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Developing an efficient catalyst to upgrade 5‐hydroxymethylfurfural (HMF) to high‐value‐added downstream chemicals is of great significance in biomass conversion. Nanorod (110)‐, nanocube (100)‐, and nanooctaheron (111)‐CeO2‐supported Au nanoparticles were prepared to investigate the intrinsic effect of CeO2 crystal faces on the oxidation of HMF to 2,5‐furandicarboxylic acid (FDCA). The experimental results and density functional theory calculation revealed that the concentration of oxygen vacancy (VO) for exposed specific crystal faces was crucial to the oxygen adsorption ability, and Au/nanorod‐CeO2 with the highest VO concentration promoted the formation of more oxygen active species (superoxide radical) on CeO2 (110) crystal face than (100) and (111) crystal faces. Besides, the higher VO concentration could provide a strong adsorption ability of HMF, greatly boosting the activation of HMF. Thus, these results led to a superior catalytic activity for HMF oxidation over Au/nanorod‐CeO2 (FDCA yield of 96.5 %). In‐situ Fourier‐transform (FT)IR spectroscopy uncovered the HMF oxidation pathway, and the possible catalytic mechanism was proposed. The deep insight into the role of regulation for crystal faces provides a basis for the rational design of highly active facets for the oxidation of HMF and related reactions. [ABSTRACT FROM AUTHOR]

A novel halloysite (Hal) based acidic catalyst was synthesized by anchoring functional alkyl group and Cr site and catalyzed the selective conversion of mannose to 5-hydroxymethylfurfural (HMF) in NaCl-H 2 O/dimethyl sulfoxide/methyl isobutyl ketone (MIBK) biphasic system. Herein, adjusting the hydrophilicity/hydrophobicity of catalyst by modifying the octyl group can facilitate the HMF yield. The density functional theory (DFT) calculation and in-situ FT-IR results revealed that increasing the hydrophobicity of catalyst surface weakened the interaction between HMF, water molecule and acid sites and inhibited the rehydration of HMF. Moreover, the synergistic effect between Cr and sulfonic group active sites remarkedly promoted the isomerization of mannose to fructose and the dehydration of fructose to HMF, and the 48.1% yield of HMF was obtained. This study provides references for the high value conversion of hemicellulose with the high efficiency reaction system. [Display omitted] • Hal as support to prepared Lewis-Brönsted acid catalyst. • Regulating wettability of catalyst can effectively inhibit rehydration of HMF. • 48.1% of HMF yield was afforded in biphasic system. [ABSTRACT FROM AUTHOR]

Separation efficiency of photogenerated carriers and CO 2 adsorption ability of the catalyst are two important factors affecting the photoreduction performance of CO 2. In view of the above analyses, leaf-vein like 2D-1D g-C 3 N 4 /P-MWNTs donor/acceptor semiconductor-carbon hybrid composite has been successfully prepared by the simple co-grinding/calcination processes. UV–vis DRS results showed that the modification of P-MWNTs can enhance the photo-absorption ability of the composite. Photoelectrochemical tests proved that 2D-1D Schottky-like barriers can enlarge the separation and transfer efficiency of photogenerated carriers. BET and CO 2 -adsorption tests exhibited that the introduction of P-MWNTs can greatly increase the CO 2 capture ability of the composite. CO 2 photoreduction experiments confirmed that the composite had much more excellent CO 2 photoreduction performance than the pure g-C 3 N 4 under the irradiation of UV–vis light or visible light. In-situ FTIR and 13C isotope tracer tests were applied to research the CO 2 photoreduction processes. Finally, the synergistic effect on CO 2 photoreduction process between electron transfer and CO 2 adsorption behavior has been discussed in total. [Display omitted] [ABSTRACT FROM AUTHOR]

The supported bimetallic AuPd nanoparticles hold great promise for the selective oxidation of 5‐hydroxymethylfurfural (HMF) to 2, 5‐furan dicarboxylic acid (FDCA), a substitute for petroleum derivative terephthalic acid (TPA). Herein, by combining a versatile Pickering high internal phase emulsions (HIPEs) template with subsequent carbonization process, cobalt‐based hierarchical porous carbon (CoOx−HPC) support was obtained. After loading bimetallic AuPd nanoparticles through the sol‐gel method, AuPd/CoOx−HPC catalyst was successfully synthesized. By changing the Pickering HIPEs parameters, carbonization temperature, the porous structure and cobalt valence of as‐synthesized catalyst can be adjusted. The obtained catalysts were systematically characterized by SEM, TEM, N2 adsorption‐desorption, XRD, XPS, and TGA. Benefiting from the synergistic effects of the high porosity of CoOx−HPC support and efficient AuPd nanoparticles, tandem oxidation of HMF to FDCA can be carried out in the water. We have clarified that the catalysts with various cobalt valence states showed superior performance, and the highest FDCA yield of 97.2 % will be obtained under the optimal reaction conditions. Meanwhile, the kinetics study indicated that the oxidation of FFCA to FDCA was the rate‐determining step. Moreover, the AuPd/CoOx−HPC catalyst revealed excellent stability in HMF oxidation during four cycles. The experimental results demonstrated that as‐prepared AuPd/CoOx−HPC catalysts are efficient towards FDCA production from the selective oxidation of HMF. [ABSTRACT FROM AUTHOR]

Developing a supported‐type metal–organic frameworks (MOFs) catalyst with multifunctional active sites is essential to broaden its application as a heterogeneous catalyst. Herein, polydopamine (PDA)‐modified graphene oxide (PDA@GO) is used as a support to prepare an acid–base bifunctional UiO‐66‐type MOFs catalyst in green solution (aqueous solution) through a one‐pot method. By adjusting the amount between GO, PDA, UiO‐66‐NH2, and UiO‐66‐SO3H, the heterogeneous solid catalyst UiO‐66‐SO3H‐NH2/PDA@GO with uniform distribution of MOFs can be obtained. The morphology and various properties of the catalyst are characterized and the catalytic performance of the catalyst for the conversion of glucose to 5‐hydroxymethylfurfural (5‐HMF) is demonstrated and discussed. Herein, the supported‐type MOFs catalyst offers an alternative way to promote current acid–base catalytic systems for achieving efficient production of 5‐HMF from sustainable biomass. [ABSTRACT FROM AUTHOR]

Highlights • A green, mild and MHT approach was reported to design UiO-66-type MOFs catalysts. • Acid–base active sites were successfully integrated into MOFs in one-pot manner. • By simply varying the synthesis conditions, acid–base strengths can be adjusted. • UiO-66-type MOFs catalysts can be used as efficient heterogeneous catalysts. Abstract Developing a green and economically viable approach for the direct synthesis of metal-organic frameworks (MOFs) catalysts with multifunctional active sites remains the key step for their applications in heterogeneous catalysis field. Herein, we report a green (aqueous solutions), mild (90°C, atmospheric pressure), and modulated hydrothermal (MHT) approach to synthesize UiO-66-type MOFs catalysts with acid–base bi-functional sites, which were obtained via the coordination of monosodium 2-sulfoterephthalate and 2-aminoterephthalic with zirconium (Zr) ions. More importantly, a series of acid, base and acid–base catalysts with varied acid–base strengths can be readily prepared, by simply varying the ratio of organic ligands for preparing MOFs. The synthesized catalysts were characterized and their performances in glucose dehydration to produce 5-hydroxymethylfurfural (5-HMF) have been evaluated. The developed approach in this work has clearly depicted a roadmap for the facile synthesis of MOFs catalysts to facilitate their potential use in acid–base catalysis. Graphical abstract Bifunctional metal-organic frameworks (MOFs) catalysts with tunable acid–base strength were prepared through a green (aqueous solutions), mild (90°C, atmospheric pressure), and MHT approach, employed for glucose to 5-hydroxymethylfurfural (5-HMF) tandem reactions. Image, graphical abstract [ABSTRACT FROM AUTHOR]

• Nitrogen-doped carbon supported bimetallic AuPd catalyst was successfully synthesized. • The obtained catalyst showed adjustable hierarchical pore and basicity. • Catalytic oxidation of HMF to FDCA was carried out under base-free condition. • The highest FDCA yield of 96.7% was achieved in water. As an important renewable alternative to the production of petroleum-derived terephthalic acid, selective aerobic oxidation of biomass derivative 5-hydroxymethylfurfural (HMF) into high value-added 2,5-furandicarboxylic acid (FDCA) is attracting increasing attention. Herein, a novel hierarchical porous nitrogen-doped carbon (NC) supported bimetallic AuPd catalyst was synthesized by Pickering high internal phase emulsions (Pickering HIPEs) templating method, subsequent carbonization and the sol-curing technique. By varying Pickering HIPEs parameter, nitrogen-doped content and the loaded AuPd nanoparticles, Au x Pd y /NC catalysts with adjustable porous structure and basicity were obtained. Benefiting from the synergistic effects of the high basicity of NC support and efficient bimetallic AuPd catalyst, tandem oxidation of HMF to FDCA reactions can be carried out under base-free condition in water, which makes the biomass transformation process environmental friendliness and economic. And the highest yield of FDCA at 96.7% was achieved under the optimal reaction conditions. Regeneration test revealed the obtained Au x Pd y /NC catalyst was recovered and reused at least five times without significant loss of catalytic activity. The present work offers a versatile strategy for developing nitrogen-doped carbon supported highly efficient bimetallic catalysts with hierarchical porous structure and adjusting basicity for a wide range of base-free catalytic oxidation in water. [ABSTRACT FROM AUTHOR]

Chemically functional microporous metal-organic frameworks (MOFs) crystals are attractive for catalysis applications, and recent results show that they can be immobilized on high stability substrates, such as carbon materials. In this work, g-C 3 N 4 supported UiO-66-type MOFs catalysts with only acid, base or acid-base bi-functional active sites, have been successfully synthesized via a green (aqueous solutions), mild (90 °C, atmospheric pressure), and one-pot modulated hydrothermal (MHT) method. The physical and chemical properties of the obtained catalysts were systematically characterized by different characterization methods. The results indicated that the synthesized catalysts have microporous structure, excellent thermostability and acid-base bi-functional active sites. One-pot synthesis of 5-hydroxymethylfurfural (5-HMF) from glucose was performed to investigate the activities of synthesized catalysts. Benefiting from the synergistic effects of the acid-base bi-functional active sites, the highest 5-HMF yield of 54.9% was achieved in an isopropanol-mediated DMSO system, under the optimal conditions. Moderate to excellent yields of 5-HMF were also obtained from one-pot conversions of other carbohydrates, including inulin, sucrose, cellobiose, maltose and starch, with our developed catalytic system. The one-pot production of 5-HMF from cellulose was also smoothly processed by the g-C 3 N 4 supported UiO-66-type MOFs catalysts in an IL-based system. This work offers a versatile strategy for developing supported UiO-66-type MOFs catalyst for a wide range of biomass transformation to platform chemicals. Image 1 • g-C 3 N 4 supported UiO-66-type MOFs catalysts were successfully synthesized. • Acid-base active sites showed synergistic effects in catalytic activity. • Moderate to high 5-HMF yields can be obtained from various carbohydrates. • The developed isopropanol-mediated solvent has a minimal environmental impact. • The catalyst can be reused without significant loss of activity. [ABSTRACT FROM AUTHOR]