Catalytic Conditions Research Articles

(Invited) In Situ X-Ray Spectroscopy for Clean Energy: Insights into Reactive Intermediates

Transition from fossil fuels requires increased use of solar energy and electrification of chemical industries. To store the excess green electricity from wind and solar generation, batteries and electrolyzers are needed. Green hydrogen can also be produced via artificial photosynthesis where water is split by energy input of sunlight. Hydrogen can be later used in fuel cells. All these applications require new, electrochemically active materials and catalysts. To boost applications in energy storage and conversion, materials with exotic redox states are often desirable. X-ray spectroscopy is an excellent tool for in situ analysis of such energy storage and conversion systems in situ under working conditions.In presentation I will discuss characterization of exotic Mn1+ proposed to play a role in the function of sodium-based Prussian blue analogues (PBA) batteries, a highly sought-out technology for industrial energy storage. Here, we report the detailed electronic structure characterization of uncharged and charged sodium-based manganese hexacyanomanganate anodes via Mn K-edge X-ray absorption spectroscopy (XAS), Kβ nonresonant X-ray emission (XES), and resonant inelastic X-ray scattering (RIXS).For electrochemical and photoelectrochemical water oxidation high oxidation states of IrV, RuV and FeV are needed to activate water and form O-O bond. These species were generated in situ under catalytic conditions and characterized by hard X-ray XAS. Active catalyst such as [Ru(H3-Tpy)(Qc)Cl] was assembled into MIL-142 metal organic framework to produce device prototype for artificial photosynthesis. It delivered high photocurrent in the photo-electrocatalytic water splitting at pH=1 and unassisted photocatalytic H2 evolution under visible light with Pt as the co-catalyst. The high activity of this new system enables hydrogen gas capture from an easy-to-manufacture, scaled-up prototype utilizing MOF deposited on FTO glass as a photoanode.

(Invited) Atomic Layer Deposited Sulfides As (Pre)Catalysts for Electrochemical Water Splitting

Electrocatalysis is projected to play a key role in building a sustainable world based on renewable energy. Electrochemical water splitting produces H2 on the cathode (hydrogen evolution reaction, HER), which can be used as a fuel and reactant in diverse industries. The oxygen evolution reaction (OER) producing O2 at the anode is a complex reaction that limits the overall efficiency of water electrolyzers. Active, stable, and affordable catalysts are required for both reactions. The range of potential catalysts has expanded from metals and oxides to others, sulfides having become one of the most actively studied material groups. Our work focuses on understanding inherent activity and structural changes under HER and OER conditions.Different water electrolyzer technologies subject the catalysts to different operating conditions, which limits the available catalyst materials. For proton exchange membrane electrolyzers featuring an acidic environment, platinum group metals are currently used. However, several earth abundant catalysts have been identified for HER in acid. Among these, molybdenum sulfides in both amorphous (a-MoSx) and crystalline (c-MoS2) forms have attracted attention.1 We developed a plasma-enhanced ALD (PEALD) process that can deposit both amorphous MoSx with adjustable S/Mo ratio (2.8–4.7) and crystalline MoS2 with different crystallinity, morphology, and electrical properties.2 Electrochemical measurements in 0.5 M H2SO4 combined with ex situ and quasi in situ XPS revealed a-MoSx films to transform into highly active a-MoS2. C-MoS2 films were less active and did not show structural changes under HER conditions.3 Alkaline electrolyzers and anion exchange membrane electrolyzers operate under alkaline conditions and use earth abundant Fe/Co/Ni based catalysts. Most if not all materials based on these metals convert to oxyhydroxides under the highly oxidizing OER conditions and readily incorporate iron present in electrolytes.4,5 Thus, the as-deposited OER catalysts are best described as precatalysts. We developed new ALD processes to deposit NiSx and Co9S8,6,7 while oxide, metal, and hydroxide thin films were deposited for comparison using different methods. Extensive electrochemical measurements in 0.1 M KOH electrolyte with controlled Fe impurities combined with ex situ XPS revealed that in absence of iron all the Ni-based precatalysts convert to an OER-active oxyhydroxide, yet at substantially different rates (NiSx ≈ Ni(OH)2 >> Ni > NiO).8 However, good OER activity and stability was only achieved in the presence of Fe impurities. The highest amount of iron incorporation and the best OER performance was found for the NiSx and Ni(OH)2 precatalysts, which convert the fastest into the active oxyhydroxide form. Studies on Co-based OER precatalysts are currently ongoing, including use of operando characterization methods.Our studies on ALD sulfides as both HER and OER catalysts showcase the importance of understanding catalyst structure and its changes under catalytic conditions. Armed with this knowledge and unique capabilities of ALD, catalysts with higher performance in electrolyzer applications can be designed and engineered.

Redirecting Configuration of Atomically Dispersed Selenium Catalytic Sites for Efficient Hydrazine Oxidation

Thorough understanding of reconstructed active sites evolving from their initial states is crucial for a variety of catalytic reactions, as it not only promotes an atomic-level comprehension of the catalytic mechanism but also guides the design of practically usable catalysts. In particular under electrochemical operation, the reconstruction phenomenon of surface sites during reactions. After reconstruction, the active site is no longer the original pristine structure but rather the newly formed surface site. Exploring surface reconstruction under Operando catalytic conditions can aid in a better understanding of the active sites and catalytic pathways, helping designing more efficient catalyst systems.Atomically dispersed catalysts (ADCs), specifically the ones based on carbon, show tremendous potential in critical electrochemical reactions, including the hydrazine oxidation reaction (HzOR), which exhibits zero-carbon emissions and possesses a high energy density, presents considerable promise for the application of hydrazine fuel cells with improved power density. The dynamic reconstruction of atomically dispersed catalytic sites during electrocatalytic processes has emerged as a subject of intensive investigation. On one hand, knowledge of the reconstruction process is crucial, as it provides deep insights into the atomically dispersed active site and catalytic mechanism, laying a firm basis for material innovation. On the other hand, atomically dispersed catalytic sites have clear and uniform coordination structures, making them ideal quasi-model catalysts for revealing reconstruction mechanisms of active sites. However, discovering these reconstruction behaviors has focused primarily on metallic atomically dispersed catalytic sites so far, leaving non-metallic ones much unexplored, despite the fact that their performance in catalysis is comparable to or even superior to that of costly noble metals. An accurate vision of active sites during reactions is vital in developing non-metallic atomically dispersed catalysts; from a scientific perspective, it is essential to extract information about possible dynamic reconstruction processes in non-metallic atomically dispersed catalytic sites, similar to that of metallic ones.Combining ex situ high resolution electron microscopy and in situ X-ray adsorption spectroscopy to monitor the structurally uniform and well-defined single atomic site of atomically dispersed catalyst as an ideal model system could provide valuable atomic insights to active sites and the corresponding catalytic reaction mechanism. In situ techniques, particularly operando near and extended X-ray absorption fine structure (EXAFS and XANES) spectroscopies, in which the probe parameters such as the edge intensity, “white line”, and its energy position are affected by spectator species adsorbed on the electrode surface and intermediates formed upon reaction, may deliver chemical fingerprints that capture evolution of active sites during reactionIn this study, we synthesized a carbonaceous, non-metallic atomically dispersed selenium (Se) catalyst and confirmed the atomically dispersed configuration of Se in a SeC4 configuration. The as-prepared Se ADCs was found active in the hydrazine oxidation reaction (HzOR) in alkaline media (-114 mV (vs. reversible hydrogen electrode) at a current density of 1 mA cm-2), even surpassing that of noble-metal platinum (Pt) catalysts. Using the Se ADCs as a quasi-model catalyst, in situ X-ray absorption spectroscopy and Fourier-Transform infrared spectroscopy were used to trace the dynamic reconstruction process of atomically dispersed Se catalytic sites. We found that pristine SeC4 will pre-adsorb an *OH ligand in alkaline aqueous solutions, and the electrochemical oxidation of the N2H4 molecule will subsequently occur on the opposite side of the OH-SeC4. Theoretical calculations suggest that the pre-adsorbed *OH group pulls electrons from the Se site, resulting in a more positively charged Se and a higher polarity of Se-C bonds, and consequently higher surface reactivity toward HzOR. Our findings provide valuable insights into the reconstruction mechanism of atomically dispersed semimetallic catalytic sites and promote their practical use in a wide range of energy systems. Figure 1

Electrogeneration of Oxygen-Centered Radicals from N-Alkoxyphthalimides and Their Use in a Remote C-H Functionalization for 5,5-Spirocycles Construction

Oxygen-centered radicals, also known as alkoxyl radicals, are highly reactive species that have been considered useful synthetic intermediates.[1] Considering their synthetic accessibility, stability, and particular reactivity, N-alkoxyphthalimides (NAPIs) offer a practical avenue for generating these radicals under mild conditions, such as via electrochemical means.[2] Recent studies have demonstrated the effectiveness of N-benzyloxyphthalimides in accessing benzylic-carbonyl compounds through electrochemical reduction.[3] To modulate the conversion of NAPIs to O-centered radicals under electroreductive conditions, it was studied and transferred the reported mechanistic insights of photocatalytic redox conditions to an electrochemical approach by employing the Hantzsch ester and rapid alternating polarity electrolysis.[4,5] The electrogenerated O-centered radicals from NAPIs were then explored for their utility in remote C-H allylation and the synthesis of 5,5-spirocycles which represent important structural motifs of diverse natural products, including Cephalosporolides.[1] A.S. Budnikov, I.B. Krylov, A.V. Lastovko, B. Yu, A.O. Terent’ev, Nalkoxyphtalimides as versatile alkoxy radical precursors in modern organic Synthesis, Asian J. Org. Chem. 11 (2022), https://doi.org/10.1002/ ajoc.202200262.[2] M.A. Syroeshkin, I.B. Krylov, A.M. Hughes, I.V. Alabugin, D.V. Nasybullina, M. Y. Sharipov, V.P. Gultyai, A.O. Terent’ev, Electrochemical behavior of Noxyphthalimides: cascades initiating self-sustaining catalytic reductive N–O bond cleavage, J. Phys. Org. Chem. 30 (2017) 1–15, https://doi.org/10.1002/poc.3744.[3] D.F. Chicas-Baños, M. Lopez-Rivas, F.J. Gonzalez, F. Sartillo-Piscil, B.A. Frontana-Uribe, Access to carbonyl compounds via the electroreduction of Nbenzyloxyphthalimides: mechanism confirmation and preparative applications, Heliyon 10 (2024) e23808, https://doi.org/10.1016/j.heliyon.2023.e23808.[4] J. Zhang, Y. Li, F. Zhang, C. Hu, Y. Chen, Generation of alkoxyl radicals by photoredox catalysis enables selective C(sp3 )-H functionalization under mild reaction conditions, Angew. Chem. Int. Ed. 55 (2016) 1872–1875, https://doi.org/ 10.1002/anie.201510014.[5] J. Romero-Ibañez, D.F. Chicas-Baños, F. Sartillo-Piscil, B.A. Frontana-Uribe, Highly efficient electrogeneration of oxygen centered radicals from N-alkoxyphthalimides employing rapid alternating polarity (RAP) electrolysis. Transferring the photoredox catalytic conditions to organic electrosynthesis, Curr. Res. Green Sustain. Chem. 8 (2024) 100404, https://doi.org/10.1016/j.crgsc.2024.100404. Figure 1

Recent Developments in the Metal-Catalyzed Synthesis of Nitrogenous Heterocyclic Compounds.

Metal-catalyzed cyclization reactions have become a powerful and efficient approach for the stereoselective construction of both carbocyclic and heterocyclic ring systems. Transition metal complexes, with their ability to activate and selectively functionalize organic substrates, have revolutionized various areas of synthetic chemistry. This review highlights recent advancements in metal-catalyzed cyclization reactions, especially in the synthesis of nitrogen-containing heterocycles like imidazoles, pyridines, pyrimidines, and indoles. These advancements have significantly impacted fields such as natural product synthesis, pharmaceuticals, functional materials, and organic electronics. Novel catalytic systems, ligand designs, and reaction conditions continue to expand the capabilities of these reactions, driving further the progress made in synthetic organic chemistry. This review provides a comprehensive overview of recent research.

Enhancing trehalose production via Bacillus species G1 cyclodextrin glucanotransferase mutants: modifying disproportionation characteristics and thermal stability.

Inefficient conversion of small molecule maltooligosaccharides into trehalose greatly affects the cost of the production of trehalose by double enzyme method [maltooligosyl trehalose synthase (MTSase) and maltooligosyl trehalose trehalohyrolase (MTHase)]. This study used directed evolution to increase oligosaccharide utilization by the cyclomaltodextrin glucanotransferase (CGTase) from Bacillus species G1. This enzyme was chosen for its adaptability and stability in trehalose production. Model analysis revealed that the hydrogen bond distance between the N33K mutant and maltose reduced from 2.6 Å to 2.3 Å, increasing maltose affinity and boosting transglycosylation activity by 2.1-fold compared to the wild type. Further mutations improved thermal stability and optimum temperature, resulting in the N33K/S211G mutant. Consistent results from repeated experiments showed that the N33K/S211G mutant increased trehalose yield by 32.6% using maltodextrin. The results enhanced the double-enzyme method formed by MTSase and MTHase for trehalose production. Overall, we have identified optimal catalytic conditions, demonstrating significant potential for industrial-scale trehalose production with enhanced efficiency and cost-effectiveness.

Ullmann coupling reaction of dihalobenzenes and malononitrile-heterocumulene adducts under ultrasound-irradiation

In this study, various benzothiazoles, benzoxazoles, and benzo[1,3]-dithiols derivatives with good yields were obtained using the Ullmann coupling reaction of dihalobenzenes and malononitrile-heterocumulene adducts in the vicinity of copper catalyst, Cs2CO3 as a base under ultrasound irradiation. The use of the popular sonochemical method, short reaction time, simple and available raw materials, mild catalytic copper reaction conditions, simple purification, and good efficiency are some of the notable characteristics of this protocol.

Cu-Supported ZnO under Conditions of CO2 Reduction to Methanol: Why 0.2 ML Coverage?

By hydrogenating carbon dioxide to value-added products such as methanol, heterogeneous catalysts can lower greenhouse gas emissions and generate alternative liquid fuels. The most common commercial catalyst for the reduction of CO2 to methanol is Cu/ZnO/Al2O3, where ZnO improves conversion and selectivity toward methanol. The structure of this catalyst is thought to be Zn oxy(hydroxyl) overlayers on the nanometer scale on Cu. In the presence of CO2 and H2 under reaction conditions, the Cu substrate itself can be restructured and/or partially oxidized at its interface with ZnO, or the Zn might be reduced, possibly completely to a CuZn alloy, making the exact structure and stoichiometry of the active site a topic of active debate. In this study, we examine Zn3 clusters on Cu(100) and Cu(111), as a subnano model of the catalyst. We use a grand canonical genetic algorithm to sample the system structure and stoichiometry under catalytic conditions: T of 550 K, initial partial pressures of H2 of 4.5 atm and CO2 of 0.5 atm, and 1% conversion. We uncover a strong dependence of the catalyst stoichiometry on the surface coverage. At the optimal 0.2 ML surface coverage, chains of Zn(OH) form on both Cu surfaces. On Cu(100), the catalyst has many thermally accessible metastable minima, whereas on Cu(111), it does not. No oxidation or reconstruction of the Cu is found. However, at a lower coverage of Zn, Zn3 clusters take on a metallic form on Cu(100), and slightly oxidized Zn3O on Cu(111), while the surface uptakes H to form a variety of low hydrides of Cu. We thus hypothesize that the 0.2 ML Zn coverage is optimal, as found experimentally, because of the stronger yet incomplete oxidation afforded by Zn at this coverage.

The Feasibility of Using Electrostatic Interactions for Immobilizing Ru-bda Catalysts in Covalent Organic Framework: A Proof-of-Concept.

Heterogenization of molecular catalysts effectively resolves the separation issues of homogeneous catalysts and expands their application scenarios. In recent years, more and more studies have been using non-covalent interactions to achieve the heterogenization of molecular catalysts. Herein, electrostatic attraction was used to immobilize molecular catalysts, Ru-bda small molecular catalysts in COF materials, where the charged Ru-bda catalysts were immobilized in the oppositely charged COF with a high [Ru] loading content of ~0.2 mmol [Ru] g-1 COF. The leakage experiment verified that the immobilization of Ru-bda catalysts in COF by electrostatic interactions is stable in 0.1 M HClO4 and less than 5 % of molecular Ru-bda catalysts were leached into the solution in 2 hours. The chemical water oxidation experiment was conducted as a model catalysis reaction to verify the feasibility of using electrostatic interactions for immobilizing Ru-bda catalysts in COFs. The prepared Ru(bda)@COFs demonstrate a high catalytic activity of 268 μmol L-1 s-1 O2 for chemical water oxidation, illustrating the electrostatic attractions between COF and small molecules that can be used to immobilize homogeneous catalysts in heterogeneous materials. However, the robustness of COF material itself under catalytic conditions should be considered in practical applications.

Products Distribution and Reaction Kinetics from Co-Pyrolysis of Pinewood and Polypropylene under Non-Catalytic and Catalytic Reaction Conditions

Abstract Co-pyrolysis technology offers vital pathways for efficient utilization of plastics and biomass resources to help reduce the environmental problems and energy resources issues. The pyrolysis characteristics of pinewood and polypropylene (PP) mixtures were analyzed using TGA. The results showed a decrease in first peak of the mixture with increase in PP in the mixture, while the second peak increased with an increase in PP in the mixture. The addition of a catalyst decreased the DTG peak heights. The reduction in the first peak with different catalysts was in the order: CaO/ZSM-5 >CaO >ZSM-5, while for the second peak showed: CaO >CaO/ZSM-5 >ZSM-5. The activation energy, calculated by Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), and Friedman models, revealed that ZSM-5 reduced the activation energy, whereas CaO/ZSM-5 increased the activation energy, as compared to no catalyst case. Increase of co-pyrolysis temperature reduced the yield of aldehydes, ketones, acids and esters, but increased the yield of hydrocarbons. The addition of CaO reduced the yield of ketones, phenols, esters, and acids, while it increased the yield of alcohols. The addition of ZSM-5 also decreased the yield of ketones, phenols, acids and hydrocarbons, but increased the yield of furans and alcohols. The addition of CaO/ZSM-5 specifically reduced the yield of aldehydes and alcohols. The results show the important role of the specific catalysts examined on the resulting products distribution for the same reaction condition.

Strong metal-support interaction induced excellent performance for photo-thermal catalysis methane dry reforming over Ru-cluster-ceria catalyst

The utilization of solar energy in driving methane dry reforming (MDR) reaction through photo-thermal synergetic catalysis could simultaneously realize the reduction of carbon footprint and the fixation of solar energy, which is an environmentally and economically beneficial route. However, the currently developed catalysts still require further optimization in catalytic performance and stability. Here, we prepared RuNC, a Ru nanoclusters catalyst anchored on CeO2 with strong metal-support interaction (SMSI) effect via a facile preparation method. The formation rates of H2 and CO over RuNC catalyst were 1.41 and 2.16 mol·gcat−1·h−1 respectively under photo-thermal catalysis (PTC) at 500 °C, which is up to one order of magnitude higher than existing PTC-MDR catalysts. Moreover, the prepared catalyst did not show significant deactivation under 100 hour test. The in-depth structure-function relationship between catalytic activity/stability and Ru nanocluster sites/induced SMSI effect were determined by systematic structural characterization. The advantages of RuNC catalyst structure under PTC catalytic conditions were demonstrated by optical characterization. Besides, the excitation-migration path of photo-electron under PTC conditions was determined by ISI-XPS experiments. Finally, the mechanism of PTC-MDR reaction and the specific reaction steps enhanced by light irradiation were determined by operando experiments. This work provided theoretical basis and excellent catalyst for the industrial application of PTC-MDR route.

SYNTHESIS OF 1-VINYL-3(5)-METHYL-4-NITROPYRAZOLE AND STUDY OF THE EFFECT OF METHYL SUBSTITUTES IN THE PYRAZOLE RING DURING RADICAL POLYMERIZATION

The aim of this work was to develop a convenient preparative method for the direct N-alkylation of 3(5)-methyl-4-nitropyrazole under conditions of phase-transfer catalysis (PTC). The need for development was also dictated by the fact that the reaction products are simultaneously intermediates in the synthesis of an important class of compounds - vinylpyrazoles. Alkylation of 3(5)-methyl-4-nitropyrazole under standard conditions of PTC (benzene-water-KOH-TEBACH (triethylbexylammonium chloride)) did not lead to the desired result. Apparently, benzene interrupts the transfer of the nitropyrazole anion from the aqueous organic medium, as a result of which the yield of the control alkyl compound is only 50%. During alkylation in the absence of benzene, under the influence of potassium hydroxide in water, deprotonation easily proceeds and the corresponding potassium salt of 3(5)-methyl-4-nitropyrazole is formed, which blocks the dehydrochlorination of 1,2-dichloroethane and leads to the selective course of the process of alkylation of the taken nitropyrazole. At an equimolar ratio of nitropyrazole and potassium hydroxide, the yield of a mixture of the resulting 1-(2-chloroethyl)-3- and 1-(2-chloroethyl)-5-methyl-4-nitropyrazoles reaches 80%. The dehydrochlorination of the obtained substituted chloroethylpyrazoles in a methanol solution, under conditions of PTC, and in an aqueous solution of N-methylmorpholine-N-oxide (NMO/H2O), in the presence of potassium hydroxide was also studied. Although the homogeneous method of dehydrochlorination is technologically imperfect, however, it makes it possible to obtain a mixture of 1-vinyl-3- and 1-vinyl-5-methyl-4-nitropyrazole isomers with a yield of 45%. Dehydrochlorination under PTC conditions is an alternative to a homogeneous process; however, it is not able to provide a high yield of the expected compounds - 20%. It has been established that the dehydrochlorination of the studied 1-(2̕'-chloroethyl)-3(5)-methyl-4-nitropyrazoles proceeds significantly successfully in the presence of KOH in the NMO/H2O system, leading to the total yield of 1-vinyl-3- and 1-vinyl -5-methyl-4-nitropyrazoles up to 60%. The effects of methyl substituents of the pyrazole ring during radical polymerization have been studied. The identified monomers exhibit different activities under the same conditions. Thus, in the process of radical polymerization, the isomer in which the methyl group is in the fifth position of the pyrazole ring polymerizes at a higher rate than the isomer in which the methyl group is in the third position. For citation: Bichakhchyan L.A., Markosyan A.J., Shakhatuni A.G., Badalyan K.S., Attaryan O.S., Khachatryan A.N. Synthesis of 1-vinyl-3(5)-methyl-4-nitropyrazole and study of the effect of methyl substitutes in the pyrazole ring during radical polymerization. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 12. P. 39-46. DOI: 10.6060/ivkkt.20246712.7065.

Nitrate-Anion-Induced Formation of a 2D Metal-Organic Framework with an Unconventional Kagomé Lattice Exhibiting Methanol-Mediated Ketone Catalysis.

Metal-organic frameworks (MOFs) with kagomé lattice are attractive for their unique physical and chemical properties, but little attention has been paid to their catalytic properties. Herein, we report a 2D MOF based on a phosphonato-amino-carboxylate ligand (NaHL), i. e., [Na0.33Co(L)(CH3OH)2](NO3)0.33 (2), which exhibits an unconventional kagomé lattice. The formation of this kagomé lattice is caused by the selective recognition of the NO3 - anion by the phenolato group of L2- as evidenced by theoretical calculations. Compound 2 can be utilized for the α-methoxymethylation and aminomethylation of aromatic ketones using methanol as a C1 source. Interestingly, compound 2 can be exfoliated in-situ into nanosheets with one-layer thickness under catalytic reaction conditions, which improves the catalytic efficiency. Based on the results of experiments and theoretical calculations, we proposed possible pathways for the catalytic reaction.

Reactions of In Situ-Generated Difluorocarbene (:CF2) with Aromatic/Heteroaromatic Alcohols, Thiols, Olefins, and Alkynes under Environmentally Responsible Conditions.

Environmentally respectful methods for generating and utilizing difluorocarbene (:CF2) in the synthesis of a wide array of valuable difluoromethylated compounds are disclosed. In particular, the insertion of the CF2 moiety into aromatic/heteroaromatic alcohols, thiols, olefins, and alkynes under neat or aqueous micellar catalysis conditions is demonstrated. These methods yield both satisfactory results and significantly lower E-Factors compared to traditional synthetic approaches. Key applications of these methodologies include optimization en route to a pantoprazole intermediate and development of a representative one-pot chemoenzymatic sequence. Additionally, analysis via calorimetry indicates no significant safety risk in the context of the developed solvent-free conditions.

One-step condensation synthesis of di-tertiary ammonium salt protic ionic liquid for efficiently catalytic CO2 cycloaddition reaction under cocatalyst- and solvent-free conditions

A novel protic ionic liquid di-tertiary ammonium bromide ionic liquid (DTAB-IL) was synthesized by one-step condensation at 0 ℃ with 85 % yield. DTAB-IL also exhibited effective catalytic activity for CO2 cycloaddition without cocatalyst and solvent. The catalytic reaction conditions were optimized to 90 ℃, 4 h, 1 MPa, and the yield of propylene carbonate was obtained 96 % with high selectivity 99 %. Under the optimal conditions, DTAB-IL catalyst exhibited good recyclability and universality to various epoxides. Furthermore, temperature influence and kinetic investigation for propylene carbonate synthesis were studied. The activation energy for DTAB-IL catalyzing CO2 cycloaddition reaction was 43.93 kJ/mol, and the reaction was found to follow first-order for propylene oxide. Efficient cycloaddition reaction of CO2 and epoxide was attributed to the activation of epoxide and CO2 by di-tertiary ammonium and epoxide ring-opening by bromide anion in DTAB-IL.

Multicomponent Cyanation of 2‐Amino‐3‐cyano‐4H‐chromenes in Aqueous Media

AbstractChromenes represent a pivotal molecular structure found in a diverse range of biologically active compounds. Specifically, derivatives of 2‐amino‐3‐cyano‐4H‐chromene have demonstrated pharmacological applications, displaying potential antioxidant and anticancer activities. This has heightened interest in the exploration of new and more efficient methods for their synthesis. In recent years, few examples have emerged, focusing on the organocatalytic and enantioselective synthesis of 2‐amino‐3‐cyano‐4H‐chromene derivatives, although the overall number of works to date is limited. In this study, we present the results of the synthesis of 2‐amino‐4H‐chromen‐3,4‐dicarbonitriles through a Michael addition of cyanide to 2‐iminochromenes. To achieve this, we utilized a mild source of cyanide (acetone cyanohydrin), green solvents and catalytic conditions at room temperature, via a multicomponent approach. Furthermore, we initiated the enantioselective study of this process using chiral organocatalysts obtaining promising preliminary results.

Bright Nanocomposites based on Quantum Dot‐Initiated Photocatalysis

AbstractIntegrating quantum dots (QDs) into polymer matrix to form nanocomposites without compromising the QD photoluminescence (PL) is crucial to emerging QD light‐emitting and solar energy conversion fields. However, the most widely‐used bulk polymerization technique, where monomers serve as the QD solvent, usually leads to QD PL quenching caused by radical initiators. Here we demonstrate high‐brightness nanocomposites with near‐unity PL quantum yield (QY), through a novel QDs‐catalyzed (‐initiated) bulk polymerization without using any radical initiators. Different from previous reports where QDs were designed as photo‐sensitizers/catalysts (always with cocatalysts) and hence non‐emissive in catalytic conditions, our QDs combine high brightness with highly effective catalysis, a combination that was previously considered to be hardly possible. In our case, apart from emitting light (at a large probability), the photoexcited QDs act as ‘overall reaction’ catalysts by simultaneously employing photoexcited electrons and holes to produce active radicals without the need of any sacrificial agents. These active radicals, though with a small amount, are sufficient to initiate effective chain reaction‐dominated bulk polymerization, eliminating the requirement of extra radical initiators. This study provides new insights for understanding and development of QDs for energy applications.

Bright Nanocomposites based on Quantum Dot-Initiated Photocatalysis.

Integrating quantum dots (QDs) into polymer matrix to form nanocomposites without compromising the QD photoluminescence (PL) is crucial to emerging QD light-emitting and solar energy conversion fields. However, the most widely-used bulk polymerization technique, where monomers serve as the QD solvent, usually leads to QD PL quenching caused by radical initiators. Here we demonstrate high-brightness nanocomposites with near-unity PL quantum yield (QY), through a novel QDs-catalyzed (-initiated) bulk polymerization without using any radical initiators. Different from previous reports where QDs were designed as photo-sensitizers/catalysts (always with cocatalysts) and hence non-emissive in catalytic conditions, our QDs combine high brightness with highly effective catalysis, a combination that was previously considered to be hardly possible. In our case, apart from emitting light (at a large probability), the photoexcited QDs act as 'overall reaction' catalysts by simultaneously employing photoexcited electrons and holes to produce active radicals without the need of any sacrificial agents. These active radicals, though with a small amount, are sufficient to initiate effective chain reaction-dominated bulk polymerization, eliminating the requirement of extra radical initiators. This study provides new insights for understanding and development of QDs for energy applications.

Investigation into the Internal Factors for the Catalytic Oxidation of Cyclohexane by Zr(IV)-Based Metal-Organic Frameworks.

Three porous Zr(IV)-based MOFs, UiO-66, MOF-808 and MOF-802, were selected to catalyze cyclohexane oxidation in order to reveal the intrinsic factors of the active site and catalytic performance. It was found that reducing the number of Zr6O8 ligand linkages could improve the catalytic efficiency of cyclohexane oxidation. The main reason for this is the different enrichment abilities of MOFs with different linkage numbers for cyclohexane, which was confirmed by the TPD of cyclohexane and also by GCMC simulations. Meanwhile, the catalytic effect of MOF-802 was lower than expected due to its low porosity and narrow inner pore size. The by-products were identified in detail by GC-MS, providing evidence for this catalytic mechanism. In addition, the potential of this catalyst for industrial applications in cyclohexane oxidation was demonstrated by optimizing the catalytic conditions.

KINETICS OF ANILINE-FORMALDEHYDE INTERACTION UNDER CONDITIONS OF HOMOGENEOUS CATALYSIS

The work is devoted to the kinetic modeling of reactions for the production of 4,4-diaminodiphenylmethane (MDA) in the presence of a catalyst. FASHION is a solid substance from colorless to pale yellow in color with a faint odor. It is used on an industrial scale mainly for the manufacture of polyurethanes, which have many applications, for example, insulating materials in mail containers. MDA is also used for the manufacture of coating materials, adhesives, spandex fibers, dyes, and rubber. This product belongs to the categories of medium and low-tonnage industries, which determines its importance in the chemical industry. The importance of the process of obtaining MDA and the application of kinetic modeling of a chemical reaction is described. The paper proposes a model that allows us to predict the kinetic curves of the studied reaction for obtaining MDA. The proposed model can be used to calculate flow-through or ring-shaped chemical reactors. The type and parameters of the model were obtained by minimizing deviations of experimental and calculated values of concentrations of reagents and products, while the model showed its adequacy to the experiment. The limits of its applicability were checked using computational experiments under various conditions - the ratio "aniline:formaldehyde", reaction temperature. As a result, the kinetic curves of the reactions for obtaining MDA in the presence of a catalyst at a given temperature were predicted. Computational experiments were carried out to predict the kinetic curves of the reactions of obtaining MDA in the presence of a catalyst at a given temperature. The calculation results were compared with experimental data. It is shown that the developed model can be used to predict the kinetics of the reaction of obtaining MDA in the presence of a catalyst at a given temperature. The subsequent kinetic experiment showed the coincidence of the experimental and predicted curves. For citation: Shishanov M.V., Tsvetkov I.D., Yashunin D.V., Kuk Kh.G., Dosov K.A., Bolshakov I.A., Morozov N.V. Kinetics of aniline-formaldehyde interaction under conditions of homogeneous catalysis. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 11. P. 55-62. DOI: 10.6060/ivkkt.20246711.7030.