Copper-based catalysts with tunable acidic and basic sites for the selective conversion of levulinic acid/ester to γ-valerolactone or 1,4-pentanediol
γ-Valerolactone (GVL) and 1,4-pentanediol (1,4-PDO) are value-added chemicals that can be produced from levulinic acid/ester via hydrogenation coupled with acid/base-catalyzed reactions. In this study, we demonstrate that the Cu-based catalysts produced via the hydrotalcite precursors with tunable distribution of acidic and basic sites could, according to the requirement of the target products, effectively tune the production of GVL or to 1,4-PDO from levulinic acid/ester. The abundant Brønsted acid sites over the CuAl catalyst suppressed the opening of the ring of GVL, achieving a higher GVL selectivity while inhibiting 1,4-PDO formation. The introduction of Mg species to the catalyst significantly increased the abundance of the basic sites on the surface of the catalyst, which was essential for the selective conversion of GVL to 1,4-PDO via the opening of the ring structure of GVL, the rate-determining step in the conversion from levulinic acid/ester to 1,4-PDO. In addition, the CuMgAl catalyst showed a much superior catalytic stability to the CuMg or CuAl catalyst due to the more stable crystal structure, the more developed porous structure, the higher dispersion of the Cu species and the higher capability to suppress the growth of metallic Cu species under hydrothermal conditions.
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