Conversion of blonde glycerin to acrolein using Nb2O5/SiO2 catalysts synthesized by the Pechini method

Abstract

Niobia catalysts dispersed in amorphous silica were synthesized using the Pechini method for the catalytic conversion of blonde glycerin into acrolein. The samples were calcined at 500°C and incorporated with different niobia contents: 10 %, 15 %, and 20 % by mass, designated as 10NbSi500, 15NbSi500, and 20NbSi500, respectively. The X-ray diffraction patterns revealed the formation of the TT-Nb₂O₅ phase, whose crystallinity depends on the calcination temperature and niobia content. FTIR spectra showed the presence of Nb-OH and Si-OH groups on the surface of the impregnated solids. Stain micrographs revealed a porous surface with Nb species, and their incorporation did not alter the silica matrix. The 15NbSi500 sample stood out with a high specific surface area (255.9 m².g⁻¹), larger pore distribution and volume (13 nm and 0.83 cm³.g⁻¹), a high concentration of acid sites (4.30 μmol.m⁻²), and a higher L/B ratio (FTIR-py results), which is crucial in reducing coke formation. The solids containing 15 % and 20 % niobia exhibited high catalytic performance after 180 min, with conversions of 96.02 % and 96.44 % and selectivity to acrolein of 76.25 % and 75.79 %, respectively. The high selectivity to acrolein was attributed to the conversion of LAS to BAS during the reaction. Catalytic tests over 600 min were conducted for 15NbSi500 and 20NbSi500. The superiority of the solid with 15 % niobia was attributed to its excellent acidic and textural properties, achieving 77 % conversion and 84 % selectivity to acrolein. After three reuse cycles, the catalyst maintained 62 % conversion and 75 % selectivity values, indicating its promise for near-industrial applications in enhancing the biodiesel production chain.