Add time:07/26/2019         Source:sciencedirect.com

In this work, very high acidity niobium oxide was obtained by surface modification with sulfate groups. This modification increased the Brønsted acidity of niobium oxide and the functionalized material showed noticeable activity in the biodiesel production using the esterification of oleic acid as a reaction model. The characterization of the functionalized materials by nitrogen adsorption/desorption, scanning electron microscopy (SEM), and X-ray diffraction (XRD) showed the amorphous morphology and high surface area of these materials. Temperature programmed reduction (TPR) and Fourier Transform Infrared Spectroscopy (FTIR) confirmed the presence of sulfate groups on the niobium oxide surface, and the acid surface sites on the catalyst were evaluated by adsorption of pyridine and Temperature-programmed desorption of ammonia (NH3-TPD). Reactions of methyl oleate production from oleic acid with methanol were evaluated by 1H-NMR and the sulfated niobium oxide exhibited a conversion up to 92% for esterification depending on the oleic acid/methanol ratio, as well as the catalyst amount. In addition, kinetic studies showed that the sulfated niobium oxide was able to promote a significant reduction in the activation energy of the esterification reaction from 68.4 kJ mol−1 to 34.7 kJ mol−1. The direct reuse of the catalyst was also evaluated up to five cycles with minimal activity loss.

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