THE EFFECTS OF OXYGEN ON SELECTIVITY - THE REACTIONS OF 2-PROPANETHIOLATE ON OXYGEN-COVERED RH(111)

The selective oxidation of 2-propanethiolate on oxygen-covered Rh(111) was studied using temperature programmed reaction and high resolution electron energy loss spectroscopy. On Rh(111)-p(2x1)-O, reaction is proposed to proceed through carbon-sulfur bond breakage, affording 2-propyl followed by rapid beta-hydrogen elimination to propene or oxygen addition to 2-propoxide. The 2-propoxide immediately reacts to form acetone or combustion products. The selectivities for the different products depend strongly on the oxygen coverage. Oxygen influences the product distributions by (1) passivating the rhodium surface with respect to nonselective decomposition, (2) scavenging surface hydrogen so as to inhibit propane formation ar high oxygen coverages, and (3) reacting with 2-propyl to form 2-propoxide. The observed addition of oxygen to 2-propyl is very promising in light of great industrial interest in selective alkane oxidation, which is generally thought;to proceed via alkyl radicals.