Mechanistic Insights into the Solvent-Driven Adsorptive Hydrodeoxygenation of Biomass Derived Levulinate Acid/Ester to 2-Methyltetrahydrofuran over Bimetallic Cu–Ni Catalysts

Abstract

A highly efficient bimetallic Cu−Ni catalytic system for selective hydrogenation of levulinic acid/ester to 2-methyltetrahydrofuran (2-MTHF) promoted by the solvent was presented. A 98% yield of 2-MTHF was achieved with optimal 10Cu-5Ni/ Al 2 O 3 catalyst at a mild temperature in the presence of nonpolar organic solvent n-hexane and molecular hydrogen. A mechanistic study revealed a synergistic effect between Cu and Ni nanoparticles, wherein Ni primarily activated H 2 and hydrogenated levulinic acid/ester to GVL and Cu facilitated the hydrogenation of GVL to 2-MTHF. Detailed studies on solvent effects revealed that the n-hexane possessed higher H 2 dissolvability and enhanced adsorption of GVL on the catalyst surface to facilitate its conversion to 2-MTHF, providing a lower apparent activation energy barrier of 48.9 kJ/mol for the rate-determining step. DFT calculations also indicated a highest adsorption energy of GVL with Al 2 O 3 over other substrates and solvent molecules, further highlighting the promotion effect of nonpolar n-hexane solvent.

Catalytic Reductive Alcohol Etherifications with Carbonyl‐Based Compounds or CO2 and Related Transformations for the Synthesis of Ether Derivatives

“…In addition, several mechanistic investigations, including density functional theory (DFT), indicated the crucial role of the non‐polar solvent used in this reaction ( n ‐hexane) facilitating H 2 solubility and GVL adsorption. This material showed activity at the mildest reported temperature of 180 °C for this kind of catalysts [144] …”

“…Similarly to previous Cu−Ni based materials active for this reaction, high hydrogen pressures and T >200 °C are required to achieve good selectivities towards 2‐MeTHF versus GVL. More recently, Wang, Li, Huang and co‐workers published the last example of a Cu−Ni nanocatalyst able to afford 2‐MeTHF in excellent yields from LA and EL (Scheme 29M) [144] . The authors designed a Cu−Ni/Al 2 O 3 material in which a Cu−Ni synergy is established, entailing a LA‐to‐GVL step catalyzed by Ni and a Cu‐catalyzed GVL‐to‐2‐MeTHF reduction.…”

“…More recently, Wang, Li, Huang and co‐workers published the last example of a Cu−Ni nanocatalyst able to afford 2‐MeTHF in excellent yields from LA and EL (Scheme 29 M). [144] The authors designed a Cu−Ni/Al 2 O 3 material in which a Cu−Ni synergy is established, entailing a LA‐to‐GVL step catalyzed by Ni and a Cu‐catalyzed GVL‐to‐2‐MeTHF reduction. The acidic properties of the Al 2 O 3 support also play an important role in this reaction.…”

“…This material showed activity at the mildest reported temperature of 180 °C for this kind of catalysts. [144] …”

Recent Advances in Hydrogenation Reactions Using Bimetallic Nanocatalysts: A Review

“…Levulinic acid is another platform molecule that can undergo acid hydrolysis to give products like �-valerolactone (GVL), 2-methyltetrahydrofuran (2-MTHF), 1,4pentanediol, and valerate acid/ester as shown in Scheme 2. [18] Huang and co-workers used 10Cu-5Ni/Al 2 O 3 catalysts for hydrogenation of levulinic acid to selectively form 2-MTHF. Any change in the concentration of Cu/Ni decreased the yield from 98%.…”