Properties of Molybdate Species Supported on Silica

DOI: 10.1039/f19898501607

Source and publish data:

Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases p. 1607 - 1618 (1989)

Update date:2022-08-10

Topics:

Authors:

Liu, Tuan-chi

Forissier, Michel

Coudurier, Gisele

Vedrine, Jacques C.

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Article abstract of DOI:10.1039/f19898501607

Molybdenum species have been deposited on a high surface area silica by the impregnation method and further calcination at 500 deg C in air.Mo loading was varied from 0-10 wtpercent Mo.I.r., u.v.-visible, XPS and EDX-STEM techniques have been used to characterize the nature of the molybdenum species as a function of Mo loading.At low Mo content (< 3 wtpercent Mo) interaction between silanol groups and molybdate ions occurred resulting in the formation of monomeric tetrahedral MoO4^2- species with a u.v. band near 245 nm.For intermediate loadings (3-8 wtpercent) polymeric octahedral molybdate species were identified with a u.v. band near 340 nm.At high Mo content crystallites of MoO3 were also observed.Catalytic properties for both isopropyl alcohol conversion in air at 100 deg C and propene oxidation at 400 deg C were studied as a function of Mo loading.It was observed that the catalysts are acidic as evidenced by isopropyl alcohol dehydration into propene at low Mo content and their activity increased with Mo content following the amount of MoO4^2- species.Polymeric molybdate species were observed to exhibit mainly redox-type properties as evidenced by isopropyl alcohol oxidative dehydrogenation into acetone and by propene oxidation into propanal (electrophilic attack) and into acrolein (allylic-type reaction).MoO3 crystallites were observed to exhibit usual properties of unsupported MoO3 catalysts.