H-Beta zeolite is a solid acid catalyst commonly utilized in the catalytic conversion of biomass resources. In this study, H-Beta zeolite was calcined at different temperatures (350, 550, 750, and 1000 °C) to explore the effects of high temperature-induced dealumination on its physicochemical properties and its catalytic ability to convert glucose into 5-hydroxymethylfurfural (HMF). It was shown that as the calcination temperature increased, the Si-O-Al bond of H-Beta zeolite was broken and its dealumination effect was enhanced. Dealumination led to the collapse of the framework of H-Beta zeolite and a reduction in the number of acid sites, which in turn reduced its catalytic performance and the efficiency of HMF formation from glucose. Furthermore, H-Beta zeolite exhibited an extraordinary catalytic ability for the production of HMF from carbohydrates. Using glucose and cellulose as substrates, superior HMF yields of 91% and 46%, respectively, were achieved under optimal reaction conditions. Further, calcination removes carbon deposits in the recovered H-Beta zeolite, but it affects the cycling stability of the catalyst. Meanwhile, the by-products formed during the synthesis of HMF from glucose catalyzed by H-Beta zeolite catalyst were also clearly detected.
The utilization of racemic lactic acid (rac-LA) produced via chemocatalytic conversion for polylactic acid (PLA) synthesis remains limited due to the formation of undesired mesomeric lactide (meso-LD), a by-product that arises during the conversion process. This study proposes the use of shape-selective H-Beta zeolite to reduce the formation of meso-LD in lactide (LD) by leveraging its selectivity towards different lactic dimers (L2A) in a one-step catalytic conversion of rac-LA to LD. Experimental results from various LA solutions with different L2A content indicate that the L2A content is critical for maximizing the selectivity of racemic lactide (D/L-LD), thus confirming the shape-selective nature of H-Beta zeolite towards L2A. Additionally, it is found that increasing the reaction temperature and employing structurally reconstructed H-Beta zeolite with more regularized channels as a catalyst can further decrease meso-LD formation, and a LD yield of 60% with a D/L-LD/meso-LD ratio of 2.26 can be achieved under optimal catalyst and reaction conditions. Despite the coexistence of D/L-LD and meso-LD in the final product, this study marks a significant step towards controlling the stereoisomer distribution of LD synthesized from rac-LA derived from chemical conversion.
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