AN ATOMIC-FORCE MICROSCOPY STUDY OF THE MORPHOLOGICAL EVOLUTION OF THE MOO3(010) SURFACE DURING REDUCTION REACTIONS

Atomic force microscopy was used to characterize the nanometer-scale s tructural evolution of the MoO3 (010) surface during reaction with hyd rogen at 400 degrees C. Two primary surface modifications were identif ied. First, water vapor, when present in the reactor either as an impu rity or as an oxidation product, accelerates the volatilization of MoO 3 and leads to the formation of surface voids. The presence of these v oids increases the density of (100) and (h01)-type surface sites on th e basal planes. Second, oxygen removal leads to the formation of cryst allographic shear planes. The intersection of these defects with the ( 010) surface creates 2 Angstrom high steps along [001] and their prese nce indicates that the surface vacancy concentration has reached an up per limit. The mechanisms by which these structural changes might infl uence the reactivity of molybdenum oxide catalysts are discussed. (C) 1996 academic Press, Inc.