AN EXAFS STUDY OF THE SPREADING OF MOO3 ON THE SURFACE OF GAMMA-AL2O3

An EXAFS analysis has been carried out of physical mixtures of MoO3 with γ-Al2O3 prior to and after thermal treatment at 720 K in the absence and presence of water vapor. The degree of order in the MoO3/Al2O3 samples decreases during calcination. This loss of long-range order is even more pronounced in the presence of water vapor than in its absence. The local order around molybdenum after thermal treatment in a dry atmosphere still resembles that in MoO3, while significant structural modifications are induced when water vapor is present. After calcination a new Mo-X distance was observed which may correspond to a MoAl contribution in a MoOAl configuration. The EXAFS results support earlier conclusions from ion scattering and Raman spectroscopy studies on identical samples, which suggests a spreading Of MoO3 over the surface of alumina as a result of solid-solid wetting. © 1991.