(49e) Selective Production of Para-Xylene from Biomass-Derived 2,5-Dimethylfuran through Tandem Diels–Alder/Dehydration Reactions with Bifunctional Zeolite Catalysts

Para-xylene (p-xylene) is a key building precursor for the manufacture of polyethylene terephthalate (PET) among other commodity chemicals. Conventionally, p-xylene is produced from steam cracking of naphtha, which involves high energy consumption and results in relatively low aromatics selectivity. These drawbacks and the need for sustainable production of commodity chemicals have motivated research to develop alternative routes. One promising example for p-xylene production from renewables is the cycloaddition of biomass-derived dimethylfuran (DMF) with ethylene, and subsequent dehydration of the formed Diels–Alder adduct to p-xylene. It has been reported that zeolite beta (*BEA) outperforms other zeolites where it has been shown that Lewis and Brønsted acid (LA and BA) sites have crucial roles in activating Diels-Alder cycloaddition and dehydration reactions, respectively. In this presentation, we will highlight our studies using *BEA as bifunctional catalyst with partial substitution of aluminum with the heteroatom gallium. Our findings reveal that Ga,Al-*BEA exhibits higher DMF conversion (more than 70%) and p-xylene selectivity (more than 80%) over Al-*BEA. The former also results in fewer byproducts, such as 2,5-hexanedione, 1-methyl-4-propyl-benzene, alkylated products, and oligomers. Comparisons of zeolites with different Ga content revealed the turnover frequency of p-xylene over Ga,Al-*BEA is 50% higher than that over pure Al-*BEA. We observed a remarkable correlation of p-xylene selectivity and yield with Ga content, which is attributed in part to Ga framework sites (i.e., BA sites with reduced acid strength compared to Al) and the Lewis acidity of extra-framework Ga species. The latter contribution was confirmed by analysis of Ga-impregnated Al-*BEA zeolites, which have a positive effect on both p-xylene selectivity and yield. Our findings indicate that tuning zeolite acidity by optimizing the amount of heteroatom incorporation in the crystal framework to tailor ratios and strengths of LA and BA sites is beneficial to maximize p-xylene production from renewable resources.