Kowalska-Kuś Jolanta, Janiszewska Ewa, Góra-Marek Kinga, Jankowska Aldona, Held Agnieszka
Faculty of Chemistry, Adam Mickiewicz University, Uniwersytetu Poznańskiego 8, Poznań, Poland.
Faculty of Chemistry, Jagiellonian University in Krakow, Gronostajowa 2, 30-387 Kraków, Poland.
Dalton Trans. 2024 Aug 13;53(32):13537-13549. doi: 10.1039/d4dt01523a.
Silicalite-1 is a silica with a zeolitic MFI (Mobil Five) structure devoid of noticeable catalytically active (, acid) sites. In this study, we present its modification with NHF solutions of varying concentrations (0.5-3 M), which generates efficient and selective acid sites for the acetalization of glycerol with acetone towards solketal (2,2-dimethyl-1,3-dioxolane-4-methanol). The creation of acid sites is attributed to the partial elimination of external silanol groups in silicalite-1 and the generation of some framework defects, resulting also in increased porosity. The characterization of the modified materials was performed using various techniques, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed desorption of ammonia (TPD-NH), and Fourier-transform infrared spectroscopy (FTIR). The results demonstrate that the newly created acidic sites of Brønsted and Lewis nature exhibit significantly higher acidic strength and enhanced accessibility for reagents compared to the pristine one, resulting in exceptional glycerol conversion in the acetalization of glycerol with acetone and notable selectivity towards solketal. Glycerol conversion over modified silicalite-1 reached nearly 70%, with the selectivity to solketal exceeding 98% at 70° C after 1 hour of reaction time, using a mixture of glycerol and acetone in a 1 : 1 ratio. The proposed reaction mechanism takes into account a combination of Brønsted and Lewis acid sites. The obtained results indicated that Brønsted acid sites, especially those of higher strength, are the most beneficial in this process. The remarkable catalytic performance and stability of modified silicalite-1 make it a promising candidate for potential industrial applications in the utilization of waste glycerol formed in the biofuel industry.
硅沸石-1是一种具有沸石MFI（美孚五号）结构的二氧化硅，没有明显的催化活性（酸性）位点。在本研究中，我们展示了用不同浓度（0.5 - 3 M）的NHF溶液对其进行改性，这为甘油与丙酮缩合生成丙酮缩甘油（2,2 - 二甲基 - 1,3 - 二氧戊环 - 4 - 甲醇）产生了高效且选择性的酸性位点。酸性位点的产生归因于硅沸石-1中外部硅醇基团的部分消除以及一些骨架缺陷的产生，这也导致了孔隙率的增加。使用各种技术对改性材料进行了表征，包括X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、氨程序升温脱附（TPD - NH）和傅里叶变换红外光谱（FTIR）。结果表明，与原始材料相比，新产生的布朗斯特和路易斯性质的酸性位点表现出显著更高的酸性强度和对试剂增强的可及性，从而在甘油与丙酮的缩合反应中实现了优异的甘油转化率以及对丙酮缩甘油的显著选择性。在反应1小时后，使用1∶1比例的甘油和丙酮混合物，在70℃下，改性硅沸石-1上的甘油转化率接近70%，对丙酮缩甘油的选择性超过98%。所提出的反应机理考虑了布朗斯特和路易斯酸性位点的组合。所得结果表明，布朗斯特酸性位点，尤其是那些强度较高的位点，在这个过程中是最有利的。改性硅沸石-1卓越的催化性能和稳定性使其成为生物燃料行业中利用产生的废甘油进行潜在工业应用的有前途的候选材料。
