Further studies on ligand-promoted oxide dissolution during supported catalysts preparation: evidence for the formation of aluminoheteropolytungstates in the case of the WOx/γ-Αl2O3 system.
作者： X. Carrier , J.F. Lambert , M. Che
DOI: 10.1016/S0167-2991(98)80213-9
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摘要: This study deals with the importance of alumina dissolution on speciation tungstic species encountered in WOX/Al2O3 catalysts preparation by equilibrium adsorption method. The support is enhanced formation soluble alumino-heteropolytungstates solution and this can be rationalised words geochemists as a "ligand-promoted dissolution" effect. We have first synthesised different types obtained 27Al NMR fingerprints these compounds. All compounds adopt Keggin-type structure. aluminium ions exist two environments: either tetrahedral (δ = 71 to 73 ppm) or octahedral = 5 12 ppm). Some structures are lacunary removal some tungsten octahedra. By comparison 27A1 reference compounds, we show here that during catalysts, formed reaction between dissolved precursors (mono, para, metatungstate) even at near neutral pH where solubility supposed negligible. situation appears much more complex than molybdates since several least three factors influence chemistry system: pH, nature oxide/water ratio. system, well previously studied ΜοΟX/Αl2O3, clear examples showing not chemically inert. It play role stoechiometric reagent.
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