Abstract

Step and kink sites at Pt surfaces have crucial importance in catalysis. We employ a high dimensional neural network potential (HDNNP) trained using first-principles calculations to determine the adsorption structure of CO under ambient conditions (T = 300 K and P = 1 atm) on these surfaces. To thoroughly explore the potential energy surface (PES), we use a modified basin hopping method. We utilize the explored PES to identify the adsorbate structures and show that under the considered conditions several low free energy structures exist. Under the considered temperature and pressure conditions, the step edge (or kink) is totally occupied by on-top CO molecules. We show that the step structure and the structure of CO molecules on the step dictate the arrangement of CO molecules on the lower terrace. On surfaces with (111) steps, like Pt(553), CO forms quasi-hexagonal structures on the terrace with the top site preferred, with on average two top site CO for one multiply bonded CO, while in contrast surfaces with (100) steps, like Pt(557), present a majority of multiply bonded CO on their terrace. Short terraced surfaces, like Pt(643), with square (100) steps that are broken by kink sites constrain the CO arrangement parallel to the step edge. Overall, this effort provides detailed analysis on the influence of the step edge structure, kink sites, and terrace width on the organization of CO molecules on non-reconstructed stepped surfaces, yielding initial structures for understanding restructuring events driven by CO at high coverages and ambient pressure.

Highlights

  • The active phase of transition metal heterogeneous catalysts presents atoms in different coordinations and environments

  • We show that the CO organization on the terrace is strongly affected by the geometry of the step ((100) or (111) facets), which controls the ratio between top and multiply bonded CO molecules, that quasihexagonal CO lattices are formed on these terraces to the case of Pt(111)[17,21] and that step edges are in most cases fully covered with one top site CO molecule on each step Pt atom

  • Pt(553) can be represented as Pt(S)-[5(111) Â (111)] in step notation since it is formed by a 5 atom wide Pt(111) terrace followed by a mono-atomic 111-type step as shown in Fig. 1(a) and (b)

Read more

Summary

Introduction

The active phase of transition metal heterogeneous catalysts presents atoms in different coordinations and environments. Open surface structures or surfaces with a high Miller index o en show enhanced activity.[1,2,3,4,5] The high-index planes, denoted by a set of Miller indices (hkl) with at least one index being larger than one, have a high density of atomic steps and kinks. The low coordination atoms which de ne the atomic step/kink sites on the catalyst surface o en enable enhanced binding of reactant molecules and exhibit higher activity for bond breaking.[6,7,8,9,10,11,12,13] At the same time, steps play an important role in other surface processes like adsorbate induced reconstructions. The surface atoms at the step/kink site act as natural locations for crystal growth and erosion

Methods
Results
Conclusion
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call