INFRARED SPECTROSCOPIC STUDY ON CO-INDUCED STRUCTURAL-CHANGES OF IRIDIUM ON AN ALUMINA SUPPORT

The interaction of CO with alumina-supported iridium, reduced at different temperatures, was investigated by infrared spectroscopy. The dominant spectral features for the low-temperature reduced samples (TR = 473-673 K) at 300 K are the bands at 2090-2107 and 2010-2037 cm-1. No spectral changes were observed, even after an extended adsorption time. In the case of high-temperature reduced samples (TR = 773-1173 K), the adsorption of CO at 300 K initially produces a broad absorption band peaking at around 2060 cm-1, but after an extended adsorption time, bands at 2090-2107 and 2010-2037 cm gradually appear and grow in intensity. This process is attributed to the oxidative fragmentation of Irx crystallites and to the formation of isolated indium sites (Ir0 and IrI), which involves the participation of OH groups on alumina When the sample exhibiting strong adsorption bands at 2090-2107 and 2010-2037 cm-1 is heated to 423-573 K in the presence of CO, both bands are gradually reduced in intensity and a strong band is formed at 2050-2080 cm-1. This process is explained by the reductive agglomeration of IrI sites. © 1990 American Chemical Society.