Effect of MnO₂ Crystal Structure on Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

Abstract

Aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) as a bioplastics monomer is efficiently promoted by a simple system based on a nonprecious-metal catalyst of MnO2 and NaHCO3. Kinetic studies indicate that the oxidation of 5-formyl-2-furancarboxylic acid (FFCA) to FDCA is the slowest step for the aerobic oxidation of HMF to FDCA over activated MnO2. We demonstrate through combined computational and experimental studies that HMF oxidation to FDCA is largely dependent on the MnO2 crystal structure. Density functional theory (DFT) calculations reveal that vacancy formation energies at the planar oxygen sites in α- and γ-MnO2 are higher than those at the bent oxygen sites. β- and λ-MnO2 consist of only planar and bent oxygen sites, respectively, with lower vacancy formation energies. Consequently, β- and λ-MnO2 are likely to be good candidates as oxidation catalysts. On the other hand, experimental studies reveal that the reaction rates per surface area for the slowest step (FFCA oxidation to FDCA) decrease in the order of β-MnO2 > λ-MnO2 > γ-MnO2 ≈ α-MnO2 > δ-MnO2 > ε-MnO2; the catalytic activity of β-MnO2 exceeds that of the previously reported activated MnO2 by three times. The order is in good agreement not only with the DFT calculation results, but also with the reduction rates per surface area determined by the H2-temperature-programmed reduction measurements for MnO2 catalysts. The successful synthesis of high-surface-area β-MnO2 significantly improves the catalytic activity for the aerobic oxidation of HMF to FDCA.

Aerobic Oxidation of 5‐Hydroxymethylfurfural to 2,5‐Furandicarboxylic Acid over Holey 2 D Mn2O3 Nanoflakes from a Mn‐based MOF

“…The spin‐orbit splitting value of 11.8 eV was estimated from the Figure a, which was very close to the value of Mn 2 O 3 . The asymmetrical Mn 2p 3/2 peaks at 641.8 eV can be deconvoluted into several sub‐peaks with binding energies of 640.8, 641.6, 642.8, and 644.8 eV, which were assigned to Mn 2+ , Mn 3+ , Mn 4+ , and shake‐up peaks, respectively . The relative intensities of Mn 2+ /Mn 4+ and Mn 3+ /Mn 4+ were 0.36 and 0.77, respectively, indicating the existence of relative high proportion of Mn 4+ and potential redox recycle of Mn cations.…”

Regulating the Catalytic Dynamics Through a Crystal Structure Modulation of Bimetallic Catalyst

“…In this regard, catalytic behaviors linked to the morphology and phase/surface structure of catalysts have been intensively investigated for aqueous electrolyte systems like fuel cells, as well as metal–oxygen batteries . As for MnO 2 polymorphs, the structure‐induced activities are well documented for their electrochemical reaction, and gas‐ and liquid‐phase reactions, which correlated their activities with chemical states of Mn or O, active sites, electron/mass transfer on different phase structure . Additionally, Jin et al very recently reported that a synergistic change of structural disorder inducing the changed surface electron density of layered δ‐MnO 2 can improve aqueous OER and non‐aqueous ORR/OER performance…”

Cu−Ni Bimetallic Hydroxide Catalyst for Efficient Electrochemical Conversion of 5‐Hydroxymethylfurfural to 2,5‐Furandicarboxylic Acid

“…Thus, developing a new method that utilizes inexpensive catalysts and work under ambient conditions attracts more and more attention. Now, researchers successfully found that the electrochemical oxidation of 5‐HMF was an advantageous method due to its environmentally benign, using water as the oxygen source, and proceeding at ambient temperatures/pressures . Then, Chadderdon et al and Choi et al reported the Au and Pt based catalysts for electrocatalytic oxidation of 5‐HMF to 2,5‐FDCA.…”