Blanco-Sánchez Miguel, Pfab Evan, Lázaro Noelia, Balu Alina M, Luque Rafael, Pineda Antonio
Departamento de Química Orgánica, Universidad de Córdoba, Córdoba, Spain.
Department of Chemistry, People's Friendship University of Russia (RUDN University), Moscow, Russia.
Front Chem. 2020 Jan 31;8:42. doi: 10.3389/fchem.2020.00042. eCollection 2020.
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 NHF 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), N 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.
通过球磨法制备了负载不同铌含量（0.25 - 1 wt.%）以及不同氟含量（以前体NHF通过湿浸渍法引入）的Al-SBA-15功能化材料，对其酸度进行了表征，并研究了这些材料在戊酸酯化生成戊酸酯反应中的性能。通过X射线衍射（XRD）、N物理吸附测量、漫反射红外光谱（DRIFT）等手段对母体Al-SBA-15载体以及负载了Nb和/或F的改性材料进行了表征。特别关注了通过吡啶程序升温脱附研究的材料酸度。有趣的是，含氟材料的表征结果显示，尽管酸位点数量减少，但酸度强度有所增加。在微波辅助的戊酸酯化生成戊酸酯的反应中研究了所制备催化剂的催化性能。因此，虽然与催化载体（Al-SBA-15）相比，铌改性的材料表现出较低的催化活性，但负载在Al-SBA-15或Nb1%/Al-SBA-15材料上的氟材料呈现出更高的戊酸转化率。所以，可以说通过引入氟形成的强度增强的新酸位点促进了戊酸与醇酯化生成相应的戊酸酯。
