Nonclassical Adsorption of Methanol on Palladium: The Competition between Adsorption of Single Molecules and Clusters

Abstract

The adsorption of methanol on the Pd(111) surface at 80, 90, and 100 K has been studied by polarization modulation infrared reflection–absorption spectroscopy. It is found that the adsorption of methanol on the palladium surface does not proceed via the layer-by-layer mechanism. At temperatures below 100 K, methanol adsorbs molecularly to form clusters containing several hydrogen-bonded CH3OH molecules. These clusters have low thermal stability and decompose even at 100 K to form isolated methanol molecules bonded with palladium atoms. As a result, at a temperature between 100 and 120 K, methanol adsorbs intact to produce adsorbed isolated molecules. These adsorbed species fast desorb at a temperature above 120 K. The dehydration of methanol is not observed under used conditions.