Search Results (115)

Ammonia is indispensable to the fertilizer and chemical industries, yet its manufacture still relies predominantly on the energy-intensive Haber–Bosch process operated at 400–500 °C and 150–250 bar, with a substantial carbon footprint. Single-atom catalysts (SACs) and sub-nanometric clusters have recently emerged as promising alternatives for thermocatalytic ammonia synthesis under milder conditions because they maximize metal utilization and enable precise control of the active site environment. This review first summarizes how the transition from conventional Fe and Ru nanoparticles to isolated or few-atom sites fundamentally alters the kinetic landscape, favoring associative N₂ activation pathways that lower apparent activation energies and alleviate H₂ poisoning. We then discuss Ru-based SACs and SAAs supported on zeolites, carbons, ceria, and MXenes, highlighting how strong metal–support and promoter interactions, tandem single-atom/nanoparticle motifs, and alloying strategies tune N₂ and H₂ binding to deliver high NH₃ productivities at 200–400 °C and ≤30 bar. In parallel, we review emerging non-noble systems based on Fe and Co, including high-loading Fe–N₄ sites prepared via MOF-derived post-metal-replacement routes and Co single atoms or Co₂ clusters on N-doped carbons, which already rival or surpass Ru benchmarks under similar conditions. Collectively, these studies show that tailoring the number of atom metal sites, coordination, and support polarity around isolated metal sites provides a useful tool to mitigate some aspects of volcano and scaling-relation limitations, indicating that SACs could contribute to low-temperature ammonia synthesis when combined with appropriate process design. Full article

The electrochemical reduction of carbon dioxide (CO₂RR) into value-added chemicals using renewable electricity is a pivotal strategy for achieving a sustainable carbon cycle. However, this process is plagued by intrinsic challenges, including poor product selectivity, competing hydrogen evolution, and catalyst instability. Metal–organic frameworks (MOFs), with their highly designable periodic structures, atomically dispersed active sites, and tunable pore microenvironments, have emerged as a uniquely versatile platform to address these issues. This review articulates a multi-scale design philosophy that enables precise steering of the CO₂RR pathway. We systematically elaborate on hierarchical tuning strategies, beginning with molecular-scale engineering of active sites (metal nodes and organic ligands) to define intrinsic activity and intermediate binding. This is synergistically integrated with the optimization of electronic structure and charge transport to overcome conductivity bottlenecks, meso-scale modulation of crystal morphology and defects to enhance mass transport and site accessibility, and the construction of heterogeneous interfaces for tandem catalysis and synergistic effects. Through this coherent, cross-scale design framework, MOF-based catalysts demonstrate exceptional capability in the precise control of reaction pathways, leading to remarkably selective synthesis of target high-value products, from C₁ compounds (CO, HCOOH, CH₄, CH₃OH) to C₂⁺ species (C₂H₄, C₂H₅OH) and urea. Finally, we outline future directions centered on dynamic mechanistic understanding, electrode engineering for industrial current densities, and stability enhancement, thereby providing a comprehensive material design guideline to advance CO₂RR technology. This work positions MOFs as a quintessential tunable catalytic platform for the sustainable conversion of CO₂. Full article

CO₂-assisted catalytic pyrolysis presents a viable and promising approach to addressing plastic waste pollution and mitigating climate change. However, the effects of the metal–catalyst combination mode and the spatial distance between metal–acid sites on catalytic performance remain unclear. In this study, the reaction behaviors of the configurations, Fe₃O₄ and ZSM-5 in tandem catalysis (Fe₃O₄&HZ), their physical mixture (Fe₃O₄-HZ), and Fe-loaded ZSM-5 (Fe/HZ), were compared in polypropylene pyrolysis under a CO₂ atmosphere. The aromatic contents followed this order: Fe/HZ > Fe₃O₄-HZ > Fe₃O₄&HZ > ZSM-5 > Fe₃O₄. Specifically, Fe/HZ with the highest degree of metal–zeolite proximity achieved an aromatic content of 66.1%, significantly higher than the 34.2% obtained with Fe₃O₄&HZ, demonstrating that closer metal–acid proximity promoted aromatic formation. Moreover, Fe/HZ significantly reduced coke deposition. Based on characterization results from XRD, SEM, TEM, XPS, and NH₃-TPD, the enhanced spatial proximity between metal and acid sites strengthened the functional synergy between iron-based redox sites and zeolitic Brønsted acid sites. This synergy facilitated the reverse water–gas shift reaction of CO₂, which consumed hydrogen generated during aromatization and shifted the reaction equilibrium toward enhanced aromatic production. These findings would offer theoretical and strategic insights into the optimization of CO₂-assisted catalytic pyrolysis systems for the sustainable upcycling of plastic waste. Full article

Effective electrochemical CO₂ reduction to liquid fuels requires that the local catalytic environment facilitates the desired reactivity, yet a microscopic understanding of this environment is difficult to achieve from experiment alone. In this work, a 3D reaction-diffusion model was developed to explore the effects of electrode surface area and local geometry on the performance of a heterogeneous catalyst that performs a two-step CO₂ reduction cascade reaction to CO and then CH₃OH under aqueous conditions. Kinetic parameters for the model were inspired by experimental results using a cobalt phthalocyanine (CoPc) catalyst. Three-dimensional architectures composed of arrays of square pillars with varying dimensions and either smooth or periodically modulated surfaces were tested, revealing the extent to which geometry modulates the performance of the cascade reactions. Although structural variations modulate local concentration gradients, we find that electrochemically active surface area predominantly governs the overall cascade reaction. Moreover, the results suggest that supersaturation of CO, with concentrations up to ten-fold higher than the equilibrium solubility limit, might be critical for more efficient conversion to CH₃OH. For any given geometry, the spatially averaged ratio of [CO] to [CO₂] is dictated by the electrochemically active surface area and determines the yield of CH₃OH. For a fixed surface area, geometries that spatially confine the electrolyte yield moderate local [CO] to [CO₂] ratios within small volumes. In contrast, less confining geometries result in a broader distribution of local ratios spread over larger volumes, with both configurations yielding the same spatially averaged [CO] to [CO₂] ratio. These insights provide valuable design principles—highlighting the critical importance of surface area and possibly CO supersaturation—for engineering advanced electrode architectures that leverage intermediate trapping and CO supersaturation to enhance overall performance in tandem CO₂ reduction systems. Full article

Potentially biologically active α-aminophosphonic derivatives were prepared by the Kabachnik–Fields condensation of α-amino-α-aryl-methylphosphonates, arylaldehydes, and diethyl phosphite to afford bis(α-aryl-methylphosphonoyl)-amines as a mixture of racemic and meso isomers. To go “green”—performing the transformations under microwave irradiation—there was no need for a catalyst. On the other hand, the phospha-Mannich reaction of α-amino-α-phenyl-methylphosphonate with arylaldehydes led to (α-aryl-methylphosphonoyl)-(α-phenyl-methylphosphonoyl)-amines as a mixture of SS/RR and SR/RS racemates. Moreover, the respective symmetric products with identical aryl groups were also present. The outcome was similar, when α-amino-α-aryl-methyl-phosphonates were condensed with benzaldehyde and diethyl phosphite. The products were analyzed by 1D and 2D NMR spectroscopy. The combined NMR analysis of the products confirmed their structure. Full article

Al-rich NH₄-ZSM-5 with highly oriented crystals was directly synthesized through a one-pot hydrothermal technique, using ammonium nitrate as a metal-free mineralizer. The samples were characterized by XRD, N₂ adsorption–desorption, SEM, FTIR, Py-FTIR, ²⁷Al MAS NMR, ²⁹Si MAS NMR, ¹H MAS NMR, and TGA techniques. The impact of aluminum source, ammonium source, and H₂O/SiO₂ molar ratio was studied. XRD results showed that the ZSM-5 catalyst with a low Si/Al ratio (13) was successfully synthesized without any amorphous phase, including a microporous/mesoporous structure. A low H₂O/SiO₂ molar ratio (75) resulted in coffin-shape surface morphology, large b-axis-oriented particles (ca. 19 µm), and high specific surface area (>300 m² g⁻¹), providing a large portion of straight channels (90.5%). The catalytic activity of the catalysts was evaluated in the CO₂ hydrogenation reaction in tandem configuration with a Na/Fe₂O₃ catalyst. The results confirmed that highly b-oriented crystals improved the product shape selectivity to p-xylene by affecting the diffusion resistance. Therefore, the developed catalyst provided high CO₂ conversion (45%) and high aromatic selectivity (77%), with p-xylene accounting for 82% of the produced xylene compounds, over a long-term time on stream (17 h). These results demonstrate the effectiveness of the direct synthesis strategy in producing Al-rich ZSM-5 catalysts with tailored textural and acidic properties for tandem and shape-selective catalysis. Full article

In this study, the feasibility of tetracycline (TC) degradation in water using Fe–Mo co–supported biochar (FeMoBC) as catalyst combined with ozone and peroxymonosulfate (O₃/PMS) system is discussed. The experiment showed that the mineralization rate of TC by O₃/PMS/FeMoBC process reached 60.1% within 60 min, which was significantly higher than the treatment effect of O₃ or O₃/PMS system alone. Meanwhile, this process showed higher degradation efficiency under the background of raw water, and the loss of FeMoBC cycle attenuation performance was small. Twelve intermediates in the degradation of TC were identified by ultra-high performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS), and the possible degradation paths were inferred by quantum chemical calculation. In addition, the toxicity of intermediate products was evaluated by ecological structure–activity relationships (ECOSAR) and toxicity estimation software tool (T.E.S.T.) software, and the results showed that with the degradation of TC, its toxicity showed a downward trend as a whole. Therefore, this study confirmed that O₃/PMS/FeMoBC had high efficiency in degrading TC in actual water, which provided a new idea for the treatment of high concentration organic wastewater. Full article

The efficient generation of structurally diverse rare ginsenosides from abundant precursors remains a significant challenge. In this study, a heterogeneous catalyst, 12-tungstosilicic acid supported on mesoporous silica (HSiW@mSiO₂), was developed for the transformation of ginsenoside Re in aqueous ethanol solution. The reaction was conducted under mild conditions, and the products were systematically analyzed using high-performance liquid chromatography coupled with multistage tandem mass spectrometry and high-resolution mass spectrometry. A total of 24 transformation products were identified, arising from deglycosylation, epimerization, dehydration, cyclization, and nucleophilic addition reactions. Structural elucidation revealed the formation of deglycosylated, hydrated and dehydrated derivatives, C-20 epimers, and novel ethoxylated protopanaxatriol-type ginsenosides resulting from solvent incorporation at the C-24(25) or C-20 position. Product distribution varied with reaction parameters, including solvent composition, reaction time, temperature, and catalyst dosage. The synthesized HSiW@mSiO₂ catalyst could be readily recovered by centrifugation and reused for five consecutive cycles, with complete conversion of ginsenoside Re maintained in the first two runs and a gradual decline in conversion to approximately 50% by the fifth cycle. This work demonstrates the efficacy of solid acid catalysts in enabling the structural diversification of ginsenosides through solvent-involved pathways. Full article

Sustainable lignosulfonate was employed as a key component for coordinating with various metal ions, affording metal-coordinated lignosulfonate catalysts (Hf-LigS) for hexose transformation. We first investigated the contribution of bare or tandem Lewis/Brønsted acid sites in each of the reaction steps. The results indicated that glucose isomerization was synergistically catalyzed by Lewis acid–base couple sites, and Brønsted acid sites were preferred for consecutive fructose dehydration to 5-hydroxymethylfurfural (HMF). DMSO and deep eutectic solvents enhanced the glucose dehydration and inhibited the isomerization reaction, leading to the formation of Levoglucosan (LGA) intermediate. Considering this, the Hf-LigS with moderate Lewis acid/base sites and Brønsted acid sites exhibited the best catalytic activity for hexose transformation, especially the isomerization reaction at high glucose concentration in ethanol (>20 wt%). This study established a fundamental understanding of the role of catalytic sites and solvent, guiding the selective transformation of hexose. Full article

Waste orange peels (WOP) are a major orange processing residue, and they may be a rich source of precious bioactive polyphenols. Amongst the various WOP constituents, hesperidin holds a prominent position as the most abundant polyphenolic metabolite, with proven biological properties. The current work was performed to provide detailed information on the effect of various acid catalysts to assist hesperidin recovery, using an ethanol organosolv treatment. The treatment developed was first examined by comparing inorganic (HCl) and natural organic (oxalic, citric) acids for their influence on process performance, extraction kinetics, and severity. Following this, optimization was accomplished through response surface methodology, and the extracts produced were investigated with respect to their polyphenolic composition and antioxidant characteristics. The HCl-catalyzed treatment, carried out with 70% ethanol/2% HCl, was proven the most efficacious, giving a total polyphenol yield of 30.7 mg gallic acid equivalents per g of dry mass, and it was shown that the treatment yield was related to severity, obeying a power model. Liquid chromatography–tandem mass spectrometry analysis of the extract generated under optimized conditions (170 min, 80 °C) revealed that hesperidin was extensively hydrolyzed into hesperetin 7-O-glucoside and aglycone (hesperetin). Such an effect was very limited with the oxalic acid-catalyzed treatment, whereas citric acid did not affect the original polyphenolic composition. Overall, the HCl-catalyzed treatment was of significantly higher performance, providing a total flavanone yield of 21.22 mg per g dry mass. The results of this investigation may be of value in adjusting treatment settings for (i) increased flavonoid recovery from WOP and (ii) producing extracts enriched in hesperidin and/or its hydrolysis derivatives. Such practical recommendations may assist the establishment of WOP valorization processes in an integrated biorefinery prospect. Full article

Electrochemical nitrate reduction to ammonia offers a sustainable route for nitrogen fixation, yet achieving high efficiency and selectivity remains challenging. Here, a Sustainion-enabled Cu/Co tandem catalyst is developed to couple compositional synergy with ionomer-mediated interfacial regulation. The optimized Cu₆₀Co₄₀/Sus/C electrode delivers a Faradaic efficiency of 91.3% and an NH₃ yield rate of 2.63 mmol g_cat.⁻¹ h⁻¹ at −0.3 V vs. RHE, surpassing Cu-Co/Nafion/C and Cu-Co/C counterparts. Structural analyses confirm that Sustainion prevents nanoparticle aggregation and maintains robust Cu/Co interfaces. Electrochemical and in situ spectroscopic studies reveal that the cationic quaternary ammonium groups of Sustainion electrostatically enrich NO₃⁻/NO₂⁻ intermediates, facilitating their adsorption and hydrogenation toward NH₃ formation. The combined structural stabilization and intermediate modulation enable efficient tandem catalysis between Cu-driven nitrate activation and Co-mediated hydrogenation. This work provides molecular-level insight into ionomer–catalyst interactions and highlights interfacial engineering as a powerful strategy for sustainable ammonia synthesis. Full article

An atomically dispersed rhodium on TiO₂ catalyst enables a tandem process, combining hydrogenative reduction with α,β-hydrogen–deuterium exchange of cinnamic acid, in which D₂O serves as the deuterium source. In contrast with previous reductive deuteration methods that yield only partially labeled 3-phenylpropanoic acids (D^α-inc.: ≤50%, D^β-inc.: ≤50%), this heterogeneous system delivers near-quantitative deuterium incorporation (D^α-inc.: 94%, D^β-inc.: 99%) under mild conditions, outperforming Rh nanoparticles and homogeneous Rh catalysts. Mechanistic studies indicate that α-C–H activation is the slowest transformation step within the overall process, owing to the exceptional C–H bond activation capability of the atomically dispersed catalyst; efficient α-C–H hydrogen–deuterium exchange is readily achieved. In addition, although catalyst recyclability is constrained by Rh aggregation, no Rh leaching is detected. This work provides a concise, operationally simple route to alkyl fully deuterated 3-phenylpropanoic acids (d₄-PA) and showcases the application of an atomically dispersed catalyst in tackling challenging deuterium-labeling transformations. Full article

Today, biocatalytic methodologies are well established as useful tools in green organic synthesis, since biocatalysts are mild, sustainable, and environmentally friendly catalysts which provide selectivity to the reactions they catalyse. Albumin, the most abundant protein of mammalian blood, is a versatile and mild biocatalyst in vitro. The aim of this review is to provide a perspective on the synthetic applications of albumin over the last decade. These cover transformations with a diverse chemical basis, such as additions, eliminations, and oxidations, including formation of carbon–carbon and carbon–heteroatom bonds. Albumin can also be applied in tandem and multicomponent reactions and offers a mild alternative for the synthesis of different heterocyclic cores. In addition to its synthetic possibilities, the remarkable reusability of this protein offers interesting potential from a biotechnological point of view. Full article

The coordination chemistry of benzimidazole ligands combines σ donation and π backbonding. Owing to this electronic flexibility, benzimidazole ligands stabilize both electron deficient and electron-rich transition states in the catalytic cycle of Ziegler-Natta polymerizations. In this study, Fe(III) and Ni(II) complexes of 2-substituted-benzimidazoles were tested as catalysts for ethylene and 1-butene oligomerization. The tests realized in toluene yielded mainly butenes and minor amounts of hexenes. When dichloromethane was used as solvent, a tandem reaction took place and 1-butene produced by ethylene dimerization was further oligomerized, yielding octenes and dodecenes as main products. All tested catalysts exhibited moderate selectivity for 1-octene, indicating 1-ω enchainment in 1-butene dimerization. Beyond catalytic tests, a theoretical study of the ligand 2,2′-(furan-2,5-diyl)bis(1H-benzimidazole) confirmed the planar structure of this compound as evidenced by NMR spectroscopy. Full article

The rational design of photoanode materials is pivotal for advancing photoelectrochemical (PEC) water splitting toward sustainable hydrogen production. This review highlights recent progress in the machine learning (ML)-assisted development of nanostructured metal oxide photoanodes, focusing on bridging materials discovery and device-level performance optimization. We first delineate the fundamental physicochemical criteria for efficient photoanodes, including suitable band alignment, visible-light absorption, charge carrier mobility, and electrochemical stability. Conventional strategies such as nanostructuring, elemental doping, and surface/interface engineering are critically evaluated. We then discuss the integration of ML techniques—ranging from high-throughput density functional theory (DFT)-based screening to experimental data-driven modeling—for accelerating the identification of promising oxides (e.g., BiVO₄, Fe₂O₃, WO₃) and optimizing key parameters such as dopant selection, morphology, and catalyst interfaces. Particular attention is given to surrogate modeling, Bayesian optimization, convolutional neural networks, and explainable AI approaches that enable closed-loop synthesis-experiment-ML frameworks. ML-assisted performance prediction and tandem device design are also addressed. Finally, current challenges in data standardization, model generalizability, and experimental validation are outlined, and future perspectives are proposed for integrating ML with automated platforms and physics-informed modeling to facilitate scalable PEC material development for clean energy applications. Full article