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Applied Catalysis B: Environmental

Volumes 108–109, 11 October 2011, Pages 161–167

Niobium-containing MCM-41 silica catalysts for biodiesel production

Cristina García-Sancho, Ramón Moreno-Tost, Josefa M. Mérida-Robles, José Santamaría-González, Antonio Jiménez-López, Pedro Maireles-Torres ,

Departamento de Química Inorgánica, Cristalografía y Mineralogía (Unidad Asociada al ICP-CSIC), Facultad de Ciencias, Universidad de Málaga, Campus de Teatinos s/n, 29071 Málaga, Spain

Received 19 April 2011, Revised 8 August 2011, Accepted 18 August 2011, Available online 25 August 2011

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DOI: 10.1016/j.apcatb.2011.08.025
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Abstract
This research focuses on the synthesis and characterization of mesoporous niobosilicate molecular sieves and their catalytic activity in biodiesel production by transesterification of sunflower oil with methanol. Catalysts were prepared by two procedures: impregnation of a MCM-41 silica with different amounts of niobium oxalate and subsequent calcination, and structural incorporation of Nb into a MCM-41 silica during the synthesis step. Characterization techniques such as XRD, XPS, TEM, NH3-TPD and N2 sorption have been employed to characterize the synthesized catalysts. The biodiesel yield increases with the catalyst acidity, attaining a value of 95% with a 7.5 wt% of a MCM-41 silica impregnated with a 8% of Nb2O5, at 200 °C, after 4 h of reaction and a methanol/oil molar ratio of 12. The potential of this family of catalysts to treat low-grade oils has been demonstrated by increasing the acidity of the sunflower oil by adding oleic acid (1.1 wt%) and water (0.2 wt%) to the reaction mixture, since the biodiesel yield is maintained close to 80%. Moreover, the catalyst reutilization has been demonstrated during five catalytic runs by employing a low-grade oil, with no leaching of the active phase.

Graphical abstract
Niobium-containing MCM-41silica catalysts are very active in the methanolysis of sunflower oil at 200 °C, even in the presence of an acidity of 1.1 wt% and 0.2 wt% water, without leaching.

Highlights
Nb2O5 containing mesoporous silica is active for the acid-catalyzed biodiesel production. The catalysts can be reutilized, without leaching of the active phase. They catalyze the methanolysis of triglycerides, even in the presence of water and FFA.

KeywordsNiobium oxide; Mesoporous silica; Biodiesel; Transesterification; Acid catalysis
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Copyright © 2011 Elsevier B.V. All rights reserved.

http://www.sciencedirect.com/science/article/pii/S0926337311003948