Transesterification of canola oil catalized by calcined Mg–Al hydrotalcite doped with nitratine

•Hydrotalcite doped with 7 wt% NaNO3 converts canola oil to biodiesel up to 91%.•The activity of hydrotalcite-NaNO3 is due to Mg2+–O2− pairs and Na2O phase.•NaNO3 promotes the regeneration of hydrotalcite catalysts.•Na2O induces the conversion of canola oil to biodiesel as MgO provides active sites.

Mg–Al hydrotalcite substrates having an X=Al+3/(Al+3+Mg+2) metal molar ratio equal to 0.2, were synthesized at pH=8 from a coprecipitation method combined with microwave radiation exposure to induce the crystalline network growth of the precursory hydrogel. The hydrotalcite materials were obtained either pristine or with the inclusion of nitratine at different amounts; this compound being added during the washing procedure of the hydrogel. The hydrotalcite substrates were calcined in air at 570 °C for 18 h, thus generating the corresponding mixed metal oxides. The final substrates were characterized by infrared spectroscopy, while also displaying the characteristic X-ray diffraction patterns of the hydrotalcite phase before calcination. The mixed metal oxide solids were used as catalysts (CI–CV) and were tested in the transesterification reaction of canola oil. It was found that the conversion to biodiesel increased, depending on the nitratine content existing in hydrotalcite as well as on the extension of the formed periclase phase. Among all catalysts, one of the substrates (containing 7 wt% of nitratine) exhibited the highest conversion of canola oil to biodiesel (91%), which, in this material, can be attributed to the preponderant presence of periclase and promoting effect of Na2O. The latter material and a catalyst with no nitratine content were characterized by scanning electron microscopy, and their elemental surface composition was evaluated by Energy Dispersive X-ray Spectroscopy; in turn, their basic character was assessed by CO2 Temperature Programmed Desorption. The conversion of synthesized Fatty Acid Methyl-Esters was calculated from the area under the signal peaks registered by Nuclear Magnetic Resonance spectroscopy.

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