Significant quantum effects in hydrogen activation

Georgios Kyriakou, Erlend R.M. Davidson, Guowen Peng, Suyash Singh, Matthew B. Boucher, Matthew D. Marcinkowski, Manos Mavrikakis, Angelos Michaelides, E. Charles H. Sykes

Research output: Contribution to journalArticle

Abstract

Dissociation of molecular hydrogen is an important step in a wide variety of chemical, biological, and physical processes. Due to the light mass of hydrogen, it is recognized that quantum effects are often important to its reactivity. However, understanding how quantum effects impact the reactivity of hydrogen is still in its infancy. Here, we examine this issue using a well-defined Pd/Cu(111) alloy that allows the activation of hydrogen and deuterium molecules to be examined at individual Pd atom surface sites over a wide range of temperatures. Experiments comparing the uptake of hydrogen and deuterium as a function of temperature reveal completely different behavior of the two species. The rate of hydrogen activation increases at lower sample temperature, whereas deuterium activation slows as the temperature is lowered. Density functional theory simulations in which quantum nuclear effects are accounted for reveal that tunneling through the dissociation barrier is prevalent for H2 up to ∼190 K and for D2 up to ∼140 K. Kinetic Monte Carlo simulations indicate that the effective barrier to H2 dissociation is so low that hydrogen uptake on the surface is limited merely by thermodynamics, whereas the D2 dissociation process is controlled by kinetics. These data illustrate the complexity and inherent quantum nature of this ubiquitous and seemingly simple chemical process. Examining these effects in other systems with a similar range of approaches may uncover temperature regimes where quantum effects can be harnessed, yielding greater control of bond-breaking processes at surfaces and uncovering useful chemistries such as selective bond activation or isotope separation.
LanguageEnglish
Pages4827–4835
Number of pages9
JournalACS Nano
Volume8
Issue number5
Early online date31 Mar 2014
DOIs
Publication statusPublished - 27 May 2014

Fingerprint

Hydrogen
Chemical activation
activation
hydrogen
Deuterium
dissociation
deuterium
Temperature
reactivity
temperature
isotope separation
Kinetics
kinetics
Isotopes
Density functional theory
simulation
Thermodynamics
chemistry
density functional theory
Atoms

Bibliographical note

Copyright © 2014 American Chemical Society. ACS AuthorChoice - Terms of Use CC-BY

Keywords

  • quantum tunneling
  • hydrogen
  • activation
  • single-atom alloy
  • path integral density functional theory
  • kinetic Monte Carlo simulation

Cite this

Kyriakou, G., Davidson, E. R. M., Peng, G., Singh, S., Boucher, M. B., Marcinkowski, M. D., ... Sykes, E. C. H. (2014). Significant quantum effects in hydrogen activation. ACS Nano, 8(5), 4827–4835. https://doi.org/10.1021/nn500703k
Kyriakou, Georgios ; Davidson, Erlend R.M. ; Peng, Guowen ; Singh, Suyash ; Boucher, Matthew B. ; Marcinkowski, Matthew D. ; Mavrikakis, Manos ; Michaelides, Angelos ; Sykes, E. Charles H. / Significant quantum effects in hydrogen activation. In: ACS Nano. 2014 ; Vol. 8, No. 5. pp. 4827–4835.
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Kyriakou, G, Davidson, ERM, Peng, G, Singh, S, Boucher, MB, Marcinkowski, MD, Mavrikakis, M, Michaelides, A & Sykes, ECH 2014, 'Significant quantum effects in hydrogen activation' ACS Nano, vol. 8, no. 5, pp. 4827–4835. https://doi.org/10.1021/nn500703k

Significant quantum effects in hydrogen activation. / Kyriakou, Georgios; Davidson, Erlend R.M.; Peng, Guowen; Singh, Suyash; Boucher, Matthew B.; Marcinkowski, Matthew D.; Mavrikakis, Manos; Michaelides, Angelos; Sykes, E. Charles H.

In: ACS Nano, Vol. 8, No. 5, 27.05.2014, p. 4827–4835.

Research output: Contribution to journalArticle

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AU - Kyriakou, Georgios

AU - Davidson, Erlend R.M.

AU - Peng, Guowen

AU - Singh, Suyash

AU - Boucher, Matthew B.

AU - Marcinkowski, Matthew D.

AU - Mavrikakis, Manos

AU - Michaelides, Angelos

AU - Sykes, E. Charles H.

N1 - Copyright © 2014 American Chemical Society. ACS AuthorChoice - Terms of Use CC-BY

PY - 2014/5/27

Y1 - 2014/5/27

N2 - Dissociation of molecular hydrogen is an important step in a wide variety of chemical, biological, and physical processes. Due to the light mass of hydrogen, it is recognized that quantum effects are often important to its reactivity. However, understanding how quantum effects impact the reactivity of hydrogen is still in its infancy. Here, we examine this issue using a well-defined Pd/Cu(111) alloy that allows the activation of hydrogen and deuterium molecules to be examined at individual Pd atom surface sites over a wide range of temperatures. Experiments comparing the uptake of hydrogen and deuterium as a function of temperature reveal completely different behavior of the two species. The rate of hydrogen activation increases at lower sample temperature, whereas deuterium activation slows as the temperature is lowered. Density functional theory simulations in which quantum nuclear effects are accounted for reveal that tunneling through the dissociation barrier is prevalent for H2 up to ∼190 K and for D2 up to ∼140 K. Kinetic Monte Carlo simulations indicate that the effective barrier to H2 dissociation is so low that hydrogen uptake on the surface is limited merely by thermodynamics, whereas the D2 dissociation process is controlled by kinetics. These data illustrate the complexity and inherent quantum nature of this ubiquitous and seemingly simple chemical process. Examining these effects in other systems with a similar range of approaches may uncover temperature regimes where quantum effects can be harnessed, yielding greater control of bond-breaking processes at surfaces and uncovering useful chemistries such as selective bond activation or isotope separation.

AB - Dissociation of molecular hydrogen is an important step in a wide variety of chemical, biological, and physical processes. Due to the light mass of hydrogen, it is recognized that quantum effects are often important to its reactivity. However, understanding how quantum effects impact the reactivity of hydrogen is still in its infancy. Here, we examine this issue using a well-defined Pd/Cu(111) alloy that allows the activation of hydrogen and deuterium molecules to be examined at individual Pd atom surface sites over a wide range of temperatures. Experiments comparing the uptake of hydrogen and deuterium as a function of temperature reveal completely different behavior of the two species. The rate of hydrogen activation increases at lower sample temperature, whereas deuterium activation slows as the temperature is lowered. Density functional theory simulations in which quantum nuclear effects are accounted for reveal that tunneling through the dissociation barrier is prevalent for H2 up to ∼190 K and for D2 up to ∼140 K. Kinetic Monte Carlo simulations indicate that the effective barrier to H2 dissociation is so low that hydrogen uptake on the surface is limited merely by thermodynamics, whereas the D2 dissociation process is controlled by kinetics. These data illustrate the complexity and inherent quantum nature of this ubiquitous and seemingly simple chemical process. Examining these effects in other systems with a similar range of approaches may uncover temperature regimes where quantum effects can be harnessed, yielding greater control of bond-breaking processes at surfaces and uncovering useful chemistries such as selective bond activation or isotope separation.

KW - quantum tunneling

KW - hydrogen

KW - activation

KW - single-atom alloy

KW - path integral density functional theory

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Kyriakou G, Davidson ERM, Peng G, Singh S, Boucher MB, Marcinkowski MD et al. Significant quantum effects in hydrogen activation. ACS Nano. 2014 May 27;8(5):4827–4835. https://doi.org/10.1021/nn500703k