Catalytic System Research Articles

Highly efficient photoenzymatic CO2 reduction dominated by 2D/2D MXene/C3N5 heterostructured artificial photosynthesis platform

Photoenzyme-coupled catalytic systems offer a promising avenue for selectively converting CO2 into high-value chemicals or fuels. However, two key challenges currently hinder their widespread application: the heavy reliance on the costly coenzyme NADH, and the necessity for metal-electron mediators or photosensitizers to address sluggish reaction kinetics. Herein, we present a robust 2D/2D MXene/C3N5 heterostructured artificial photosynthesis platform for in situ NADH regeneration and photoenzyme synergistic CO2 conversion to HCOOH. The efficiencies of utilizing and transmitting photogenerated charges are significantly enhanced by the abundant π-π conjugation electrons and well-engineered 2D/2D hetero-interfaces. Noteworthy is the achievement of nearly 100 % NADH regeneration efficiency within just 2.5 h by 5 % Ti3C2/C3N5 without electron mediators, and an impressive HCOOH production rate of 3.51 mmol g−1h−1 with nearly 100 % selectivity. This study represents a significant advancement in attaining the highest NADH yield without electron mediator and provides valuable insights into the development of superior 2D/2D heterojunctions for CO2 conversion.

Efficient 2,3-Butanediol Production from Ethanol by a Modified Four-Enzyme Synthetic Biosystem.

2,3-butanediol (2,3-BD) is a versatile bio-based platform chemical. An artificial four-enzyme synthetic biosystem composed of ethanol dehydrogenase, NADH oxidase, formolase and 2,3-butanediol dehydrogenase was designed for upgrading ethanol to 2,3-BD in our previous study. However, a key challenge in developing in vitro enzymatic systems for 2,3-BD synthesis is the relatively sluggish catalytic efficiency of formolase, which catalyzes the rate-limiting step in such systems. Herein, this study reports how engineering the tunnel and substrate binding pocket of FLS improved its catalytic performance. A series of single-point and combinatorial variants were successfully obtained which displayed both higher catalytic efficiency and better substrate tolerance than wild-type FLS. Subsequently, a cell-free biosystem based on the FLS:I28V/L482E enzyme was implemented for upgrading ethanol to 2,3-BD. Ultimately, this system achieved efficient production of 2,3-BD from ethanol by the fed-batch method, reaching a concentration of 1.39 M (124.83 g/L) of the product and providing both excellent productivity and yield values of 5.94 g/L/h and 92.7%, respectively. Taken together, this modified enzymatic catalysis system provides a highly promising alternative approach for sustainable and cost-competitive production of 2,3-BD.

Copper‐Catalyzed Regiodivergent Asymmetric Difunctionalization of Terminal Alkynes

AbstractWe herein describe the first example of ligand‐controlled, copper‐catalyzed regiodivergent asymmetric difunctionalization of terminal alkynes through a cascade hydroboration and hydroallylation process. The catalytic system, consisting of (R)‐DTBM‐Segphos and CuBr, could efficiently achieve asymmetric 1,1‐difunctionalization of aryl terminal alkynes, while ligand switching to (S,S)‐Ph‐BPE could result in asymmetric 1,2‐difunctionalization exclusively. In addition, alkyl substituted terminal alkynes, especially industrially relevant acetylene and propyne, were also valid feedstocks for asymmetric 1,1‐difunctionalization. This protocol is characterized by good functional group tolerance, a broad scope of substrates (>150 examples), and mild reaction conditions. We also showcase the value of this method in the late‐stage functionalization of complicated bioactive molecules and simplifying the synthetic routes toward the key intermediacy of natural product (bruguierol A). Mechanistic studies combined with DFT calculations provide insight into the mechanism and origins of this ligand‐controlled regio‐ and stereoselectivity.

A green approach to synthesize polybutene lubricants from mixed C4 monomers using supported dendritic ionic liquids

Lubricants, composed of a base oil and various additives, reduce friction and abrasion between moving surfaces. High-performance lubricants, especially in the automotive and space industries, have driven advancements in synthetic oils like polyalphaolefins (PAOs), known for their high viscosity index and stability. Low molecular weight polyisobutylenes (PIBs) are used in multiple applications, including as viscosity improvers. PIBs are produced via cationic polymerization of isobutylene using Lewis acid initiators and co-initiators, often conducted at low temperatures with harmful substances like BF3. Efforts are being made to develop more eco-friendly processes, such as using AlCl3 and ionic liquids (ILs). In this research, boehmite-supported dendritic ILs (Gen1 and Gen2) were synthesized and tested as co-initiators in Raffinate-1 polymerization. The ILs improved the stability of the catalytic system, allowing for reduced AlCl3 usage, and produced PIBs with desirable molecular weight and viscosity characteristics. Density Functional Theory calculations unveiled the importance of the interaction of AlCl3 with the ionic liquids.

Synergistically Photocatalytic Conversion of Two Greenhouse Gases to Liquid‐Phase Oxygenates under Anaerobic Conditions

Collaborative conversion of methane and carbon dioxide into sustainable chemicals is an appealing solution to simultaneously overcome both environmental problems and energy crisis. However, this reaction is limited to the preparation of syngas with the unfavorable feature for transportation and storage. Herein, liquid formaldehyde as product is fabricated by the collaborative conversion of methane and carbon dioxide using anatase phase titanium dioxide as photocatalyst. The productivity reaches 14.65 mmol g−1 with 88.32% selectivity. In situ diffuse reflectance Fourier transform infrared spectroscopy, isotope testes, and theoretical calculation clarify that the photoexcited holes and electrons engage into methane oxidation and carbon dioxide reduction over anatase using surface hydroxyl species and oxygen vacancy as active sites, respectively. The consumption of surface hydroxyl species on methane oxidation promotes the oxygen vacancy formation for carbon dioxide adsorption, mutually the carbon dioxide provides the oxygen atom for surface hydroxyl species facilitating methane oxidation. The consumption of photoelectrons and photoholes on carbon dioxide reduction and methane oxidation balances the number of photogenerated carriers and ensures the catalytic system stability. In this work, the avenue is broadened toward the co‐conversion of greenhouse gas into desirable chemical products in a sustainable way.

Visible light induced cooperative catalysis by 4CzIPN and Mg(NO3)2·6H2O to furnish C-P functionalization of alkenes and indoles

Carbon-carbon or carbon-heteroatom bond formation from simple substrates using photoredox-Lewis acid dual catalytic systems is an intriguing area of research. Herein, an expedient photocatalytic strategy for selective C-P bond formation by employing 4CzIPN-Mg(NO3)2·6H2O mediated cooperative catalysis is reported. Following this versatile protocol, various organo-phosphorus compounds like phosphorylated oxindoles, malononitriles, malonates, coumarin esters, and indoles were effectively synthesized. This visible-light-promoted transition-metal-free method originated from the synergistic interaction of 4CzIPN-Mg(NO3)2·6H2O and substrates. Control experiments and other mechanistic studies were carried out to understand this cooperative photocatalytic process.

Synergistic scavenging of sulfamethoxazole and hexavalent chromium in groundwater sample induced by iron-char composites activated persulfate triggering dominant electron transfer process

Effectively scavenging combined pollutants in complex water matrix via dominant electron transfer pathway using modified zero-valent iron (ZVI) remains challenging. Herein, novel iron-based catalysts were synthesized using ball milling and pre-oxidation modified biochar (MOBC), which featured abundant pore structure and oxygen-rich functional moieties to support nZVI in activating persulfate (PS). The most suitable catalytic system achieved ultrafast simultaneous removal of 89.0 % of sulfamethoxazole (SMX) and nearly 100 % of hexavalent chromium (Cr(VI)) within 5 min (with nearly complete removal of SMZ and Cr(VI) in 60 min). By serving as an electron shuttle, MOBC700 could accelerate electron transfer from SMX to PS adsorbed on the nZVI1.0@MOBC700 for SMX decomposition, with reactive oxygen species (ROSs) also contributing. Moreover, nZVI facilitated the reduction of Cr(VI) adsorbed on nZVI1.0@MOBC700 through electron transfer. The dissolved Fe(II) generated via PS activation and Cr(VI) reduction further facilitated Cr(VI) removal from the solution, while the gradual consumption of excess Fe(II) ensured continued ROSs-mediated degradation of SMX. Additionally, the system also demonstrated resistance to interference from NO3-, CO32-, and humic acid, and was effective in remediating four different water samples. Overall, this study presents a promising method for designing iron-char composites to address combined antibiotic and heavy metal contamination in groundwater samples via dominant electron transfer process.

Benzoquinone Ligand-Enabled Ruthenium-Catalyzed Deaminative Coupling of 2-Aminoaryl Aldehydes and Ketones with Branched Amines for Regioselective Synthesis of Quinoline Derivatives.

The catalytic system generated in situ from the cationic Ru-H complex [(C6H6)(PCy3)(CO)RuH]+BF4- (1) with 2,3,4,5-tetrachloro-1,2-benzoquinone (L1) was found to be highly effective for promoting the deaminative coupling reaction of 2-aminoaryl aldehydes with branched amines to form 2-substituted quinoline products. The analogous deaminative coupling reaction of 2-aminoaryl ketones with branched amines led to the regioselective formation of 2,4-disubstituted quinoline products. A number of biologically active quinoline derivatives including graveolinine and a triplex DNA intercalator have been synthesized by using the catalytic method.

Synergistic Photoredox/Palladium Catalyzed Enantioconvergent Carboxylation of Racemic Heterobiaryl (Pseudo)Halides with CO2.

Herein, we report a synergistic photoredox/palladium catalytic system for the efficient enantioconvergent synthesis of axially chiral esters from racemic heterobiaryl (pseudo)halides (bromides/triflates) with CO2 and alkyl bromides under mild conditions. A wide range of axially chiral esters were obtained in good to high yields with excellent enantioselectivities. Detailed mechanistic studies unveiled that the ratio of photocatalyst and palladium catalyst exhibited significant impact on the chemo- and enantioselectivities of the reaction. Kinetic studies and control experiments supported the proposed mechanism involving cascade asymmetric carboxylation followed by SN2 substitution. The achievement of high enantioselectivity relies not only on the choice of synergistic metallaphotoredox catalysts but also on the utilization of alkyl bromides, which trap the generated chiral carboxylic anions in situ, thus preventing their immediate racemization.

Role of non-redox innocent ligand units in the oxidation of alcohols with H2O2 catalyzed by μ-oxido-diiron(III) bis-phenolato polypyridyl complexes

Redox non-innocent ligands hold the potential to expand the redox chemistry and activity of transition metal catalysts. The impact of the additional redox chemistry of phenol ligands in oxidation catalysis is explored here in the complex μ-oxido-diiron(III) polypyridyl (1) [(L)Fe(III)(μ–O)Fe(III)(L)](ClO4)2 (where HL is 2-(((di(pyridin-2-yl)methyl) (pyridin-2-ylmethyl) amino)methyl)phenol) and its tert-butyl substituted analog 2, in which each of the Fe(III) centers is coordinated to a phenolato moiety of the ligand. Complex 1 was shown earlier to catalyse the oxidation of benzyl alcohols to aldehydes with H2O2. In particular acid was found to accelerate the reactions by removal of a lag period before catalysis initiated. Here, we use reaction monitoring with resonance Raman, UV/vis absorption and EPR spectroscopy to show that under catalytic conditions, i.e. with excess H2O2, rapid (< 5 s) loss of the phenolato moiety occurs, resulting in the formation of an N4 ligated Fe(III) complex. This N4 coordinated complex forms a Fe(III)-OOH species, which is responsible for alcohol oxidation and over time a relatively stable oxido-bridged dinuclear Fe(III) complex forms as a resting state in the catalytic system. The main role of acid in the catalysis is shown to be to facilitate the initial coordination of H2O2 by driving the formation of mononuclear complexes from 1 and 2. The data show that although the phenolato moiety imparts interesting redox properties on complex 1, it does not contribute directly to the oxidation catalysis observed with H2O2.

Enhanced catalytic performance for aerobic dehydrogenation of N-heterocycles over bimetallic CoOX-CeO2 catalysts derived from Ce-based MOFs

N-heteroaromatics as one of cornerstones in chemical processes are in the limelight, so the synthesis of N-heteroaromatics have been attracted a great deal of attention. Among the elegant methods for the preparation of N-heteroaromatics, the direct oxidative dehydrogenation of saturated compounds affording N-heteroaromatics is a simple and efficient tactic. In this work, CoOX-CeO2 composites synthesized by the pyrolysis of Co/Ce-BTC MOFs as the precursor were employed as a heterogeneous catalyst for the dehydrogenation of N-heterocycles under aerobic conditions. CoOX-CeO2 composites were analyzed by diversified characterization techniques of SEM, TEM, BET, XRD, XPS, and ICP-OES. The characterization results demonstrate that abundant oxygen vacancies on the surface and the synergistic effect of CoOX-CeO2 composites remarkably enhance the catalytic performance of CoOX-CeO2 catalysts. Furthermore, the catalytic performance of CoOX-CeO2 composites remained excellent after six recycles. This catalytic system provides an alternative tool for the effective synthesis of aromatic compounds.

Partial substitution of rhodium with ruthenium in Pd-Rh nanoalloys and its impact on catalytic characteristics

In the present work, alumina-supported trimetallic Pd-Rh-Ru catalysts were synthesized and studied in comparison with the bimetallic Pd-Rh reference sample. The alloy nanoparticles were formed on the surface of the alumina support by thermolysis of the complex salts [Rh(NH3)5Cl][Pd(NO2)4] and [Rh(NH3)5Cl]0.5[Ru(NH3)5Cl]0.5[Pd(NO2)4], preliminary deposited via an incipient wet impregnation method. The influence of the conditions of the thermolysis process on the phase composition of the final products and the size of the trimetallic particles was established. Thus, nanoscale trimetallic (Rh-Ru-Pd) alloy particles of a given composition were obtained. The catalytic performance of the alumina-supported samples was examined in a CO oxidation reaction under prompt thermal aging conditions. It was ascertained that the addition of ruthenium only improves both the initial activity and thermal stability of the catalytic system. The state of each metal in the alloy nanoparticles was characterized by diffuse reflectance UV–vis spectroscopy and X-ray photoelectron spectroscopy.

(Semi)hydrogenation of enoates and alkynes effected by a versatile, particulate copper catalyst

We communicate a versatile and user-friendly Cu-based catalytic method that allows for the selective hydrogenation of enoates and alkynes. The introduced protocol is free from any ex ante modifications of the used Cu(I) precursors by air-sensitive phosphines or elaborate N-heterocyclic carbene ligands. The conjugate hydrogenation of enoates and the (selective) reduction of CC bonds is achieved through a [Cu(CH3CN)4]+/tert-butoxide pair whereby we describe a delicate influence of the base cation on the chemoselectivity of the respective transformation. In case of the ester-to-alcohol reduction, a combination of simple CuI and NaOtBu proved to be successful. Deuteration experiments are included to address certain mechanistic aspects of the introduced catalytic system. All requisite chemicals are readily obtainable through commercial channels and the catalyst assembly is set up on the bench without the need for special lab-technical precautions.

Co‐W (Hydr)oxide with Ultralow Ru Promotes Water Dissociation Coupled H+ Abstraction in Alkaline HER

The hydrogen evolution reaction in alkaline water electrolysis is facilitated through the electrodeposition of trimetallic catalyst on nickel foam using the chronoamperometry technique. Specifically, the trimetallic catalyst CoWRu@NF is deposited onto a nickel foam substrate. The catalytic performance of this trimetallic catalytic electrode for the Hydrogen Evolution Reaction (HER) is then assessed in a 1.0 M potassium hydroxide (KOH) solution. This specially designed trimetallic catalytic electrode system efficiently provides the more active sites through the Co component. Subsequently, it facilitates the reduction of protons (H+) to generate hydrogen gas using the Ru component. Tungsten acts as a co‐catalyst in the system for water dissociation promotor by removing hydroxide formed after water dissociation and preventing the deactivation of Ruthenium by certain reaction intermediates. The CoWRu@NF trimetallic catalyst demonstrates excellent activity, showcasing a low overpotential (‐8 mV) to achieve a current density of ‐10 mA/cm2. Additionally, it exhibits low Tafel slope values (101.2 mV dec‐1), credited to the presence of cobalt and tungsten alongside Ruthenium in the catalytic system. This configuration is specifically designed to enhance the kinetics of the hydrogen‐evolving reaction.

Full Selectivity Control over the Catalytic Hydrogenation of Nitroaromatics Into Six Products

AbstractA full selectivity control over the catalytic hydrogenation of nitroaromatics leads to the production of six possible products, i.e., nitroso, hydroxylamine, azoxy, azo, hydrazo or aniline compounds, which has however not been achieved in the field of heterogeneous catalysis. Currently, there is no sufficient evidence to support that the catalytic hydrogenation of nitroaromatics with the use of heterogeneous metal catalysts would follow the Haber's mechanistic scheme based on electrochemical reduction. We now demonstrate in this work that it is possible to fully control the catalytic hydrogenation of nitroaromatics into their all six products using a single catalytic system under various conditions. Employing SnO2‐supported Pt nanoparticles facilitated by the surface coordination of ethylenediamine and vanadium species enabled this unprecedented selectivity control. Through systematic investigation into the controlled production of all products and their chemical reactivities, we have constructed a detailed reaction network for the catalytic hydrogenation of nitroaromatics. Crucially, using oxygen‐isolated characterization techniques is essential for identifying unstable compounds such as nitroso, hydroxylamine, hydrazo compounds. The insights gained from this research offer invaluable guidance for selectively transforming nitroaromatics into a wide array of functional N‐containing compounds, both advancing fundamental understanding and fostering practical applications in various fields.

Variable valence I3−/I− ionic bridge assisting CuI nanoparticle/BiOI nanosheet S-scheme photocatalyst with hydrophobic surface for boosting CO2 conversion with 100 % CO selectivity

The photocatalyst film, composed of tetragonal BiOI nanosheets and cubic phase CuI nanoparticles, was synthesized on the FTO substrate by a simple electro-deposition method. The orderly crisscrossed nanosheet structure caused exterior hydrophobic property, resisting the excess H2O molecules and further inhibiting the competitive H2O reduction process. The novel BiOI/CuI catalyst exhibited excellent photocatalytic ability of CO2 reduction into CO with 100 % selectivity in H2O vapor. Typically, the optimal 150BiOI/CuI photocatalyst exhibited CO yield of 7237.65 μmol/cm2 after 11 h of simulated sunlight illumination, achieving quantum efficiency of 2.5 % at 380 nm. The excellent performance of the BiOI/CuI composite film in photocatalytic CO2 reduction can be attributed to the construction of hydrophobic surface and S-scheme heterojunction with I3−/I− redox mediator, as confirmed by the in-situ XPS, hole injection test and cyclic voltammetry results. This study lays the groundwork for employing highly efficient iodide-based photocatalysts in gas-liquid-solid triphase catalytic systems.

General Defluoroalkylation of Trifluoromethylarenes with Both Electron-Donating and -Withdrawing Alkenes.

The incorporation of gem-difluoromethylene units into organic molecules remains a formidable challenge. Conventional methodologies for constructing aryldifluoromethyl derivatives relied on the use of high-functional fluorinating regents under harsh conditions. Herein, we report general and efficient photoredox catalytic systems for defluoroalkylation of readily available trifluoromethylarenes through selective C-F cleavage to deliver gem-difluoromethyl radicals which proceed through reductive addition to both electron-donating and withdrawing alkenes under transition-metal free conditions. Mechanistic studies reveal that thiol serves as both photocatalyst and HAT reagent under visible light irradiation. This synergistic photocatalysis and HAT catalysis protocol exhibits ample and salient features such as high chemo- and regioselectivity, broad substrate scope, amenable gram-scale synthesis and late-stage modification of bioactive molecules.

Kinetic investigation of aschalcha heavy oil oxidation in the presence of cobalt biocatalysts during in-situ combustion

The catalytic effect of cobalt tall oil and cobalt sunflower oil catalysts on the oxidation kinetics of heavy crude oil was investigated in this study. Comprehensive kinetic analyses, employing differential scanning calorimetry, thermogravimetric analysis, and kinetic modeling techniques, revealed that the presence of these catalysts significantly influenced the oxidation behavior of heavy oil. The catalysts exhibited pronounced shifts in the DSC and TG curves towards lower temperatures, indicating facilitated initiation of oxidation reactions at lower onset temperatures. Quantitative kinetic parameters, including activation energies and frequency factors, were determined using the Friedman and Kissinger-Akahira-Sunose analyses. The cobalt tall oil catalyst demonstrated superior performance, effectively lowering the activation energy barrier and increasing oxidation rates, particularly at higher conversion degrees. Catalyst characterization techniques, including X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy, revealed the formation of highly crystalline cobalt oxide nanoparticles with optimal dispersion and size distribution, as well as the presence of favorable functional groups for surface interactions. The results elucidated the role of these catalysts in facilitating the oxidation process through the provision of active sites, altered reaction pathways, favorable steric environments, and efficient oxygen activation capabilities. These findings contribute to the development of efficient catalytic systems for heavy oil upgrading processes and offer insights for further optimization of catalyst properties to achieve desired oxidation kinetics behavior.

Full Selectivity Control over the Catalytic Hydrogenation of Nitroaromatics Into Six Products.

A full selectivity control over the catalytic hydrogenation of nitroaromatics leads to the production of six possible products, i.e., nitroso, hydroxylamine, azoxy, azo, hydrazo or aniline compounds, which has however not been achieved in the field of heterogeneous catalysis. Currently, there is no sufficient evidence to support that the catalytic hydrogenation of nitroaromatics with the use of heterogeneous metal catalysts would follow the Haber's mechanistic scheme based on electrochemical reduction. We now demonstrate in this work that it is possible to fully control the catalytic hydrogenation of nitroaromatics into their all six products using a single catalytic system under various conditions. Employing SnO2-supported Pt nanoparticles facilitated by the surface coordination of ethylenediamine and vanadium species enabled this unprecedented selectivity control. Through systematic investigation into the controlled production of all products and their chemical reactivities, we have constructed a detailed reaction network for the catalytic hydrogenation of nitroaromatics. Crucially, using oxygen-isolated characterization techniques is essential for identifying unstable compounds such as nitroso, hydroxylamine, hydrazo compounds. The insights gained from this research offer invaluable guidance for selectively transforming nitroaromatics into a wide array of functional N-containing compounds, both advancing fundamental understanding and fostering practical applications in various fields.

Ceria nanocatalyst-supported oxidative organic transformations of aromatic alcohols and p-nitrotoluene

Hydrothermally derived nanocubes of CeO2(10 nm) were explored as an efficient heterogeneous catalyst in the partial oxidation of aromatic alcohols to the corresponding aldehydes and aerobic oxidation ofp-nitrotoluene top-nitrobenzoic acid. The CeO2nanocatalyst was characterized by x-ray diffraction, transmission electron microscopy (TEM), energy dispersive spectroscopy, x-ray photoelectron spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis, Fourier transform infrared spectroscopy, thermal gravimetric analysis and ultraviolet-visible spectroscopy. TEM/high-resolution TEM micrographs reveal a morphology of mostly cubic nanostructures with exposed highly active {100} and {110} facets. The surface area of nanoceria was determined by BET analysis and found to be 33.8 m2g-1. To demonstrate the universality of the catalytic system, the selective oxidation of different substrates of benzylic alcohol and complete oxidation ofp-nitrotoluene was investigated under mild conditions. Absolute selectivity towards their respective aldehydes was found to be 99.50% (benzaldehyde), 90.18% (p-chlorobenzaldehyde), 99.71% (p-nitrobenzaldehyde), 98.10% (p-fluorobenzaldehyde), 94.66% (p-anisaldehyde) and 86.14% (cinnamaldehyde). Moreover, the catalytic oxidative transformation of nitrotoluene results in 100% conversion with 99.29% selectivity towards nitrobenzoic acid.