CATALYTIC UPGRADING OF GLYCEROL TO ADVANCED FUEL ADDITIVES

Hierarchical zeolites offer enhanced molecular diffusion and improved accessibility of active sites, making them attractive catalysts for reactions involving bulky molecules. This work presents the generation of hierarchical porosity with different Si/Al ratios via post-synthetic modifications (PSM) while preserving the frameworks’ crystallinity and acidity. Moreover, the novelty of this study lies in the combination of conventional and advanced methods, including pore-directing agent (PDAs) and microwave-assisted (MW) treatments.

A series of different zeolitic structures (beta-Hβ, mordenite-HMOR, L-KLTL, and ultra-stable Y-HUSY) were subjected to demetallation, namely desilication and dealumination, according to their Si/Al ratio. Each process was performed either conventionally (Des-C/Deal-C), or with ethylenediamine as the PDA for desilication (Des-EDA) and via microwave irradiation for dealumination (Deal-MW). Samples undergoing both desilication and dealumination were denoted as Desal-C and Desal-MW, respectively. As a result, XRD patterns highlighted that desilication with PDAs and MW-assisted dealumination showed improvement over conventional method while, maintaining structural integrity. Furthermore, the prepared catalysts were employed in the acetalization of glycerol with various carbonylic compounds, a reaction of great interest for producing five and six-ring ketals used as fuel additives in order to boost octane, cold flow and also reduce emissions.

Under the optimized reaction conditions, hierarchical zeolites showed high catalytic efficiency, >80% conversion and >60% selectivity toward the desired ketals. In terms of recyclability, the most stable catalyst retained its activity over at least three recycling cycles.

The combination of multiple PSM strategies enabled the formation of hierarchical zeolites with superior catalytic efficiency, emphasizing the critical role of tailored porosity in enhancing reaction rates and product selectivity. The influence of the textural, acid/base, density, distribution of active sites, and type of PSM properties on the efficiency of the catalysts in the aforesaid processes will be discussed.