XAFS study of niobium species formed during the preparation of Nb/SiO2 catalysts by the equilibrium adsorption method

✍ Scribed by Hisao Yoshida; Tsunehiro Tanaka; Tomoko Yoshida; Takuzo Funabiki; Satohiro Yoshida

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 137 KB
• Volume: 208-209
• Category: Article
• ISSN: 0921-4526
• DOI: 10.1016/0921-4526(94)00787-v

✦ Synopsis

Nb K-edge XAFS has been investigated to clarify the most significant step controlling the dispersion of Nb species in Nb/SiO2 catalysts prepared by the equilibrium adsorption method from impregnating solutions at various pH. In solution, the Nb ion is present as the [NbO(C204)2H20] -complex regardless ofpH. The Nb complex adsorbed on silica has the same structure as that in a solution of pH 4, while the complex is bonded to silica by an Nb-O-Si bond in a solution of pH 0.8. After calcination at 773 K followed by evacuation, the Nb species on silica is stabilized as NbO4 tetrahedra and/or its aggregates. The Nb species in a catalyst prepared in solution at pH 0.8 is highly dispersed, because of the formation of a tight bond between the Nb complex and the silica surface during equilibrium adsorption.