Local characterisation of inhomogeneous Cu surfaces by surface-enhanced Raman scattering

An attempt was made to compare surface-enhanced Raman spectra (SERS) of the probe molecules adsorbed on highly dispersed Cu surfaces of both real catalyst and various model systems produced from pure Cu. In particular, we searched for the Cu clusters with adsorption properties significantly differing from the properties of the clusters produced from pure copper on the surface of highly active copper-containing catalysts. The SERS spectra of pyridine used as a probe molecule were collected with a Raman spectrometer connected to a microscope having a focal radius of less than 10−6 m. It was found, for example, that for the very active catalyst produced from 50Cu–50Zr amorphous precursor by high-pressure hydrogen charging, the relative intensities of pyridine bands are considerably different at some places to those observed for copper. At other areas on the sample, however, the spectrum is similar to that observed for pure Cu. This indicates that the local SERS technique has the potential to investigate adsorbate properties that are usually hidden by averaging if the signal is collected from a larger surface area.