2-Methylimidazole-modulated 2D Cu metal-organic framework for 5-hydroxymethylfurfural hydrodeoxygenation

Preparation of the high value-added chemical 2,5-dimethylfuran (2,5-DMF) from the biomass-derived platform molecule 5-hydroxymethylfurfural (HMF) is of great significance in the preparation of biofuels. Here, a bottom-up strategy was used to prepare a metal-organic framework (MOF) material with a two-dimensional nanosheet morphology, named CPM, in which an additive 2-methylimidazole was introduced into the hydrothermal process of Cu2+ ions and terephthalic acid. Subsequently, CPM-700 prepared by heat treatment under an inert atmosphere showed excellent catalytic performance in the reaction of HMF hydrodeoxygenation to 2,5-DMF. The materials before and after pyrogenation were characterized by PXRD, XPS, TEM, N2 adsorption and desorption and so on. It was confirmed that compared with the catalyst derived from the cubic MOF material self-assembled by Cu2+ and terephthalic acid, the morphology of 2D nanosheets was beneficial for the reaction of HMF to 2,5-DMF. Combined with the experimental data, the possible reaction path of 2,5-DMF preparation from HMF is that 2,5-dihydroxymethylfuran was formed by hydrogenation of the aldehyde group on the furan ring, and then 2,5-DMF was obtained by hydrogenolysis. This paper provides an effective route for 2D MOF-derived catalytic materials in the selective hydrogenation of HMF.

Recent advancements and challenges in emerging applications of biochar-based catalysts

The sustainable utilization of biochar produced from biomass waste could substantially promote the development of carbon neutrality and a circular economy. Due to their cost-effectiveness, multiple functionalities, tailorable porous structure, and thermal stability, biochar-based catalysts play a vital role in sustainable biorefineries and environmental protection, contributing to a positive, planet-level impact. This review provides an overview of emerging synthesis routes for multifunctional biochar-based catalysts. It discusses recent advances in biorefinery and pollutant degradation in air, soil, and water, providing deeper and more comprehensive information of the catalysts, such as physicochemical properties and surface chemistry. The catalytic performance and deactivation mechanisms under different catalytic systems were critically reviewed, providing new insights into developing efficient and practical biochar-based catalysts for large-scale use in various applications. Machine learning (ML)-based predictions and inverse design have addressed the innovation of biochar-based catalysts with high-performance applications, as ML efficiently predicts the properties and performance of biochar, interprets the underlying mechanisms and complicated relationships, and guides biochar synthesis. Finally, environmental benefit and economic feasibility assessments are proposed for science-based guidelines for industries and policymakers. With concerted effort, upgrading biomass waste into high-performance catalysts for biorefinery and environmental protection could reduce environmental pollution, increase energy safety, and achieve sustainable biomass management, all of which are beneficial for attaining several of the United Nations Sustainable Development Goals (UN SDGs) and Environmental, Social and Governance (ESG).

Synergistic contribution of metal-acid sites in selective hydrodeoxygenation of biomass derivatives over Cu/CoOx catalysts

The efficient hydrodeoxygenation (HDO) of biomass derivatives to yield specific products is a significant yet challenging task. In the present study, a Cu/CoO_x catalyst was synthesized using a facile co-precipitation method, and subsequently used for the HDO of biomass derivatives. Under optimal reaction conditions, the conversion of 5-hydroxymethylfurfural reached 100% with a selectivity of ∼99% to 2,5-diformylfuran. In combination with the experimental results, systematic characterizations revealed that CoO_x, as the acid site, tended to adsorb CO bonds, and the metal sites of Cu⁺ were inclined to adsorb CO bonds and enhance CO bond hydrogenation. Meanwhile, Cu⁰ was the main active site for 2-propanol dehydrogenation. The excellent catalytic performance could be attributed to the synergistic effects of Cu and CoO_x. Further, by optimizing the ratio of Cu to CoO_x, the Cu/CoO_x catalysts exhibited notable performance in HDO of acetophenone, levulinic acid, and furfural, which verified the universality of the catalysts in the HDO of biomass derivatives.

Current trends and prospects in catalytic upgrading of lignocellulosic biomass feedstock into ultrapure biofuels

Eco-friendly renewable energy sources have recommended as fossil fuel alternatives in recent years to reduce environmental pollution and meet future energy demands in various sectors. As the largest source of renewable energy in the world, lignocellulosic biomass has received considerable interest from the scientific community to advance the fabrication of biofuels and ultrafine value-added chemicals. For example, biomass obtained from agricultural wastes could catalytically convert into furan derivatives. Among furan derivatives, 5-hydroxymethylfurfural (HMF) and 2, 5-dimethylfuran (DMF) are considered the most useful molecules that can be transformed into desirable products such as fuels and fine chemicals. Because of its exceptional properties, e.g., water insolubility and high boiling point, DMF has studied as the ideal fuel in recent decades. Interestingly, HMF, a feedstock upgraded from biomass sources can easily hydrogenate to produce DMF. In the present review, the current state of the art and studies on the transformation of HMF into DMF using noble metals, non-noble metals, bimetallic catalysts, and their composites have discussed elaborately. In addition, comprehensive insights into the operating reaction conditions and the influence of employed support over the hydrogenation process have demonstrated.

Tuning the Selectivity of the Hydrogenation/Hydrogenolysis of 5-Hydroxymethylfurfural under Batch Multiphase and Continuous-Flow Conditions

The hydrogenation/hydrogenolysis of 5-hydroxymethylfurfural (HMF) has been carried out either under single (aqueous) phase or batch multiphase (MP) conditions using mutually immiscible aqueous/hydrocarbon phases, 5 % Ru/C as a catalyst, and both with and without the use of trioctylmethyl phosphonium bis-(trifluoro methane) sulfonimide ([P₈₈₈₁ ][NTf₂ ]) as an ionic liquid (IL). Alternatively, the hydrogenation of HMF was explored in the continuous-flow (CF) mode with the same catalyst. By changing reaction parameters, experiments were optimized towards the formation of three products: 2,5-bis(hydroxy methyl)furan (BHMF), 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF), and 1-hydroxyhexane-2,5-dione (HHD), which were obtained in up to 92, 90, and 99 % selectivity, respectively, at quantitative conversion. In particular, the single (aqueous) phase reaction of HMF (0.2 m) carried out for 18 h at 60 °C under 30 bar of H₂ , allowed the exclusive synthesis of BHMF from the partial (carbonyl) hydrogenation of HMF, while the MP reaction run at a higher T and p (100 °C and 50 bar) proved excellent to achieve only HHD derived from a sequence of hydrogenation/hydrogenolysis. It is worth noting that under MP conditions, the catalyst was perfectly segregated in the IL, where it could be recycled without any leaching in the aqueous/hydrocarbon phases. Finally, the hydrogenation of HMF was explored in a H-Cube® flow reactor in the presence of different solvents, such as ethyl acetate, tetrahydrofuran, and ethanol. At 100 °C, 50 bar H₂ , and a flow rate of 0.1 mL min^-1 , the process was optimized towards the formation of the full hydrogenation product BHMTHF. Ethyl acetate proved the best solvent.

Selective Hydrogenation of 5-Hydroxymethylfurfural to 1-Hydroxy-2,5-hexanedione by Biochar-Supported Ru Catalysts

The development of sustainable and efficient catalysts -namely Ru supported on activated biochars- is carried out for the selective hydrogenation of 5-hydroxymethylfurfural (HMF) to 1-hydroxy-2,5-hexanedione (HHD). Activated biochars obtained from pyrolysis and steam-based physical activation of two different biomasses from animal (leather tannery waste; A_Lw ) and vegetal (hazelnut shells; A_HSw ) origins show completely different chemical, textural, and morphological properties. Compared to A_Lw , after impregnation with 0.5 wt % Ru, A_HSw , with inner micro-mesochannels and cavities and higher layer stacking disorder, leads to better trapping and anchoring of Ru nanoparticles on the catalyst and a suitable Ru single crystal dispersion. This leads to a highly active Ru/A_HSw catalyst in the proposed reaction, giving more than 80 % selectivity to HHD and full HMF conversion at 100 °C with 30 bar H₂ for 3 h. Ru/A_HSw also shows promising performance compared to a commercial Ru/C catalyst.

Sustainable Catalytic Transformation of Biomass-Derived 5-Hydroxymethylfurfural to 2,5-Bis(hydroxymethyl)tetrahydrofuran

5-Hydroxymethylfurfural (5-HMF), one of the most important platform molecules in biorefinery, can be directly obtained from a vast diversity of biomass materials. Owing to the reactive functional groups (-CHO and -CH₂ OH) in the structure, this versatile building block undertakes several transformations to provide a wealth of high value-added products. Among numerous well-established paradigms, the catalytic hydrogenation of 5-HMF towards 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) is of great interest because this downstream diol can be exploited in a wide range of industrial applications. Not surprisingly, incessant endeavors from both academia and industry to upgrade this catalytic process have been established over the years. The main aim of this Review was to provide a comprehensive overview on the development of heterogeneous metal catalysts for the 5-HMF-to-BHMTHF transformation. Herein, the rational design and utility of hydrogenating catalysts were elaborated in many aspects including metal types (Ni, Co, Pd, Ru, Pt, and bimetals), solid supports, preparation method, recyclability, operating conditions, and reaction regime (batch and continuous flow). In addition, the assessment of cooperative catalysts to convert carbohydrates into BHMTHF under one-pot cascade, tentative mechanism, as well as prospects and challenges for the chemo-selective hydrogenation of 5-HMF were also highlighted.

Recent Advances in Reductive Upgrading of 5-Hydroxymethylfurfural via Heterogeneous Thermocatalysis

The catalytic conversion of 5-hydroxymethylfufural (HMF), one of the vital platform chemicals in biomass upgrading, holds great promise for producing highly valuable chemicals through sustainable routes, thereby alleviating the dependence on fossil feedstocks and reducing CO₂ emissions. The reductive upgrading (hydrogenation, hydrogenolysis, ring-opening, ring-rearrangement, amination, etc.) of HMF has exhibited great potential to produce monomers, liquid fuel additives, and other valuable chemicals. Thermocatalytic conversion has a significant advantage over photocatalysis and electrocatalysis in productivity. In this Review, the recent achievements of thermo-reductive transformation of HMF to various chemicals using heterogeneous catalytic systems are presented, including the catalytic systems (catalyst and solvent), reaction conditions, (reaction temperature, pressure, etc.), and reaction mechanisms. The current challenges and future opportunities are discussed as well, aiming at guiding the catalyst design and practical scalable productions.

MIL-100(Fe) Supported Pt-Co Nanoparticles as Active and Selective Heterogeneous Catalysts for Hydrogenation of 1,3-Butadiene

Superior catalytic performance for selective 1,3-butadiene (1,3-BD) hydrogenation can usually be achieved with supported bimetallic catalysts. In this work, Pt-Co nanoparticles and Pt nanoparticles supported on metal-organic framework MIL-100(Fe) catalysts (MIL=Materials of Institut Lavoisier, PtCo/MIL-100(Fe) and Pt/MIL-100(Fe)) were synthesized via a simple impregnation reduction method, and their catalytic performance was investigated for the hydrogenation of 1,3-BD. Pt1Co1/MIL-100(Fe) presented better catalytic performance than Pt/MIL-100(Fe), with significantly enhanced total butene selectivity. Moreover, the secondary hydrogenation of butenes was effectively inhibited after doping with Co. The Pt1Co1/MIL-100(Fe) catalyst displayed good stability in the 1,3-BD hydrogenation reaction. No significant catalyst deactivation was observed during 9 h of hydrogenation, but its catalytic activity gradually reduces for the next 17 h. Carbon deposition on Pt1Co1/MIL-100(Fe) is the reason for its deactivation in 1,3-BD hydrogenation reaction. The spent Pt1Co1/MIL-100(Fe) catalyst could be regenerated at 200 °C, and regenerated catalysts displayed the similar 1,3-BD conversion and butene selectivity with fresh catalysts. Moreover, the rate-determining step of this reaction was hydrogen dissociation. The outstanding activity and total butene selectivity of the Pt1Co1/MIL-100(Fe) catalyst illustrate that Pt-Co bimetallic catalysts are an ideal alternative for replacing mono-noble-metal-based catalysts in selective 1,3-BD hydrogenation reactions.

Insights into the interfacial effects in Cu-Co/CeOx catalysts on hydrogenolysis of 5-hydroxymethylfurfural to biofuel 2,5-dimethylfuran

The interface site between metal and support possess unique electronic and morphological structure, providing distinct active centers for favorable reaction in catalytic conversion of biomass derivatives to valuable chemicals. In this study, a series of Cu-Co/CeO_x catalysts were prepared for hydrogenolysis of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) via reduction of the corresponding layered double hydroxide precursors. The characterizations indicated the formation of CoCe-Vö interface (Vö denotes oxygen vacancy) and the effect of hydrogen spillover from Cu species to CoCe-Vö interface. Furthermore, the experiments and theoretical calculations verified that CoCe-Vö interface could activate the CO bond. The optimized catalyst showed a DMF yield of > 90% at 180 °C and 1.5 MPa H₂ with no deactivation in the cycling tests. This study reveals the interfacial effects of the nanocatalysts, including the oxygen vacancies and hydrogen spillover, on hydrogenolysis of HMF, which provided a simple and efficient approach for synthesis of high-performance non-noble metal nanocatalysts applied to the hydrogenolysis of various biomass derivatives.

Functionalized and Platinum-Decorated Multi-Layer Oxidized Graphene as a Proton, and Electron Conducting Separator in Solid Acid Fuel Cells

In the present article, electrodes containing a composite of platinum on top of a plasma-oxidized multi-layer graphene film are investigated as model electrodes that combine an exceptional high platinum utilization with high electrode stability. Graphene is thereby acting as a separator between the phosphate-based electrolyte and the platinum catalyst. Electrochemical impedance measurements in humidified hydrogen at 240 °C show area-normalized electrode resistance of 0.06 Ω·cm−2 for a platinum loading of ∼60 µgPt·cm−2, resulting in an outstanding mass normalized activity of almost 280 S·mgPt−1, exceeding even state-of-the-art electrodes. The presented platinum decorated graphene electrodes enable stable operation over 60 h with a non-optimized degradation rate of 0.15% h−1, whereas electrodes with a similar design but without the graphene as separator are prone to a very fast degradation. The presented results propose an efficient way to stabilize solid acid fuel cell electrodes and provide valuable insights about the degradation processes which are essential for further electrode optimization.