Site distribution studies of Rh supported on Al2O3—An infrared study of chemisorbed CO

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Abstract
Using infrared spectroscopy, chemisorbed CO has been employed as a surface probe to observe differences in Rh site distributions on Al2O3-supported Rh. It has been found that higher loadings of Rh lead to Rh site distributions resembling those found on Rh(111) single crystals, whereas low Rh loadings produce isolated Rh sites preferentially. The isolated Rh sites yield infrared spectra characteristic of a species Rh(CO)2. Chemisorption of oxygen onto the CO-covered surface effectively eliminates crystalline Rh sites, leaving only the isolated Rh sites which maintain their bonding to CO as seen by infrared spectroscopy. Estimates of the infrared extinction coefficient for Rh(CO)2 have been made. The results are consistent with data from other laboratories which indicate that the Rh is in a Rhd+ oxidation state.