Low Catalyst Loading Research Articles

Intermolecular C-H silylations of arenes and heteroarenes with mono-, bis-, and tris(trimethylsiloxy)hydrosilanes: control of silane redistribution under operationally diverse approaches.

Efficient catalytic protocols for C-H silylations of arenes and heteroarenes with sterically and electronically different hydrosiloxysilanes are disclosed. The silylations are catalyzed by a well-defined Rh-complex (1 mol%), derived from [Rh(1,5-hexadiene)Cl]2 and a bulky BINAP type ligand. This catalyst not only promotes C-Si bond formation affording the desired products in up to 95% isolated yield, but also can suppress the silane redistribution side reactions of HSiMe2(OTMS). The protocol can also be applied for the C-H silylations of more reactive HSiMe(OTMS)2 with a much lower catalyst loading (0.25 mol%) and even with sterically demanding HSi(OTMS)3. The steric bulk of the arene substituent and hydrosiloxysilane is a major factor in determining the regioselectivity and electronic effect as secondary. The current method can be performed under operationally diverse conditions: with/without a hydrogen scavenger or solvent.

Synthesis of indol-3-yl-benzofurans and carbazoles via Cu(OTf)2-catalyzed [3 + 2] and [4 + 2] cycloaddition.

An efficient Cu(OTf)2-catalyzed [3 + 2] cycloaddition of indole-3-acrylate with p-benzoquinone has been developed to construct two distinct indole-tethered benzofuran scaffolds, offering the first-ever selective access to these scaffolds. Moreover, the [4 + 2] cycloaddition reaction of indole-3-acrylate with vinyl ketone derivatives was used to synthesize carbazoles in a one-pot manner. The disclosed strategies provided a series of selective transformations under low-catalyst loading, with a broad substrate scope featuring diverse applicability and practical simplicity of the developed protocol with easily available substrates.

Low platinum loading electrocatalyst supported on a carrier derived from carbon dots doped ZIF-67 for the ORR and zinc-air batteries.

The development of economical and efficient platinum-based catalysts for the oxygen reduction reaction (ORR) is considered the most promising strategy for the widespread application of clean energy conversion devices. Herein, Co nanoparticles encapsulated in N-doped carbon carriers, CoCN(CDs-X), were constructed by pyrolyzing carbon dots (CDs) doped ZIF-67 and further used to anchor Pt to prepare low Pt loading catalysts, PtCoCN(CDs-X). The introduction of CDs not only improves the conductivity for efficient electron transfer, but also regulates the interaction between Pt and the CoCN(CDs-X) support and alleviates the oxidation of Pt. The optimized PtCoCN(CDs-0.10) displays decent ORR behavior with onset and half-wave potentials of 0.95 V and 0.83 V, respectively, in alkaline media and superior catalytic stability and methanol tolerance. While employing PtCoCN(CDs-0.10) as a cathode catalyst for an as-assembled zinc-air battery (ZAB), it delivers an excellent power density of 194.2 mW cm-2 and exceptional operation stability, which is indicated by a voltage efficiency loss of only 7.7% after a long cycle life of 100 h, demonstrating its great potential applications.

Controlled ring-opening copolymerization of epoxides and cyclic anhydrides through bifunctional thiourea–quaternary ammonium salt catalysts

Bifunctional thiourea–quaternary ammonium salt catalysts exhibited significantly higher activity over a two-component system with a similar structure at a low catalyst loading for the ring-opening copolymerization of epoxides and cyclic anhydrides.

Simultaneously improving the pore structure and electron conductive network of the anode catalyst layer via SnO2 doping for proton exchange membrane water electrolysis.

Proton exchange membrane water electrolysis (PEMWE) is a promising technology for green hydrogen production. However, its large-scale commercial application is limited by its high precious metal loading, because low catalyst loading leads to reduced electron transport channels and decreased water transportation, etc. Herein, we study the electrode level strategy for reducing Ir loading by the optimization of the micro-structure of the anode catalyst layer via SnO2 doping. The pore structure and electron conductive network of the anode catalyst layer can be simultaneously improved by SnO2 doping, under appropriate conditions. Therefore, mass transfer polarization and ohmic polarization of the single cell are reduced. Moreover, the enhanced pore structure and improved electron conduction network collectively contribute to a decreased occurrence of charge transfer polarization. By this strategy, the performance of the single cell with the Ir loading of 1.5 mg cm-2 approaches the single cell with the higher Ir loading of 2.0 mg cm-2, which means that SnO2 doping saves about 25% loading of Ir. This paper provides a perspective at the electrode level to reduce the precious metal loading of the anode in PEMWE.

Nanoscale and chiral metal-organic frameworks for asymmetric reactions in water: bridging Lewis acid catalysis and biological systems.

Nowadays, stereoselective control over the sheer variety of chemical transformations benefits from the multipotency of chiral Lewis acids. Their use under biocompatible conditions has long posed a challenge because profuse amounts of biogenic nucleophiles readily deactivate them. To bridge the gap between chiral Lewis acid catalysis and biocompatible chemistry, the conversion of UiO(BPY)-type nanosized metal-organic frameworks (NMOFs) into chiral variants was herein exemplified. The combination of an elongated 2,2'-bipyridyl linker and scandium salt with a hydrophobic anion proved essential to implement traits such as robustness, biocompatibility, and catalytic activity. The catalyst could construct sufficiently hydrophobic environments sequestered within the framework, catalyzing asymmetric ring-opening reactions of meso-epoxide with low catalyst loading to afford β-amino acid alcohols in high yield (up to >99%) with high enantioselectivity (up to 88%). Most impressively, it exhibited a tolerance to the ex vivo poisoning of chiral Lewis acid catalysis by biogenic nucleophiles in sharp contrast to conventional water-compatible Lewis acids.

Palladium nanoparticles for the synthesis of phenanthridinones and benzo[c]chromenes via C-H activation reaction.

In the present work, derivatives of phenanthridine-6(5H)-ones and benzo[c]chromenes were efficiently prepared through an intramolecular C-H bond functionalization reaction catalyzed by photochemically synthesized Pd-PVP nanoparticles. The heterocycles were obtained via intramolecular arylation of the corresponding N-methyl-N-aryl-2-halobenzamide or aryl-(2-halo)benzyl ethers using K2CO3 as base in a mixture of H2O : DMA as solvent without additives or ligands. High yields of the heterocyclic compounds were achieved (up to 95%) using a moderately low catalyst loading (1-5 mol%) under an air atmosphere at 100 °C. The reaction exhibited very good tolerance to diverse functional groups (OMe, Me, t Bu, Ph, OCF3, CF3, F, Cl, -CN, Naph), and both bromine and iodine substrates showed great reactivity. Finally, the in vitro antiproliferative activity of phenanthridine-6(5H)-ones and benzo[c]chromenes was evaluated against six human solid tumor cell lines. The more active compounds exhibit activity in the low micromolar range. 1-Isopropyl-4-methyl-6H-benzo[c]chromene was identified as the best compound with promising values of activity (GI50 range 3.9-8.6 μM). Thus, the benzochromene core was highlighted as a novel organic building block to prepare potential antitumor agents.

Automated Production of Catalyst Coated Membranes for PEM Water Electrolysis Using a Direct Ultra-Sonic Spray Coating Approach

The production of green hydrogen through polymer electrolyte water electrolysis (PEMWE) has attracted attention in recent years for its potential to enable the widespread use of green hydrogen [1, 2]. This technology particularly impacts important sectors of today’s society such as the agricultural and mobility sectors. Among the different components of an electrolysis cell, the membrane electrode assembly (MEA) is regarded as the most important component for its operation, since it is where the water-splitting reaction takes place. For this reason, the choice of materials and production approach play a highly important role to optimize its lifetime, performance, and cost [3]. Within this context, the MEA production via ultra-sonic spray coating has been lately gaining relevance due to its potential to yield high-activity electrode layers with a low catalyst loading.Conventionally, electrodes for PEMWE have been fabricated using other catalyst deposition techniques such as the doctor blade, airbrush spray coating or rod coating on a separate substrate, which is then transferred onto the membrane via hot pressing. However, the shortcomings of these approaches which include an additional hot press step were recently reported, particularly due to the complexity associated with electrodes with low catalyst loadings due to their sensitivity towards mechanical stress [1, 4]. On the other hand, effective approaches involving a direct ink deposition onto the membrane using ultra-sonic spray coating have been long reported for fuel cell applications [5, 6].In this work, we take the approach of direct ink deposition via ultra-sonic spray coating to produce iridium based MEAs for PEMWE. Furthermore, the dependency of the MEA electrochemical activity on the process and material choice are studied in an iterative manner. Of particular interest for this study is the material transfer rate from the catalyst ink to the membrane, the reproducibility of the developed spray coating process and the variation of materials used for the MEA fabrication. The spray process was performed with an ultra-sonic spray nozzle attached to an automized 3-axis rig and coupled with a syringe pump. The fabricated MEAs were characterized using a single cell setup with an active area of 4 cm2. The results of the first generation of the fabricated MEAs show that the material ratios in ink composition play an important role in the ink flowability through the piping which carries the ink to the ultra-sonic nozzle. Furthermore, this behavior has a direct and strong influence on the final composition of the catalyst layer, which consequently directly affects the cell performance.

(Invited) Electron Microscopy Investigation of Electrolyzer Degradation

Low-temperature proton exchange membrane water electrolyzers (PEMWEs) are a key technology for green hydrogen production from renewable energy sources. Developing efficient and durable components for the membrane electrode assembly (MEA) at the heart of the electrolyzer is critical for meeting DOE’s Hydrogen Shot target of $1 per kg of hydrogen by 2031. Of key interest to the efficiency and longevity of the electrolyzer is the anode-side of the MEA, where the costly iridium (Ir) catalyst is prone to dissolution at the high potentials and acidic conditions experienced in the cell. Further, the interfacial contact resistance between the catalyst and porous transport layer (PTL) plays a key role in electrolyzer performance and can degrade over time. Understanding and mitigating these degradation modes is critical for reducing the cost the PEMWEs and enabling commercialization.Here we will present the results of electron microscopy characterization performed on degraded anode catalyst layers and coated PTLs. Cross sections of MEAs submitted to different cycling protocols (square wave, triangle wave, steady-state, etc.) were prepared by diamond-knife ultramicrotomy and studied with in the scanning transmission electron microscope (STEM). Using energy dispersive X-ray spectroscopy (EDS), the dissolution and migration of Ir into the membrane was tracked and correlated with performance losses. The impact of PTL contact area on inhomogeneous degradation in anodes with low catalyst loadings will also be presented. In addition, PTL coating thickness and uniformity will be correlated with interfacial contact resistance measurements using a combination of focused ion beam (FIB), scanning electron microscopy (SEM) and STEM-EDS.Funding for this work was provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office through the H2NEW Consortium. Electron microscopy research conducted as part of a user project at the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.

Manufacturable Microporous Layers on Sintered Titanium for PEM Electrolysis Applications

Renewed interest in green hydrogen has prompted a re-examination of the components of proton-exchange membrane water electrolyzers to improve stack durability and lower net hydrogen cost. A key component identified as a driver of cell performance and durability is the anode porous transport layer (PTL). The PTL dictates electrical resistance between anode and flow field, manages two-phase flow at the anode interface, and sinks heat from the electrolysis reaction.Efforts to optimize the PTL have typically focused on limiting titanium passivation and optimizing delivery of water and discharge of oxygen at the anode. However, recent work has shown another important effect related to the contact area of the PTL with the anode catalyst layer. Multiple investigators have shown that highly flat and smooth PTLs enhance cell durability, particularly in the case of low anode catalyst loadings (< 0.5 mgIr/cm2). In those studies1–5, commercial PTLs were modified to obtain more uniform surfaces. In some cases this is effected by attachment of finely structured microporous layers (MPLs) that improve catalyst utilization and eliminate localized heating.An integrated manufacturing approach is required to enable commercial adoption of advanced PTLs featuring microporous layers. In this contribution, we investigate multiple routes and materials systems for obtaining manufacturable MPLs. We assess the relative merits of each method with respect to feasibility and resultant component characteristics, and validate ex situ characterization with single-cell electrolyzer durability testing using catalyst-coated membranes with low Ir loadings. References (1) Lettenmeier, P.; Kolb, S.; Sata, N.; Fallisch, A.; Zielke, L.; Thiele, S.; Gago, A. S.; Friedrich, K. A. C Energy Environ. Sci. 2017, 10 (12), 2521–2533. https://doi.org/10.1039/C7EE01240C.(2) Kang, Z.; Yang, G.; Mo, J.; Yu, S.; Cullen, D. A.; Retterer, S. T.; Toops, T. J.; Brady, M. P.; Bender, G.; Pivovar, B. S.; Green, J. B.; Zhang, F.-Y. Int. J. Hydrog. Energy 2018, 43 (31), 14618–14628. https://doi.org/10.1016/j.ijhydene.2018.05.139.(3) Lee, J. K.; Lee, C.; Fahy, K. F.; Kim, P. J.; LaManna, J. M.; Baltic, E.; Jacobson, D. L.; Hussey, D. S.; Stiber, S.; Gago, A. S.; Friedrich, K. A.; Bazylak, Energy Convers. Manag. 2020, 226, 113545. https://doi.org/10.1016/j.enconman.2020.113545.(4) Schuler, T.; Ciccone, J. M.; Krentscher, B.; Marone, F.; Peter, C.; Schmidt, T. J.; Büchi, F. N. Adv. Energy Mater. 2020, 10 (2), 1903216. https://doi.org/10.1002/aenm.201903216.(5) Lee, J. K.; Schuler, T.; Bender, G.; Sabharwal, M.; Peng, X.; Weber, A. Z.; Danilovic, N. Appl. Energy 2023, 336, 120853. https://doi.org/10.1016/j.apenergy.2023.120853. Figure 1

1D One-Phase Modeling of the Anode Catalyst Layer/Porous Transport Layer Interface Affecting Proton Exchange Membrane Water Electrolysis

Optimizing the structure of the porous transport layer (PTL) is crucial for improving the performance of proton exchange membrane water electrolysis (PEMWE), particularly for cells with low anode catalyst loadings. A growing number of studies reveal that catalysts are normally not entirely utilized in PEMWE, whereas the degree of catalyst utilization strongly depends on the structure of the PTL. As the oxygen evolution reaction (OER) at the anode is the limiting reaction step in PEMWE, inefficient use of the anode catalyst layer (aCL) would result in higher activation losses and, thus, cause a waste of unused catalysts [1–3]. This phenomenon becomes more serious when catalyst loading is reduced to meet the eco-friendly requirement of $2 per kgH2 while conserving noble material resources [4].Schuler et al. [1, 5] combined commercial CCMs with different PTL configurations, and found that with different aCL/PTL interface properties, the activation overpotential could have a maximum deviation of 20 mA at 0.1 A/cm2. Peng et al. [2] manufactured an ultra-low Ir loading CCM with 0.03 mgIr/cm2. Optimizing the aCL/PTL interface showed that the activation overpotential can have a maximum deviation of 40 mV at 0.75 A/cm2. Previous studies concluded that the aCL/PTL interface is crucial for improving the catalyst utilization. Consequently, the triple-phase boundary (TPB) site concept at the aCL/PTL interface is gaining more and more attention: the catalysts can only be entirely activated at reaction sites with sufficient water supply, ionic and electronic conductivities, and oxygen removal pathways [3]. According to TPB, not all reaction sites on the aCL meet these requirements. Figure 1 shows the corresponding physical picture. At the contact point of aCL and PTL (S) offers much greater electronic conductivity compared to the pore area (P), where electron removal is limited by the aCL in-plane conductivity (i.e., 1.85×106 S/m vs. 65.8 S/m) [3]. However, beneath the contact area (S), mass transport of oxygen is limited, indicating the necessity of optimizing the aCL/PTL interface.Figure 1: Illustration of physical picture at aCL/PTL interface.In our contribution, we implement a one-dimensional, one-phase model to investigate the interplay between PTL geometry at the aCL/PTL interface and catalyst utilization. The PTL transports water toward the aCL and electrons and oxygen toward the cathode and anode bipolar plates, respectively [6]. To simplify the physical conditions, we assume sufficient water supply and ion removal for the reaction sites on the aCL. Therefore, mass transport and electron transport limitations are only influenced by the aCL/PTL interface properties. Oxygen is assumed to dissolve in water only so that bubble formation does not disturb the reaction sites. Additionally, an ideal heat management condition is assumed in the model to achieve an isothermal condition. Our simulation results are in good agreement with literature, enabling the prediction of activation overpotentials corresponding to the PTL structure at aCL/PTL interface. Moreover, our results illustrate the local aCL behavior, which can be used to optimize the porous structure at the aCL/PTL interface, maximizing catalyst utilization. With our model, we aim to screen for an optimum PTL structure for a given aCL, allowing us to improve PEMWE cell performance by minimization of activation losses.

Incorporation of PEDOT:PSS to Reduce Iridium Loading at Anode Catalyst Layer for Proton Exchange Membrane Water Electrolysis

Proton exchange membrane water electrolysis (PEMWE) is one of the most promising technologies to produce green hydrogen with high efficiency. However, its commercialization is hindered by the large usage of expensive iridium as anode electrocatalyst [1-3] . Incorporation of cheap conductive materials into the catalyst ink, e.g., titanium powder [4], is a straightforward and efficient method to reduce noble metal loading of membrane electrode assembly (MEA). In this study, we aimed to use a conductive polymer PEDOT:PSS to build the low Ir loading catalyst layer for PEMWE.The MEAs at 0.3 mgIr cm-2 loading were fabricated with different PEDOT:PSS contents. In practice, the dispersion of IrO2 particles is difficult in catalyst ink, leading to the formation of big IrO2 agglomerates. We found that the zeta potential of the anode catalyst ink gained obvious enhancement after the addition of PEDOT:PSS. This indicated that PEDOT:PSS as dispersant could increase the stability of the catalyst ink. The morphology of anode catalyst layers was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface and cross-sectional images of morphology exhibited small IrO2 particles and porous structure in the catalyst layer with the addition of PEDOT:PSS, which would contribute to the water/gas movement in triple-phase boundaries. Electrochemical measurements such as polarization curves, electrochemical impedance spectroscopy (EIS), cyclic voltammogram (CV) and durability tests were conducted in a PEMWE single cell. The MEA using PEDOT:PSS as binder displayed better electrochemical performance (3.4 A cm-2@2.0 V) than other references with Nafion only (2.4 A cm-2@2.0 V). Moreover, the addition of PEDOT:PSS improved the high-frequency resistance due to its excellent electronic conductivity. In consideration of the conductive binder and dispersant effect of PEDOT:PSS, future research will focus on reducing Ir loading below 0.1 mg cm-2 through designing novel structure of anode catalyst layer with PEDOT:PSS. Keywords:PEM water electrolysis, low iridium loading, PEDOT:PSS

Impact of Low Catalyst Loading and Incorporation of Additives on Structure and Performance of PEM Electrolyzer Catalyst Layers

Polymer electrolyte membrane water electrolyzers (PEMWEs) are an important technology that can produce renewable hydrogen on demand, although with challenges posed by the slow kinetics of the anodic oxygen evolution reaction (OER) and degradation issues. The degradation of membrane electrode assemblies (MEAs) prepared with Ir-based catalysts is not well understood, especially with lower-loading catalyst layers and intermittent load inputs. This work investigates low-loading IrO2 catalyst layers made with different carbon-based additives, including high-surface-area carbon (HSC), graphitized HSC (gHSC), Vulcan, graphitic carbon nanofibers (gCNFs), graphitic nanoplatelets (gNPs), nitrogen-doped carbon spheres (NCs), Ti carbide (TiC) and Ti carbonitride (TiCN). While carbon-based supports have issues with corrosion at high oxidizing potentials, these materials provide a range of variations in morphology, shape, size, surface area, graphitization, and composition, allowing exploration of the impact of these parameters on catalyst layer structure to identify promising routes to improve catalyst layer structures. Catalyst layers were characterized with electron microscopy and x-ray spectroscopy to assess the distribution of catalyst, carbon additive, and ionomer. This information was correlated with electrochemical performance measurements to elucidate the impact on kinetic site access and mass transport. Selected samples were also subjected to more extended operation to investigate how the initial structures and their performance evolved.

Understanding Porous Transport Layer Structure-Property-Performance Relationships in PEM Water Electrolyzers

Low temperature electrolysis (LTE) is a very promising technology to help with the decarbonization of the energy sector through the production of green hydrogen from renewable energy sources. The DOE has recently launched the first Energy Earthshot targeting the reduction of clean hydrogen cost by 80% to $1 per 1 kg H2 produced in 1 decade. To reach such ambitious targets the technology development needs to consider both capital expenditures (CAPEX) such as material and component costs and their lifetimes, as well as operational expenditures (OPEX) such as cell performance and efficiency. One component that touches on either expenditure is the porous transport layer (PTL). The PTL provides various key functions within an electrolysis cell/stack. It provides transport pathways for electrons, water and gas, and mechanical support for the membrane. Its interface with the catalyst layer is crucial with regards to the limitation of ohmic overpotentials, but also heat transport within the cell. PTLs are currently fabricated from sintered Ti materials that are required to be coated with a PGM material when operated with low loading catalyst layers. Multi-layer PTL materials may further improve cell performance and enable the thrifting of catalyst loadings and the utilization of thin membrane materials. This presentation will introduce the various functionalities of the PTL and highlight research and development efforts including those of DOE’s H2New Consortium and NREL. Specifically impacts of PTL morphology, PTL coatings, and PTL/catalyst layer interactions will be discussed.

Gas Diffusion Electrode for Oxygen Evolution Reaction Catalyst Testing

The oxygen evolution reaction (OER) is one of the major contributors of efficiency loss in water electrolysis and consequently, development of OER catalysts to improve the electrolyser efficiency is a major reasearch theme in the field. Though the current commercial PEMWE may operate at anode potential <1.60 V, futue PEMWE may operate at potential higher than this as the drive to operate PEMWE at high current density is inceasing. Inorder to achieve this, an active and stable catalyst is required that can operate at this regime. Also, the potential experienced by the anode during the startup/shutdown of an electrolyser are different to the steady state value.Conventional OER testing involves catalysts coated on a conductive substrate submerged in an electrolyte solution, in a three electrode cell. However, such techniques are generally limited to low current densities due to oxygen bubble formation and site blocking at high current density limiting the system to study the OER kinetics below realistic operating current density. Although Rotating Disk Electrode(RDE) is widely employed to mitigate this, the RDE system is still not effective enough to remove the bubbles1.A floating electrode system developed by Kucernak et al2 shows that combining direct access with a lower catalyst loading improves the O2 gas mass transport and a higher current density could be achieved for the ORR. This technique also used for OER by Arenz et al.3, for easier bubble removal. Combining these two above mentioned systems, we have developed a new GDE cell system which allows screening of OER catalyst at industrially relevant current densities. This cell allows to study the OER kinetics at very realistic voltage/current regime and the information obtained helps to develop more active/stable catalyst.The OER catalyst diagnostics test from our GDE cell was comparable to the standard three electrode cell with an additional advantage of extended potential window upto 1.80 V vs.RHE. Preliminary results obtained from our study shows a promising opportunity to study the OER at high current densities.Reference FathiTovini, A.Hartig-Weiß, H.A.Gasteigerand, H.A.El Sayed, Journal of The ElectrochemicalSociety, 2021, 168, 014512.M.Zalitis,D.KramerandA.R.Kucernak,Phys.Chem.Chem.Phys.,2013,15,4329-4340Schröder,V.A.Mints,A.Bornet,E.Berner,M.FathiTovini,J.Quinson,etal., JACS Au 2021,1(3),247-25

MCM‐41@CPTMS as an Efficient and High‐Performance Catalyst for One‐Pot Construction of Indeno[1,2‐b]quinolin‐8‐one Derivatives**

AbstractIn this work, MCM‐41@CPTMS nanoparticles were readily prepared and evaluated as acidic nanosilica spheres for the synthesis of indeno[1,2‐b]quinolinone derivatives through one‐pot three‐component reaction of 1‐naphthylamine, aromatic aldehydes and 1,3‐indandione. A high surface area, a hexagonal array of uniform mesoporous, high thermal stability, recyclability, nontoxicity and the easy separation of the nanocatalyst, make this nanocatalyst very useful for the synthesis of organic compounds. Mesoporous silica nanoparticles (MSN) was prepared easily and affirmed to be effective and prepared the products with excellent yields under reflux conditions. The structure of obtained nanoparticles was characterized by FE‐SEM, TEM, EDX, FT‐IR, XRD, TGA and BET. This synthetic protocol provides several benefits such as excellent yields in short reaction times (83–97 %),saving costs, reusability of the catalyst (five runs), and low catalyst loading.

Organocatalytic Stereospecific Appel Reaction.

Herein we report a new method for the catalytic Appel reaction by P(III)/P(V) redox cycling at very low catalyst loadings of 1-2 mol % using low amounts of hexachloroacetone as the halogen source and phenylsilane as the terminal reductant. Twenty-six alcohols and nine epoxides containing a wide variety of functional groups were converted to the respective chlorides and dichlorides in yields of up to 97%, enantiospecificities of up to >99%, and enantiomeric ratios of up to >99:1.

Performance scrutiny of spent lithium-ion batteries cathode material as a catalyst for oxidation of benzyl alcohol

The widespread use of Li-ion batteries (LIBs) in energy storage devices has resulted in the generation of additional waste which contains valuable metal ions and these metal ions are well known for their catalytic activities. The recovered black mass of cathode material was exposed to pretreatment with final calcination for 2 h at 800 0C. After the calcination, the material was subjected to structural characterization (XRD, FE-SEM, EDAX, and XPS). In the present work, we have used spent LIBs cathode material as a catalyst for the oxidation reaction of benzyl alcohol to benzoic acid. The catalytic activity of this recovered cathode material was found to be highly efficient showing 100% conversion of benzyl alcohol with >99% selectivity of benzoic acid with lower catalyst loading of even 2%.

Unsymmetrical Bis‐Coumarin Based on o‐Hydroxy Aldehydes and 4‐Hydroxy Coumarin: Expedient Synthesis, Single Crystal X‐rays and DFT Studies

AbstractBis‐coumarins are distinguished derivatives of coumarin which bear numerous pharmaceutical and other applications. In continuation of our ongoing research towards the development of benign protocols for various heterocyclic systems, herein we report an Amberlyst 15 mediated synthesis of unsymmetrical bis‐coumarins via in situ generation and cyclization of symmetrical bis‐coumarinyl methanes derived from o‐hydroxy aromatic aldehydes and 4‐hydroxy coumarin. Aldehydes of both electron‐donating and electron‐withdrawing units underwent smooth conversion to their respective unsymmetrical bis‐coumarins (76–98 % yield) without leaving any side products or intermediates. The catalyst used in the present protocol is cost‐effective, eco‐friendly, and readily available which could be recovered and reused several times. This methodology offers operational simplicity, low catalyst loading, and avoids the use of toxic solvents/reagents and the product can be isolated without chromatography. DFT study indicated that the driving force for the cyclisation of symmetrical bis‐coumarin is the minimization of the tetrahedral bond angle deviations along with other small non‐covalent interactions. Some DFT data was also verified with the data obtained from the X‐rays crystallographic study.

A Sequential Transition Metal and Organocatalytic Approach to the Enantioselective Synthesis of C2-Spiroindoline Systems.

We report herein an organocatalyzed enantioselective spirocyclization strategy to access valuable C2-spiroindoline scaffolds bearing a quaternary stereocenter via an aza-Michael addition reaction, wherein the acid additive plays the role of dual functionality. The substrates for this key step were put together by an exo-selective, Pd-catalyzed γ-arylation of silyldienol ethers of the corresponding cyclohexenones. A close alliance between a low catalyst loading and a slow reaction rate yields C2-spiroindolines with good enantioselectivity.