Abstract:

In situ infrared spectroscopy has been used to study CO and/or NO adsorbed on reduced as/SiO2 and Rh-V/SiO2 catalysts. On Rh/SiO2 catalyst reduced at 573K,CO adsorption results in the formation of linear and bridged CO species as well as gem-dicarbonyl to give adsorption bands at 2060, 1867, 2085 and 2028cm-1 respectively; NO adsorption bands appeared at 1726 and 1650cm-1 .However, on V/SiO2 catalyst reduced at 573K, no CO bands were observed, and two NO bands appeared at 1907 and 1810cm-1.Furthermore, the NO bands shifted to 1890 and 1756cm-1 when the V/SiO2 catalyst was reduced at 773K. Introduction of vanadium to the An/SiO2 catalyst showed a slight effect on the intensity of the gem-dicarbonyl species and particularlly caused a remarkable decrease of the linear and bridged CO species in intensities. Simultaneously, the high frequeny band of the gem-dicarbonyl shifted upwards by about 10cm-1. These results indicate that the electron transfer from Rh0 to vanadium ions was enhanced in Rh-V/SiO2 catalyst. Also promotion of reduction of V oxide by Rh was observed during the pretreatment of Rh-V/SiO2 catalyst as detected by ESR experiment. From the results of CO and No coadsorption, it was found that the absorbed NO species decreased CO adsorption on Rh, particularly, the linear CO species was completely disappeared. For the effects of NO adsorption on CO adsorption, there are two possibilities: (1) direct replacement of CO with NO, (2) oxidation of Rh0 sites through NO dissociative adsorption. During the coadsorption, two possible intermediates, i.e., RhCONO and Rh(CO)2NO, were suggested for the surface process, which requires further investigation. 

Key words: CO and/or NO adsorption, IR spectoscopy, Rh-V/SiO₂ catalyst