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How the size of the Pt-cluster over Nb2O5affects the catalytic performance for the hydrodehydration of 2,5-furandicarboxylic acid (FDCA) is not yet clear at the molecular level. We rationally designed the Pt1/Nb2O5([Pt1]) and Pt3/Nb2O5([Pt3]) catalyst models. Over them, the catalytic mechanism for the hydrodehydration of FDCA to adipic acid (AA) has been theoretically investigated in aqueous solution at the GGA-PBE/DNP level together with its side reactions. The hydrodehydration of FDCA to AA is associated with the ring-opening of furan as the rate-determining step, whereas the decarboxylation of FDCA to furan is related to the cleavage of the C–C bond as the rate-determining step. For the conversion of FDCA, [Pt3] shows higher catalytic activity than [Pt1], because of the less positive charge of Pt1–Pt2 dual-sites over [Pt3] than that of the Pt1 single-site over [Pt1]. Here, the Pt1–Pt2 dual-sites over [Pt3] have a more important synergistic effect on the cleavage of both C5–O3 and C5–C6 bonds compared with the Pt single-site over [Pt1]. Furthermore, [Pt3] selectively favors the FDCA-to-AA hydrodehydration, whereas [Pt1] selectively promotes the FDCA-to-furan decarboxylation. The current research results should provide some theoretical clues for designing novel supported cluster metal oxide catalysts for the hydrogenation of biomass.

The hydrogenolysis of lignin model compounds (MCs) into high-value chemicals has received increasing attention, but their catalytic reaction mechanisms are not yet very clear. Here, we report the reaction mechanisms of the hydrogenolysis of MC into 4-acetylanisole (AAL) and guaiacol (GAL) catalyzed by LRuCl3(L = 4′-(4-methoxyphenyl)-2,2′:6′,2″-terpyridine) with MC, H2, and 1-phenylethan-1-ol (PEO) as the H-sources in aqueous solution with the Bro̷nsted base (NaOH), at the M06/def2-TZVP, 6-311++G (d,p) theoretical level, namely, RS-Self, RS-H2, and RS-PEO, respectively. After dissociation in NaOH aqueous solution, the LRuCl3compound can form a stable complex LRh (OH)3as the initial catalytically active species. Their rate-determining steps are related to the cleavage of the −CαO–H bond in both RS-Self-and RS-PEO, whereas it is associated with the heterolysis of the H–H bond in RS-H2. From NaOH aqueous solution, the OH–ligand of LRh(OH)3promotes the cleavage of the −CαO–H bond with MC and PEO as H-sources, whereas it advances the heterolysis of the H–H bond with H2as the H-source, owing to its strong Bro̷nsted basicity. Furthermore, the Rh center of LRh(OH)3mediates the cleavage of the −Cα–H bond, because of its Lewis acidity. The reaction activity lowers as RS-Self > RS-PEO ≫ RS-H2, which is positively dependent on the protonation degree of the departing H atom. Compounds containing both −CαO–H and −Cα–H groups can act as effective donors for H-sources. In the meantime, the stronger the electron-withdrawing groups they contain, the more pronounced the protonation of the −CαO–H group and the higher the reaction activity in providing H-sources. The present results provide insights into utilizing lignin’s own functional groups as a hydrogen source for high-value conversion.

Ru–N/C catalysts demonstrate good catalytic performance toward the reductive amination of furfural (FAL) to furfurylamine (FAM). However, its underlying catalytic mechanism remains unclear at the molecular level. In this study, a single-atom Ru1–N3/C surface was modeled, which can simultaneously activate NH3and H2to an appropriate level. Over Ru1–N3/C, the catalytic mechanisms for the reductive amination of FAL to FAM, as well as the dimerization of FAM to difurfurylamine (DFAM), have been investigated theoretically in methanol solution at the GGA-PBE/DNP level. Molecular dynamic simulation results indicate the preferential adsorption of NH3over Ru1–N3/C. The preferential activation of NH3facilitates the formation of furfurylimine (FIM). However, the prior activation of H2leads to the formation of furfuryl alcohol (FOL), which hinders the production of FAM. The Ru–N–C group in the amination of FAL with FIM as an intermediate enhances the C–O bond cleavage more efficiently due to the nucleophilicity of the N atom. Lower temperatures are crucial for preserving FAM formation, whereas FAM undergoes dimerization with increasing temperature elevating kinetically. The current research results should provide some theoretical insights for designing highly selective catalytic systems toward the reductive amination of aldehydes/ketones.

Al-containing catalysts, e.g., Al(OTf)3, show good catalytic performance toward the conversion of cellulose to fructose in methanol solution. Here, we report the catalytic isomerization and alcoholysis mechanisms for the conversion of cellobiose to fructose at the PBE0/6-311++G(d,p), aug-cc-pVTZ theoretical level, combining the relevant experimental verifications of electrospray ionization mass spectrometry (ESI-MS), high-performance liquid chromatography (HPLC), and the attenuated total reflection-infrared (ATR-IR) spectra. From the alcoholysis of Al(OTf)3in methanol solution, the catalytically active species involves both the [CH3OH2]+Brønsted acid and the [Al(CH3O)(OTf)(CH3OH)4]+Lewis acid. There are two reaction pathways, i.e., one through glucose (glycosidic bond cleavage followed by isomerization, w-G) and another through cellobiulose (isomerization followed by glycosidic bond cleavage, w-L). The Lewis acid ([Al(CH3O)(OTf)(CH3OH)4]+) is responsible for the aldose–ketose tautomerization, while the Brønsted acid ([CH3OH2]+) is in charge of ring-opening, ring-closure, and glycosidic bond cleavage. For both w-Gand w-L, the rate-determining steps are related to the intramolecular [1,2]-H shift between C1–C2 for the aldose–ketose tautomerization catalyzed by the [Al(CH3O)(OTf)(CH3OH)4]+species. The Lewis acid ([Al(CH3O)(OTf)(CH3OH)4]+) exhibits higher catalytic activity toward the aldose–ketose tautomerization of glycosyl-chain-glucose to glycosyl-chain-fructose than that of chain-glucose to chain-fructose. Besides, the Brønsted acid ([CH3OH2]+) shows higher catalytic activity toward the glycosidic bond cleavage of cellobiulose than that of cellobiose. Kinetically, the w-Lpathway is predominant, whereas the w-Gpathway is minor. The theoretically proposed mechanism has been experimentally testified. These insights may advance on the novel design of the catalytic system toward the conversion of cellulose to fructose.