Bismuth behavioral effect

Bismuth forms both 3+ and 5+ cations, although the former are by far the more common in nature. The ionic radius of Bi is even closer to that of La, than Ac, so again La is taken as the proxy. As noted above, Bi has the same electronic configuration as Pb, with a lone pair. It is unlikely therefore that the Shannon (1976) radius for Bi is universally applicable. Unfortunately, there is too little known about the magmatic geochemistry of Bi, to use its partitioning behavior to validate the proxy relationship, or propose a revised effective radius for Bi. The values of DWD u derived here should be viewed in the light of this uncertainty. 

This result is consistent with the observed effective poisoning of the CO oxidation reaction as reflected in the increased potential induced by bismuth in the cyclic voltammetry on the supported platinum electrodes (Figure 10a). The voltammetry of CO stripping on the supported catalysts indicates a similar behavior to that found on Pt(llO) in that bismuth results in a higher overpotential for CO oxidation. One must conclude that the morphology of the supported platinum catalyst results in facets more akin to the more open-packed Pt(l 10) surface than the Pt(lll) surface, a conclusion supported by comparison of the bismuth redox chemistry on the supported catalyst and the single-crystal surfaces [77]. 

Only for bismuth faces has the temperature effect been studied (for cyclohexanol adsorption in 50mM/Na2SO4 and H2SO4 aqueous solutions) from 281 to 321 The different behavior of the (111) face from that of the (Oil) and (211) faces, suggested that the chemical interactions between bismuth atoms and cyclohexanol are reinforced by temperature for the two last faces but that, for (111), there is only physical adsorption. This could explain why Fmax (surface excess at saturation) diminishes with increasing temperature for (111) and increases for the two other faces. Bismuth crystallizes in the rhombohedral system, the (111) face is less densely packed in atoms than the two other faces, and bismuth is a semimetal, not a metal. 

Formation of open adlayers via UPD is not a universal phenomena. Other metals such as lead, thallium and bismuth form close-packed mcommensurate monolayers and exhibit an effect which has been termed electrocompression. This refers to a gradual compression of the monolayer in the region between the monolayer deposition and bulk deposition regions. There is a slow reduction of the monolayer lattice parameter until it is about 3% compressed with respect to the bulk metal [22 - 23]. This type of behavior is expected for close-packed commensurate monolayers on the basis of effective medium theory [24]. 

Often the catalyst is bonded or compounded with silica, and the presence or absence of silica appears to have little effect on the reactions. Likewise, results are reported both with and without phosphorus which do not differ greatly. Studies of the effect of the Bi/Mo ratio have been made in efforts to find the reasons for the markedly different catalytic behavior of bismuth molybdate, so-called, relative to bismuth and molybdenum oxides. The phase diagram for this system was published by Belyaev and Smolyaninov 144), and was confirmed and refined by... 

Bismuth as an adatom or alloying element with Pt has been proposed as an extremely active co-catalyst for HCOOH oxidation on Pt. The unusual activity of Bi has been attributed to a combination of geometric (third-body) and electronic effects [155-157]. However, the role of Bi is quite complex and in some cases contradictory results were obtained. Tripkovic et al. clearly showed flie activity of PtBi is dependent on flie redox behavior of Bi and on its surface arrangement [158]. Oxidized Bi species such as Bi203 and BiO(OH) were identified by XPS on the surface at both open circuit and anodic potentials. Furthermore, the possibility of Bi leaching was proposed, with subsequent underpotential deposition of the resulting Bi on flie surface forming in-situ an adlayer, which could also contribute to the enhanced catalytic activity, as shown by a shift of the HCOOH oxidation onset potential by -0.25 V compared to pure Pt [158]. 

Hajjaji, Effect of bismuth and silver on the corrosion behavior of Sn-9Zn alloy in NaCl 3wt.% solution. Mater. Sci. Eng. B176 (2011) 1032- 1036. 

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