High-temperature reduction , effects hydrogen

Borides of Group Via. As with the borides of Group Va, the incorporation of free metal in the Group Via borides is difficult to avoid. Both tungsten and molybdenum borides are obtained at high temperature by the hydrogen reduction of the mixed bromides.Bonding appears a more effective method to form these borides in thin layers (see Sec. 2.2 above). 

This promotion of C=0 activation in these systems cannot be accounted neither for a geometric effect nor for an electronic effect in an SMSI-like state. Actually, this is better explained by the creation of new catalytic sites, mixed sites, very active for C=0 hydrogenation (Figure 14). However, electronic effects were also considered as operating at a second level, in Pt/ZnO catalysts, for instance [122]. Upon high-temperature reduction, Pt -Zn entities form an electron enrichment of Pt would occur, which repels the C C bond farther from the Pt surface. 

TABLE 7.6. Effect of High-Temperature Reduction on the Rate of Ethane Hydrogenation and on the Rate of the Simultaneous H2 + D2 Reaction over Varions Platinnm Catalysts. 

The Pd-MR performance can be enhanced by using air or CO as the sweep gas. This enables a more effective removal of hydrogen due to a reaction with the permeated hydrogen. In addition, the heat produced due to this reaction can compensate for the endothermic dehydrogenation reaction and maintain a heat balance in the system. However, an oxide layer may form on the Pd/Ag membrane surface, leading to a decrease in membrane performance. In order to suppress any potential oxide formation, the oxygen or CO concentrations in the sweep gas should be lower than 5% or 2%, respectively. The potential formation of metallic oxide on the membrane surface can be eliminated by a high-temperature reduction with H2 prior to the reaction experiments [19]. 

An even more effective homogeneous hydrogenation catalyst is the complex [RhClfPPhsfs] which permits rapid reduction of alkenes, alkynes and other unsaturated compounds in benzene solution at 25°C and 1 atm pressure (p. 1134). The Haber process, which uses iron metal catalysts for the direct synthesis of ammonia from nitrogen and hydrogen at high temperatures and pressures, is a further example (p. 421). 

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