Group 6 hexacarbonyls supported on alumina: temperature-programmed decomposition and reduction

Group 6 hexacarbonyls were supported on aluminas pretreated at three differ ent temperatures. The degree of dehydroxylation was found to affect the tem perature-programmed decomposition (TPDE) profile of Mo(CO)(6) more than tho se of Cr(CO)(6) and W(CO)(6). Different reducible chromium surface species on alumina 500 were suggested: Two reduction maxima appeared when the sampl e was heated to 200 degrees C and oxidised with pulse chemisorption of oxyg en prior to reduction. After heating to 500 degrees C only one broad reduct ion maximum appeased. Partially oxidised molybdenum on alumina 500 gave a t emperature-programmed reduction (TPR) maximum art about 365 degrees C, inde pendent of the decarbonylation conditions. Successive reduction-oxidation c ycles showed the irreversibility of partially oxidised molybdenum. (C) 2000 Elsevier Science B.V. All rights reserved.