Spectroscopic Characterization of Thermal Methane Activation by Lewis-Acid-Base Pair in a Gas-Phase Metal Nitride Anion TaN.

Activation and transformation of methane is one of the "holy grails" in catalysis. Understanding the nature of active sites and mechanistic details via spectroscopic characterization of the reactive sites and key intermediates is of great challenge but crucial for the development of novel strategies for methane transformation. Herein, by employing photoelectron velocity-map imaging (PEVMI) spectroscopy in conjunction with quantum chemistry calculations, the Lewis acid-base pair (LABP) of [Ta-N] unit in TaN acting as an active center to accomplish the heterolytic cleavage of C-H bond in CH has been confirmed by direct characterization of the reactant ion TaN and the CH-adduct intermediate TaNCH . Two active vibrational modes for the reactant (TaN ) and four active vibrational modes for the intermediate (TaNCH ) were observed from the vibrationally resolved PEVMI spectra, which unequivocally determined the structure of TaN and TaNCH . Upon heating, the LABP intermediate (TaNCH ) containing the NH and Ta-CH unit can undergo the processes of C-N coupling and dehydrogenation to form the product with an adsorbed HCN molecule.