster compounds. 

Combined with their kinetic measurements, the authors proposed CO from the gas phase could directly react with oxygen atoms in the surface oxides, accounting for relatively high reactivity of this phase for CO oxidation. This mechanism, termed as Mars-Van Krevelen mechanism, challenges the general concept that CO oxidation on Pt group metals is dominated by the Langmuir-Hinshelwood mechanism, which proceeds via (1) the adsorption of CO and the dissociative adsorption of 02 and (2) surface diffusion of COa(j and Oa(j atoms to ultimately form C02. 

The first step in the preparation of Pt-group metals is the dissolution of the raw materials (primary deposits, ores, metal scraps, supported catalysts, etc.). According to the characteristics of their content in the different mixed noble metals, different dissolution methods are used. Typical processes are dissolution in... 

Underpotential Deposition on Single-Crystal Pt Group Metals... 

E. F. Westrum, and G. L. Goodman Heat capacities and electronic spectra of the Pt-group metal hexafluoride molecules down to liquid He temperatures. Proc. Internat. Conf. Low Temp. Phys., 8 >, London, 405 (1962). 

Pt-Group Metals. Among the six metals (Ru, Rh, Pd, Os, Ir, and Pt) in the platinum group, rhodium (Rh), paradium (Pd), and platinum (Pt) assist the formation of SWNTs (48). Of the three metals, Rh is the most effective for producing SWNTs. Cathode soot produced from Rh contains SWNTs densely, whereas the density in SWNTs is comparable with that for rare-earth metal catalysts such as Y, La, and Ce. 

Due to their electronic properties, early transition metal carbides should in principle have some advantages in controlling the selective activation of C-H and C=C bonds. As discussed earlier, the electronic properties of early transition metal carbides are similar, up to the Fermi level, to those of Pt group metals (Group 8-10 metals in general). Therefore, by comparing with the parent metals, these carbides should be less active for C=C bond cleavage and more effective for C-H bond activation. Furthermore, the broadened unfilled portion of the d-band should make these carbides better electronic acceptors than both the parent metals and... 

These electronic properties in turn give rise to some unique catalytic properties for vanadium carbide. Compared to metallic vanadium, vanadium carbide shows an enhancement in the activation of the C-H bond of alkanes and a reduction in the interaction with the C=C bond of alkenes. The surface reactivity of VC/V(110) can be generally described as similar to those of Pt group metals, although the VC/V(110) surface might have an even higher activity towards the activation of C-H bonds. The dehydrogenation of isobutane on VC powder catalysts will be compared to the reactivities of the VC/V(110) model surfaces. 

Supported Au catalysts are, in general, less active than Pt group metal catalysts in the complete oxidation of hydrocarbons. However, by choosing appropriate metal oxide supports Au catalysts are also applicable to the removal of HCHO at room temperature. 

It is important to note that the formation of CO from the reverse water gas shift reaction (C02 + H2 = CO + H20) has been detected at low temperature with the commonly used Pt group metals [49, 50]. Under the operational conditions used to carry out these reactions, the CO coverage is relatively low and concentrated on specific sites such as the step and kink. This has been considered a possible explanation for the fact the catalytic performances are generally unaffected unless demanding reactions that require the catalytic action of specific sites on the catalyst surface are considered, as is the case with enantioselective hydrogenation reactions [49]. 

Reduction at Pt electrodes and Pt group metals of Ir and Rh in aqueous solution has led to CO production [56-58]. Intermediate-adsorbed species have been studied by Giner in acidic solution at Pt [59], while similar spectroscopic experiments at Pt electrodes have also been conducted by Nicolic et al. [60], It appears that the reduction of C02 occurs by reaction with adsorbed hydrogen atoms to produce both linear and bridge-bonded CO. The reduced C02 species at Pt electrodes, however, caused a rapid poisoning of the electrodes to further C02 reduction [61]. 

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