The preparation and properties of rhenia-alumina catalysts

A series of rhenia-alumina catalysts were made using an equilibrium adsorption technique. These were characterized by laser Raman, infrared, and visible reflectance spectroscopy. Only a monomeric rhenia species was found bound to the alumina of the resulting catalysts. The visible reflectance spectra showed, however, that the symmetry around the Re was lower than tetrahedral, possibly C2v or C3v, i.e., distorted tetrahedral. The laser Raman spectra were sensitive to moisture; the alumina-bound rhenia could be readily hydrolyzed to HReO4. The extremely broad band (hump) between about 300 and 800 cm−1 decreased with increase in loading and nearly disappeared from spectra of samples evacuated at temperatures above 350 °C. It may therefore be attributed to fluorescence from the surface hydroxyl groups on the alumina support. A brief temperature programmed reduction (TPR) study revealed that most of the rhenia could be reduced to Re0 at 275 °C, but a very small amount appeared to resist reduction up to 500 °C.