Remarkable spreading behavior of molybdena on silica catalysts. Anin situ EXAFS-Raman study

Abstract

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EXAFS study of molybdenum oxide on the structure Al2O3

“…2 -5 A number of studies have been published on the structure of supported molybdenum oxide on Al 2 O 3 using Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, 95 Mo-NMR, extended x-ray absorption fine structure/nearedge structure (EXAFS/XANES) and XPS, but the structure is still a matter of debate. Konigsbarger et al 6 showed that there are at least three types of MoO 3 phase-tetrahedraland octahedral-coordinated surface phases and a crystalline phase. Leliveld et al 7 described small molybdenum oxide particles possessing a highly distorted octahedral structure with one terminal Mo O bond and 5-6-fold oxygen coordination ranging from 1.71 to 1.95Å.…”

Selectivities in methanol oxidation over silica supported molybdena

“…in ambient environment) [16,17]. Heating the catalyst during the calcination converts polymolybdate to an isolated monodispersed Mo 6+ species [18]. The polymolybdate cluster is reformed after rehydration.…”

“…Polymolybdate, such as heptamolybdate, was identified by Raman spectroscopy for the hydrated state of the catalyst [15][16][17]. Upon dehydration by thermal heating, spreading of Mo species occurs and yields isolated Mo 6+ species [18].…”

Use of Oxide Ligands in Designing Catalytic Active Sites

“…are recognized as industrially important catalysts for numerous chemical reactions [1][2][3][4][5][6][7][8][9][10][11]. For example, these catalysts are utilized for o-xylene oxidation to phthalic anhydride [12,13], methane/methanol oxidation to formaldehyde [14], and selective catalytic reduction (SCR) of NO with ammonia to N 2 over supported vanadia catalysts [15][16][17][18][19]; SCR of NO with ammonia and selective oxidation of methane over supported molybdena catalysts [20][21][22]; olefin metathesis and hydrocarbon isomerization reactions over tungsta catalysts; and metathesis of olefins and alkanes over supported rhenia catalysts [23][24][25]. These supported metal oxide catalysts consist of highly dispersed surface metal oxide species -the catalytic active sites -anchored to the underlying oxide support.…”