SURFACE CHARACTERIZATION OF CU-TI SYSTEMS - AN IR STUDY

A comparative study of the surface properties of Cu-Ti samples prepared by impregnation of TiO2 with a Cu(NO3)2 solution or from amorphous CuTi alloy precursors diluted with TiO2 has been made. The samples were submitted to vacuum and H-2 treatments at increasing temperatures, from 493 up to 773 K; at the end of the pretreatments the specimens were contacted with CO, from RT up to 573 K. The surface species produced were monitored by FTIR spectroscopy. On all the samples a band of CO adsorbed on Cu surface sites, significantly blue-shifted in comparison with that observed on Cu monocrystalline surfaces and on Cu particles supported on other n-type oxidic semiconductors, was observed. The blue-shift, that is maximum on the most strongly reduced samples, was interpreted as due to an electronic interaction of copper with reduced titania and to the fact that, on the more strongly reduced samples, copper particles are almost completely covered by reduced titania and copper sites are almost isolated. The NO interaction on CO precovered samples produces a strong intensity increase and a red-shift of the CO absorption band, indicating that in oxidizing conditions and in the presence of CO the exposed Cu grows up.