Now showing items 1-18 of 18

    • Efficient photo-thermal catalysis unlocks the use of ammonia as a hydrogen carrier

      Sousa, Angel (2023-02-13) [Poster]
      Ammonia (NH3) plays a crucial role in the low-carbon economy as a promising carrier molecule to supply hydrogen (H2). However, the traditional thermal NH3 decomposition demands temperatures as high as 500-550oC, highlighting its controversiality for energy production. To address this challenge, photo-thermal catalysis arises offering a green pathway to promote the NH3 cracking using sunlight as its unique driving force. In this work, we demonstrate the use of a MOF-derived photo-thermal catalyst for the continuous production of H2 from NH3 under mild conditions, and with no external heating added. Under optimal conditions, a conversion rate of approximately 80% was reached, with no deactivation sign. The synergistic effect of light and heat was evaluated by performing mechanistic studies.
    • Constructing Structure-Property Relationships to Guide Selection of N-Heterocyclic Carbenes in Catalysis

      Takasao, Gentoku (2023-02-13) [Poster]
      N-heterocyclic carbenes (NHC) have acquired a fundamental role as ligands in organometallic chemistry and as catalysts in organocatalysis. More than 2000 NHC topologies have been synthesized and made available to the chemical community. However, this enormous synthetical effort is of limited use if no clear guidelines exist for selecting the NHC having the desired properties for the chemical problem in hand. To fill this gap and organize the complex chemical space of NHCs we decided to build a quantitative structure-property relationships of the currently available NHC topologies using a data-driven approach. We started assembling a dataset consisting of about 8000 redundant crystal structures of NHCs. This dataset will be used to determine average properties of NHCs using geometric and DFT-calculated properties, for a total of more than one hundred molecular descriptors. Statistical analysis of the dataset will allow evidencing the most relevant features capable to differentiate NHCs. Our analysis could be used in the selection of the NHCs matching the desired requirements.
    • Photocatalytic Alkylation of C(sp3)-H Bonds Using Sulfonylhydrazones

      Bonciolini, Stefano (2023-02-13) [Poster]
      The ability to construct C(sp3)?C(sp3) bonds from easily accessible reagents is a crucial, yet challenging endeavor for synthetic organic chemists. Herein, we report the realization of such a cross-coupling reaction, which combines N-sulfonyl hydrazones and C(sp3)?H donors through a diarylketone-enabled photocatalytic hydrogen atom transfer and a subsequent fragmentation of the obtained alkylated hydrazide. This mild and metal-free protocol was employed to prepare a wide array of alkyl-alkyl cross-coupled products and is tolerant of a variety of functional groups. The application of this chemistry further provides a preparatively useful route to various medicinally-relevant compounds, such as homobenzylic ethers, aryl ethyl amines, ?-amino acids and other moieties which are commonly encountered in approved pharmaceuticals, agrochemicals and natural products.
    • Intermolecular Organophotocatalytic Cyclopropanation of Unactivated Olefins

      Fischer, David (2023-02-13) [Poster]
      Intermolecular cyclopropanation of mono-, di-, and trisubstituted olefins with ?-bromo-?-ketoesters and ?-bromomalonates under organophotocatalysis is reported. The reaction displays broad functional group tolerance, including substrates bearing acids, alcohols, halides, ethers, ketones, nitriles, esters, amides, carbamates, silanes, stannanes, boronic esters, as well as arenes and furnishes highly substituted cyclopropanes. The transformation may be performed in the presence of air and moisture with 0.5 mol % of a benzothiazinoquinoxaline as organophotocatalyst. Mechanistic investigations, involving Stern-Volmer quenching, quantum yield determination, and deuteration experiments, are carried out, and a catalytic cycle for the transformation is discussed.
    • A General Iridium-Catalyzed Reductive Dienamine Synthesis Allows a Five-Step Synthesis of Catharanthine via the Elusive Dehydrosecodine

      Almehmadi, Yaseen A. (2023-02-13) [Poster]
      We developed a new catalytic, highly stereo- and regioselective approach towards the rapid construction of highly functionalized isoquinuclidines (ISQs). These bridged bicycles are abundant in active principle ingredients and natural products, such as catharanthine, 18-methoxycoronaridine, cononusine, and caldaphinidine D. Our new methodology relies on the use of an iridium (I) complex to hydrosilylate ?,?-unsaturated ?-lactams, which can lead to the downstream formation of a reactive dienamine intermediate, before undergoing a concerted [4+2] cycloaddition reaction with a wide range of dienophiles. This remarkable transformation proceeds with high stereocontrol, low catalyst loading, and from readily available starting materials, resulting in the formation of complex isoquinuclidine polycyclic products. This new robust synthetic approach was also extended to acyclic, aliphatic starting materials, enabling the formation of cyclohexene-substituted amine products and has enables the shortest (five-step) synthetic route to access catharanthine to date, an alkaloid that also happens to be a building block for vinblastine (a widely used anticancer drug approved by the World Health Organization for several aggressive cancers such as brain, lung, testicular, bladder, and melanoma cancer).
    • Reductive Cross-Coupling of ?-Oxy Halides Enabled by Thermal Catalysis, Photocatalysis, Electrocatalysis, or Mechanochemistry

      Yue, Huifeng (2023-02-13) [Poster]
      The development of methods to access alcohol derivatives is one of the main concerns of considerable research. Herein, we report a reductive cross-coupling reaction of ?-oxy halides, simply generated from aldehydes, with a series of C(sp2) and C(sp)-electrophiles. A wide range of aryl and heteroatom aryl halides, vinyl bromides, alkynyl bromides, and acyl chlorides react with unhindered and hindered aldehyde-derived ?-oxy halides by providing protected alcohols as well as ?-hydroxy ketones. Noteworthy, the reductive couplings are achieved not only through thermal catalysis with the use of metal reductants but also by photocatalysis, electrochemistry, and mechanochemistry. The unrestricted interchange of the four strategies indicates their underlying mechanistic similarities. The generation of NiI intermediate is proposed to be the key point for ketyl radical formation via a single electron transfer (SET) event, which was rationalized by an array of control experiments and density functional theory (DFT) calculations.
    • Nitrogen Reduction to Ammonia by a Phosphorus-Nitrogen PN3P-Mo(V) Nitride Complex: Significant Enhancement via Ligand Post-Modification

      Han, Delong (2023-02-13) [Poster]
      As it can reduce dinitrogen in a mild condition, the transition metal complex has been investigated for decades. A breakthrough was obtained by Schrock and coworkers in 2003 that successfully transformed N2 into NH3 by using a Mo complex at ambient conditions.1 Recently, the pincer complex was for the first time successfully applied to catalyze N2 fixation by Nishibayashi s group.2 For now, more attention has been focused on the pincer complexes to further develop their N2 fixation ability, while, complexes including pincer complexes usually have flaws like requiring strong reductants and poor efficiency thus are worthy of being further developed. As an extensive study on pincer complex,3 a post-modified PN3P-Mo pincer complex (2) which was hard to afford in conventional synthetic methods were presented for the first time by our group. Meanwhile, Inspired by the literature during the same period,4 it was employed on the N2 fixation that an excellent yield of NH3 (94%) and a high number of NH3/Mo (3525) were achieved in the presence of SmI2 as a reductant. In sharp contrast, the yield was 33% for the unmodified complex 1, and 80% of it decomposed in just one cycle. Moreover, since supported by the anionic pincer ligand, 2 furnished a high oxidation state Mo(V) nitride complex as a plausible key intermediate in the catalytic process via N2-cleavage, suggesting a catalytic cycle that involves different oxidation states (II/V) from those in the literature.5 (1) Yandulov, D. V.; Schrock, R. R., Catalytic Reduction of Dinitrogen to Ammonia at a Single Molybdenum Center. Science 2003, 301, 76-78. (2) Arashiba, K.; Miyake, Y.; Nishibayashi, Y., A molybdenum complex bearing PNP-type pincer ligands leads to the catalytic reduction of dinitrogen into ammonia. Nat. Chem. 2011, 3, 120-125. (3) (a) Wang, X.; Yao, L.; Pan, Y.; Huang, K.-W., Synthesis of group 10 metal complexes with a new unsymmetrical PN3P-pincer ligand through ligand post-modification: Structure and reactivity. J. Organomet. Chem. 2017, 845, 25-29. (b) Li, H.; Gonçalves, T. P.; Lupp, D.; Huang, K.-W., PN3(P)-Pincer Complexes: Cooperative Catalysis and Beyond. ACS Catal. 2019, 9, 1619-1629. (4) Ashida, Y.; Arashiba, K.; Nakajima, K.; Nishibayashi, Y., Molybdenum-catalysed ammonia production with samarium diiodide and alcohols or water. Nature 2019, 568, 536-540. (5) Han, D.; Huang, K.-W., Nitrogen Reduction to Ammonia by a Phosphorus-Nitrogen PN3P-Mo(V) Nitride Complex: Significant Enhancement via Ligand Post-Modification CCS Chem. 2022, DOI: 10.31635/ccschem.022.202202385
    • Highly active and selective metal-free nanofibers for H2O2 electroproduction via F/S dual-doping

      Xiang, Fei (2023-02-13) [Poster]
      Electrocatalytic synthesis of hydrogen peroxide (H2O2) via two-electron oxygen reduction reaction (2e- ORR) provides a promising alternative to the traditional energy-intensive anthraquinone process, allowing for clean, sustainable, and decentralized H2O2 production. However, developing inexpensive, highly active, and selective catalysts is still a challenge for the electroproduction of H2O2. Here, we engineer large-scale electrocatalysts based on metal-free carbon nanofibers with a fluorine and sulfur dual-doping strategy. Optimized samples yield an onset potential of 0.814 V versus reversible hydrogen electrode (RHE) and a near-unity H2O2 selectivity of 99.1%, superior to most reported carbon/metal-based counterparts. Experimental and theoretical computation results demonstrate that the manipulated free energy profiles and reduced energy barrier of the reaction route stem from the synergistic effect of intermolecular charge transfer coupled with electron spin redistribution after suitable F and S dual-doping, contributing to enhanced performances. This technique paves the way for the design and implementation of sustainable, large-scale, and highly efficient catalysts for the electroproduction of H2O2 and enjoys versatility in other catalytic fields, such as CO2 reduction, water splitting, and ammonia production.
    • An Efficient Metal-Organic Framework - Derived Nickel Catalyst for the Light Driven Methanation of CO2

      Garzon Tovar, Luis Carlos (2023-02-13) [Poster]
      The use of carbon dioxide (CO2) as feedstock for the production of value-added products is a potential route to achieve CO2 mitigation. In this scenario, the direct photocatalytic conversion of CO2 into fuels using sunlight is a promising approach as it allows for both the recycling of CO2 and the storage of solar energy in the form of chemical bonds. However, traditional photocatalytic systems rely on wide bandgap semiconductors that are mainly active under UV light, thus limiting enormously their large-scale application.[1] Recently, photo-thermal catalysis,which combines both thermal and non-thermal contributions of sunlight has emerged as abright alternative to overcome the limitations of classical photocatalysis as it enables the whole exploitation of the solar spectrum and provides localized heating to further enhance productivity rates.[2] In this context, carbon-based catalysts have shown great potential in photo-thermal catalysis due to their broadband light absorption and high efficiency in the conversion of photo-energy into thermal energy.[3] In particular, carbon-based catalysts derived from Metal-Organic Frameworks (MOFs) have attracted great interest due their exceptional properties, including low graphitization degrees, micro-porosity and high loading and well-dispersed metallic nanoparticles. In addition, the high tunability of MOFs opens the opportunity to access mixed oxides that are not always possible to obtain by traditional synthetic methods.[4] Here, we report the synthesis of a highly active and stable metal-organic framework derived Ni-based catalyst (Ni@C-600) for the photo-thermal reduction of CO2 to CH4. Ni@C-600 was obtained by the thermal decomposition of Ni-MOF-74 under a continuous flow of N2 and at an optimal pyrolysis temperature of 600 oC. High?angle annular dark?field scanning transmission electron microscopy (HAADF?STEM) images and X-ray powder diffraction (XRPD) performed on Ni@C-600 confirmed the formation of highly dispersed Ni nanoparticles confined within a graphitic carbon matrix with an average particle size of 9.5 ± 5.3 nm (Figure 1a). The catalytic performance of the Ni@C-600 in photo-thermal methanation reaction under visible and IR irradiation revealed that our material achieved very high CH4 production rates of 488 mmol g-1 h-1 (Figure 1b). Additionally, we studied the relationship between reaction rate and light intensity and we found an exponential correlation between the photon flux and the CH4 production, suggesting that this system is mainly operated by an effective light-to-heat conversion. The stability of Ni@C-600 was evaluated by performing ten consecutive reaction cycles, in which no particle aggregation or significant loss of activity were observed. Finally, the stability of the catalyst under long-term reaction conditions was studied in flow. Under these conditions, Ni@C-600 exhibited an excellent stability for more than 12 consecutive hours of reaction (Figure 1c). In conclusion, we demonstrated the effectiveness of the MOF-mediated approach for the synthesis of highly active photo-thermal catalysts based on Ni.[5]
    • Customized 3D printed metal reactors to accelerate transport phenomena

      Dos Santos, Vinicius L. (2023-02-13) [Poster]
      A common issue in chemical processes is that their operation is limited by mass and heat transfer.One example is the uncontrolled increase of temperature for exothermic reactions, generating hotspots, which may damage the reactor structure [1]. Recently, the boost of new manufacturing technologies has permitted the catalysis area to go beyond, and test more complex reactor designs.Additive manufacturing (AM), also known as 3D printing, can significantly contribute to process intensification of unitary processes removing heat and mass transfer limitations [2]. 3D printing allows fabricating free-form sophisticated designs of units like chemical reactors that can be customized to maximize productivity of specific chemistry. Our group uses a lithographic AM method for printing across scales in polymers, metals, ceramics, and their composites in a commercially ready viable way to produce milli-reactors [3]. This platform provides enormous freedom for materials and designs of the next-generation multiscale structured metallic reactors. Fractals are a special group of space-filling curves (SFC). They are infinite self-repeating patterns, and their concept can be used to describe some natural structures, e.g., ferns, trees, and the seacoast [4]. Recently, the utilization of space-filling curves (as well as other geometries) has been revisited for reactor design, as AM can overcome economic manufacturing constraints. SFC curves have the potential to offer compact, and high-volume reactors, offering the possibility to decrease mass and heat transfer limitations, and different mixing levels [5]. A typical fractal reactor designed using a 2D Hilbert-curve is shown in Figure 1.Figure 1. Fractal reactor using Hilbert curve 3D printed in polymer (a) and metal (b).2 The same approach can be used to design other unitary processes like separation vessels. Additionally, reactor internals can be optimized in the same manner to customize heat transfer or/and pressure drop. This approach can be done using lattices [6], triple periodical minimal surfaces (TPMS) [7] or new structures with imprinted porosity that result from the combination of lattices and TPMS solids [8]. Examples of these novel designs and their manufacture in stainless steel are shown in Figure 2. In this work, we will show the recent progress of our group in this area. Results of residence time distribution of different fractal reactors manufactured with the 2D Hilbert curve will be shown for different designs with a fixed volume. Apart from fractal reactors, pressure drop and thermal field across TPMS structures with imprinted porosity will be shown. The pressure drop and heat transfer across TPMS structures with different topologies were determined by CFD simulations under varying operating conditions. In summary, independent on the application target, the uniqueness of this fully digital approach is that the CAD design of the reactor can be used for assessing its performance, adapting the shape of the reactor until the specified KPIs are satisfied. Only at the point where the desired result is obtained, the reactor can be physically manufactured. Our main target is to contribute to the generation of intensified chemical reactors with milli-scale dimensions, where shape customization can enable the production of targeted chemicals, especially under demanding conditions or in challenging environments [9]. References: [1] Cambie, D., Bottecchia, C., Straathof, N. J., Hessel, V., & Noel, T., Applications of continuous-flow photochemistry in organic synthesis, material science, and water treatment. Chemical reviews, 2016, 10276-10341. [2] Stankiewicz, Andrzej I., and Jacob A. Moulijn. (Process intensification: transforming chemical engineering.)Chemical engineering progress, 2000, 22-34.3 [3] Melentiev R., Harakály G., Stögerer J., Mitteramskogler G., Grande C., Lithography Metal Additive Manufacturing. Additive Manufacturing, 2023 (Submitted). [4] Prusinkiewicz, Przemyslaw, and Aristid Lindenmayer. The algorithmic beauty of plants. Springer Science & Business Media, 2012. [5] Grande, C., Compact reactor architectures designed with fractals. Reaction Chemistry & Engineering, 2021,1448-1453. [6] Rebelo, N. F. B.; Andreassen, K. A.; Rios, L. I. S.; Camblor, J. C. P.; Zander, H. J.; Grande, C. A., Pressure drop and heat transfer properties of cubic isoreticular foams. Chemical Engineering and Processing-Process Intensification, 2018, 36-42. [7] Zimmer, Arthur, et al. Effect of manufacturing techniques in pressure drop on triple periodical minimal surface packings. Chemie Ingenieur Technik, 2021, 967-973. [8] Asif, M.; Grande, C. A., TPMS Contactors Designed with Imprinted Porosity: Numerical Evaluation of Momentum and Energy Transport. Industrial & Engineering Chemistry Research, 2022, 18556-185. [9] Grande, Carlos A., and Terje Didriksen. Production of Customized Reactors by 3D Printing for Corrosive and Exothermic Reactions. Industrial & Engineering Chemistry Research, 2021, 16720-16727.
    • Overcoming the kinetic and deactivation limitations of Ni-catalyst by alloying it with Zn during the dry reforming of methane

      Virpurwala, Quaid Johar (2023-02-13) [Poster]
      Stimulated by the capacity of Zn to improve the adoption of CO2 and CH4, we doped a Ni-supported ZrO2 catalyst with Zn to enhance the catalyst performance and stability in the dry reforming of methane. We prepared a set of catalysts with different proportions of Ni:Zn:Zr and made an extensive ex situ and in situ characterization to prove that in reductive conditions and at 750 °C, we formed a Ni-Zn alloy. The combination of a tailored morphology of the alloy nanoparticles, strong metal-support (ZnO-ZrO2) interactions, and additional oxygen vacancies created by Zn inclusion leads to an improved catalyst with 15% higher initial activity and extended stability over 100 h on stream than the Zn-free catalyst. Our experimental and modeling results proved that the 10Ni/ZnO-ZrO2 catalyst improves the adsorption and reaction rates of CH4 and CO2 while extending the catalyst s lifetime by enhanced coke precursor gasification, compared with the Zn-free counterpart. We discuss the basis for a structure-function correlation based on our detailed theoretical and experimental observations.
    • Redox-Neutral Imination of Alcohol with Azide: A Sustainable Alternative to the Staudinger/Aza-Wittig Reaction

      Yang, Li (2023-02-13) [Poster]
      The traditional Staudinger/aza-Wittig reaction represents one of the most powerful tools for imine formation. However, for this multistep procedure, the sacrificial phosphine has to be used, resulting in difficulties in the purification process and waste disposal at the same time. Here, we report a redox-neutral azide-alcohol imination methodology enabled by a base-metal nickel PN3 pincer catalyst. The one-step, waste-free, and high atom-economical features highlight its advantages further. Moreover, mechanistic insight suggests a non-metal-ligand cooperation pathway based on the observation of intermediate and density functional theory calculations.
    • Efficient and chemoselective hydrogenation of aldehydes catalyzed by well-defined PN3 -pincer manganese (II) catalyst precursor

      Aldakhil, Abdullah (2023-02-13) [Poster]
      Well-defined and air-stable PN3-pincer manganese (II) complexes were synthesized and used for the hydrogenation of aldehydes into alcohols under mild conditions using MeOH as a solvent. This protocol is applicable for a wide range of aldehydes containing various functional groups. Importantly, ?,?-Unsaturated aldehydes, including ynals, are hydrogenated with the C=C double bond/C?C triple bond intact.
    • Photoexcited Base-Metal Catalysis

      El-Sepelgy, Osama (2023-02-13) [Poster]
      Innovative fundamental research is crucial to face urgent challenges posed by our current societal, environmental and economic demands. Among the most pressing challenges of the 21st century is the utilization of abundant but unreactive feedstock as development of these technologies would enable the sustainable production of vitally important fine and bulk chemicals. To pursue this goal, our group focuses on the development of unprecedented sustainable concepts through the merger of base-metal catalysis with the visible light available from the sun. We believe that shining visible light on base-metal catalysts can change the reaction outcome through unpredictable catalytic pathways.
    • Ni-Catalyzed Aryl Acylation of Alkynes via tether Acyl Group Migration: An Entry to functionalized acyclic tetra-substituted alkenes

      Shinde, Prashant (2023-02-13) [Poster]
      We herein report an unconventional Ni-catalyzed cascade reaction of 2-alkynyl phenol ester with boronic acid that incorporates an arylation of alkynes induced acyl group migration to produce tetra substituted functionalized alkenes in good-to-excellent yields with exclusive E-selectivity. Mechanistically, the transformation involves the generation of a nucleophilic vinyl Ni(II) species by the regioselective syn-aryl nickelation of an alkyne, which undergoes an intramolecular acyl migration with tether phenol ester to yield highly functionalized acyclic tetra-substituted alkenes. The steric and electronic trialkyl phosphine ligand is crucial for providing high regio- and stereocontrolled for efficient migratory carbo-acylation of alkynes. Finally, the synthetic utility of the obtained products is also demonstrated.
    • Reactivity in Nickel-Catalyzed Multi-component Sequential Reductive Cross-Coupling Reactions

      Chen, Haifeng (2023-02-13) [Poster]
      The nickel-catalyzed three-component reductive carbonylation of alkyl halides, aryl halides, and ethyl chloroformate is described. Ethyl chloroformate is utilized as a safe and readily available source of CO in this multi-component protocol, providing an efficient and practical alternative for the synthesis of aryl-alkyl ketones. The reaction exhibits a wide substrate scope and good functional group compatibility. Experimental and DFT mechanistic studies highlight the complexity of the cross-electrophile coupling and provide insight into the sequence of the three consecutive oxidative additions of aryl halide, chloroformate, and alkyl halide.