Tuning the Acidity of BEA Zeolite Catalysts for Glycerol Conversion

What is it about?

The effect of Si/Al ratio and the nature of the silicon-substituting element (Fe, Ga, B) on the acidic and catalytic properties of BEA-type zeolites in glycerol conversion in the range of 300-340 °C was investigated. Data on the physicochemical and structural characteristics of zeolites obtained by X-ray diffraction (XRD), BET, SEM, FTIR spectroscopy, MAS NMR, and Raman spectroscopy have been described and discussed. An increase in the Si/Al ratio reduces both Brønsted (BAS) and Lewis (LAS) acid site concentrations, thereby decreasing the total acidity of the zeolites. In HAlSiBEA samples, the BAS/LAS ratio correlates with the proportion of tetrahedrally coordinated aluminum (AlIV) to pentahedrally coordinated aluminum (AlV), indicating that BAS is associated with AlIV, while LAS is predominantly associated with AlV. The products of glycerol conversion over all the studied catalysts are acetaldehyde and acrolein. Both Si/Al ratio and the nature of the silicon-substituting element have a greater effect on the overall catalytic activity than on the product distribution. The acetaldehyde selectivity tends to increase with temperature, while the acrolein selectivity decreases. Studies show that variation of elements isomorphically introduced into the structure of BEA zeolites is a more effective tool for increasing their catalytic activity than dealumination of the aluminosilicate HAlSiBEA. Moreover, isomorphously substituted aluminium-free HESiBEA catalysts are less prone to carbonization during catalysis than HAlSiBEA. These findings provide new insights into the structure–activity relationships of BEA-type zeolites, offering guidance for the rational design of catalysts for glycerol valorization

Featured Image

Why is it important?

Comparison of the catalytic behavior of BEA-zeolite catalysts shows that, generally, isomorphously substituted zeolites (especially HFeSiBEA and HGaSiBEA) are characterized by better performance compared to HAlSiBEA. The results obtained in this work allow us to conclude that variation of the isomorphous introduced element in the structure of BEA zeolites is a more effective tool for tuning their catalytic activity than the dealumination of aluminosilicate HAlSiBEA