MOF-Encapsulating Metal–Acid Interfaces for Efficient Catalytic Hydrogenolysis of Biomass-Derived Aromatic Aldehydes

Abstract

Developing an efficient and selective catalyst for C–O hydrogenolysis of biomass-derived aromatic aldehydes, such as 5-methylfurfural (MF), 5-hydroxymethylfurfural (HMF), and vanillin (VA), is highly significant for the synthesis of biofuel and fine chemicals. Herein, metal–organic framework (MOF)-encapsulating metal–acid interfaces (Pd@UiO–CH2SO3H, Pd@UiO–PhSO3H) were first reported. Compared with traditionally supported catalysts (Pd/UiO–SO3H, Pd/UiO–NH2), Pd–acid-interface-encapsulated MOFs show much higher activity and selectivity for MF to 2,5-dimethylfuran (DMF), HMF to DMF, and VA to 2-methoxy-4-methylphenol (MMP) reactions. In particular, Pd@UiO–SO3H shows the best catalytic performance with 89.0 and 86.0% DMF yield from MF and HMF and a 99.4% MMP yield from VA based on its suitable hydrophilicity, high hydrogen activation ability, and abundant Pd–SO3H interface active sites. According to the catalytic performance of Pd/UiO–NH2 and the results of an ATR-IR test, the acidic sites on the Pd–acid interface can accelerate the activation of the hydroxyl group for these hydrogenolysis reactions. This work provides an effective design strategy for the preparation of MOF-encapsulating metal–acid interfaces and shows the powerful synergistic effect of hydrogenation and acid catalysis.

Highly Effective Activated Carbon‐Supported Ni‐Mn Bifunctional Catalyst for Selective Hydrodeoxygenation of 5‐Hydroxymethylfurfural to 2,5‐Dimethylfuran

“…Contrary to Ni catalyst, the reaction of hydrogenation of C=O bond to DHMF hardly proceeded over Ni‐Mn catalyst as shown in Figure 9b, because we detected only trace amounts of DHMF but detected a great amounts of intermediates MFF and 5‐MFA at the beginning of the reaction (Figure 9b). This indicates that the addition of Mn accelerates the C−OH cleavage of 5‐HMF to generate intermediate MFF, which is attributed to the Lewis acid sites from MnO x , being consistent with the report [18] . According to the free energy diagram for these reactions calculated using density functional theory (Table S3 and Figure 9c), formation of DHMF was determined to be more thermodynamically unfavorable than formation of MFF.…”

“…This indicates that the addition of Mn accelerates the CÀ OH cleavage of 5-HMF to generate intermediate MFF, which is attributed to the Lewis acid sites from MnO x , being consistent with the report. [18] According to the free energy diagram for these reactions calculated using density functional theory (Table S3 and Figure 9c), formation of DHMF was determined to be more thermodynamically unfavorable than formation of MFF.…”

“…For the CÀ O cleavage step, which is an important step in the selective HDO of 5-HMF to 2,5-DMF, the synergistic effect of acidic site and metal site is important through tandem hydroxy group protonation, dehydration, and hydrogenation. A recent study by Deng et al [18] demonstrated that Pd-acid-interface-encapsulated metal-organic frameworks (MOFs) show high activity and selectivity for 5-HMF to 2,5-DMF, and the acid sites on the Pd-acid interface can accelerate the activation of the hydroxy group for the hydrogenolysis reaction. Besides solid acid supports, oxophilic metal promoters (MO x ) were introduced into the catalytic system to prepare bifunctional catalysts, which showed good catalytic performance in hydrodeoxygenation reactions.…”

Promoted Hydrogenolysis of Furan Aldehydes to 2,5‐Dimethylfuran by Defect Engineering on Pd/NiCo2O4

“…The main product is BHMF at a low temperature of 120 °C, and some humins and small molecular alkanes are formed by polymerization and cracking at a high temperature of 180 °C. Finally, under the optimal conditions (150 °C, 1.0 MPa), Pd/NiCo 2 O 4‐ x ‐P shows 99.9 % conversion of HMF, 90.6 % selectivity of DMF, and 90.5 % yield of DMF (Figure 4e), which shows comparable DMF synthesis efficiency with previous reports under a relatively low metal content [4a,5,8d,e,g–j,10a,23] . Besides, Pd/NiCo 2 O 4‐ x ‐P exhibited a higher turnover frequency (TOF) value (215.8 h −1 ) than that of many catalysts (Table S2).…”

“…The results indicate that Brønsted acidity in Pd/NiCo 2 O 4‐ x ‐P is an active site for etherification and promotes the rapid consumption of MFA. More importantly, the C−O bond cleavage of IMMF is more facile relative to parent MFA with a higher IMMF hydrogenolysis rate over Pd/NiCo 2 O 4‐ x ‐P (0.63 vs. 0.55 h −1 , Figure S7b), which suggests that IPA acts as a promoter for hydrogenolysis by the etherification [4a] …”