Site-Specific Selectivity of Stepped Pt Surfaces for Methane Dehydrogenation at Low Temperatures

Thanks to a combination of Supersonic Molecular Beam and Reflection Absorption Infrared Spectroscopy experiments, for stepped-like Pt surfaces it has been recently possible to measure the different reactivities of metal atoms in the step and in the terrace of Pt(211)[1-2]. Interestingly, these site-specific measurements have also brought to light new intriguing issues concerning the vibrational properties of the products of methane dehydrogenation at low surface temperatures (e.g. below ~150K). For instance, i) the blue-shifted frequency of the dissociation product in the step with respect to that in the terrace, and ii) the origin of the double-peak of the partially deuterated dissociation product in the step when dosing Pt(211) with CH3D instead of CH4, have been considered “a bit of mystery”[2-5]. 
In this talk I will present and discuss the results of a study based on DFT calculations that provides an explanation for thsese and other previously overlooked surprising exerimental findings. In a few words, DFT results indicate that at low temperatures, the dissociation products of methane dissociation on step and terrace sites of Pt(211) are not the same as it had been assumed. Methyl would be the product on terrace sites whereas methylene would be the product in the step[6]. This conciliates theory and experiments and shows that steps not only tend to exhibit a higher reactivity than terraces (as usually expected) but also illustrates that vicinal surfaces can also provide a route to control surface selectivity.

[1] Gutiérrez-González, A.; Beck, R. D. Quantum state and surface-site-resolved studies of methane chemisorption by vibrational spectroscopies. Phys. Chem. Chem. Phys. 22 (2020) 17448−17459.
[2] Gutiérrez-González, A. Bond-selective and surface-site-specific dissociation of methane on Platinum. Ph.D. Thesis, Ecole Polytechnique Fedrale de Lausanne, 2019.
[3] Chadwick, H.; Guo, H.; Gutiérrez-Gonzá lez, A.; Menzel, J. P.; Jackson, B.; Beck, R. D. Methane dissociation on the steps and terraces of Pt(211) resolved by quantum state and impact site. J. Chem. Phys. 148 (2018) 014701.
[4] Gutiérrez-González, A.; Crim, F. F.; Beck, R. D. Bond selective dissociation of methane (CH3D) on the steps and terraces of Pt(211). J. Chem. Phys. 149 (2018) 074701.
[5] Miller, J. L. Vibrational spectroscopy dissects a surface reaction. Phys. Today 71 (2018) 17−19.
[6] Torio, M.E.; Busnengo, H.F. Site-Specific Product Selectivity of Stepped Pt Surfaces for Methane Dehydrogenation. J. Phys. Chem. C 124 (2020) 19649−19654.
Host: Maite Alducin

Hybrid Seminar, Donostia International Physics Center


Heriberto Fabio Busnengo, Instituto de Física Rosario, Argentina

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