Pyrene: hydrogenation, hydrogen evolution, and π-band model.
Jakob Arendt Rasmussen1, Graeme Henkelman, Bjørk Hammer
1Interdisciplinary Nanoscience Center (iNANO) and Department of Physics and Astronomy, Ny Munkegade, Building 1520, Aarhus University, DK-8000 Aarhus C, Denmark.
The Journal of Chemical Physics
|May 3, 2011
Summary
Hydrogenation of pyrene is exothermic, with edge carbon atoms being most reactive. Molecular hydrogen evolution from dihydrogenpyrene has a significant energy barrier, suggesting stability.
Area of Science:
- Physical Chemistry
- Computational Chemistry
- Materials Science
Background:
- Polycyclic aromatic hydrocarbons (PAHs) like pyrene are abundant in various environments.
- Understanding their reactivity with hydrogen is crucial for astrochemistry and materials science.
- Previous studies have explored PAH hydrogenation with varying theoretical approaches.
Purpose of the Study:
- To theoretically investigate the hydrogenation of pyrene by atomic hydrogen.
- To determine the energetics and kinetics of hydrogen binding to pyrene.
- To explore the subsequent molecular hydrogen evolution from hydrogenated pyrene.
Main Methods:
- Density Functional Theory (DFT) at the GGA-PBE level was employed for primary calculations.
- Hybrid-DFT (PBE0) was used to complement specific DFT calculations.
- A tight-binding model was developed to analyze electronic structure and predict binding sites.
Main Results:
- Hydrogenation of pyrene is exothermic (up to 1.6 eV) with a strong site dependence, favoring edge carbon atoms.
- Low activation barriers (down to 0.06 eV) were found for initial hydrogen binding, with second hydrogen binding barrierless at many sites.
- The most stable dihydrogenpyrene structure is energetically favored over pyrene plus molecular hydrogen, with a substantial 3.7 eV barrier for hydrogen evolution.
Conclusions:
- Edge carbon atoms in pyrene are the most reactive sites for hydrogenation.
- Hydrogenated pyrene species exhibit significant stability against molecular hydrogen evolution.
- The projected density of π-states is a useful descriptor for predicting hydrogen binding sites on PAHs.
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