Probing Copper and Copper–Gold Alloy Surfaces with Space-Quantized Oxygen Molecular Beam

Abstract

The orientation and motion of reactants play important roles in reactions. The small rotational excitations involved render the reactants susceptible to dynamical steering, making direct comparison between experiments and theory rather challenging. Using space-quantized molecular beams, we directly probed the (polar and azimuthal) orientation dependence of O 2 chemisorption on Cu(110) and Cu 3 Au(110). We observed polar and azimuthal anisotropies on both surfaces. Chemisorption proceeded rather favorably with the O–O bond axis oriented parallel (vs perpendicular) to the surface and rather favorably with the O–O bond axis oriented along [001] (vs along [1̅10]). The presence of Au hindered the surface from further oxidation, introducing a higher activation barrier to chemisorption and rendering an almost negligible azimuthal anisotropy. The presence of Au also prevented the cartwheel-like rotations of O 2 .

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

“…For instance, as displayed in Figure 22, using space-quantized oxygen molecular beam as reactant, the activation on Cu (110) and Cu 3 Au(110) alloy surface is measured, respectively, which indicates that O 2 molecule with helicopter configuration can be activated on Cu (110) surface, while the O 2 activation is prohibited on Cu 3 Au(110) alloy surface. 218 Another typical example is the study of geometric structure of PdAu surface for acetoxylation of ethylene to vinyl acetate, which suggests that only the Pd atoms deposited on Au(100) surface are close enough for catalyzing the coupling reaction, while the Pd atoms on Au (111) surface are not active due to their large distance. 219,220 The lessons accumulated in surface science studies can be translated to practical catalysts based on bimetallic nanoclusters/nanoparticles for fundamental understanding of the structure−reactivity relationships.…”

“…(c) Illustration of the reactivity of O 2 molecule on Cu(110) and Cu 3 Au­(110) surface. Reproduced with permission from ref . Copyright 2022 American Chemical Society.…”

Adsorption dynamics of O2 on Cu(111): a supersonic molecular beam study

“…41 For O 2 dissociative adsorption on Cu(110), charge transfer causing creation of a short-lived intermediate O 2 δ − state on the way to dissociation at higher impact energies was suggested from a combined theoretical and experimental study that involved state-selection and alignment of impacting O 2 . 18 For the current system, we believe that a similar intermediate species may be involved, although the main bottle neck to dissociation on defect-free Cu(111) seems to be the barrier in the entrance channel. According to the PES, this barrier varies at least between approximately 100 and 200 meV for impact with the internuclear axis parallel to the surface.…”

“…The geometric corrugation for the molecular state seems very large from the reported cuts of the PES. 20 Molecular scattering experiments at higher incident energies, spin and alignment control of the impacting and scattering O 2 , 18,42 or angle-and energy-resolved scattering/ desorption measurements 43 may provide evidence. Finally, we reiterate that in an absolute sense, we find mostly higher reactivities for O 2 impinging onto Cu(111) than the only earlier published results.…”

“…17 Anisotropy in the potential that affects adsorption and dissociation was studied in great detail using space-quantization and alignment of the impinging O 2 molecules by Kurahashi and coworkers. 18 For Cu(100), Valden and coworkers interpreted the adsorption dynamics of O 2 also as including a precursor or steering-mediated adsorption at defects. 19 Kasai and co-workers suggest different roles of vibration and rotation of O 2 in the dissociation process for all low Miller index Cu surfaces, but did not address whether Cu(111) also participates in precursor and direct dissociation processes in parallel.…”