(186g) Investigation of the Aqueous, Low-Temperature, Anodic Electrocatalytic Conversion of Methane to Oxygenates at Pt Surfaces

The dramatic increase in supply of natural gas in North America has motivated development of new catalytic processes that utilize light hydrocarbons for chemical manufacturing and fuel synthesis. These technologies are dependent on a strong fundamental understanding of oxidative functionalization of C-H bonds at the surfaces of heterogeneous catalysts. However, methods that enable direct conversion of natural gas constituents, such as methane, to useful products are limited, primarily because of their strong C-H. The stable C-H single bonds of alkanes can be activated at high temperatures in the gas phase, but desired products, including oxygenates and alcohols, are quickly oxidized to COx under these conditions. As an alternative, electrochemical processes show unique potential to enable low-temperature selective chemical conversions. Here, we investigate the electrocatalytic oxidation of methane at Pt surfaces at room temperature and ambient pressure to understand the mechanism underlying its conversion to oxygenates. A series of experiments involving a variety of electrochemical and spectroscopic techniques have been carried out. Adsorbed intermediates were characterized by two complementary techniques: surface enhanced infrared adsorption spectroscopy (SEIRAS) and electrochemical stripping voltammetry methods. Surface defects on Pt surfaces are found to be crucial for the initial C-H bond activation. Multiple reaction potentials were applied to understand the effect of surface adsorbates on methane activation, and the reaction pH dependence was explored to intentionally modify the chemical state of the Pt surface. The accompanying Figure shows representative results: (left) the reaction-time-dependent electrochemical stripping of adsorbed products resulting from methane decomposition, and (right) operando FTIR probing the potential-dependent adsorption composition.