Special Active Pt(100) Site for Room Temperature Electrochemical Activation of Methane

Wednesday, 4 October 2017
Prince George's Exhibit Hall D/E (Gaylord National Resort and Convention Center)
H. B. Ma (Department of Chemistry´╝îXiamen University), T. Sheng (Deprtment of Chemistry, Xiamen University, China), Z. Y. Zhou (Xiamen University), and S. G. Sun (Department of Chemistry, Xiamen University)
Methane is the main component of natural gas and a byproduct of oil refining and chemical processing. Due to its inertness, high temperature and high pressure are required for the most popular way of converting methane. Electrochemical conversion of methane has been put a lot of interests due to its facile control of selectivity by monitor electrode potential and its relatively mild working conditions. Although many studies have been conducted to improve methane conversion rate and selectivity based on solid oxide fuel cells, the basic methane electrooxidation mechanism remians poorly understood. Single crystal electrode with defined atomic arrangement proves to be a good model for the study of surface reaction mechanism.

In this study, the interaction between methane and well-defined Pt single crystal surfaces at room temperature was studied by electrochemical method and in situ FTIR spectroscopy. The results demonstrated that, amongst the three basal planes of Pt single crystal (Pt(111), Pt(110), Pt(100)), only Pt(100) can activate methane, in which the dissociation of methane could be detected at potentials above 0.0 V (vs.SCE) (Fig.1). At potential range between 0.0 V and 0.15 V, methane may be mainly dehydrogenated to produce spices like CO/COH, resulting in the decrease of Hudp on Pt(100). At potentials above 0.15 V, such spices can be further oxidized to form CO2. In situ FTIR spectroscopy studies indicated that methane can be oxidized to CO on Pt(100) surface and the CO mainly bound to hollow sites, moreover no oxidation product was detected on Pt(111) and Pt(110). DFT calculations show that on Pt(111) and Pt(100), the most stable surface species both are CH*, while on Pt(100) the most stable one is CH2*. On Pt(100), CH* prefers to be oxidized by O* with the lowest barrier being 0.4 eV. However, on Pt(110) and Pt(111), CHx* oxidation is much more difficult since the coupling between the carbon species and OH* is as high as 1.03 eV and 0.85 eV, respectively.

This study revealed the surface structure-reactivity in methane activation on platinum catalyst, and will give more insight into the design and synthesis of electrocatalyst for methane conversion.