Palladium aspect ratio

Fig. 21. Schematic models of truncated cuboctahedra of various sizes and aspect ratios, exhibiting a (111) top facet and (1 1 1) and (100) side facets. According to HRTEM images of palladium nanoparticles, the terraces may be incomplete, leading to surface facets with steps. For structural characteristics, see Table II.

Kita and Nakajima [89] found that the cis—trans ratio of 6.3 of 2-butene formed from 2-butyne at a palladium black cathode was not influenced by neither cathode potential nor pressure. On the other hand, Nonaka and coworkers [90] examined the cis—trans ratios of dimethyl 2-butenedioate formed from dimethyl acetylenedicarboxylate on a palladium black cathode and catalytic hydrogenation at various pH levels and found that an increase in pH resulted in a decrease in the ratio in both the electrolytic and catalytic hydrogenations, but the former was less strongly influenced by pH. They also performed similar comparative studies with olefins and ketones from a stereochemical aspect. 

Tables 13 and 14) [31]. These countries report huge reserves, but with different mine ratios of Pt to Pd to Rh (Table 15). The concentration of Pt, Pd and Rh in the raw ore is reported to be in the order of magnitude of a few parts per million, whereas their concentration in automotive catalysts is in the order of magnitude of about 3 000 ppm for Pt and about 600 ppm for Rh. These aspects contribute to the increasing interest in the recycling of the precious metals out of used automotive emission control catalysts. By 1996 about 16% of the platinum demand for automotive catalysts, about 5% of the palladium demand and about 10% of the rhodium demand for automotive catalysts was supplied from the recycling of these catalysts [32, 33],... 

Some aspects of the regiochemistry of the reductive elimination in palladium y-allylic complexes were analyzed using the allylic isomers in Scheme 73. Either regioisomer affords different products, and it was observed that the C-C bond formation in the least substituted carbon is faster. The isomerization of the complexes for the phosphite complex is slow and the ratio of organic products (a b = 76 24) reproduces the ratio of isomeric complexes (a b = 78 22). The isomerization seems to be fast for the triphenylphosphine complex, and in this case, the equilibrium ratio of the complexes is mantained during decomposition (a b = 85 15) the ratio of products (a b = 25 75) is a consequence of the different rates of reductive elimination. ... 

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