Kinetics of unimolecular decomposition on surfaces: Methanol on Ni(110)

The decomposition of methanol on a clean Ni(110) surface has been studied with temperature programmed reaction spectroscopy, low energy electron diffraction and temperature programmed electron energy loss spectroscopy: a new technique for the characterization of surface dynamic properties. Adsorption of methanol at 170 K results in the formation of a methoxy (CH3O) species. Near 270 K the methoxy decomposes into adsorbed hydrogen and carbon monoxide. For initial methoxy coverages greater than 0.20 monolayer (ML) the decomposition is rate limited by the desorption of product hydrogen. For initial methoxy coverages less than 0.20 ML the abstraction of the first methoxy hydrogen is rate limiting. This step is modeled by first order kinetics with an activation energy of 16 kcal mol−1 and a preexponential factor of 1012 s−1. A normal kinetic isotope effect (kH/kD>1) is observed confirming that C–H bond scission is the rate limiting step at low coverages.