Low Catalyst Loading Research Articles

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.

Enhanced photocatalytic degradation of methylene blue dye using eco-friendly synthesized rGO@ZnO nanocomposites

Industrial chemical pollutants such as methylene blue (MB) dye are released into the water body and potentially cause harm to the human and aquatic biosphere. Therefore, this study aims to synthesize eco-friendly nanocatalysts, i.e., reduced graphene oxide (rGO), zinc oxide (ZnO), and reduced graphene oxide-zinc oxide (rGO@ZnO) nanocomposites, for efficient photocatalytic degradation of MB dye. A graphite rod was obtained from waste dry cell batteries for the electrochemical exfoliation synthesis of graphene oxide (GO) and rGO. For the eco-friendly synthesis of ZnO and rGO@ZnO nanocatalysts, Croton macrostachyus leaf extract was used as a reducing and capping agent. The synthesized nanocatalysts were characterized using a UV–Vis spectrophotometer, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy with energy-dispersive X-ray. The eco-friendly synthesized rGO, ZnO, and rGO@ZnO nanocatalysts were applied for the photocatalytic degradation of MB dye using direct sunlight irradiation. At optimum parameters, photocatalytic degradation of MB dye efficiency reached up to 66%, 96.5%, and 99.0%, respectively. Furthermore, kinetics of the photodegradation reaction based on rGO, ZnO, and rGO@ZnO nanocatalysts follow pseudo-first-order with a rate constant of 2.16 × 10–3 min−1, 4.97 × 10−3 min−1, and 5.03 × 10−3 min−1, respectively. Lastly, this study promotes a low catalyst load (20 mg) for the efficient photodegradation of MB dye.

Dirhodium-Catalyzed Enantioselective Synthesis of Difluoromethylated Cyclopropanes via Enyne Cycloisomerization.

(Difluoromethylated cyclopropane represents an important motif, which is widely found in bioactive and functional molecules. Despite significant progress in modern chemistry, the atom-economic and enantioselective synthesis of difluoromethylated cyclopropanes is still challenging. Herein, an Rh2 (II)-catalyzed asymmetric enyne cycloisomerization is described to construct chiral difluoromethylated cyclopropane derivatives with up to 99% yield and 99% ee in low catalyst loading (0.2 mol%), which can be easily transformed into highly functionalized difluoromethylated cyclopropanes with vicinal all-carbon quaternary stereocenters by ozonolysis. Mechanistic studies and the crystal structures of alkyne-dirhodium complexes reveal that the cooperative weak hydrogen bondings between the substrates and the dirhodium catalyst may play key roles in this reaction.).

Markovnikov-Selective Cobalt-Catalyzed Wacker-Type Oxidation of Styrenes into Ketones under Ambient Conditions Enabled by Hydrogen Bonding.

The replacement of palladium catalysts for Wacker-type oxidation of olefins into ketones by first-row transition metals is a relevant approach for searching more sustainable protocols. Besides highly sophisticated iron catalysts, all the other first-row transition metal complexes have only led to poor activities and selectivities. Herein, we show that the cobalt-tetraphenylporphyrin complex is a competent catalyst for the aerobic oxidation of styrenes into ketones with silanes as the hydrogen sources. Remarkably, under room temperature and air atmosphere, the reactions were exceedingly fast (up to 10 minutes) with a low catalyst loading (1 mol %) while keeping an excellent chemo- and Markovnikov-selectivity (up to 99 % of ketone). Unprecedently high TOF (864 h-1 ) and TON (5,800) were reached for the oxidation of aromatic olefins under these benign conditions. Mechanistic studies suggest a reaction mechanism similar to the Mukaiyama-type hydration of olefins with a change in the last fundamental step, which controls the chemoselectivity, thanks to a unique hydrogen bonding network between the ethanol solvent and the cobalt peroxo intermediate.

Markovnikov‐Selective Cobalt‐Catalyzed Wacker‐Type Oxidation of Styrenes into Ketones under Ambient Conditions Enabled by Hydrogen Bonding

AbstractThe replacement of palladium catalysts for Wacker‐type oxidation of olefins into ketones by first‐row transition metals is a relevant approach for searching more sustainable protocols. Besides highly sophisticated iron catalysts, all the other first‐row transition metal complexes have only led to poor activities and selectivities. Herein, we show that the cobalt‐tetraphenylporphyrin complex is a competent catalyst for the aerobic oxidation of styrenes into ketones with silanes as the hydrogen sources. Remarkably, under room temperature and air atmosphere, the reactions were exceedingly fast (up to 10 minutes) with a low catalyst loading (1 mol %) while keeping an excellent chemo‐ and Markovnikov‐selectivity (up to 99 % of ketone). Unprecedently high TOF (864 h−1) and TON (5,800) were reached for the oxidation of aromatic olefins under these benign conditions. Mechanistic studies suggest a reaction mechanism similar to the Mukaiyama‐type hydration of olefins with a change in the last fundamental step, which controls the chemoselectivity, thanks to a unique hydrogen bonding network between the ethanol solvent and the cobalt peroxo intermediate.

Convenient access to amidines by mesoionic singlet palladium carbene catalyzed hydrazone-isocyanide-amine (HIA) coupling: Scope and mechanistic insights

Facile synthesis of amidines 5(a-j), 6(a-g) and 7(a-j) by the tandem three-component coupling of N-tosylhydrazones, isocyanides and amines catalysed by the molecular binuclear Pd mesoionic singlet carbene complexes namely, [(R)-1,1′-(C10H6)2–2,2′-(OCH2(1-CH2Ph-3-R-1,2,3-triazol-5-ylidene))2]Pd2I4(NC5H5)2 [R = Me (4a) and Et (4b)] was achieved in good to excellent yields of ca. 51–97% at a low catalyst loading of 0.5 mol% in 6 h of the reaction time. A large opportunity for the utility of this coupling reaction was evident from its broader substrate scope arising from the use of a wide range of N-tosyl hydrazones, amines, and aromatic as well as aliphatic isocyanides. Combined experimental and computational studies performed on the representative substrates namely, PhCHNNHTs, 2,6-Me2C6H3NC, and morpholine indicated that the catalysis proceeded via the formation of palladium (0) active species [(R)-1,1′-(C10H6)2–2,2′-(OCH2(1-CH2Ph-3-R-1,2,3-triazol-5-ylidene))2]Pd2(2,6-Me2C6H3NC)2 [R = Me (B1), Et (B2)] alongside the generation of a ketenimine intermediate 2,6-Me2C6H3NCCHPh in the tricomponent coupling reaction. The dinitrogen elimination from the metal-coordinated diazo intermediate represents the rate-determining step of the reaction. The mechanistic revelations brought forth in this study hold promising potential for enriching our understanding of multi-component reactions leading to amidines enabled by transition metal catalysts.

Biodiesel from Waste Cooking Oil: Highly Efficient Homogeneous Iron(III) Molecular Catalysts

This article presents an efficient iron(III) molecular catalyst for the production of biodiesel from waste vegetable oils. The approach involved an initial screening of eight salophen complexes with various substituents on the arene rings, leading to the selection of the simplest unsubstituted species as the most active catalyst. Under optimized conditions, this catalyst demonstrated the capability to achieve complete conversion of the oil at a low catalyst loading (0.10% mol/mol) and convenient conditions (160 °C, 20/1 MeOH/oil ratio).

Functionalized Coal Fly Ash Is an Efficient Catalyst for Synthesizing Furfural from Xylose at a Low Catalyst Load

In this study, coal fly ash was functionalized, using a simple one-step process (loading with Al3+ and sulfonation), to yield a solid acid catalyst (S/Al-CFA) with strong acid sites. The catalyst was then used to produce furfural from xylose in a biphasic system (H2O(NaCl)/tetrahydrofuran). The furfural yield reached 82% at 180 °C–60 min with catalyst/xylose ratio of 0.2:1.0 (w/w). With the reaction completed, all of the components could be effectively separated, and the furfural was 97.6% pure. The cycle and regeneration of the catalyst were evaluated, and the catalyst deactivation mechanism was investigated.

Synthesis and Antibacterial Activity of Spiro[4H-pyran-3,3'-oxindoles] Catalyzed by Tröger's Base Derivative.

Two classes of spiro[4H-pyran-3,3'-oxindole] derivatives were prepared via the one pot reaction of chain diketones (1-phenyl-1,3-butanedione or dibenzoyl methane), substituted isatins and malononitrile successfully catalyzed by a Tröger's base derivative 1b (5,12-dimethyl-3,10-diphenyl-bis-1H-pyrazol[b,f][4,5]-1,5-diazadicyclo[3.3.1]-2,6-octadiene). The antibacterial activity of products against three wild-type bacteria (B. subtilis, S. aureus, and E. coli) and two resistant strains (Methicillin-resistant S. aureus (18H8) and E. coli carrying the BlaNDM-1 gene (18H5)) was evaluated using the minimum inhibitory concentration (MIC).. 1-Phenyl-1,3-butanedione 2 or dibenzoylmethane 2' (0.42 mmol), substituted isatin 3 (0.4 mmol), malononitrile 4 (0.8 mmol), Tröger's base derivative 1b (0.08 mmol), and 10 mL of acetonitrile were added to a 50 mL round bottom flask and refluxed. After the completion (TLC monitoring), water (10 mL) was added to the reaction mixture; pH = 7 was adjusted with saturated NaHCO3 (aq.), and the mixture was extracted with CH2Cl2 (50 mL × 3). Organic layers were combined and dried with anhydrous Na2SO4; the solvent was removed under vacuum, and the residue was purified by column chromatography (VDCM: VMeOH = 80: 1) to afford product 5. The antibacterial activity was tested by the MTT method. Seventeen spiro[4H-pyran-3,3'-oxindole] derivatives were synthesized through the reaction of chain diketones (1-phenyl-1,3-butanedione or dibenzoyl methane), substituted isatins, and malononitrile in one-pot in medium to high yields. Four compounds showed antibacterial activity, and two of them showed the same activity as the positive control Ceftazidime on S. aureus (MIC = 12.5 μg/mL). Two classes of spiro[4H-pyran-3,3'-oxindole] derivatives were prepared, and their antibacterial activity was evaluated. Tröger's base derivative 1b (5,12-dimethyl-3,10-diphenyl-bis-1H-pyrazol[b,f][4,5]- 1,5-diazadicyclo[3,3,1]-2,6-octadiene) was used as an efficient organocatalyst for the reaction of low reactive chain diketones (1-phenyl-1,3-butanedione or dibenzoyl methane), substituted isatins, and malononitrile in one-pot successfully and effectively by providing multiple active sites and alkaline environment. By the theoretical calculation, we explained the possible reaction sequence and mechanism. Due to the superiority and high efficiency of the TB framework as an organocatalyst, the reaction showed many advantages, including mild reaction conditions, low catalyst loading, and a wide substrate range. It expanded the application of Tröger's base to the multicomponent reaction in organocatalysis. Some products were screened due to their high antibacterial activity in vitro, showing their potential in new antibacterial drug development.

Chemical-Dealloying-Derived PtPdPb-Based Multimetallic Nanoparticles: Dimethyl Ether Electrocatalysis and Fuel Cell Application.

In this work, we report a novel multimetallic nanoparticle catalyst composed of Pt, Pd, and Pb and its electrochemical activity toward dimethyl ether (DME) oxidation in liquid electrolyte and polymer electrolyte fuel cells. Chemical dealloying of the catalyst with the lowest platinum-group metal (PGM) content, Pt2PdPb2/C, was conducted using HNO3 to tune the catalyst activity. Comprehensive characterization of the chemical-dealloying-derived catalyst nanoparticles unambiguously showed that the acid treatment removed 50% Pb from the nanoparticles with an insignificant effect on the PGM metals and led to the formation of smaller-sized nanoparticles. Electrochemical studies showed that Pb dissolution led to structural changes in the original catalysts. Chemical-dealloying-derived catalyst nanoparticles made of multiple phases (Pt, Pt3Pb, PtPb) provided one of the highest PGM-normalized power densities of 118 mW mgPGM-1 in a single direct DME fuel cell operated at low anode catalyst loading (1 mgPGM cm-2) at 70 °C. A possible DME oxidation pathway for these multimetallic catalysts was proposed based on an online mass spectrometry study and the analysis of the reaction products.

KA2 Coupling, Catalyzed by Well‐Defined NHC‐Coordinated Copper(I): Straightforward and Efficient Construction of α‐Tertiary Propargylamines**

AbstractA new, straightforward, highly efficient, and mild catalytic protocol for the synthesis of α‐tertiary propargylamines, via the multicomponent KA2 reaction (Ketone‐Amine‐Alkyne), employing well‐defined, sustainable copper(I) complexes bearing N‐heterocyclic carbene ligands, is reported herein. The methodology uses very low catalyst loading under moderate heating to achieve the construction of a wide range of propargylamines in good to excellent yields in very short reaction times. Challenging substrates, including acyclic linear ketones, aromatic ketones, and electron‐poor aromatic alkynes, as well as substrates bearing synthetically valuable functionalities, are well tolerated.

Allylation of C-, N-, and O-Nucleophiles via a Mechanochemically-Driven Tsuji-Trost Reaction Suitable for Late-Stage Modification of Bioactive Molecules.

We present the first solvent-free, mechanochemical protocol for a palladium-catalyzed Tsuji-Trost allylation. This approach features exceptionally low catalyst loadings (0.5 mol %), short reaction times (<90 min), and a simple setup, eliminating the need for air or moisture precautions, making the process highly efficient and environmentally benign. We introduce solid, nontoxic, and easy-to-handle allyl trimethylammonium salts as valuable alternative to volatile or hazardous reagents. Our approach enables the allylation of various O-, N-, and C-nucleophiles in yields up to 99 % even for structurally complex bioactive compounds, owing to its mild conditions and exceptional functional group tolerance.

Allylation of C-, N-, and O-Nucleophiles via a Mechanochemically-Driven Tsuji-Trost Reaction Suitable for Late-Stage Modification of Bioactive Molecules.

We present the first solvent-free, mechanochemical protocol for a palladium-catalyzed Tsuji-Trost allylation. This approach features exceptionally low catalyst loadings (0.5 mol %), short reaction times (<90 min), and a simple setup, eliminating the need for air or moisture precautions, making the process highly efficient and environmentally benign. We introduce solid, nontoxic, and easy-to-handle allyl trimethylammonium salts as valuable alternative to volatile or hazardous reagents. Our approach enables the allylation of various O-, N-, and C-nucleophiles in yields up to 99 % even for structurally complex bioactive compounds, owing to its mild conditions and exceptional functional group tolerance.