Oxygen Exchange in the Selective Oxidation of 2-Butanol on Oxygen Precovered Au(111)

Direct evidence for C-O bond cleavage in the partial oxidation of 2-butanol on oxygen precovered Au(111) is provided using temperature programmed desorption (TPD) and molecular beam reactive scattering (MBRS) under ultrahigh vacuum (UHV) conditions. The oxygen precovered Au(111) surface can promote the partial oxidation of 2-butanol into 2-butanone with near 100% selectivity at low oxygen coverages, while 2-butanol adsorbs and desorbs molecularly on the clean Au(111) surface. Both (C2H5COCH3)-O-16 and (C2H5COCH3)-O-18 are observed in TPD after 2-butanol ((C2H5CHOHCH3)-O-16) was dosed onto Au(111) precovered with O-18(a). This oxygen exchange phenomenon serves as strong evidence for the C-O bond cleavage in 2-butanol partial oxidation to 2-butanone. Two surface intermediates are proposed for the selective oxidation of 2-butanol: 2-butoxide and eta(2)-aldehyde. As oxygen coverage increases, full oxidation is activated in addition to selective partial oxidation.