BISMUTH CARBOXYLATES AS PRECURSORS FOR THE INCORPORATION OF BISMUTH IN OXIDE-BASED MATERIALS

The use of bismuth(III) carboxylates (acetate, oxoacetate, lactate, ox alate) as precursors for the incorporation of this element on oxide su pports is evaluated as a new tool to generate bismuth-based oxide phas es at the surface of MoO3 or WO3 supports. These insoluble precursors are deposited as small particles from a slurry in a liquid hydrocarbon under appropriate experimental conditions, Bismuth molybdate and tung state phases are produced by solid-state reactions between in situ gen erated Bi2O3 and the supporting oxide at 673 K. The samples are charac terized by specific surface area measurements, X-ray diffractometry, a nd X-ray photoelectron spectroscopy, The selective oxidation of isobut ene to methacrolein is employed as a reaction test to demonstrate the applicability of this approach, The use of precursors containing lacta te or acetate-type ligands is found to generate materials displaying e nhanced specific surface area and high bismuth-to-molybdenum surface a tomic ratios. This bismuth enrichment of the surface is indicative of the presence of dispersed crystallites of either Bi2O3 itself or terna ry Bi-Mo-O or Bi-W-O phases, which are known to promote partial oxidat ion of alkenes, The performances of these materials in the isobutene t o methacrolein conversion are indeed in most cases definitely better t han those of the so-called reference materials obtained from the simpl e mixtures of the same oxides prepared separately. (C) 1996 Academic P ress, Inc.