Molecular Catalysis, 2018,
In the design of catalysts, an extremely important point is to determine, control and increase the availability of active sites on the surface. In the present work, active sodium oxide species have been identified and it is demonstrated how its dispersion can be suitably improved by combining sodium loading degree and calcination heating rate in order to increase the catalyst basic character and consequently, its performance. The different synthesized materials were characterized by: small-angle X-ray scattering (SAXS), high angle X-ray diffractions (XRD), atomic absorption spectroscopy (AA), BET method (specific surface determination), Fourier-transform infrared spectroscopy (FT-IR), carbon dioxide temperature programed desorption (CO2 TPD) and X-ray photoelectron spectroscopy (XPS). The obtained catalyst using 10 wt% of sodium loading followed by calcination at 500 °C, employing an 8 °C/min heating rate, showed the highest activity towards the transesterification of sunflower oil reaction (5 h, 60 °C, 14:1 methanol to oil molar ratio, 2 wt% catalyst, vigorous magnetic stirring), achieving a 90% biodiesel yield.