%0 Journal Article %1 Seimanides1989 %A Campbell, J. M. %A Seimanides, S. %A Campbell, C. T. %D 1989 %J Journal of physical chemistry %K science}, {microcalorimetry} {surface %N 2 %P 815--826 %R 10.1021/j100339a057 %T Probing ensemble effects in surface reactions: 2. Benzene adsorption on clean and bismuth covered Pt(111) %U http://pubs.acs.org/doi/pdf/10.1021/j100339a057 %V 93 %X The interactions of benzene with the clean and Bi-dosed Pt( 11 1) surface have been studied between 110 and 850 K with a combination of thermal desorption mass spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Below -350 K, benzene adsorbs molecularly. The first monolayer saturates at a coverage of 0.16 (molecules per Pt atom). About 55% of this dehydrogenates upon heating to liberate H2 in a series of steps between 450 and 800 K. This leaves residual carbon on the surface in a graphitic overlayer. The remaining benzene desorbs molecularly at -505 K (Ed N 30.8 kcal/mol) and 350 K (Ed N 21 kcal/mol). Substantial isotopic scrambling is seen in TDS from coadsorbed mixtures of C6H6 and C6D6. The activation energies for dehydrogenation of perdeuterated benzene are - 1.2 kcal/mol larger than for C6H6 When benzene is coadsorbed with bismuth adatoms, the competition between dehydrogenation and molecular desorption is strongly influenced. Dehydrogenation is almost completely suppressed by Oei = 0.15, with a corresponding increase in molecular desorption. Since the activation energies for desorption and dehydrogenation are not strongly influenced by such low Bi coverages, this result is attributed to the steric blocking by Bi of free Pt sites needed for dehydrogenation. On the basis of these results and kinetic modeling, it is estimated that an ensemble of 1 6 free Pt atoms is required for the dehydrogenation of an adsorbed benzene molecule (in addition to the -6 Pt atoms needed to accommodate the benzene molecule itself). At higher Bi coverages, steric and electronic effects of Bi manifest themselves as the desorption temperature of benzene shifts to lower temperature, and its C(1s) XPS peak shifts to higher binding energy.

@article{Seimanides1989, abstract = {The interactions of benzene with the clean and Bi-dosed Pt( 11 1) surface have been studied between 110 and 850 K with a combination of thermal desorption mass spectroscopy (TDS), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Below -350 K, benzene adsorbs molecularly. The first monolayer saturates at a coverage of 0.16 (molecules per Pt atom). About 55% of this dehydrogenates upon heating to liberate H2 in a series of steps between 450 and 800 K. This leaves residual carbon on the surface in a graphitic overlayer. The remaining benzene desorbs molecularly at -505 K (Ed N 30.8 kcal/mol) and 350 K (Ed N 21 kcal/mol). Substantial isotopic scrambling is seen in TDS from coadsorbed mixtures of C6H6 and C6D6. The activation energies for dehydrogenation of perdeuterated benzene are - 1.2 kcal/mol larger than for C6H6 When benzene is coadsorbed with bismuth adatoms, the competition between dehydrogenation and molecular desorption is strongly influenced. Dehydrogenation is almost completely suppressed by Oei = 0.15, with a corresponding increase in molecular desorption. Since the activation energies for desorption and dehydrogenation are not strongly influenced by such low Bi coverages, this result is attributed to the steric blocking by Bi of free Pt sites needed for dehydrogenation. On the basis of these results and kinetic modeling, it is estimated that an ensemble of 1 6 free Pt atoms is required for the dehydrogenation of an adsorbed benzene molecule (in addition to the -6 Pt atoms needed to accommodate the benzene molecule itself). At higher Bi coverages, steric and electronic effects of Bi manifest themselves as the desorption temperature of benzene shifts to lower temperature, and its C(1s) XPS peak shifts to higher binding energy.}, added-at = {2009-10-30T10:04:05.000+0100}, author = {Campbell, J. M. and Seimanides, S. and Campbell, C. T.}, biburl = {https://www.bibsonomy.org/bibtex/20f4047d174d6cd65e55d4302e7117c96/jfischer}, doi = {10.1021/j100339a057}, groups = {public}, interhash = {bb02ee06423e4b1afd10bfbb75201653}, intrahash = {0f4047d174d6cd65e55d4302e7117c96}, issn = {0022-3654}, journal = {Journal of physical chemistry}, keywords = {science}, {microcalorimetry} {surface}, number = 2, pages = {815--826}, timestamp = {2009-10-30T10:04:10.000+0100}, title = {Probing ensemble effects in surface reactions: 2. Benzene adsorption on clean and bismuth covered Pt(111)}, url = {http://pubs.acs.org/doi/pdf/10.1021/j100339a057}, volume = 93, year = 1989 }