Effect of Silicon Sources on the Synthesis of Nanosized Beta Zeolite Aggregates as Catalysts for Conversion of Lactic Acid to Lactide

Abstract

Silicon sources play a crucial role in determining the structure and properties of the resulting zeolites. However, the correlation between the structure and performance of nanosized beta zeolite aggregates (e.g., morphology, Al distribution, acidity, and catalytic properties) arising from solid Si sources requires further investigation. In this study, nanosized beta zeolites (FS-Z, SG-Z, and CT-Z) were synthesized using three selected Si sources: fumed silica (FS), silica gel (SG), and Celite (CT). Comprehensive characterization revealed that SG-Z, which is nanosheet zeolite aggregates, exhibited the largest pore volume (0.47 cm³/g), the highest acid quantity (0.80 mmol/g), and better uniform Al distribution and stability compared to FS-Z and CT-Z. Additionally, the crystallization process of the three nanosized beta zeolites indicated that the choice of solid Si source is a key factor influencing the morphology, Al distribution, and acid content of the resulting nanosized zeolites. The laminated stacking structure of SG-Z is attributed to a balanced dissolution rate, which facilitates coordination between nucleation and crystal growth under the guidance of l-lysine. Furthermore, SG-Z exhibited excellent catalytic performance in a sustainable catalytic system for lactic acid (LA) conversion, achieving up to 98% lactide (LT) yield, and exhibited no significant decrease after five cycles. This research emphasizes the critical role of solid Si source selection in tailoring nanosized beta zeolite properties, offering insights for optimizing their catalytic applications in acid-catalyzed reactions and providing a strategy for the design of an industrial catalytic reaction.