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 and Sykes, E. Charles H. (2014). Significant quantum effects in hydrogen activation. ACS Nano, 8 (5), 4827–4835.

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.

Publication DOI: https://doi.org/10.1021/nn500703k
Divisions: Engineering & Applied Sciences
Engineering & Applied Sciences > European Bioenergy Research Institute (EBRI)
Additional Information: Copyright © 2014 American Chemical Society. ACS AuthorChoice - Terms of Use CC-BY
Uncontrolled Keywords: quantum tunneling,hydrogen,activation,single-atom alloy,path integral density functional theory,kinetic Monte Carlo simulation
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Related URLs: https://pubs.ac ... .1021/nn500703k (Publisher URL)
Published Date: 2014-05-27
Authors: Kyriakou, Georgios
Davidson, Erlend R.M.
Peng, Guowen
Singh, Suyash
Boucher, Matthew B.
Marcinkowski, Matthew D.
Mavrikakis, Manos
Michaelides, Angelos
Sykes, E. Charles H.

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