Palladium band parameters

Figure 4.5. Calculated change in the sum of the one-electron energies using the Newns-Anderson model. The parameters are chosen to illustrate an oxygen 2p level interacting with the d states of palladium with a varying d band center, ed. In all cases, the number of d electrons is kept fixed. The corresponding variations in the metal and adsorbate projected densities of states are shown above. Notice that the adsorbate-projected density of states has only a small weight on the antibonding states since it has mostly metal character. Adapted from Ref. [4].

Compensation effects have been reported for the oxidation of ethylene on Pd-Ru and on Pd-Ag alloys (207, 254, 255) discussion of the activity patterns for these catalysts includes consideration of the influence of hydrogen dissolved in the metal on the occupancy of energy bands. Arrhenius parameters reported (208) for ethylene oxidation on Pd-Au alloys were an appreciable distance from the line calculated for oxidation reactions on palladium and platinum metals (Table III, H). Oxidation of carbon monoxide on Pd-Au alloys also exhibits a compensation effect (256). 

The complex Pd2(dba)3 in solution shows electronic absorption bands at 350, 380, and 545 nm. The band at 350 nm is due to an intraligand charge transfer transition. The band at 380 nm is due to an intermetallic da pa transition, and the lowest energy band at 545 nm is due to an MLCT transition. " The triplet emission from this complex is observed at 730 nm. By comparison, the absorption bands for Pt2(dba)3 are found at 350,400, and 620 nm, respectively, and the triplet emission is observed at 800 nm. An analysis of the ground state spectroscopic parameters reveals that both the palladium and the platinum complexes have only weak intermetallic interactions. For Pd2(dba>3 the intermetallic stretching frequency V (M-M) is found at 76 cm , which corresponds to a force constant of 0.18 mdyn A By comparison the corresponding stretching frequency in Pt2(dba)3 is found at 72 cm" which corresponds to a force constant of 0.30 mdyn A" when the mass difference is taken into consideration. ... 

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