We report the synthesis and characterization of new niobium oxyhydroxide catalysts from ammonium niobium oxalate (NH4[NbO(C2O4)2(H2O)](H2O)n) or niobium chloride (NbCl5) precursors. The materials have been modified by incorporating a surfactant, specifically cetyltrimethylammonium bromide, on the catalyst surface to impart partial hydrophobicity to the catalyst. The change in the precursor during the synthesis changes properties associated with the morphology, texture and number of acid sites. These properties provide increased contact at the interface between the hydrophilic and hydrophobic regions to improve the catalytic properties, particularly in biphasic reactions. Acetalization reactions were tested using three different glycerols: commercial glycerol p.a., a crude residual originating from biodiesel production and the same material after desalination. The results show 65 and 60 % conversion for the acetalization under mild reactions conditions.

In this study, Ca–Al mixed oxide produced from the thermal decomposition of a synthetic hydrocalumite was prepared and evaluated as a catalyst in the transesterification reaction for biodiesel production, using the following reagents: refined soybean oil, crude macauba kernel oil, methanol, and ethanol. The synthetic hydrocalumite and the mixed oxide were characterized by powder X-ray diffraction, thermogravimetry–differential scanning calorimetry coupled with mass spectrometry, specific surface area measurement, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and temperature-programmed desorption of CO2. The catalytic tests indicated that the reactions using methanol exhibited more favorable activity than those employing ethanol, regardless of the type of oil used (soybean or macauba). Ethanolysis produced better results for the higher-molar-mass oil (soybean), because of the effect of the ethanol cosolvent. The catalyst was efficient for transesterification, with conversions of 97% and 95% for soybean and macauba oil, respectively, after 1.5 h of reaction, under atmospheric pressure condition and reflux temperature.

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