Solar-Driven Biomass Reforming for Hydrogen Generation: Principles, Advances, and Challenges

Hydrogen (H2) has emerged as a clean and versatile energy carrier to power a carbon-neutral economy for the post-fossil era. Hydrogen generation from low-cost and renewable biomass by virtually inexhaustible solar energy presents an innovative strategy to process organic solid waste, combat the energy crisis, and achieve carbon neutrality. Herein, the progress and breakthroughs in solar-powered H2 production from biomass are reviewed. The basic principles of solar-driven H2 generation from biomass are first introduced for a better understanding of the reaction mechanism. Next, the merits and shortcomings of various semiconductors and cocatalysts are summarized, and the strategies for addressing the related issues are also elaborated. Then, various bio-based feedstocks for solar-driven H2 production are reviewed with an emphasis on the effect of photocatalysts and catalytic systems on performance. Of note, the concurrent generation of value-added chemicals from biomass reforming is emphasized as well. Meanwhile, the emerging photo-thermal coupling strategy that shows a grand prospect for maximally utilizing the entire solar energy spectrum is also discussed. Further, the direct utilization of hydrogen from biomass as a green reductant for producing value-added chemicals via organic reactions is also highlighted. Finally, the challenges and perspectives of photoreforming biomass toward hydrogen are envisioned.

Metal-doped niobate pyrochlores and double-perovskites for glycerol valorization: structural and electronic properties and DFT calculations

In this study, metal-doped niobates and perovskites were obtained by a solid-state reaction. The solids were evaluated in the esterification of glycerol in the presence of acetic acid to produce valuable esters of glycerol. The structural features of the solids indicated the ZnNb2O6, Pb2.8Nb2O7.8 and CuNb2O6 columbite main phases and La2MnFeO6 double-perovskite. Density functional theory (DFT) studies of Pb2.8Nb2O7.8 clearly confirmed the existence of a robust orthorhombic structure and its electronic properties were correlated with the Nb and Pb interactions. The morphological and elemental analyses also indicated that not all surface elements, as well as morphology, were crucial for catalytic properties. All solids were active and selective toward triacetin formation upon glycerol esterification with acetic acid. The catalytic performance depends mainly on the availability of the surface and its structural stability, as well as defects formation. Recyclability studies indicated that the La2MnFeO6 double-perovskite was an efficient catalyst, achieving glycerol conversion of 68% and triacetin selectivity of 25% up to 4 cycles of use in the reaction. The structural defects near the Mn4+/Mn3+ surface sites resulted in the diffusion of anions and an increased concentration of oxygen vacancies contributed to the stable performance of the solid in glycerol ester production.

Advances in Naked Metal Clusters for Catalysis

The properties of sub-nano metal clusters are governed by quantum confinement and their large surface-to-bulk ratios, atomically precise compositions and geometric/electronic structures. Advances in metal clusters lead to new opportunities in diverse aspects of sciences including chemo-sensing, bio-imaging, photochemistry, and catalysis. Naked metal clusters having synergic multiple active sites and coordinative unsaturation and tunable stability/activity enable researchers to design atomically precise metal catalysts with tailored catalysis for different reactions. Here we summarize the progress of ligand-free naked metal clusters for catalytic applications. It is anticipated that this review helps to better understand the chemistry of small metal clusters and facilitates the design and development of new catalysts for potential applications.

The refinery of the future

Fossil fuels-coal, oil and gas-supply most of the world's energy and also form the basis of many products essential for everyday life. Their use is the largest contributor to the carbon dioxide emissions that drive global climate change, prompting joint efforts to find renewable alternatives that might enable a carbon-neutral society by as early as 2050. There are clear paths for renewable electricity to replace fossil-fuel-based energy, but the transport fuels and chemicals produced in oil refineries will still be needed. We can attempt to close the carbon cycle associated with their use by electrifying refinery processes and by changing the raw materials that go into a refinery from fossils fuels to carbon dioxide for making hydrocarbon fuels and to agricultural and municipal waste for making chemicals and polymers. We argue that, with sufficient long-term commitment and support, the science and technology for such a completely fossil-free refinery, delivering the products required after 2050 (less fuels, more chemicals), could be developed. This future refinery will require substantially larger areas and greater mineral resources than is the case at present and critically depends on the capacity to generate large amounts of renewable energy for hydrogen production and carbon dioxide capture.

Effective Photocatalytic Ethanol Reforming into High-Value-Added Multicarbon Compound Coupled with H2 Production Over Pt-S3 Sites at PtSA-ZnIn2S4 Interface

Selective photocatalytic production of high-value acetaldehyde concurrently with H2 from bioethanol is an appealing approach to meet the urgent environment and energy issues. However, the difficult ethanol dehydrogenation and insufficient active sites for proton reduction within the catalysts, and the long spatial distance between these two sites always restrict their catalytic activity. Here, guided by the strong metal-substrate interaction effect, an atomic-level catalyst design strategy to construct Pt-S3 single atom on ZnIn2S4 nanosheets (PtSA-ZIS) is demonstrated. As active center with optimized H adsorption energy to facilitate H2 evolution reaction, the unique Pt single atom also donates electrons to its neighboring S atoms with electron-enriched sites formed to activate the O─H bond in *CH3CHOH and promote the desorption of *CH3CHO. Thus, the synergy between Pt single atom and ZIS together will reduce the energy barrier for the ethanol oxidization to acetaldehyde, and also narrow the spatial distance for proton mass transfer. These features enable PtSA-ZIS photocatalyst to produce acetaldehyde with a selectivity of ≈100%, which will spontaneously transform into 1,1-diethoxyethane via acetalization to avoid volatilization. Meanwhile, a remarkable H2 evolution rate (184.4 µmol h-1) is achieved with a high apparent quantum efficiency of 10.50% at 400 nm.

Synthesis and Catalytic Applications of Advanced Sn- and Zr-Zeolites Materials

The incorporation of isolated Sn (IV) and Zr (IV) ions into silica frameworks is attracting widespread attention, which exhibits remarkable catalytic performance (conversion, selectivity, and stability) in a broad range of reactions, especially in the field of biomass catalytic conversion. As a representative example, the conversion route of carbohydrates into valuable platform and commodity chemicals such as lactic acid and alkyl lactates, has already been established. The zeotype materials also possess water-tolerant ability and are capable to be served as promising heterogeneous catalysts for aqueous reactions. Therefore, dozens of Sn- and Zr-containing silica materials with various channel systems have been prepared successfully in the past decades, containing 8 membered rings (MR) small pore CHA zeolite, 10-MR medium pore zeolites (FER, MCM-56, MEL, MFI, MWW), 12-MR large pore zeolites (Beta, BEC, FAU, MOR, MSE, MTW), and 14-MR extra-large pore UTL zeolite. This review about Sn- and Zr-containing metallosilicate materials focuses on their synthesis strategy, catalytic applications for diverse reactions, and the effect of zeolite characteristics on their catalytic performances.

Recent Advances in Reversible Liquid Organic Hydrogen Carrier Systems: From Hydrogen Carriers to Catalysts

Liquid organic hydrogen carriers (LOHCs) have gained significant attention for large-scale hydrogen storage due to their remarkable gravimetric hydrogen storage capacity (HSC) and compatibility with existing oil and gas transportation networks for long-distance transport. However, the practical application of reversible LOHC systems has been constrained by the intrinsic thermodynamic properties of hydrogen carriers and the performances of associated catalysts in the (de)hydrogenation cycles. To overcome these challenges, thermodynamically favored carriers, high-performance catalysts, and catalytic procedures need to be developed. Here, significant advances in recent years have been summarized, primarily centered on regular LOHC systems catalyzed by homogeneous and heterogeneous catalysts, including dehydrogenative aromatization of cycloalkanes to arenes and N-heterocyclics to N-heteroarenes, as well as reverse hydrogenation processes. Furthermore, with the development of metal complexes for dehydrogenative coupling, a new family of reversible LOHC systems based on alcohols is described that can release H2 under relatively mild conditions. Finally, views on the next steps and challenges in the field of LOHC technology are provided, emphasizing new resources for low-cost hydrogen carriers, high-performance catalysts, catalytic technologies, and application scenarios.

Highly Efficient Ru-Based Catalysts for Lactic Acid Conversion to Alanine

The primary objective of this research was to develop efficient solid catalysts that can directly convert the lactic acid (LA) obtained from lignocellulosic biomass into alanine (AL) through a reductive amination process. To achieve this, various catalysts based on ruthenium were synthesized using different carriers such as multi-walled carbon nanotubes (MWCNTs), beta-zeolite, and magnetic nanoparticles (MNPs). Among these catalysts, Ru/MNP demonstrated a remarkable yield of 74.0% for alanine at a temperature of 200 °C. This yield was found to be superior not only to the Ru/CNT (55.7%) and Ru/BEA (6.6%) catalysts but also to most of the previously reported catalysts. The characterization of the catalysts and their catalytic results revealed that metallic ruthenium nanoparticles, which were highly dispersed on the external surface of the magnetic carrier, significantly enhanced the catalyst's ability for dehydrogenation. Additionally, the -NH2 basic sites on the catalyst further facilitated the formation of alanine by promoting the adsorption of acidic reactants. Furthermore, the catalyst could be easily separated using an external magnetic field and exhibited the potential for multiple reuses without any significant loss in its catalytic performance. These practical advantages further enhance its appeal for applications in the reductive amination of lactic acid to alanine.

Two-Dimensional Zeolites-Potential Catalysts for Biomass Valorization

Valorization of biomass and biomass-derived molecules has become a viable route to get fuels and useful chemicals as fossil feedstocks are dwindling and the demand for renewable feedstocks and sustainable energy sources are rising. Zeolites have been promising catalysts for biomass conversion owing to their structural features and active sites. However, the use of conventional zeolites was limited due to molecular diffusion constraints, which paved the way for the emergence of two-dimensional (2D) zeolites. The high external surface area, bimodal porosity (micropores and mesopores), and 2D structure of these zeolites envisage smooth diffusion of bulky molecules, enhanced accessibility to active sites, and slow deactivation, which are benefits in the valorization of biomass. In this brief review, current advancements in the use of layered 2D zeolites for biomass conversions are discussed. The relationship between the structural features and the catalytic potential of 2D zeolites in some of the major biomass conversion processes like pyrolysis, hydrodeoxygenation, alkylation, acetalization, condensation, and dehydration is discussed and multistep reactions that proceed via a cascade mechanism are highlighted.

Regulating Lewis Acidic Sites of 1T-2H MoS2 Catalysts for Solar-Driven Photothermal Catalytic H2 Production from Lignocellulosic Biomass

Solar-driven photothermal catalytic H2 production from lignocellulosic biomass was achieved by using 1T-2H MoS2 with tunable Lewis acidic sites as catalysts in an alkaline aqueous solution, in which the number of Lewis acidic sites derived from the exposed Mo edges of MoS2 was successfully regulated by both the formation of an edge-terminated 1T-2H phase structure and tunable layer number. Owing to the abundant Lewis acidic sites for the oxygenolysis of lignocellulosic biomass, the 1T-2H MoS2 catalyst shows high photothermal catalytic lignocellulosic biomass-to-H2 transformation performance in polar wood chips, bamboo, rice straw corncobs, and rice hull aqueous solutions, and the highest H2 generation rate and solar-to-H2 (STH) efficiency respectively achieves 3661 μmol·h-1·g-1 and 0.18% in the polar wood chip system under 300 W Xe lamp illumination. This study provides a sustainable and cost-effective method for the direct transformation of renewable lignocellulosic biomass to H2 fuel driven by solar energy.

Catalytic Conversion of Lignin into Valuable Chemicals: Full Utilization of Aromatic Nuclei and Side Chains

ConspectusIn recent years, significant efforts have been directed toward achieving efficient and mild lignocellulosic biomass conversion into valuable chemicals and fuels, aiming to address energy and environmental concerns and realize the goal of carbon neutrality. Lignin is one of the three primary building blocks of lignocellulose and the only aromatic renewable feedstock. However, the complex and diverse nature of lignin feedstocks, characterized by their three-dimensional, highly branched polymeric structure and intricate C-O/C-C chemical bonds, results in substantial challenges. To tackle these challenges, we carried out extensive research on selectively activating and transforming chemical bonds in lignin for chemical synthesis. In this Account, we discuss our recent progress in catalytic lignin conversion.Our work is focused on two main objectives: (i) achieving precise and selective transformation of C-O/C-C bonds in lignin (and its model compounds) and (ii) fully utilizing the aromatic nuclei and side chains present in lignin to produce valuable chemicals. Lignin consists of interconnected phenylpropanoid subunits linked by interlaced C-C/C-O bonds. To unlock the full potential of lignin, we propose the concept of "the full utilization of lignin", which encompasses both the aromatic nuclei and the side chains (e.g., methoxyl and polyhydroxypropyl groups).For the conversion of aromatic nuclei, selective activation of C-O and/or C-C bonds is crucial in synthesizing targeted aromatic products. We begin with model compounds (such as anisole, phenol, guaiacol, etc.) and then transition to protolignin feedstocks. Various reaction routes are developed, including self-supported hydrogenolysis, direct Caryl-Csp3 cleavage, coupled Caryl-Csp3 cleavage and Caryl-O hydrogenolysis, and tandem selective hydrogenation and hydrolysis processes. These tailored pathways enable high-yield and sustainable production of a wide range of aromatic (and derived) products, including arenes (benzene, toluene, alkylbenzenes), phenols, ketones, and acids.In terms of side chain utilization, we have developed innovative strategies such as selective methyl transfer, coupling depolymerization-methyl shift, selective acetyl utilization, and new activation methods such as amine-assisted prefunctionalization. These strategies enable the direct synthesis of methyl-/alkyl-derived products, such as acetic acid, 4-ethyltoluene, dimethylethylamine, and amides. Additionally, aromatic residues can be transformed into chemicals or functionalized ingredients that can serve as catalysts or functional biopolymer materials. These findings highlight promising opportunities for harnessing both the aromatic nuclei and side chains of lignin in a creative manner, thereby improving the overall atom economy of lignin upgrading.Through innovative catalyst engineering and reaction route strategies, our work achieves the sustainable and efficient production of various valuable chemicals from lignin. By integrating side chains and aromatic rings, we have successfully synthesized methyl-/alkyl-derived and aromatic-derived products with high yields. The full utilization of lignin not only minimizes waste but also opens up new possibilities for generating chemical products from lignin. These novel approaches unlock the untapped potential of lignin, expand the boundaries of lignin upgrading, and enhance the efficiency and economic viability of lignin biorefining.

Synthesis of novel solid scale inhibitors based on silver tungstate loaded KIT-6 for scale removal from produced water: static and modeling evaluation

Oilfield scaling is a major problem in the oil and gas industry. Scaling issues cost the industry millions of dollars in damage and lost production every year as scaling is one of the main causes of global production decline. In this study, solid scale inhibitors based on silver tungstate loaded KIT-6 were synthesized and evaluated using a static scale inhibition test. The synthesized materials were characterized using wide and low XRD, N2 adsorption-desorption, TGA, and FTIR, SEM, and XPS analyses. Small-angle XRD patterns showed that KIT-6 had 3D-mesopore diffraction peaks with a cubic Ia3d space group. Wide-angle XRD patterns of silver tungstate loaded KIT-6 confirmed the crystallinity. The prepared catalysts are characterized by higher surface areas (394-918 m2 g-1), large pore volumes (0.63-0.98 cm3 g-1), narrow pore size distributions (5.3 nm), and high thermal stability up to 1000 °C. The results of this study demonstrate that the inhibition efficiency of the scale inhibitor increases and that of the calcite scale inhibitor decreases with increasing pH (2 to 8). This proposes that the scale inhibitor is more effective under alkaline conditions. An inhibition efficiency of 99% on calcium carbonate can be achieved at an optimal dosage of 7.5 ppm at 55 °C, indicating that the scale inhibitor exhibits a relatively good inhibition performance on calcium carbonate. The use of these materials can potentially lead to more efficient and cost-effective solutions for scale inhibition in various industrial processes.

Solar-Driven Photothermal Catalytic Lignocellulosic Biomass-to-H2 Conversion

The conversion of lignocellulosic biomass to chemical fuel can achieve the sustainable use of lignocellulosic biomass, but it was limited by the lack of an effective conversion strategy. Here, we reported a unique approach of photothermal catalysis by using MoS2-reduced graphene oxide (MoS2/RGO) as the catalyst to convert lignocellulosic biomass into H2 fuel in alkaline solution. The RGO acting as a support for the growth of MoS2 results in the high exposed Mo edges, which act as efficient Lewis acidic sites for the oxygenolysis of lignocellulosic biomass dissolved in alkaline solution. The broad light absorption capacity and abundant Lewis acidic sites make MoS2/RGO to be efficient catalysts for photothermal catalytic H2 production from lignocellulosic biomass, and the H2 generation rate with respect to catalyst under 300 W Xe lamp irradiation in cellulose, rice straw, wheat straw, polar wood chip, bamboo, rice hull, and corncob aqueous solution achieve 223, 168, 230, 564, 390, 234, and 55 μmol·h-1·g-1, respectively. It is believed that this photothermal catalysis is a simple and "green" approach for the lignocellulosic biomass-to-H2 conversion, which would have great potential as a promising approach for solar energy-driven H2 production from lignocellulosic biomass.

Recent developments in X-ray diffraction/scattering computed tomography for materials science

X-ray diffraction/scattering computed tomography (XDS-CT) methods are a non-destructive class of chemical imaging techniques that have the capacity to provide reconstructions of sample cross-sections with spatially resolved chemical information. While X-ray diffraction CT (XRD-CT) is the most well-established method, recent advances in instrumentation and data reconstruction have seen greater use of related techniques like small angle X-ray scattering CT and pair distribution function CT. Additionally, the adoption of machine learning techniques for tomographic reconstruction and data analysis are fundamentally disrupting how XDS-CT data is processed. The following narrative review highlights recent developments and applications of XDS-CT with a focus on studies in the last five years. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

Sodium phosphate solid base catalysts for production of novel biodiesel by transesterification reaction

The efficient sodium phosphate (Na3PO4) solid base catalysts were prepared and applied in the production of novel biodiesel: ethylene glycol monomethyl ether monolaurate (EGMEML) by transesterification. The calcined sodium phosphate catalysts (NaP-T) were characterized using thermogravimetry analysis (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) and so on. The effects of calcination temperature of Na3PO4 and main reaction parameters such as molar ratio of ethylene glycol monomethyl ether (EGME) to methyl laurate (ML), dosage of catalyst, reaction time and temperature on the yield of EGMEML were examined. The results showed that the maximum yield of EGMEML could reach 90% under 120 °C within 4 h and 5 wt% of Na3PO4 calcined at 400°, and the catalysts displayed good stability and recovery. In addition, the kinetics of transesterification reaction was explored and the results showed that the transesterification reaction followed 1st order kinetics when a large excess of EGME was used, the activation energy (Ea) was found to be 40.2 kJ mol-1.

One-Pot Chitin Conversion to High-Activity Antifungal N,N-Dimethyl Chitosan Oligosaccharides

Chitosan oligosaccharide and its derivatives are known for their diverse biological activities. In this study, we communicate a convenient one-pot synthesis of N,N-dimethyl chitosan oligosaccharide (DMCOS) from chitin via acid-catalyzed tandem depolymerization-deacetylation-N-methylation pathway using formaldehyde as the methylation reagent. The synthesis protocol offers 77 % DMCOS that features a high degree of deacetylation, a high degree of methylation, and a low average molecular weight. Compared to chitosan, DMCOS exhibits superior antifungal activity against Candida species. Mechanism study reveals a previously non-reported hydroxyl group-assisted effect that facilitates the reductive amination reaction under strong acidic conditions. Overall, our findings demonstrate the feasibility of direct synthesis of DMCOS from chitin, highlighting its potential use in anti-fungal applications.

Regulation of Redox Molecular Junctions in Covalent Organic Frameworks for H2 O2 Photosynthesis Coupled with Biomass Valorization

H2 O2 photosynthesis coupled with biomass valorization can not only maximize the energy utilization but also realize the production of value-added products. Here, a series of COFs (i.e. Cu3 -BT-COF, Cu3 -pT-COF and TFP-BT-COF) with regulated redox molecular junctions have been prepared to study H2 O2 photosynthesis coupled with furfuryl alcohol (FFA) photo-oxidation to furoic acid (FA). The FA generation efficiency of Cu3 -BT-COF was found to be 575 mM g-1 (conversion ≈100 % and selectivity >99 %) and the H2 O2 production rate can reach up to 187 000 μM g-1 , which is much higher than Cu3 -pT-COF, TFP-BT-COF and its monomers. As shown by theoretical calculations, the covalent coupling of the Cu cluster and the thiazole group can promote charge transfer, substrate activation and FFA dehydrogenation, thus boosting both the kinetics of H2 O2 production and FFA photo-oxidation to increase the efficiency. This is the first report about COFs for H2 O2 photosynthesis coupled with biomass valorization, which might facilitate the exploration of porous-crystalline catalysts in this field.

Recent Developments on the Catalytic and Biosensing Applications of Porous Nanomaterials

Nanoscopic materials have demonstrated a versatile role in almost every emerging field of research. Nanomaterials have come to be one of the most important fields of advanced research today due to its controllable particle size in the nanoscale range, capacity to adopt diverse forms and morphologies, high surface area, and involvement of transition and non-transition metals. With the introduction of porosity, nanomaterials have become a more promising candidate than their bulk counterparts in catalysis, biomedicine, drug delivery, and other areas. This review intends to compile a self-contained set of papers related to new synthesis methods and versatile applications of porous nanomaterials that can give a realistic picture of current state-of-the-art research, especially for catalysis and sensor area. Especially, we cover various surface functionalization strategies by improving accessibility and mass transfer limitation of catalytic applications for wide variety of materials, including organic and inorganic materials (metals/metal oxides) with covalent porous organic (COFs) and inorganic (silica/carbon) frameworks, constituting solid backgrounds on porous materials.

Pd-Based Nano-Catalysts Promote Biomass Lignin Conversion into Value-Added Chemicals

Lignin, as a structurally complex biomaterial, offers a valuable resource for the production of aromatic chemicals; however, its selective conversion into desired products remains a challenging task. In this study, we prepared three types of Pd-based nano-catalysts and explored their application in the depolymerization of alkali lignin, under both H₂-free (hydrogen transfer) conditions and H₂ atmosphere conditions. The materials were well characterized with TEM, XRD, and XPS and others, and the electronic interactions among Pd, Ni, and P were analyzed. The results of lignin depolymerization experiments revealed that the ternary Pd-Ni-P catalyst exhibited remarkable performance and guaiacols could be produced under H₂ atmosphere conditions in 14.2 wt.% yield with a selectivity of 89%. In contrast, Pd-Ni and Pd-P catalysts resulted in a dispersed product distribution. Considering the incorporation of P and the Pd-Ni synergistic effect in the Pd-Ni-P catalyst, a possible water-involved transformation route of lignin depolymerization was proposed. This work indicates that metal phosphides could be promising catalysts for the conversion of lignin and lignin-derived feedstocks into value-added chemicals.

Critical Techniques for Overcoming the Diffusion Limitations in Heterogeneously Catalytic Depolymerization of Lignin

Heterogeneously catalyzed depolymerization of lignin to value-added chemicals is increasingly attractive but highly challengeable. Particularly, the diffusion limitation of lignin macromolecule to the solid catalyst surface is a big barrier, which significantly decreases the yield of monomer while increasing char formation. Therefore, for the potential industrial utilization of lignin, new knowledge focused on the size of lignin particles is of great importance to offer guidance for promoting lignin depolymerization and suppressing condensation in the heterogeneously catalytic systems. In this Review, the size of lignin particles and macromolecules are summarized. Previous approaches for improving the mass diffusion including enhancing the solubility of lignin and exploitation of hierarchical and "solubilized" materials are also discussed. Based on these, a constructive perspective is proposed. Thus, this work provides a new insight on the rational design of heterogeneous catalytic techniques for efficient utilization of the aromatic polymer of lignin.

On the gelation of humins: from transient to covalent networks

Humins are a by-product of many acid-catalyzed biorefinery processes converting polysaccharides into platform chemicals. The valorization of humin residue to increase the profit of biorefinery operations and reduce waste is a field that is growing interest as the production of humins continues to increase. This includes their valorization in materials science. For successful processing of humin-based materials, this study aims to understand the thermal polymerization mechanisms of humins from a rheological perspective. Thermal crosslinking of raw humins leads to an increase in their molecular weight, which in turn leads to the formation of a gel. Humin's gels structure combines physical (thermally reversible) and chemical (thermally irreversible) crosslinks, and temperature plays an essential role in the crosslink density and the gel properties. High temperatures delay the formation of a gel due to the scission of physicochemical interactions, drastically decreasing their viscosity, whereas upon cooling a stronger gel is formed combining the recovered physicochemical bonds and the newly created chemical crosslinks. Thus, a transition from a supramolecular network to a covalently crosslinked network is observed, and properties such as the elasticity or reprocessability of humin gels are influenced by the stage of polymerization.

Methane Oxidation over the Zeolites-Based Catalysts

Zeolites have ordered pore structures, good spatial constraints, and superior hydrothermal stability. In addition, the active metal elements inside and outside the zeolite framework provide the porous material with adjustable acid–base property and good redox performance. Thus, zeolites-based catalysts are more and more widely used in chemical industries. Combining the advantages of zeolites and active metal components, the zeolites-based materials are used to catalyze the oxidation of methane to produce various products, such as carbon dioxide, methanol, formaldehyde, formic acid, acetic acid, and etc. This multifunction, high selectivity, and good activity are the key factors that enable the zeolites-based catalysts to be used for methane activation and conversion. In this review article, we briefly introduce and discuss the effect of zeolite materials on the activation of C–H bonds in methane and the reaction mechanisms of complete methane oxidation and selective methane oxidation. Pd/zeolite is used for the complete oxidation of methane to carbon dioxide and water, and Fe- and Cu-zeolite catalysts are used for the partial oxidation of methane to methanol, formaldehyde, formic acid, and etc. The prospects and challenges of zeolite-based catalysts in the future research work and practical applications are also envisioned. We hope that the outcome of this review can stimulate more researchers to develop more effective zeolite-based catalysts for the complete or selective oxidation of methane.

Solvent-Free Aldol Condensation of Cyclopentanone with Natural Clay-Based Catalysts: Origin of Activity & Selectivity

The conversion of biomass resources into high-value fuels and chemicals using thermochemical methods has become an attractive method of energy utilization. In this study, natural minerals were used as raw materials; the acidic sites were introduced by ball-milling modification, and the aldol condensation reaction of the biomass-based cyclopentanone molecule was carried out under solvent-free conditions. It was found that the SO3H-APG catalyst—with strong medium-based sites when the -SO3H loading was 4 mmol/g—exhibited excellent acid–base co-activation effects and a significant catalytic effect in the cyclopentanone condensation reaction. The optimization of the reaction conditions showed that the conversion of cyclopentanone reached 85.53% at the reaction temperature of 150 °C and reaction time of 4 h. The selectivity of the dimer and trimer was 69.04% and 28.41%, respectively. The investigation of the cyclopentanone condensation mechanism and kinetic analysis showed that the acid–base presence of an acid–base bifunctional catalyst was important to facilitate the condensation reaction. This research route is in line with the concept of sustainable green production and also provides a promising pathway for catalyst design and the synthesis of long-chain hydrocarbons.

Recent Advances in the Efficient Synthesis of Useful Amines from Biomass-Based Furan Compounds and Their Derivatives over Heterogeneous Catalysts

Bio-based furanic oxygenates represent a well-known class of lignocellulosic biomass-derived platform molecules. In the presence of H2 and different nitrogen sources, these versatile building blocks can be transformed into valuable amine compounds via reductive amination or hydrogen-borrowing amination mechanisms, yet they still face many challenges due to the co-existence of many side-reactions, such as direct hydrogenation, polymerization and cyclization. Hence, catalysts with specific structures and functions are required to achieve satisfactory yields of target amines. In recent years, heterogeneous catalytic synthesis of amines from bio-based furanic oxygenates has received extensive attention. In this review, we summarize and discuss the recent significant progress in the generation of useful amines from bio-based furanic oxygenates with H2 and different nitrogen sources over heterogeneous catalysts, according to various raw materials and reaction pathways. The key factors affecting catalytic performances, such as active metals, supports, promoters, reaction solvents and conditions, as well as the possible reaction routes and catalytic reaction mechanisms are studied and discussed in depth. Special attention is paid to the structure–activity relationship, which would be helpful for the development of more efficient and stable heterogeneous catalysts. Moreover, the future research direction and development trend of the efficient synthesis for bio-based amines are prospected.

Advancements in Basic Zeolites for Biodiesel Production via Transesterification

The excessive utilization of petroleum diesel has led to the depletion of fossil resources and severe environmental pollution. Biodiesel produced from renewable triglycerides (TGs) or waste lipids is a low-emission fuel substitute for diesel. Biodiesel is mainly produced by transesterification reactions over homogeneous base catalysts with excellent activity and low cost. In comparison, solid base catalysts are more attractive due to their lower environmental impact and simpler production and purification processes. It remains a challenge to further improve the stability and activity of solid base catalysts. Because of the high surface area, superior stability, and tunable basicity, basic zeolites, especially two-dimensional zeolites, have emerged as promising solid basic catalysts for the transesterification of TGs. In this review, we present recent advancements in the synthesis, characterization, and catalytic performance of basic zeolites for the transesterification of TGs. Challenges and development prospects of basic zeolites for biodiesel production via transesterification are also pointed out. We expect that this review will inspire the more efficient and rational design of zeolites for sustainable fuel production.

Hydrogenolysis-Isomerization of Waste Polyolefin Plastics to Multibranched Liquid Alkanes

Upcycling of waste polyolefin plastics still meets with economic and technological challenges in practice. In this work, the catalytic hydrogenolysis-isomerization of nondegradable polyolefin plastic waste to high-value gasoline, diesel, and light lubricants with highly branched chain is achieved over a bifunctional Rh/Nb₂ O₅ catalyst under relatively mild conditions. Owing to the high efficiency of metallic Rh active sites, the dehydrogenation/hydrogenation of long carbon chains of polyolefins is enhanced. With the assistance of strong Brønsted acidity of Nb₂ O₅ , the cleavage of C-C bonds, skeletal rearrangements, as well as the β-scission of alkylcarbenium ions occurs, which boosts the one-step solvent-free catalytic hydrogenolysis and isomerization of polyolefins. In addition, the preliminary economic analysis shows that this technology is economical, feasible, and has great potential in accelerating the transition to a circular plastics economy for sustainable development.

Recent Advances in Tetra- (Ti, Sn, Zr, Hf) and Pentavalent (Nb, V, Ta) Metal-Substituted Molecular Sieve Catalysis

Metal substitution of molecular sieve systems is a major driving force in developing novel catalytic processes to meet current demands of green chemistry concepts and to achieve sustainability in the chemical industry and in other aspects of our everyday life. The advantages of metal-substituted molecular sieves include high surface areas, molecular sieving effects, confinement effects, and active site and morphology variability and stability. The present review aims to comprehensively and critically assess recent advances in the area of tetra- (Ti, Sn, Zr, Hf) and pentavalent (V, Nb, Ta) metal-substituted molecular sieves, which are mainly characterized for their Lewis acidic active sites. Metal oxide molecular sieve materials with properties similar to those of zeolites and siliceous molecular sieve systems are also discussed, in addition to relevant studies on metal-organic frameworks (MOFs) and some composite MOF systems. In particular, this review focuses on (i) synthesis aspects determining active site accessibility and local environment; (ii) advances in active site characterization and, importantly, quantification; (iii) selective redox and isomerization reaction applications; and (iv) photoelectrocatalytic applications.

Complete Low-Temperature Transformation and Dissolution of the Three Main Components in Corn Straw

The conversion of biomass faces the challenge of mass and heat transfer, as well as the exertion of heterogeneous catalyst, because raw biomass exists usually in solid state. In this work, the simultaneous transformation and dissolution of the three main components (hemicellulose, cellulose, lignin) in corn straw were achieved in ethanol/ valerolactone (GVL)/H₂ O (10 : 10 : 40, v/v/v) co-solvent system. With the assistance of AlCl₃  ⋅ 6H₂ O, the conversion of hemicellulose, lignin and cellulose was >96 % at 170 °C. The conversion of solid biomass into fluid, overcoming the mass transfer restrictions between solid biomass and solid catalysts, provides new raw materials to further upgrading. H₂ O could penetrate inside the crystalline cellulose to swell even dissolve it, while ethanol and GVL acted as media to dissolve especially the G unit in lignin. The H⁺ derived from AlCl₃  ⋅ 6H₂ O hydrolysis could break the linkages of lignin-hemicellulose and glycosidic bond in saccharides, and aluminum chloride promoted the next degradation of polysaccharides to small molecules. Consequently, as high as 33.2 % yield of levulinic acid and 42.2 % yield of furfural were obtained. The cleavage of β-O-4 and C_β -C_γ bonds in lignin produced large amounts of lignin-derived dimers and trimers. The total yield of monomeric phenols is up to 8 %.

Sustainable routes to alkenes: applications of homogeneous catalysis to the dehydration of alcohols to alkenes

Homogeneous catalysis applied to alcohol dehydration.

Catalytic Production of Functional Monomers from Lysine and Their Application in High-Valued Polymers

Lysine is a key raw material in the chemical industry owing to its sustainability, mature fermentation process and unique chemical structure, besides being an important nutritional supplement. Multiple commodities can be produced from lysine, which thus inspired various catalytic strategies for the production of these lysine-based chemicals and their downstream applications in functional polymer production. In this review, we present a fundamental and comprehensive study on the catalytic production process of several important lysine-based chemicals and their application in highly valued polymers. Specifically, we first focus on the synthesis process and some of the current industrial production methods of lysine-based chemicals, including ε-caprolactam, α-amino-ε-caprolactam and its derivatives, cadaverine, lysinol and pipecolic acid. Second, the applications and prospects of these lysine-based monomers in functional polymers are discussed such as derived poly (lysine), nylon-56, nylon-6 and its derivatives, which are all of growing interest in pharmaceuticals, human health, textile processes, fire control and electronic manufacturing. We finally conclude with the prospects of the development of both the design and synthesis of new lysine derivatives and the expansion of the as-synthesized lysine-based monomers in potential fields.

Controlled Growth of Platinum Nanoparticles on Amorphous Silica from Grafted Pt-Disilicate Complexes

Supported platinum nanoparticles are currently the most functional catalysts applied in commercial chemical processes. Although investigations have been performed to improve the dispersion and thermal stability of Pt particles, it is challenging to apply amorphous silica supports to these systems owing to various Pt species derived from the non-uniform surface structure of the amorphous support. Herein, we report the synthesis and characterization of amorphous silica-supported Pt nanoparticles from (cod)Pt-disilicate complex (cod = 1,5-cyclooctadiene), which forms bis-grafted surface Pt species regardless of surface heterogeneity. The synthesized Pt nanoparticles were highly dispersible and had higher hydrogenation activity than those prepared by the impregnation method, irrespective of the calcination and reduction temperatures. The high catalytic activity of the catalyst prepared at low temperatures (such as 150 °C) was attributed to the formation of Pt nanoparticles triggered by the reduction of cod ligands under H₂ conditions, whereas that of the catalyst prepared at high temperatures (up to 450 °C) was due to the modification of the SiO₂ surface by grafting of the (cod)Pt-disilicate complex.

Valorisation of Corncob Residue towards the Sustainable Production of Glucuronic Acid

The production of glucuronic acid (GA) directly from actual biomass via chemocatalysis is of great significance to the effective valorisation of biomass for a sustainable future. Herein, we have developed a one-step strategy for the conversion of cellulose in corncob residue into GA with the cooperation of Au/CeO2 and maleic acid, achieving a 60.3% yield. Experimental and density functional theory (DFT) results show that maleic acid is effective in the fractionation of cellulose from corncob residue and the depolymerisation of cellulose fragments to glucose, on account of the good capacity for proton migration. Au/CeO2 is responsible for the selective oxidation of glucose to GA, in which the formation of glucaric acid is restrained, due to the weak capacity of Au/CeO2 on the proton transfer without the occurrence of the ring-opening reaction of glucose. Therefore, the relay catalysis of Au/CeO2 and maleic acid enables the production of GA via the complex cascade reactions. This work may provide insight regarding the conversion of actual biomass to targeted products.

Enhanced Catalytic Performance of a Ce/V Oxo Cluster through Confinement in Mesoporous SBA-15

To increase catalytic efficiency, mesoporous supports have been widely applied to immobilize well-defined metal oxide clusters due to their ability to stabilize highly dispersed clusters. Herein, a redox-active heterometallic Ce₁₂V₆-oxo cluster (CeV) was first presynthesized and then incorporated into mesoporous silica, SBA-15, via a straightforward impregnation method. Scanning transmission electron microscopy (STEM) and Fourier transform infrared spectroscopy (FTIR), in concert with scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), verified the successful introduction of the CeV cluster inside the pore of SBA-15. The ⁵¹V magic angle spinning solid-state nuclear magnetic resonance (⁵¹V MAS NMR) spectroscopy and differential pair distribution function (dPDF) analysis confirmed the structural integrity of the CeV cluster inside the SBA-15. The composite was then benchmarked for liquid-phase oxidation of 2-chloroethyl ethyl sulfide (CEES) under mild conditions and gas-phase oxidative dehydrogenation (ODH) of propane under high temperatures (up to 550 °C). The catalytic reactivity results demonstrated 8- and 14-fold increase in turnover frequency (TOF) values of the composite (CeV@10SBA-2) than the bulk CeV cluster under the same conditions for CEES oxidation and ODH, respectively. These results highlight the improved reactivity of the catalytically active CeV cluster as attributed to the higher dispersion of the discrete cluster upon immobilization within the SBA-15 support.

Upgrading Organic Compounds through the Coupling of Electrooxidation with Hydrogen Evolution

The electrocatalytic splitting of water is recognized to be the most sustainable and clean technology for the production of hydrogen (H₂ ). Unfortunately, the efficiency is seriously restricted by the sluggish kinetics of the oxygen evolution reaction (OER) at the anode. In contrast to the OER, the electrooxidation of organic compounds (EOO) is more thermodynamically and kinetically favorable. Thus, the coupling of the EOO and hydrogen evolution reaction (HER) has emerged as an alternative route, as it can greatly improve the catalytic efficiency for the production of H₂ . Simultaneously, value-added organic compounds can be generated on the anode through electrooxidation upgrading. In this Minireview, we highlight the latest progress and milestones in coupling the EOO with the HER. Emphasis is focused on the design of the anode catalyst, understanding the reaction mechanism, and the construction of the electrolyzer. Moreover, challenges and prospects are offered relating to the future development of this emerging technology.

Efficient Synthesis of Furfuryl Alcohol from Corncob in a Deep Eutectic Solvent System

As a versatile and valuable intermediate, furfuryl alcohol (FOL) has been widely used in manufacturing resins, vitamin C, perfumes, lubricants, plasticizers, fuel additives, biofuels, and other furan-based chemicals. This work developed an efficient hybrid strategy for the valorization of lignocellulosic biomass to FOL. Corncob (75 g/L) was catalyzed with heterogenous catalyst Sn-SSXR (2 wt%) to generate FAL (65.4% yield) in a deep eutectic solvent ChCl:LA–water system (30:70, v/v; 180 °C) after 15 min. Subsequently, the obtained FAL liquor containing FAL and formate could be biologically reduced to FOL by recombinant E. coli CF containing aldehyde reductase and formate dehydrogenase at pH 6.5 and 35 °C, achieving the FOL productivity of 0.66 g FOL/(g xylan in corncob). The formed formate could be used as a cosubstrate for the bioreduction of FAL into FOL. In addition, other biomasses (e.g., sugarcane bagasse and rice straw) could be converted into FOL at a high yield. Overall, this hybrid strategy that combines chemocatalysis and biocatalysis can be utilized to efficiently valorize lignocellulosic materials into valuable biofurans.

Cooperative Coupling of H2 O2 Production and Organic Synthesis over a Floatable Polystyrene-Sphere-Supported TiO2 /Bi2 O3 S-Scheme Photocatalyst

Cooperative coupling of photocatalytic H₂ O₂ production with organic synthesis has an expansive perspective in converting solar energy into storable chemical energy. However, traditional powder photocatalysts suffer from severe agglomeration, limited light absorption, poor gas reactant accessibility, and reusable difficulty, which greatly hinders their large-scale application. Herein, floatable composite photocatalysts are synthesized by immobilizing hydrophobic TiO₂ and Bi₂ O₃ on lightweight polystyrene (PS) spheres via hydrothermal and photodeposition methods. The floatable photocatalysts are not only solar transparent, but also upgrade the contact between reactants and photocatalysts. Thus, the floatable step-scheme (S-scheme) TiO₂ /Bi₂ O₃ photocatalyst exhibits a drastically enhanced H₂ O₂ yield of 1.15 mm h^-1 and decent furfuryl alcohol conversion to furoic acid synchronously. Furthermore, the S-scheme mechanism and dynamics are systematically investigated by in situ irradiated X-ray photoelectron spectroscopy and femtosecond transient absorption spectrum analyses. In situ Fourier transform infrared spectroscopy and density functional theory calculations reveal the mechanism of furoic acid evolution. The ingenious design of floatable photocatalysts not only furnishes insight into maximizing photocatalytic reaction kinetics but also provides a new route for highly efficient heterogeneous catalysis.

Leveraging Pt/Ce1-xLaxO2-δ To Elucidate Interfacial Oxygen Vacancy Active Sites for Aerobic Oxidation of 5-Hydroxymethylfurfural

The interfacial oxygen-defective sites of oxide-supported metal catalysts are generally regarded as active centers in diverse redox reactions. Identification of their structure-property relationship at the atomic scale is of great importance but challenging. Herein, a series of La³⁺-doped three-dimensionally ordered macroporous CeO₂ (3D-Ce_1-xLa_xO_2-δ) were synthesized and applied as supports for Pt nanoparticles. The pieces of evidence from a suite of in-situ/ex-situ characterizations and theoretical calculations revealed that the La³⁺-mono-substituted La-□(-Ce)₂ sites (where □ represents an oxygen vacancy) exhibited superior charge transfer ability, behaving as trapping centers for Pt nanoparticles. The resulting interfacial Pt^δ+/La-□(-Ce)₂ sites served as the reversible active species in the aerobic oxidation of 5-hydroxymethylfurfural to boost catalytic performance by simultaneously promoting oxygen activated capacity and the cleavage of O-H/C-H bonds of adsorbed hydroxymethyl groups. Consequently, the Pt/3D-Ce_0.9La_0.1O_2-δ catalyst possessing the highest number of Pt^δ+/La-□(-Ce)₂ sites showed the best catalytic performance with 99.6% yield to 2,5-furandicarboxylic acid in 10 h. These results offer more insights into the promoting mechanism of interfacial oxygen-defective sites for the liquid-phase aerobic oxidation of aldehydes and alcohols.

Direct 3D Printing of Binder-Free Bimetallic Nanomaterials as Integrated Electrodes for Glycerol Oxidation with High Selectivity for Valuable C3 Products

Net-zero carbon strategies and green synthesis methodologies are key to realizing the United Nations' sustainable development goals (SDGs) on a global scale. An electrocatalytic glycerol oxidation reaction (GOR) holds the promise of upcycling excess glycerol from biodiesel production directly into precious hydrocarbon commodities that are worth orders of magnitude more than the glycerol feedstock. Despite years of research on the GOR, the synthesis process of nanoscale electrocatalysts still involves (1) prohibitive heat input, (2) expensive vacuum chambers, and (3) emission of toxic liquid pollutants. In this paper, these knowledge gaps are closed via developing a laser-assisted nanomaterial preparation (LANP) process to fabricate bimetallic nanocatalysts (1) at room temperature, (2) under an ambient atmosphere, and (3) without liquid waste emission. Specifically, PdCu nanoparticles with adjustable Pd:Cu content supported on few-layer graphene can be prepared using this one-step LANP method with performance that can rival state-of-the-art GOR catalysts. Beyond exhibiting high GOR activity, the LANP-fabricated PdCu/C nanomaterials with an optimized Pd:Cu ratio further deliver an exclusive product selectivity of up to 99% for partially oxidized C₃ products with value over 280000-folds that of glycerol. Through DFT calculations and in situ XAS experiments, the synergy between Pd and Cu is found to be responsible for the stability under GOR conditions and preference for C₃ products of LANP PdCu. This dry LANP method is envisioned to afford sustainable production of multimetallic nanoparticles in a continuous fashion as efficient electrocatalysts for other redox reactions with intricate proton-coupled electron transfer steps that are central to the widespread deployment of renewable energy schemes and carbon-neutral technologies.

A unified view on catalytic conversion of biomass and waste plastics

Originating from the desire to improve sustainability, producing fuels and chemicals from the conversion of biomass and waste plastic has become an important research topic in the twenty-first century. Although biomass is natural and plastic synthetic, the chemical nature of the two are not as distinct as they first appear. They share substantial structural similarities in terms of their polymeric nature and the types of bonds linking their monomeric units, resulting in close relationships between the two materials and their conversions. Previously, their transformations were mostly studied and reviewed separately in the literature. Here, we summarize the catalytic conversion of biomass and waste plastics, with a focus on bond activation chemistry and catalyst design. By tracking the historical and more recent developments, it becomes clear that biomass and plastic have not only evolved their unique conversion pathways but have also started to cross paths with each other, with each influencing the landscape of the other. As a result, this Review on the catalytic conversion of biomass and waste plastic in a unified angle offers improved insights into existing technologies, and more importantly, may enable new opportunities for future advances.

Biomass and plastic share structural similarities in their composition and types of bond linkage between their monomeric units. Reviewing their catalytic conversion technologies in a unified angle provides new insights and opportunities for future advances.

MoloVol: an easy-to-use program for analyzing cavities, volumes and surface areas of chemical structures

Cavities are a ubiquitous feature of chemical structures encountered in various fields ranging from supramolecular chemistry to molecular biology. They are involved in the encapsulation, transport and transformation of guest molecules, thus necessitating a precise and accessible tool for estimating and visualizing their size and shape. MoloVol, a free user-parametrizable open-source software, developed for calculating a range of geometric features for both unit-cell and isolated structures, is presented here. MoloVol utilizes up to two spherical probes to define cavities, surfaces and volumes. The program was optimized by combining an octree data structure with voxel-partitioned space, allowing for even high-resolution protein structure calculations on reasonable timescales. MoloVol comes with a user-friendly graphic interface along with a command-line interface for high-throughput calculations. It was written in C++ and is available on Windows, macOS and Linux distributions.

Hierarchical Pores-Confined Ultrasmall Cu Nanoparticles for Efficient Oxidation of 5-Hydroxymethylfurfural

Pyrolysis is one of the most widely utilized protocols for the preparation of nanoconfined metal species for heterogeneous catalysis, but it still suffers from the uncontrollable composition evolution process with undesired metal sintering and porous structure collapse. Herein, a novel and versatile molten salt-assisted pyrolysis strategy was demonstrated for the preparation of ultrasmall transition-metal nanoparticles embedded in hollow hierarchical carbon skeletons. The preparation only involved the fabrication of metal-organic framework templates and subsequent pyrolysis with the addition of KCl-KBr molten salt, which played a crucial role in pore size extending and metal sintering inhibiting. Benefitting from the encapsulation effect, the as-synthesized Cu@HHC materials exhibited remarkable catalytic performance and recycling stability in the selective oxidation of biomass-derived 5-hydroxymethylfurfural into 2,5-diformylfuran under mild reaction conditions.

Thermal Hydroquinone Oxidation on Co/N-doped Carbon Proceeds by a Band-Mediated Electrochemical Mechanism

Molecular metal complexes catalyze aerobic oxidation reactions via redox cycling at the metal center to effect sequential activation of O₂ and the substrate. Metal surfaces can catalyze the same transformations by coupling independent half-reactions for oxygen reduction and substrate oxidation mediated via the exchange of band-electrons. Metal- and nitrogen-doped carbons (MNCs) are promising catalysts for aerobic oxidation that consist of molecule-like active sites embedded in conductive carbon hosts. Owing to their combined molecular and metallic features, it remains unclear whether they catalyze aerobic oxidation via the sequential redox cycling pathways of molecules or band-mediated pathways of metals. Herein, we simultaneously track the potential of the catalyst and the rate of turnover of aerobic hydroquinone oxidation on a cobalt-based MNC catalyst in contact with a carbon electrode. By comparing operando measurements of rate and potential with the current-voltage behavior of each constituent half-reaction under identical conditions, we show that these molecular materials can display the band-mediated reaction mechanisms of extended metallic solids. We show that the action of these band-mediated mechanisms explains the fractional reaction orders in both oxygen and hydroquinone, the time evolution of catalyst potential and rate, and the dependence of rate on the overall reaction free energy. Selective poisoning experiments suggest that oxygen reduction proceeds at cobalt sites, whereas hydroquinone oxidation proceeds at native carbon-oxide defects on the MNC catalyst. These findings highlight that molecule-like active sites can take advantage of band-mediated mechanisms when coupled to conductive hosts.