Current topics of catalysts containing niobium and tantalum, especially in
the field of solid acid catalysis and selective oxidation of hydrocarbons a
re reviewed. Hydrated niobium oxide and hydrated tantalum oxide are highly
acidic. Hydrated niobium oxide is active for the hydration of ethene to eth
anol, and Nb-W mixed metal oxide is more active for the reaction. Acid prop
erties of tantalum oxide are changed by being supported on SiO2. Ta oxide/S
iO2, prepared by the chemical reaction between tantalum alkoxide and surfac
e hydroxyl groups of SiO2, is active and selective for the gas phase Beckma
nn rearrangement of cyclohexanoneoxime to caprolactam. Niobium oxide and ta
ntalum oxide easily react with many other oxides to form mixed metal oxide
phases with complex structure. Mixed metal oxide catalysts, containing moly
bdenum, vanadium, certain elements together with niobium are active for the
selective oxidation of hydrocarbons. Especially, the selective oxidation o
f propane by such mixed metal oxide catalysts has been paid attention. Addi
tionally, recent progress of environmental catalysts, promoted by niobium a
nd tantalum compounds, namely catalysts for the pollution abatement is revi
ewed. (C)2000 Elsevier Science B.V. All rights reserved.