Catalytic Reaction Research Articles

Terminal {Ni(II)-SH} complex promoted anaerobic catalytic sulfur atom transfer reaction: implication to the sulfide oxidase function of Cu/Zn-superoxide dismutase.

In mitochondria, the detoxification of molar excess H2S as polysulfide proceeded via an oxidation process promoted by Cu/Zn containing superoxide dismutase (SOD1) enzyme, which has been very recently reported as the alternative enzyme for cytosolic H2S oxidation. Herein, we present Ni(II) complexes bearing the terminal SH group as a synthetic functional analogue for the sulfide oxidase function of SOD1. Synthesis, crystal structure and complete spectroscopic characterization of two sets of complexes, [NiLOMe/tBu(PPh3)] (2OMe/tBu) and tetraethyl salt of [NiLOMe/tBu(SH)]-1 (3OMe/tBu), were described (LOMe = (E)-2-methoxy-6-(((2-sulfidophenyl)imino)methyl)phenolate and LtBu = (E)-2,4-di-tert-butyl-6-(((2-sulfidophenyl)imino)methyl)phenolate). Under anaerobic conditions, 3OMe/tBu responded to a catalytic sulfur atom transfer (SAT) reaction with PPh3 to produce SPPh3. The SAT reaction was analyzed using detailed studies of 1H and 31P NMR spectra. Finally, the SAT reactivity pattern was compared with the same in the native enzyme of SOD1.

Constructing Functional Radiation-Resistant Thorium Clusters for Catalytic Redox Reactions.

When catalytic reactions are interfered with by radiation sources, thorium clusters are promising as potential catalysts due to their superior radiation resistance. However, there is currently very little research on the design synthesis and catalytic application of radiation-stable thorium clusters. In this work, we have elaborately engineered and fabricated three high-nuclear thorium cluster catalysts denoted as Th12L3-MA12, Th12L3-MA6-BF6, and Th12L3-Fcc12, which did not undergo any significant alterations in their molecular structures and compositions after irradiation with 690 kGy γ-rays. We systematically investigated the photocatalytic/thermocatalytic properties of these radiation-resistant thorium clusters for the first time and found that γ-rays could not alter their catalytic activities. In addition, it was found that ligand engineering could modulate the catalytic activity of thorium clusters, thus expanding the range of catalytic applications of thorium clusters, including reduction reactions (nitroarene reduction) and some oxidation reactions (N-heterocyclic oxidative dehydrogenation and diphenylmethane oxidation). Meanwhile, all of these organic transformation reactions achieved a >80% conversion and nearly 100% product selectivity. Radiation experiments combined with DFT calculations showed that the synergistic catalysis of thorium-oxo core and ligands led to the generation of specific active species (H+, O2•-, or tBuO/tBuOO•) and activation of substrate molecules, thus achieving superior catalytic performance. This work is not only the first to develop radiation-resistant thorium cluster catalysts to perform efficient redox reactions but also provides design ideas for the construction of high-nuclearity thorium clusters under mild conditions.

Theoretical investigation of the reaction mechanism of THP oxidative rearrangement catalysed by BBOX.

γ-Butyrobetaine hydroxylase (BBOX) is a non-heme FeII/2OG dependent enzyme that is able to perform two different kinds of catalytic reactions on 3-(2,2,2-trimethylhydrazinium) propionate (THP) to produce distinct catalytic products. Although the structure of BBOX complexed with THP has been resolved, the details of its catalytic mechanism are still elusive. In this study, by employing molecular dynamics (MD) simulations and density functional theory (DFT) calculations, the mechanism of the THP oxidative rearrangement reactions catalysed by BBOX was investigated. Our calculations revealed how the enzyme undergoes a conformational conversion to initiate the catalytic reactions. In the first catalytic step, BBOX performs hydrogen abstraction from the substrate THP as a common non-heme iron enzyme. Due to the structure of the substrate stabilizing the radical species and polarizing the adjacent N-N bond, in the next step, THP takes the pathway for N-N bond homolysis but not regular hydroxyl rebounding. The cleaved ammonium radical could either react with the hydroxyl group on the iron centre of the enzyme or recombine with the other cleaved fragment of the substrate to generate the rearranged product. This study revealed the catalytic mechanism of BBOX, detailing how the enzyme and the substrate regulated the hydroxyl rebound process to generate various products.

Highly Active Oxidation Catalysts through Confining Pd Clusters on CeO2 Nano‐Islands

AbstractCeO2‐supported noble metal clusters are attractive catalytic materials for several applications. However, their atomic dispersion under oxidizing reaction conditions often leads to catalyst deactivation. In this study, the noble metal cluster formation threshold is rationally adjusted by using a mixed CeO2‐Al2O3 support. The preferential location of Pd on CeO2 islands leads to a high local surface noble metal concentration and promotes the in situ formation of small Pd clusters at a rather low noble metal loading (0.5 wt %), which are shown to be the active species for CO conversion at low temperatures. As elucidated by complementary in situ/operando techniques, the spatial separation of CeO2 islands on Al2O3 confines the mobility of Pd, preventing the full redispersion or the formation of larger noble metal particles and maintaining a high CO oxidation activity at low temperatures. In a broader perspective, this approach to more efficiently use the noble metal can be transferred to further systems and reactions in heterogeneous catalysis.

Buildup and Consumption of Species in Emulsion Droplets during Aqueous Suzuki Coupling Correlate with Yield.

Fluorescence lifetime imaging microscopy (FLIM) provides spatiotemporal resolution of the changing composition of emulsion droplets during aqueous-surfactant Suzuki coupling. In contrast to previous investigations, the present experiments characterize the full course of a catalytic chemical reaction, addressing key questions about reaction species buildup and correlating these microscale behaviors with bench-scale product yields. At low concentrations of (active) catalyst, droplet environments are stable; however, at higher concentrations, emulsion droplet environments change markedly. These changes are consistent with the buildup and consumption of reaction species inside the droplets. A combination of FLIM and bright-field imaging pinpoints limitations in catalyst solubility as controlling rate and degree of buildup of species in droplets. These solubility limitations are also identified as the cause of a reaction induction period and an origin of the rate-and-reproducibility advantage obtained by adding THF cosolvent. The subsequent mechanistic model from these data led to a bench-scale reaction optimization, wherein premixing the catalyst components bypasses the catalyst induction period, resulting in a faster reaction. The understanding generated by FLIM thus provides an early example of how visualizing changes in droplet compositions on the microscale during ongoing aqueous-organic reactions can be leveraged for enhancing efficiencies in bench-scale reactions.

Crystal phase-driven performance of MnO2 in aqueous phase low-temperature thermal catalysis: Synergistic interactions between Mn3+ and surface lattice oxygen

Catalytic oxidation at mild conditions is crucial for mitigating the high pressure and high temperature challenges associated with current catalytic wet air oxidation (CWAO) technologies in wastewater treatment. Among potential materials for catalytic oxidation reactions, polycrystalline MnO2 existed in natural minerals holds considerable promise. However, the relationships between different crystal phases of MnO2 and their catalytic activity sources in aqueous phase remain uncertain and subject to debate. In this research, we synthesized various MnO2 crystal phases, comprising α-, β-, δ-, γ-, ε-, and λ-MnO2, and assessed their catalytic oxidation efficiency during low-temperature heating for treatment of organic pollutants. Our findings demonstrate that λ-MnO2 exhibits the highest catalytic activity, followed by δ-MnO2, γ-MnO2, α-MnO2, ε-MnO2, and β-MnO2. The variations in catalytic activity among different MnO2 are attributed to variances in their oxygen vacancy abundance and redox activity. Furthermore, we identified the primary active species, which include Mn3+ and superoxide radicals (•O2–) generated by surface lattice oxygen of MnO2. This research highlights the critical role of crystal phases in influencing oxygen vacancy content, redox activity, and overall catalytic performance, providing valuable insights for the rational design of MnO2 catalysts tailored for effective organic pollutant degradation in CWAO applications.

Competitive Valerate Binding Enables RuO2-Mediated Butene Electrosynthesis in Water.

The (non)-Kolbe oxidation of valeric acid, sourced from a hydrolysis product of cellulose, provides a sustainable synthetic route to access value-added products, such as butene. An essential mechanistic step preceding product formation involves the oxidative and decarboxylative cleavage of a C-C bond. Yet, the role of the electrode surface in mediating this oxidative step remains an open question: the electron transfer can occur either via an inner-sphere or outer-sphere mechanism. Here, we report the electrochemical, in situ spectroscopic, computational, and reactivity studies of RuO2-mediated oxidative decarboxylation of valeric acid to butene in aqueous electrolytes. We find that carboxylates bind to RuO2 anode surfaces at potential values where decarboxylation products are observed. Our results are consistent with a reaction scheme where the competitive and catalytic oxygen evolution reaction (OER) is impeded by these bound carboxylate species while these species are inert toward butene formation. Our results implicate an outer-sphere electron transfer mechanism for decarboxylation where the surface chemistry of the RuO2 electrode serves to enable higher non-Kolbe reaction selectivity by suppressing the parasitic OER. Our findings delineate interfacial design principles for selective electrochemical systems that utilize water as the ultimate oxidant for sustainable decarboxylation.

Cascade C-H Activation and Two C-C Bond Forming in Reaction of Azalutetacyclopentadiene with 2-Methylbenzonitriles.

Azametallacyclopentadienes are an important class of metallacycles as the key intermediates in metal-promoted or catalyzed carbon-carbon coupling reaction of nitriles and alkynes. Rare-earth azametallacyclopentadienes have shown unique reactivity toward benzonitriles. The reaction chemistry of azalutetacyclopentadienes toward 2-methylbenzonitriles has been investigated in this work, showing different reactivity. Experimental and computational studies reveal that the reaction selectively initiates with the remote activation of the benzylic C-H bond by the Lu-N bond, followed by the intramolecular nucleophilic attack from the deprotonated benzylic carbon to form a C-C bond. Subsequently, the high ring strain promoted the generation of the uncoordinated carbanion dissociated from the lutetium center, which then undergoes intramolecular nucleophilic attack toward C≡N triple bond to give the final product containing fused 7-5-6-membered azalutetacycle. This work not only achieves highly selective three-step cascade transformation to form a unique class of rare-earth metallacycle, but also reveals a novel reaction pattern of unsaturated substrates with C-H bonds that can be activated.

Ti4+ Ions-Doped Metal-Organic Framework (MOF-74) for Photoreduction of Carbon Dioxide.

The development of efficient and sustainable methods for reducing carbon dioxide (CO2) and converting it into valuable hydrocarbons has gained significant attention. In this study, researchers focused on Ti4+-doped metal-organic framework (MOF-74) photocatalysts. The incorporation of Ti4+ ions into the MOF-74 structure was achieved through a one-pot hydrothermal method. By replacing Zn2+ ions with Ti4+ ions in a substitutional manner, researchers have aimed to enhance the photocatalytic activity of the CO2 reduction. The obtained Ti4+-doped MOF-74 photocatalysts exhibited a significantly improved performance in the reduction of CO2 into carbon monoxide (CO). The doping of Ti4+ ions induced energy bands below the conduction band minimum (CBM) of MOF-74, extending the visible response range and enabling the photocatalysts to utilize a broader spectrum of light for catalytic reactions. This extension of the visible response range enables photocatalysts to utilize a broader spectrum of light for catalytic reactions. The incorporation of Ti4+ ions not only extends the visible response range but also suppresses charge carrier recombination. This work provides valuable insights into the design principles of MOF-based photocatalysts and paves the way for their practical implementation in addressing the energy crisis and reducing greenhouse gas emissions.

Mechanistic Implications of the Varying Susceptibility of PAHs to Pyro-Catalytic Treatment as a Function of Their Ionization Potential and Hydrophobicity.

Transition metal catalysts in soil constituents (e.g., clays) can significantly decrease the pyrolytic treatment temperature and energy requirements for efficient removal of polycyclic aromatic hydrocarbons (PAHs) and, thus, lead to more sustainable remediation of contaminated soils. However, the catalytic mechanism and its rate-limiting steps are not fully understood. Here, we show that PAHs with lower ionization potential (IP) are more easily removed by pyro-catalytic treatment when deposited onto Fe-enriched bentonite (1.8% wt. ion-exchanged content). We used four PAHs with decreasing IP: naphthalene > pyrene > benz(a)anthracene > benzo(g,h,i)perylene. Density functional theory (DFT) calculations showed that lower IP results in stronger PAH adsorption to Fe(III) sites and easier transfer of π-bond electrons from the aromatic ring to Fe(III) at the onset of pyrolysis. We postulate that the formation of aromatic radicals via this direct electron transfer (DET) mechanism is the initiation step of a cascade of aromatic polymerization reactions that eventually convert PAHs to a non-toxic and fertility-preserving char, as we demonstrated earlier. However, IP is inversely correlated with PAH hydrophobicity (log Kow), which may limit access to the Fe(III) catalytic sites (and thus DET) if it increases PAH sorption to soil OM. Thus, ensuring adequate contact between sorbed PAHs and the catalytic reaction centers represents an engineering challenge to achieve faster remediation with a lower carbon footprint via pyro-catalytic treatment.

Hierarchical Carbon Nanocages as Superior Supports for Photothermal CO2 Catalysis.

The exploitation of hierarchical carbon nanocages with superior light-to-heat conversion efficiency, together with their distinct structural, morphological, and electronic properties, in photothermal applications could provide effective solutions to long-standing challenges in diverse areas. Here, we demonstrate the discovery of pristine and nitrogen-doped hierarchical carbon nanocages as superior supports for highly loaded, small-sized Ru particles toward enhanced photothermal CO2 catalysis. A record CO production rate of 3.1 mol·gRu-1·h-1 with above 90% selectivity in flow reactors was reached for hierarchical nitrogen-doped carbon-nanocage-supported Ru clusters under 2.4 W·cm-2 illumination without external heating. Detailed studies reveal that the enhanced performance originates from the strong broadband sunlight absorption and efficient light-to-heat conversion of nanocage supports as well as the excellent intrinsic catalytic reactivity of sub-2 nm Ru particles. Our study reveals the great potential of hierarchical carbon nanocages in photothermal catalysis to reduce the fossil fuel consumption of various industrial chemical processes and stimulates interest in their exploitation for other demanding photothermal applications.

Highly Efficient Carbonylation of Propylene Oxide into β‐Butyrolactone Catalyzed over Co‐Al Bimetallic Species

Rational designation of the catalyst for efficient atom‐economic conversion of propylene oxide (PO) and carbon monoxide (CO) into β‐butyrolactone is of current significance. By employing the O,N,O‐tridentate ligands R1,R2LH2 (1‐4), the aluminium compounds (R1,R2LAlCl)2 (R1,R2 = H,H (5), tBu,tBu (6), Cl,Cl (7), Br,Br (8)) and the derived anion‐cation pairs [H,HLAl(THF)3]+[Co(CO)4]ˉ (9) and [(R1,R2LAl)2Cl(THF)2]+[Co(CO)4]ˉ (R1,R2 = tBu,tBu (10), Cl,Cl (11), Br,Br (12)) as well as the aluminium‐cobalt bimetallic cluster compounds [(R1,R2LAl)2Cl(THF)][Co3(CO)10] (R1,R2 = tBu,tBu (13), Cl,Cl (14), Br,Br (15)) were prepared. Compounds 9‐12 efficiently catalyzed the PO carbonylation into β‐butyrolactone to achieve up 93.4‐98.9% yields while 13‐15 gained 95.2‐99.0% yields all at 25 °C and 0.1 MPa CO pressure. The Lewis acidic property of the aluminium compounds 5‐8 was investigated. The kinetic of the catalytic reaction using compound 10 was studied. The cooperatively catalytic reaction mechanism by the Co‐Al bimetallic species is proposed.

Strong Interaction between Molybdenum Compounds and Mesoporous CMK‐5 Supports Boosts Hydrogen Evolution Reaction

AbstractStrong metal‐support interaction (SMSI) between transition metal nanoparticles and carbon matrix offers significant structure advantages due to the ability to modulate the electronic structure of metal nanoparticles, increase the density of active sites, and improve the conductivity of catalysts. Here, ultrafine nanoparticles of metallic molybdenum compounds (MoP, Mo2C, and MoS2) strongly coupled with mesoporous carbon CMK‐5 are synthesized. The confinement growth of nanoparticles in the pores of CMK‐5 produces encapsulated nanoparticles, affording facilitated electron transfer, and enhancing the HER activity induced by the SMSI effect. The hierarchical nanostructure and strong electronic interactions between the carbon substrate and molybdenum‐based nanoparticles allow efficient mass/electron transport between the carbon substrate and molybdenum‐based nanoparticles, improving the catalytic hydrogen evolution reaction (HER) activity. The effective electron exchange between the Mo species and the CMK‐5 support is studied by X‐ray photoelectron spectroscopy (XPS) measurement, confirming the presence of the SMSI effect. The resulting MoP/CMK‐5 catalyst exhibits outstanding HER performance in alkaline (65 mV@10 mA cm−2), acidic (123 mV@10 mA cm−2), and simulated seawater electrolytes (103 mV@10 mA cm−2), making it one of the most promising catalysts reported for HER. This work provides guidance on designing high‐performance electrocatalysts with SMSI for the enhancement of the electrochemical reaction.

Electro-acidic catalytic cascade reactions for the efficient and highly selective synthesis of oxygen heterocyclic compounds from ethylene glycol

Electro-acidic catalytic cascade reactions for the efficient and highly selective synthesis of oxygen heterocyclic compounds from ethylene glycol

Transition‐Metal Catalyzed Enantioselective Aziridination Reaction: Recent Development in Catalysis and Future Perspectives

Chiral aziridines are important motifs in natural products and biologically significant compounds, as well as one of the most valuable and versatile building blocks for the construction of diverse chiral functionalized amines. Because of the importance of chiral aziridines, various novel transition‐metal‐based catalytic systems and synthetic strategies have been established to investigate the highly effective and enantioselective aziridination process. This review outlined the recent significant advances made in the transition‐metal catalyzed enantioselective aziridination reactions, as well as the challenges and potential of the field at the current stage.

Cu-alginate hydrogels in microfluidic systems: a sustainable catalytic approach for click chemistry

This work explores the innovative use of copper-alginate (Cu-alginate) hydrogels within microfluidic systems to catalyze dipolar cycloaddition reactions, emphasizing green chemistry principles and process intensification. Utilizing naturally occurring biopolymers, such as alginates, provides an environmentally friendly alternative to conventional catalyst supports due to their biocompatibility, biodegradability, and effective metal ion immobilization capabilities. The integration of these biopolymer-based catalysts into microfluidic devices allows for precise control over reaction conditions, leading to enhanced reaction kinetics and mass transfer efficiencies. Our results demonstrate that Cu-alginate hydrogels effectively catalyze the formation of 1,4-disubstituted 1,2,3-triazoles through [3 + 2] dipolar cycloaddition reactions with high regioselectivity and conversion. The microfluidic setup ensures rapid and efficient synthesis, surpassing traditional batch reaction methods in both reaction rate and environmental impact by reducing solvent usage and waste generation. Furthermore, the use of microfluidics contributes to the reproducibility and scalability of the synthesis process, important for industrial applications. The model-based design and its simulations have been employed to further understand and optimize the reaction system. Diffusion through the gel layer and catalytic reaction kinetics estimated from experimental data were included in the model, providing a theoretical foundation for a comprehensive process evaluation. This study not only advances the field of sustainable catalysis by demonstrating the practical utility of biopolymer-supported catalysts in microfluidic systems, but also sets the stage for further research into biopolymer applications in complex chemical syntheses.

Zr‐MOF nanosheets featuring benzothiadiazoles enable efficient visible light driven photooxidation of sulfides and amines

Ultrathin zirconium‐based metal–organic framework (MOF) nanosheets, embedded with photochromic units, are expected to be highly efficient heterogeneous photocatalysts, thanks to their rich catalytic sites, short diffusion paths, and effective separation of photogenerated charge carriers. Herein, we reported the synthesis of novel Zr‐MOF nanosheets (Zr‐BTDB) through a solvothermal synthesis that integrates benzothiadiazole (BTz) as a photochromic moiety within the framework of MOF. The Zr‐BTDB nanosheets processes a [Zr12(μ3‐O)8(μ3‐OH)8(μ2‐OH)6] cluster with hcp topology. Importantly, Zr‐BTDB nanosheets exhibit excellent photocatalytic activity for the photooxidation of sulfides and amines at room temperature under blue light irradiation. Notably, these nanosheets maintain their photocatalytic activity and selectivity for up to five cycles without significant loss of activity and crystallinity. Systematical catalytic reactions revealed that the Zr‐BTDB nanosheets enable the generation of singlet oxygen (1O2) and superoxide radical (O2•–) under visible light irradiation, which is critical reactive oxygen species for the photooxidation of sulfides and benzylamines. Our work represents a straightforward route for the preparation of ultrathin, water stable, and visible‐light‐activated Zr‐MOF nanosheets, offering new potentials for the selective photooxidation of sulfides and amines in an eco‐friendly way.

Study on the Effects of Fe Doping on C‐ZFe Catalyst for Catalytic Removal of NO from the Low‐Temperature Flue Gas

AbstractThe denitrification efficiency of carbon‐based zero valent iron catalyst (C‐ZFe) for low‐temperature selective catalytic reduction (SCR) (<140°C) highly depends on the structural species of iron oxide (FexOy) and the physicochemical properties of the catalyst. In the study, we investigated the main factors affecting the low‐temperature denitrification efficiency of C‐ZFe such as temperature, iron content and O2. The results showed that the average NOX conversion was 72.6 % at 135°C when the space velocity was 459 h−1 and the mass ratio of carbon to iron was 15 % to 85 %. The surface morphology and structure of C‐ZFe were characterized by the surface area and pore size distribution measurements, X‐ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and X‐ray photoelectron spectroscopy (XPS). The results indicated that the iron on the catalyst surface was oxidized by O2 to Fe2O3, which could retain NO and then formed intermediate products. NO entered the mesoporous structure along C‐ZFe surface and proceeded a catalytic reduction reaction with the adjacent carbon.

Ready, Set, Grow: From Micelles to Giant Vesicles via Biocatalytic Activation.

Controlling physicochemical processes that drive changes in supramolecular aggregates is an important objective toward creating artificial soft micro- and nanomachines. Previous research explored the morphology control of membrane-based materials subjected to externally imposed chemical stimuli. Here, we modulate the microscale morphology of pH-responsive assemblies by using biocatalysis to internally generate changes in global pH. Catalytic reactions offer flexibility in the mechanism and rate at which stimuli are introduced to responsive assemblies, ultimately enabling precision and control over size and morphology. We observed, by dynamic light scattering and fluorescence microscopy, substantial microscale differences between assemblies subjected to manually titrated pH changes compared to biocatalytically activated pH changes, including the growth of giant vesicles from micelles. Coarse-grained molecular dynamics simulations of these metastable self-assembled structures provided insight into the thermodynamics and kinetics of the preferred structures. These results demonstrate the feasibility of using biocatalytic reactions to modulate the size and morphology of supramolecular assemblies, from micelles to giant vesicles.

Ir(triNHC)‐Catalyzed Upcycling of Waste PET for Lactic Acid Production with Sustainable Isolation via Bipolar Membrane Electrodialysis

AbstractFor the upcycling of waste polyethylene terephthalate (PET), encompassing both colored and fabric PET materials, we investigated the Ir(triNHC)‐catalyzed dehydrogenative coupling of PET and methanol, leading to the production of sodium lactate with good yields. We proposed a sustainable method for isolating lactic acid from the catalytic reaction mixture of sodium lactate and regenerating the base using bipolar membrane electrodialysis (BMED). This isolation method demonstrated high effectiveness, achieving isolation of lactic acid while maintaining economic feasibility at $ 0.10 per kg of lactic acid, and enabling sustainable NaOH regeneration with complete resource circulation. We assessed the recyclability of the catalyst and elucidated the mechanism involving base‐mediated depolymerization and catalyst‐promoted dehydrogenation, highlighting the importance of triNHC ligands in enhancing catalytic activity.