Low-temperature decomposition of methanol on Au nanoclusters supported on a thin film of Al2O3/NiAl(100)

Abstract

With a variety of surface probe techniques, we investigated low-temperature decomposition of methanol on Au nanoclusters formed by vapor deposition onto an ordered Al₂O₃/NiAl(100) thin film. Upon adsorption of methanol on the Au clusters (with mean diameter 1.5–3.8 nm and height 0.45–0.85 nm) at 110 K, some of the adsorbed methanol dehydrogenates directly into carbon monoxide (CO); the produced hydrogen atoms (H) begin to desorb near 125 K whereas most of the CO desorbs above 240 K. The reaction exhibits a significant dependence on the Au coverage: the produced CO increases in quantity with the Au coverage, reaches a maximum at about 1.0–1.5 ML Au, whereas decreases with further increase of the Au coverage. The coverage-dependence is rationalized partly by an altered number of reactive sites associated with low-coordinated Au in the clusters. At least two kinds of reactive sites for the low-temperature decomposition are distinguished through distinct C–O stretching frequencies (2050 cm⁻¹ and 2092 cm⁻¹) while the produced CO co-adsorbs with H and methanol.