(569cc) The Formation Machenism of Needle-like Beta Zeolite and Its Application in Sorbitol Conversion

The conversion of sorbitol to isosorbide represents a significant advancement in the chemical industry. Isosorbide, derived from this conversion, emerges as a crucial industry feedstock with the potential to replace traditional petroleum-based raw materials. The conversion of sorbitol to isosorbide is a two-step dehydration reaction, presenting both the reactants and products as highly water-soluble and hydrophilic. While acid sites are crucial for this reaction, increased acid quantities can actually reduce conversion and yield. Among the available zeolites, Beta Zeolite has showcased superior performance over its counterparts like MOR and USY, further emphasizing its significance in the sorbitol conversion process.

Post-modification techniques of zeolites have been extensively explored to optimize their catalytic properties. Acid treatment is commonly employed to adjust the Si/Al ratio, while alkaline treatment is utilized to introduce mesoporosity into the zeolitic structures. Additionally, cetyltrimethylammonium bromide (CTAB) has been recognized for its role in the modification of zeolite morphologies. Although zeolite beta has shown promise in sorbitol conversion, challenges persist regarding its yield and selectivity. In this study, a unique 'needle-like' structure of BEA zeolites was obtained through cascade post-treatment processes.

The formation hypothesis for the needle-like beta zeolite is proposed, which involves acid treatment to generate isolated silanol groups, followed by alkaline treatment under hydrothermal conditions using cetyltrimethylammonium bromide (CTABr) as an inhibitor, finally yielding the needle-like morphology. In our investigation of the needle-like beta zeolite, we discerned that sorbitol conversion is concomitantly modulated by factors including a catalyst's acidity, external surface area, and hydrophobicity. Finally, the best performance of sorbitol dehydration was obtained with the sample coded as 0.6MAc-HBEA_Ak7D, achieving the conversion of sorbitol up to 90.0 % with a selectivity to isosorbide of 50.7 %. The TOF of 1.0MAc-HBEA_Ak7D is estimated at 2305, which is around three times the value obtained with the mother zeolite (831).