Noble vapour pressure

In the case of atoms UPS is unlikely to produce information which is not available from other sources. In addition many materials have such low vapour pressures that their UPS spectra may be recorded only at high temperatures. The noble gases, mercury and, to some extent, the alkali metals are exceptions but we will consider here only the specttum of argon. 

The vapour pressure ratio of actinides to noble metals is also the basis of the actinide metal preparation by thermal dissociation of intermetallic compounds. Such intermetallic compounds of An and noble metals can be prepared by hydrogen reduction of a mixture of an An oxide and a finely divided noble metal (Pt, Ir.. in the absence of noble metals, hydrogen reduction of An oxides is impossible. Am and Cm metals have been obtained by thermal dissociation of their intermetallic compounds with Pt and Ir High purity Th and Pa, the least volatile actinide metals, can be prepared by thermal dissociation of their iodides, which form readily by reaction of iodine vapour with car-... 

The atmophile elements (H, C, N, noble gases) condense at and below the condensation temperature of water (liquid or ice). Liquid water or water ice condenses at the temperature where the partial pressure of water vapour equals the vapour pressure over liquid water or water ice. The condensation curve for water (liquid or ice) is... 

Their most noticeable features compared with other metals are their low melting and boiling points, mercury being unique as a metal which is a liquid at room temperature. Zinc and cadmium are silvery solids with a bluish lustre when freshly formed. Mercury is also unusual in being the only element, apart from the noble gases, whose vapour is almost entirely monatomic, while its appreciable vapour pressure (1.9 x 10 mmHg,... 

Catalysts containing noble metals are known to be the most active catalysts for the complete combustion of hydrocarbons [8]. During the catalyst operation at temperatures higher than 800°C the active component starts to sinter and evaporate. Therefore, the active component should have a low vapour pressure, or it should be strongly bonded to the thermally stable support [9]. Pt and Pd are the most often used noble metals. 

Nickel is the only metal to react directly with carbon monoxide at room temperature at an appreciable rate, although iron does so on heating under pressure. Cobalt affords HCo(CO)4 with a mixture of hydrogen and carbon monoxide (p. 387). In general, therefore, direct reaction does not provide a route to metal carbonyls. The metal atom technique (p. 313) has been used to prepare carbonyls of other metals in the laboratory e.g. Cr(CO)g, but it offers no advantages over the reduction method discussed below. When metal vapours are cocondensed with carbon monoxide in frozen noble gas matrices at very low temperatures (4-20K) the formation of carbonyl complexes is observed. These include compounds of metals which do not form any stable isolable derivatives e.g. Ti(CO), Nb(CO) and Ta(CO)g as well as Pd(C0)4 and Pt(C0)4. Vibrational spectra of the matrix show that coordinatively unsaturated species such as Ni(CO) n = 1-3) or Cr(CO) (n = 3-5) are also formed under these conditions. 

A commercial nickel catalyst was used for methane steam reforming performed at a 500 °C reaction temperature, a S/C ratio of 3.0 and atmospheric pressure, while the permeate side was evacuated. The performance of the vapour deposited platinum membrane was similar to the plated dense palladium membrane. In the permeate of the deposited ruthenium and palladium membranes, small amounts of carbon oxides and also methane were observed. While it was expected that all these species had passed through the membranes by diffusion, in addition some methane was converted into carbon dioxide over the noble metals of the membranes. Kikuchi et al. demonstrated by simulations that conversion and hydrogen permeation in a membrane reactor is higher, where the first portion of the catalyst bed is not coupled to the membrane. Such an arrangement as shown in Figure 7.16 would clearly save expensive membrane surface area. Experimental work by Itoh et al. performed for methanol steam reforming [521] confirmed the assumptions of Kikuchi et al. 

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