Hydrogenation of carbon monoxide over rhodium oxide surfaces. [At 250 to 350/sup 0/C and 6 atm]

Hydrated and anhydrous rhodium oxides, Rh/sub 2/O/sub 3/ 5H/sub 2/O and Rh/sub 2/O/sub 3/ crystallites, were used as catalysts for the hydrogenation of CO at 6 atm and in the range of 250 to 350/sup 0/C. The anhydrous oxide reduced to metallic rhodium rapidly, while the hydrated oxide was quite stable under the reaction conditions. The hydrated oxide produces a high concentration of oxygenated hydrocarbons, mostly acetaldehyde in addition to C/sub 2/ to C/sub 5/ alkenes and methane, in contrast to the unsupported metal which is a mediocre methanation catalyst. The activation energy for the formation of all of the products is 26 +- 2 kcal/mole indicating that they are likely to be produced from a common precursor intermediate, C/sub x/H/sub y/. The addition of ethylene to CO and H/sub 2/ results in the conversion of the olefin to propionaldehyde. This carbonylation reaction was not observed on the rhodium metal. The slower rates of hydrogenation on the oxide and its ability to insert CO into the C/sub t/H/sub y/ intermediates appear to be responsible for the changed product distribution in the CO/H/sub 2/ reaction. Electron spectroscopy studies indicate the presence of patches of oxide and metal both participate in themore » reaction and control the production distribution.« less