Effect of electron tunneling through the oxide film grown on metal substrate upon the efficiency of molecular reaction over the oxide supported metal nanoparticles: A case of CO oxidation on Au/Al2O3/Mo(110)

Abstract

Formation of gold nanosized particles supported by aluminum oxide film grown on Mo(110) substrate and oxidation of carbon monoxide molecules on their surface have been in-situ studied in ultra-high vacuum by means of Auger electron spectroscopy (AES), reflection-absorption infrared spectroscopy (RAIRS), low energy electron diffraction (LEED), atomic force microscopy (AFM), temperature programmed desorption (TPD) and work function measurements. The main focus was to follow how the thickness of the alumina film influences the efficiency of CO oxidation in an attempt to find out an evidence of possible effect of electron tunneling between the metal substrate and the Au particle through the oxide interlayer. Providing the largest degree of surface identity of the studied metal/oxide system at different thicknesses of the alumina film (2, 4, 6 and 8 monolayers), it was found that the CO oxidation efficiency, defined as CO2 to CO TPD peaks intensity ratio, as well as the activation energy of CO oxidation, exponentially depend upon the oxide film thickness. Taking into account the known fact that the CO oxidation efficiency depends on the amount of excess charge acquired by Au particle, the latter suggests that electron tunneling adds efficiency to the oxidation process, although not significantly.