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Ammonium complex of niobium as a precursor for the preparation of Nb2O5/Al2O3 catalysts

2003; Elsevier BV; Volume: 78; Issue: 1-4 Linguagem: Inglês

10.1016/s0920-5861(02)00327-9

1873-4308

Fabiana Magalhães Teixeira Mendes, Carlos A. Perez, Ricardo Reis Soares, Fábio B. Noronha, Martín Schmal,

Semiconductor materials and devices

Ammonium oxalate complex of niobium was investigated as an aqueous precursor for the preparation of x% Nb2O5/Al2O3 (x=5, 10, 20 and 30 wt.%) samples. Catalysts with the same Nb2O5 contents were also prepared from the traditional niobium oxalate/oxalic acid aqueous solution. The catalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), temperature-programmed reduction (TPR), infrared spectroscopy of chemisorbed pyridine and X-ray photoelectron spectroscopy (XPS). A comparison with the preparation method using the niobium oxalate salt was performed. The results showed that the niobium precursor influence the species growing leading to phases with different reducibility. The XPS revealed the presence of multilayers of niobium oxide on the Nb2O5/Al2O3 samples prepared by using niobium ammonium oxalate complex, while the ones obtained from niobium oxalate led to Nb2O5 particles islands. The addition of niobium oxide decreased the fraction of Lewis acid sites and increased the fraction of Brønsted acid sites, independent of the precursor salt. However, the creation of BAS was more pronounced on the Nb2O5/Al2O3 samples prepared from niobium oxalate.