Calorimetric heats for CO and oxygen adsorption and for the catalytic CO oxidation reaction on Pt{111}

Abstract

Single crystal adsorption calorimetry was applied to investigate the heats of adsorption of CO and oxygen and the reaction heats for the CO oxidation process on Pt{111} at room temperature. Both sticking probabilities and heats of adsorption for CO and oxygen are presented as a function of coverage. These results are used to interpret the subsequent measurements taken for the CO oxidation process on the same surface. The initial heats of adsorption of CO and oxygen on Pt{111} are 180±8 and 339±32 kJ/mol, respectively. In addition the pairwise lateral repulsive interaction between CO molecules in a (√3×√3)R30° ordered layer at θ=1/3 is found to be 4 kJ/mol. A detailed Monte Carlo modeling of the dissociative adsorption and sticking probability of oxygen on Pt{111} is performed. The initial rapid fall in heat is attributed to adsorption on defect sites, and subsequent adsorption on the planar {111} surface proceeds with a third neighbor interaction energy between the oxygen adatoms ω3∼22 kJ/mol. When gaseous CO reacts with preadsorbed oxygen adatoms, the CO2 produced has an excess energy of 16±8 kJ/mol.

CO adsorption on metal surfaces: A hybrid functional study with plane-wave basis set

“…This result is certainly disappointing, and we will return to it in the conclusions. For Pt(111), experimental values are in the range of −1.71 to −1.43 eV, 62,63,64 which compare reasonably well with the PBE value. Again the hybrid functionals clearly worsen the agreement with experiment.…”

Influence of Carbon Support on Electronic Structure and Catalytic Activity of Pt Catalysts: Binding to the CO Molecule

“…75 The heat of adsorption for the CO molecule on the Pt(111) surface at low coverage (atop site) is reported 1.87±0.08 eV using single crystal adsorption calorimetry. 74 The C−O bond distance and ν CO are calculated to 1.158Å (1.186Å) and 2031.5 cm −1 (1839.8 cm −1 ) for the atop (bridge) structure, respectively. The lower ν CO for the bridge structure reflects a stronger interaction between the CO molecule and the Pt dimer and consequently a stronger back donation to the anti-bonding 2π * orbitals of the CO molecule.…”

Adsorbate interactions of CO chemisorbed on Pt(111)

“…Furthermore, the adsorption energy decreases from around 1.9 eV at low coverages to 1.66 eV at coverage 0.33 and to 1.2 eV at half coverage [8], which means that the interaction is repulsive. There is evidence that repulsive forces exist between adsorbates several lattice constants apart, and that they depend non-monotonically upon distance [9].…”

“…[7], this is the densest structure of on-top adsorbates only, and further chemisorption occurs into bridge sites, but other authors claim that a regular ( √ 3 × √ 3)R30 • structure at a coverage of 1/3 exists (Ref. [8] and references therein). The regular structure at 0.5 contains an equal number of on-top and bridge adsorbates.…”

“…The value in Ref. [8] is obtained from the change of the adsorption energy between a low coverage and a coverage of 0.33, which corresponds to a regular ( √ 3 × √ 3)R30 • structure of on-top adsorbed CO molecules. Since in this structure no lateral relaxation of Pt atoms is possible, we compare this interaction energy with one-sixth of our relaxation energy for a single CO.…”