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.
We present here the formation of a modular 2D molecular network composed of two different types of square-shaped butadiyne-bridged macrocycles, having intrinsic molecular voids, aligned alternately at the solid-liquid interface. Site-selective inclusion of a guest cation took place at every other molecular void in the molecular network with two different recognition sites.
Time-resolved luminescence was measured on a colorless anatase single crystal under pulsed-laser excitation. The time evolution of luminescence is composed of fast and slow components with time constants of 10 À6 and 10 À5 s, respectively. The fast component corresponds to a direct formation of STE. Some traps near the conduction band give a retardation effect on the slow component. The traps are occupied by conduction electrons at low temperatures and the trapped electron can be excited thermally at temperatures higher than 100 K. They compete with non-radiative recombination process. A possible model for the relaxation process is proposed. r
Mesoporous
β-MnO2 nanoparticles were synthesized
by a template-free low-temperature crystallization of Mn4+ precursors (low-crystallinity layer-type Mn4+ oxide, c-distorted H+-birnessite) produced by the reaction
of MnO4
– and Mn2+. The Mn starting materials, pH of the reaction
solution, and calcination temperatures significantly affect the crystal
structure, surface area, porous structure, and morphology of the manganese
oxides formed. The pH conditions during the precipitation of Mn4+ precursors are important for controlling the morphology
and porous structure of β-MnO2. Nonrigid aggregates
of platelike particles with slitlike pores (β-MnO
2
-1 and -2) were obtained from the combinations of NaMnO4/MnSO4 and NaMnO4/Mn(NO3)2, respectively.
On the other hand, spherelike particles with ink-bottle shaped pores
(β-MnO
2
-3) were formed in NaMnO4/Mn(OAc)2 with
pH adjustment (pH 0.8). The specific surface areas for β-MnO
2
-1, -2, and -3 were much higher than those for nonporous
β-MnO2 nanorods synthesized using a typical hydrothermal
method (β-MnO
2
-HT). On the other hand, c-distorted
H+-birnessite precursors with a high interlayer metal cation
(Na+ and K+) content led to the formation of
α-MnO2 with a 2 × 2 tunnel structure. These
mesoporous β-MnO2 materials acted as effective heterogeneous
catalysts for the aerobic oxidation of 5-hydroxymethylfurfural (HMF)
to 2,5-furandicarboxylic acid (FDCA) as a bioplastic monomer and for
the transformation of aromatic alcohols to the corresponding aldehydes,
where the catalytic activities of β-MnO
2
-1, -2, and -3 were approximately 1 order of magnitude higher than that
of β-MnO
2
-HT. β-MnO
2
-3 exhibited higher catalytic activity (especially
for larger molecules) than the other β-MnO2 materials,
and this is likely attributed to the nanometer-sized spaces.
To decouple economic growth from environmental degradation, the Chinese government proposed the circular economy (CE) strategy as part of its 11th 5-Year Plan. This strategy expands the application of CE from individual enterprises to eco-industrial parks (EIPs) and to the cities, provinces, and regions. We carried out field studies in three EIPs in Baotou, Suzhou, and Shanghai. In this paper, we discuss the current state of CE and the sustainable development of EIPs in China. We first provide detailed information on the three EIPs' infrastructures, preferential policies, CE frameworks, and eco-chains. We then examine the status of sustainable development in the three EIPs from the perspectives of socio-economic, resource and material efficiency, and environmental performance. The results indicate that the overall performance of the three EIPs is reasonably good with respect to socioeconomics, resources and materials, and efficiency and environmental protection, whereas green management is rather weak and thus requires further improvement. We found that the CE frameworks along with eco-chains within the EIPs are effectively improving resource and material efficiency. Moreover, we demonstrate that there are positive associations among socio-economic, resource and material, and environmental indicators. Given the large presence of EIPs in the local economies, these results suggest that EIPs play a key role in promoting sustainable development in China.
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