Thermal Stability and Spectroscopic Assessment of Bronsted Sites in Solid Acid-Layered Niobates

Autor(es)

Souza, Eduardo Caetano C.

• Tipo de documento: Artigo Científico
• Fonte: Journal of Physical Chemistry C; v. 123, n. 40, p. 24426-24435, OCT 10 2019.
• Citações Web of Science: 0

Resumo

Solid acid-based photocatalysts have been widely pursued to apply in different chemical conversions, as in Fischer-Tropsch synthesis and in the oxidation of alcohols and hydrocarbons. In the present work, layered niobates of composition HxM4-xNb6O17 (M = K, Rb, Cs) and HNb3O8 were synthesized by the sol gel method followed by proton exchange reaction. Local structure modifications due to proton incorporation were evaluated by X-ray powder diffraction and Raman spectroscopy. The Raman spectra point to a decrease in the symmetry of NbO6 groups with vibrational frequencies assigned to variations of Nb-O bond order. Thermally stable acid sites may reach an optimum temperature of 250 degrees C as dehydroxilation begins until total deprotonation at 570 degrees C. Impedance spectroscopy was performed to study the chemical properties of NbO-H bonds by evaluating the proton mobility under dry air and water vapor-saturated atmospheres. The impedance data show that hydrated protons are primarily bonded to the terminal oxygen of NbO6 octahedra as the electrons of hydronium H3O+ ions remain localized. The results suggest that layered HxK4-xNb6O17 hexaniobate merits further investigation as inexpensive and strong solid acid host for the photochemical conversion of gaseous reactants into renewable products at intermediate temperatures. (AU)

• Processo FAPESP: 12/15785-0 - Desenvolvimento e Caracterização de Novos Materiais Condutores a Partir de Niobatos Lamelares
• Beneficiário: Eduardo Caetano Camilo de Souza
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado