Group 6 hexacarbonyls were supported on aluminas pretreated at three different temperatures. The degree of dehydroxylation was found to affect the temperature-programmed decomposition (TPDE) profile of Mo(CO)(6) more than those of Cr(CO)(6) and W(CO)(6). Different reducible chromium surface species on alumina 500 were suggested: Two reduction maxima appeared when the sample was heated to 200 degrees C and oxidised with pulse chemisorption of oxygen prior to reduction. After heating to 500 degrees C only one broad reduction maximum appeased. Partially oxidised molybdenum on alumina 500 gave a temperature-programmed reduction (TPR) maximum art about 365 degrees C, independent of the decarbonylation conditions. Successive reduction-oxidation cycles showed the irreversibility of partially oxidised molybdenum.