EXAFS Studies on Oxidic K-MoO₃/γ-Al₂O₃ Catalysts

EXAFS measurements were performed on Mo compounds of Na₂MoO₄. 2H₂O, MoO₃,（NH₄）₆Mo₇O₂₄. 4H₂O and the oxidic K-MoO₃/γ-Al₂O₃ catalyst samples with different K contents.Na₂MoO₄. 2H₂O was used as reference compound in the process of EXAFS fit.
For the oxidic Mo compounds of MoO₃ or （NH₄）₆Mo₇O₂₄. 4H₂O which have irregular structures, Mo-O coordinations are complex with different distances. By two or three layer fit, the EXAFS analysis shows reasonable results compared to crystallographic parameters.For the oxidic sample, Since several different Mo species are formed on the surface, the Mo-O coordination becomes more complex. By two layer fit, EXAFS analysis shows that for the sample without containing potassium, part of Mo ealsts as MoO₃ crystullite with a short range order; for the samples with K/Mo=0. 8 and K/Mo=1. 5, Mo exists dominately as heptamolybdate ion （Mo₇O₂^46-）, these are in accord with the results from XRD and LRS measurements.