Manganese Catalysts Research Articles

Two-dimensional porphyrin sheet-supported single-atom manganese catalyst for CO oxidation: A DFT-D study

The mechanism of CO oxidation on two-dimensional porphyrin sheet (TDPS)-supported single atom manganese was studied using density functional theory with dispersion (DFT-D). The molecular dynamics (MD) simulation based on the first principles has been used for confirming Mn–TDPS stability. The energetic calculations indicated that CO and O2 were favorable to co-adsorb at the active center. Eley–Rideal, Langmuir–Hinshelwood (LH), and tri-molecular Eley–Rideal (TER) mechanisms were used to investigate the reaction pathways of CO oxidation on the Mn–TDPS. Results indicated that the LH and TER reaction mechanisms were feasible due to the small energy barrier of the rate-determining step. Moreover, the oxidation states of the active center of Mn–TDPS affected the reaction barrier and reaction heat, which was unfavorable for CO oxidation in Mn–TDPS. These results findings suggested that Mn–TDPS could be a high activity catalyst for CO oxidation.

Kinetika Reaksi Hidrogenasi Ester Lemak Menjadi Alkohol Lemak Dengan Katalis Tembaga- Mangan

Fatty alcohol (FAOH) can be produced by hydrogenating of fatty acid methyl ester (FAME) using the copper-based catalyst. Copper-Chrom (Cu-Cr) is the best catalyst for high-pressure reaction condition, which is copper (Cu) as the main active component and chrom (Cr) as a promoter. Since Cr is feared to be toxic, one of the best replacement candidates is manganese (Mn). The research aims is to find the kinetic equation of hydrogenation FAME to FAOH using a Cu-Mn commercial catalyst. FAME with methyl laurate and methyl myristate as the main compounds is used as feedstock. The main products are lauryl alcohol and myristyl alcohol. The reaction was carried out in an isothermal continuous fixed bed reactor under conditions of temperature 220 – 240 oC, pressure 50 bar, and liquid hourly space velocity (LHSV) 5-12.5 hr-1. The kinetic equation is determined using the power law model. The FAME hydrogenation on copper - manganese catalyst is the half order reaction. The activation energy value is 86.32 kJ/mol and the Arrhenius constant value is 5.87x106 M0.5/s.

Manganese-Catalyzed Regioselective Dehydrogenative C- versus N-Alkylation Enabled by a Solvent Switch: Experiment and Computation.

The first base metal-catalyzed regioselective dehydrogenative alkylation of indolines using readily available alcohols as the alkylating reagent is reported. A single air- and moisture-stable manganese catalyst provides access to either C3- or N-alkylated indoles depending on the solvent used. Mechanistic studies indicate that the reaction takes place through a combined acceptorless dehydrogenation and hydrogen autotransfer strategy.

Sustainable Hydrogen Production through Electrocatalytic Water Splitting with Manganese and Nickel-Based Catalysts

Solar-driven water splitting has potential for sustainable solar energy conversion and storage in the form of fuels. Its practical use requires highly effective yet non-expensive electrocatalysts synthesized from earth-abundant materials. Here we report a new electrocatalytic system with two electrocatalysts based on Mangnese and Nickel for effective electrocatalytic water splitting. We have developed a synthesis method for a manganese-based (MnOx) water oxidation catalytic films in situ fromaqueous media. This method involves two series of electrodepositions by cyclic voltammetry (CV) over different potential ranges to tune the oxidation state of the catalyst, followed by calcination to increase its crystallinity. The resulting film has a morphology of uniformly distributed fibrous nanoscale as well as stable and excellent catalytic performance toward water oxidation. The resulting onset potential is so low that a single AA alkaline battery can be used to power the water splitting process. For the hydrogen evolution reaction, we have developed an electrodeposition method to synthesize Ni/Ni(OH)2 electrocatalysts in situ on conductive surfaces. The new method uses two cycles of CV over a single potential range, producing a film with a large number of Ni(OH)2/Ni interfaces which significantly shifts performance towards that of platinum.The new method involves only two cycles of CV over a single potential range. The resulting catalytic film has a morphology of packed walnut-shaped particles. It has superior catalytic activity and good stability over long periods. To test the functionality of the entire catalytic system, we have connected the two electrocatalysts in tandem and the system has shown stable water splitting functionality with low overpotential.

Site-Selective and Product Chemoselective Aliphatic C–H Bond Hydroxylation of Polyhydroxylated Substrates

Site-selective and product chemoselective aliphatic C–H bond oxidation of 1,2-diols and of polyhydroxylated substrates using iron and manganese catalysts and hydrogen peroxide as terminal oxidant i...

Late-stage oxidative C(sp3)–H methylation

Frequently referred to as the 'magic methyl effect', the installation of methyl groups-especially adjacent (α) to heteroatoms-has been shown to dramatically increase the potency of biologically active molecules1-3. However, existing methylation methods show limited scope and have not been demonstrated in complex settings1. Here we report a regioselective and chemoselective oxidative C(sp3)-H methylation method that is compatible with late-stage functionalization of drug scaffolds and natural products. This combines a highly site-selective and chemoselective C-H hydroxylation with a mild, functional-group-tolerant methylation. Using a small-molecule manganese catalyst, Mn(CF3PDP), at low loading (at a substrate/catalyst ratio of 200) affords targeted C-H hydroxylation on heterocyclic cores, while preserving electron-neutral and electron-rich aryls. Fluorine- or Lewis-acid-assisted formation of reactive iminium or oxonium intermediates enables the use of a mildly nucleophilic organoaluminium methylating reagent that preserves other electrophilic functionalities on the substrate. We show this late-stage C(sp3)-H methylation on 41 substrates housing 16 different medicinally important cores that include electron-rich aryls, heterocycles, carbonyls and amines. Eighteen pharmacologically relevant molecules with competing sites-including drugs (for example, tedizolid) and natural products-are methylated site-selectively at the most electron rich, least sterically hindered position. We demonstrate the syntheses of two magic methyl substrates-an inverse agonist for the nuclear receptor RORc and an antagonist of the sphingosine-1-phosphate receptor-1-via late-stage methylation from the drug or its advanced precursor. We also show a remote methylation of the B-ring carbocycle of an abiraterone analogue. The ability to methylate such complex molecules at late stages will reduce synthetic effort and thereby expedite broader exploration of the magic methyl effect in pursuit of new small-molecule therapeutics and chemical probes.

Levulinic Acid Production from Delignified Rice Husk Waste over Manganese Catalysts: Heterogeneous Versus Homogeneous

Delignified rice husk waste (25.66% (wt) cellulose) was converted to levulinic acid using three types of manganese catalysts, i.e., the Mn3O4/hierarchical ZSM-5 zeolite and Mn3O4 heterogenous catalysts, as well as Mn(II) ion homogeneous counterpart. The hierarchical ZSM-5 zeolite was prepared using the double template method and modified with Mn3O4 through wet-impregnation method. The structure and physicochemical properties of the catalyst materials were determined using several solid-state characterization techniques. The reaction was conducted in a 200 mL-three neck-round bottom flask at 100 °C and 130 °C for a certain reaction time in the presence of 10% (v/v) phosphoric acid and 2% (v/v) H2O2 aqueous solution, and the product was analyzed using HPLC. In general, 5-hydroxymethyl furfural (5-HMF) as the intermediate product was produced after 2 h and decreased after 4 h reaction time. To conclude, the Mn3O4/hierarchical ZSM-5 heterogenous catalyst gave the highest yield (wt %) of levulinic acid (39.75% and 27.60%, respectively) as the main product, after 8 h reaction time.

Manganese Catalysts with Tetradentate N-donor Pyridine-Appended Bipiperidine Ligands for Olefin Epoxidation Reactions: Ligand Electronic Effect and Mechanism

In this work, we described an electron-rich manganese mesoPYBP catalyst, Mn-SR-mesoPYBP(ClO4)2, by introducing electron-donating substituents on the mesoPYBP ligand. We optimized the catalytic performance in olefin epoxidation with H2O2 in the presence of acetic acid. The electron paramagnetic resonance (EPR) and cyclic voltammetry (CV) studies supported that an electronic effect could stabilize the high-valent intermediates in the catalytic cycles of the catalyst, which largely improved the catalytic performance and the reactivity of olefin epoxidation.

Silica-Supported Manganese(II) Catalyst for Carbonyl Hydrosilylation, Hydroboration, and Transesterification

Key words manganese catalysis - silica - hydrosilylation - hydroboration - transesterification

A novel Microcystis aeruginosa supported manganese catalyst for hydrogen generation through methanolysis of sodium borohydride

In this study, Microcystis Aeruginosa (MA)- microalgae species was used for the first time as a support material with metal ions loading to fabricate a highly efficient catalyst for the hydrogen generation through methanolysis of sodium borohydride (NaBH4). Microalgae was pre-treated with hydrochloric acid (3 M HCl) for 24 h at 80 °C. Subsequently, different metal ions (Mn, Co, and Mo) were loaded to the pre-treated samples. Finally, metal-loaded samples were subjected to burning in oven to fabricate the catalyst. Primarily, manganese metal was selected based on the best metal performance. Afterwards, different metal loading ratios, burning temperatures and burning times were evaluated to synthesize the optimal MA-HCl-Mn catalyst. Results showed the optimal conditions as Mn ratio, burning temperature and time as 50%, 500 °C and 45 min, respectively. To characterize the catalyst, FTIR, SEM-EDX, XRD, XPS and TEM analyses were performed. Hydrogen generation via methanolysis was performed at various NaBH4 ratio of 1–7.5% while changing concentrations from 0.05 to 0.25 g catalysts with diverge temperatures of (30, 40, 50 and 60 °C). The maximum hydrogen generation rate (HGR) by this novel catalyst was found as 4335.3, 5949.9, 7649.4 and 8758.9 mLmin−1gcat−1, respectively. Furthermore, the activation energy was determined to be 8.46 kJ mol−1.

A pulse modulatable self-oscillation kinetics for water oxidation at large current on manganese catalyst

As a common obstacle for promoting water oxidation efficiency during the fast-charging of batteries or the industrial fuel production, it is in urgent need to clarify the unclear kinetics for the serious efficiency decline or decomposition of catalysis at a large current of >1000 A/m2. In this work, the intensified contribution of a kinetic pathway at large current to the water oxidation process on manganese catalyst was revealed. This pathway was proposed and verified by the observation of the periodic electrochemical self-oscillation, which can be modulated by external electrical pulse with different amplitude and frequency. At an external pulse with an average current of 0.08 A/cm2 and a frequency of 130 Hz, the intrinsic self-oscillation can result in ∼14.6% reduction of power consumption. The kinetic role of peroxide and Mn(III) intermediates in this pathway was also analyzed, in order to provide both a mechanism insight and possible energy-saving strategies for industrial process.

Intermolecular Iodofluoroalkylation of Unactivated Alkynes and Alkenes Mediated by Manganese Catalysts

AbstractAn approach for iodofluoroalkylation of unactivated alkynes and alkenes facilitated by an earth‐abundant and inexpensive manganese catalyst, Mn2(CO)10, is reported. This protocol employs visible light as the energy input and shows a wide substrate scope and high functional‐group compatibility. A variety of synthetically useful fluoroalkylated alkyl and alkenyl iodides can be prepared in moderate to excellent yields. The reaction features high efficiency, operational simplicity, scalability, as well as excellent chemo‐, regio‐, and E/Z selectivities.magnified image

Manganese Catalyzed Acceptorless Dehydrogenative Coupling Reactions

AbstractAcceptorless dehydrogenative coupling (ADC) has emerged as a powerful tool in the chemists’ arsenal for the construction of various carbon‐carbon and carbon‐heteroatom bonds. These protocols are highly atom economical and environmentally benign as they do not require pre‐functionalized starting material and produce only dihydrogen (and water) as the by‐product. This technique, coupled with Earths’ abundant and less toxic manganese catalysis, can prove to be a vital strategy for the generation of molecular complexity from simple starting materials. Manganese catalyzed DHC has been of growing interest, and various low‐ and high‐valent manganese catalysts have been developed. These catalysts were demonstrated to show excellent catalytic activity for the formation of carbon‐carbon, carbon‐heteroatom bonds, and cascade reactions. In this mini‐review, we would like to highlight the recent progress that has been made in manganese catalyzed ADC reactions.

Concerted proton-electron transfer reactions of manganese-hydroxo and manganese-oxo complexes.

The enzymes manganese superoxide dismutase and manganese lipoxygenase use MnIII-hydroxo centres to mediate proton-coupled electron transfer (PCET) reactions with substrate. As manganese is earth-abundant and inexpensive, manganese catalysts are of interest for synthetic applications. Recent years have seen exciting reports of enantioselective C-H bond oxidation by Mn catalysts supported by aminopyridyl ligands. Such catalysts offer economic and environmentally-friendly alternatives to conventional reagents and catalysts. Mechanistic studies of synthetic catalysts highlight the role of Mn-oxo motifs in attacking substrate C-H bonds, presumably by a concerted proton-electron transfer (CPET) step. (CPET is a sub-class of PCET, where the proton and electron are transferred in the same step.) Knowledge of geometric and electronic influences for CPET reactions of Mn-hydroxo and Mn-oxo adducts enhances our understanding of biological and synthetic manganese centers and informs the design of new catalysts. In this Feature article, we describe kinetic, spectroscopic, and computational studies of MnIII-hydroxo and MnIV-oxo complexes that provide insight into the basis for the CPET reactivity of these species. Systematic perturbations of the ligand environment around MnIII-hydroxo and MnIV-oxo motifs permit elucidation of structure-activity relationships. For MnIII-hydroxo centers, electron-deficient ligands enhance oxidative reactivity. However, ligand perturbations have competing consequences, as changes in the MnIII/II potential, which represents the electron-transfer component for CPET, is offset by compensating changes in the pKa of the MnII-aqua product, which represents the proton-transfer component for CPET. For MnIV-oxo systems, a multi-state reactivity model inspired the development of significantly more reactive complexes. Weakened equatorial donation to the MnIV-oxo unit results in large rate enhancements for C-H bond oxidation and oxygen-atom transfer reactions. These results demonstrate that the local coordination environment can be rationally changed to enhance reactivity of MnIII-hydroxo and MnIV-oxo adducts.

Manganese and rhenium-catalyzed selective reduction of esters to aldehydes with hydrosilanes.

The selective reduction of esters to aldehydes, via the formation of stable alkyl silyl acetals, was, for the first time, achieved with both manganese, -Mn2(CO)10- and rhenium -Re2(CO)10- catalysts in the presence of triethylsilane as reductant. These two methods provide a direct access to a large variety of aliphatic and aromatic alkyl silyl acetals (30 examples) and to the corresponding aldehydes (13 examples) upon hydrolysis. The reactions proceeded in excellent yields and high selectivity at room temperature under photo-irradiation conditions (LED, 365 nm, 40 W, 9 h).

Agricultural Waste Derived Catalysts for Low Temperature SCR Process: Optimization of Preparation Process, Catalytic Activity and Characterization

ABSTRACT Carbon-based catalytic materials have received significant attention for low temperature flue gas denitrification (DeNOx) process, due to their physicochemical properties and ease of modification. To improve the DeNOx efficiency, preparation of biochar catalyst supports was conducted that included the acid treatment of the agricultural wastes rice straw, corn cobs and lotus leaves. Taguchi experimental design (34) was employed to screen suitable carbon materials and optimize the preparation parameters of the biochar. All of the acid-modified and unmodified samples were evaluated to determine their performance and they were characterized by using SEM, BET and FT-IR analysis. The experimental and characterization results showed that acid modification of the biochars improved their DeNOx performance, which may have been due to the changes in the physical and chemical properties of the carbon material following the acid treatment. The optimum combination in the acid modification procedure was found to be the use of lotus leaf carbon treated with an acid/mass ratio of 1.50 and a pyrolysis temperature of 800°C. The biochar prepared using these optimum preparation parameters were then employed as a carrier to support an active catalyst component (MnOx). The lotus leaf biochar supported 10 wt% manganese catalyst prepared using ultrasonic impregnation method exhibited nearly 90% NOx conversion at 250°C at a high space velocity of 45, 000–1, and it exhibited strong resistance to H2O. Additional studies showed that higher redox capacity and suitable surface acidity were two of the deciding factors in the improved low temperature SCR performance of the 10% Mn/LBC catalysts.

Ionic liquid functionalized magnetic organosilica nanocomposite: A powerful and efficient support for manganese catalyst

A novel Mn-containing ionic liquid and ethyl based magnetic organosilica with core-shell structure (Fe3O4@OS/IL-Mn) is prepared, characterized and applied as powerful and recoverable nanocatalyst. The Fe3O4@OS/IL-Mn was prepared via simultaneous coating of tetramethoxysilane (TMOS) and 1,2-bis(triethoxysilyl)ethane (BTEE) over magnetite nanoparticles (MNPs) followed by treatment with ionic liquid and manganese acetate. This catalyst was characterized using scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), energy dispersive X-ray (EDX) spectroscopy, powder X-ray diffraction (PXRD), vibrating sample magnetometer (VSM) and FT-IR spectroscopy. The Fe3O4@OS/IL-Mn was used as an efficient catalyst for the one-pot preparation of biologically useful 2H-indazolo-[2,1-b]-phthalazin-trions under green conditions. The recoverability, reusability and durability of the designed catalyst have also been studied under applied conditions.

Manganese‐Catalyzed β‐Methylation of Alcohols by Methanol

AbstractWe report an earth‐abundant‐metal‐catalyzed double and single methylation of alcohols. A manganese catalyst, which operates at low catalyst loadings and short reaction times, mediates these reactions efficiently. A broad scope of primary and secondary alcohols, including purely aliphatic examples, and 1,2‐aminoalcohols can be methylated. Furthermore, alcohol methylation for the synthesis of pharmaceuticals has been demonstrated. The catalyst system tolerates many functional groups among them hydrogenation‐sensitive examples and upscaling is easily achieved. Mechanistic investigations are indicative of a borrowing hydrogen or hydrogen autotransfer mechanism involving a bimetallic K‐Mn catalyst. The catalyst accepts hydrogen as a proton and a hydride from alcohols efficiently and reacts with a chalcone via hydride transfer.

Manganese-Catalyzed β-Methylation of Alcohols by Methanol.

We report an earth‐abundant‐metal‐catalyzed double and single methylation of alcohols. A manganese catalyst, which operates at low catalyst loadings and short reaction times, mediates these reactions efficiently. A broad scope of primary and secondary alcohols, including purely aliphatic examples, and 1,2‐aminoalcohols can be methylated. Furthermore, alcohol methylation for the synthesis of pharmaceuticals has been demonstrated. The catalyst system tolerates many functional groups among them hydrogenation‐sensitive examples and upscaling is easily achieved. Mechanistic investigations are indicative of a borrowing hydrogen or hydrogen autotransfer mechanism involving a bimetallic K‐Mn catalyst. The catalyst accepts hydrogen as a proton and a hydride from alcohols efficiently and reacts with a chalcone via hydride transfer.

Selective Hydrogenation of Fatty Nitriles to Primary Fatty Amines: Catalyst Evaluation and Optimization Starting from Octanenitrile

AbstractIn this contribution, an evaluation of the potential of various homogeneous and heterogeneous catalysts for a selective hydrogenation of fatty nitriles toward primary amines is reported exemplified for the conversion of octanenitrile into octane‐1‐amine as a model reaction. When using heterogeneous catalysts such as the ruthenium catalyst Ru/C, the palladium catalyst Pd/C, and the platinum catalyst Pt/Al2O3, low selectivities in the hydrogenation are observed, thus leading to a large portion of secondary and tertiary amine side‐products. For example, when using Ru/C as a heterogeneous catalyst, high conversions of up to 99% are obtained but the selectivity remains low with a percentage of the primary amine being at 60% at the highest. The study further reveals a high potential of homogeneous ruthenium and manganese catalysts. When also taking into account economical considerations with respect to the metal price, in particular, manganese catalysts turn out to be attractive for the desired transformation and their application in the model reaction leads to the desired primary amine product with excellent conversion, selectivity, and high yield.Practical Applications: This work describes an optimized hydrogenation process for transforming fatty nitriles to their corresponding primary amines. In general, fatty amines belong to the most applied fatty acid‐derived compounds in the chemical industry with an annual product volume exceeding 800 000 tons per year in 2011 and are widely required in the chemical industry since such compounds are either directly used in home products such as fabric softeners, dishwashing liquids, car wash detergents, or carpet cleaners or in a broad range of industrial products, for example, lubricating additives, flotation agents, dispersants, emulsifiers, corrosion inhibitors, fungicides, and bactericides, showing additional major applications, e.g., in the detergents industry. Among them primary amines play an important industrial role. However, a major concern of current processes is the lack of selectivity and the formation of secondary and tertiary amines as side‐products. By modifying a recently developed catalytic system based on manganese as economically attractive and environmentally benign metal component an efficient and selective access to fatty amines when starting from the corresponding nitriles is achieved. For example, hydrogenation of octanenitrile leads to a synthesis of octane‐1‐amine with >99% conversion and excellent selectivity with formation of secondary and tertiary amine side‐products being suppressed to an amount of <1%.