Adsorption on platinum surfaces

Ultraviolet photoelectron spectroscopy (UPS) results have provided detailed infomiation about CO adsorption on many surfaces. Figure A3.10.24 shows UPS results for CO adsorption on Pd(l 10) [58] that are representative of molecular CO adsorption on platinum surfaces. The difference result in (c) between the clean surface and the CO-covered surface shows a strong negative feature just below the Femii level ( p), and two positive features at 8 and 11 eV below E. The negative feature is due to suppression of emission from the metal d states as a result of an anti-resonance phenomenon. The positive features can be attributed to the 4a molecular orbital of CO and the overlap of tire 5a and 1 k molecular orbitals. The observation of features due to CO molecular orbitals clearly indicates that CO molecularly adsorbs. The overlap of the 5a and 1 ti levels is caused by a stabilization of the 5 a molecular orbital as a consequence of fomiing the surface-CO chemisorption bond. 

At temperatures below 80°C, acetic acid cannot be oxidized due to its weak adsorption on platinum surfaces, as indicated by the fact that no potential-dependent CO2 signal is observed. However, in the hydrogen adsorption region, acetic acid could be reduced to form strongly adsorbed species, likely due to the generation of acetaldehyde and its subsequent dissociatimi [84]. At temperatures above 80°C, acetic acid can be further oxidized to CO2 therefore, a higher current efficiency for CO2 can be observed [85,86]. At 250 C, acetic acid oxidatimi has even faster kinetics when compared to ethanol and acetaldehyde oxidation [87],... 

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