Selectivity Control in the Tandem Aromatization of Bio‐Based Furanics Catalyzed by Solid Acids and Palladium

Bio‐based furanics can be aromatized efficiently by sequential Diels–Alder (DA) addition and hydrogenation steps followed by tandem catalytic aromatization. With a combination of zeolite H‐Y and Pd/C, the hydrogenated DA adduct of 2‐methylfuran and maleic anhydride can thus be aromatized in the liquid phase and, to a certain extent, decarboxylated to give high yields of the aromatic products 3‐methylphthalic anhydride and o‐ and m‐toluic acid. Here, it is shown that a variation in the acidity and textural properties of the solid acid as well as bifunctionality offers a handle on selectivity toward aromatic products. The zeolite component was found to dominate selectivity. Indeed, a linear correlation is found between 3‐methylphthalic anhydride yield and the product of (strong acid/total acidity) and mesopore volume of H‐Y, highlighting the need for balanced catalyst acidity and porosity. The efficient coupling of the dehydration and dehydrogenation steps by varying the zeolite‐to‐Pd/C ratio allowed the competitive decarboxylation reaction to be effectively suppressed, which led to an improved 3‐methylphthalic anhydride/total aromatics selectivity ratio of 80 % (89 % total aromatics yield). The incorporation of Pd nanoparticles in close proximity to the acid sites in bifunctional Pd/H‐Y catalysts also afforded a flexible means to control aromatic products selectivity, as further demonstrated in the aromatization of hydrogenated DA adducts from other diene/dienophile combinations.