IRON-ALUMINUM CLUSTER CATALYSTS OBTAINED BY ALKOXY SYNTHESIS .1. LIQUID-PHASE OXIDATION OF HEXADECANE

Iron-substituted boehmite gel has been prepared by alkoxy synthesis, i .e., by reaction of Fe(acac)3 with a fresh surface of AlOOH. Iron-alum inum complex oxide catalysts for liquid-phase oxidation of hexadecane were prepared by annealing the gel precursors. The gels with 0-20 wt.% of iron loading were studied by magnetic susceptibility and Mossbauer spectroscopy. Depending on the iron concentration, differing amounts of paramagnetic Fe3+ ions in the boehmite structure and small ferrimag netic spinel clusters were observed in the X-ray amorphous precursors. Thermal treatment led to formation of substituted spinels, FexAl2-xO3 , as well as gamma-ferric oxide clusters. The overall rate of hexadeca ne oxidation increased with an increase in the relative content of mag netic clusters. The inclusion of nonmagnetic Al3+ ions in the gamma-Fe 2O3 lattice reduced the number of terminal Fe3+ = O groups and the ove rall catalytic activity. The role of electronically excited terminal o xygen on the surface of gamma-ferric oxide clusters in the mechanism o f hexadecane oxidation is discussed. (C) 1994 Academic Press, Inc.