METAL PROMOTER INTERACTIONS IN VANADIUM-OXIDE PROMOTED RH/SIO2 CATALYSTS

The influence of the calcination temperature on the structure and morphology of vanadium oxide promoted, silica-supported rhodium catalysts was studied. Pure Rh/SiO2 and VOx/SiO2 served as reference systems. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), FTIR spectroscopy of adsorbed CO and BET surface-area measurements. BET, XRD and TEM investigations revealed a strong sintering of the silica support at calcination temperatures at and above 973 K. There is a crystalline silica phase, which was found exclusively in the promoted Rh/SiO2 catalyst calcined at 1173 K. XRD, TPR and TEM gave evidence for the formation of a rhodium-vanadium mixed oxide on the catalyst surface at 973 K calcination. After high-temperature reduction (HTR = 773 K) highly dispersed metal is formed from this ternary oxide phase. A C- and O-bonded carbonyl species probably located at the metal/promoter interface was detected by FTIR spectroscopy at 83 K.