Abstract
The acidity of Al-SBA-15 materials functionalized by ball milling with several niobium loadings (0. 25–1 wt.%) as well as with several fluorine loadings (by wet impregnation using NH4F as a precursor) was characterized and materials investigated in the esterification of valeric acid to alkyl valerates. The parent Al-SBA-15 support as well as the modified materials loaded with Nb and/or F have been catalysts synthesized characterized by X-ray diffraction (XRD), N2 physisorption measurements, and diffuse reflection infrared spectroscopy (DRIFT) among others. A special interest was paid on the acidity of the materials that was investigated by temperature-programmed desorption of pyridine. Interestingly, the characterization results for the materials containing fluorine showed up an increase in the acidity strength despite of a reduction in the number of acid sites. The catalytic performance of the as-prepared catalysts was investigated in the microwave-assisted esterification reaction of valeric acid to valerate esters. Thus, while the materials modified with niobium exhibited a lower catalytic activity as compared with the catalytic support (Al-SBA-15), the materials loaded with fluorine either onto Al-SBA-15 or on Nb1%/Al-SBA-15 materials presented enhanced conversion values of valeric acid. Therefore, it can be said that the new acid sites with enhanced strength formed by the incorporation of fluorine boost the esterification of valeric acid with alcohols to form the respective valerate ester.
Highlights
IntroductionBiofuels and other biomass valorization routes have emerged as sustainable solutions to address such issues and have since been a major focus in the field of green chemistry (Lange et al, 2010; Ho et al, 2014; Sheldon, 2016)
Alternative feedstocks for fuels and chemicals are critically necessary to address the environmental concerns regarding to the increase on carbon emissions and the natural resources depletion, along with a world population that is constantly growing (Lange et al, 2010; Ho et al, 2014)
The aim of the modification with both niobium and fluorine is to boost the acidity of the materials in order to get materials catalytically active in the esterification of valeric acid
Summary
Biofuels and other biomass valorization routes have emerged as sustainable solutions to address such issues and have since been a major focus in the field of green chemistry (Lange et al, 2010; Ho et al, 2014; Sheldon, 2016). In this sense the sustainable design of efficient catalytic materials in the transformation of such biomass plays a key role. An additional problem was created in attempt to solve an existing one (Palkovits, 2010)
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