Catalyst Loading Research Articles

N-Monoarylated dihydrophenazines in reduced and oxidized states as efficient organo-photocatalysts.

In this work, the synthesis of an N-monoarylated dihydrophenazine is reported together with its interconversion to its oxidized mono-cationic form. While the reduced state was employed for the dechlorination of aromatic substrates, the oxidized mono-cationic one was exploited for the formation of C-N bonds between aryl rings and azoles, which was achieved with high yields and very low catalyst loadings (down to 0.5 mol%).

Study of the self-degradation performance of a passive direct methanol fuel cell with an Fe-N-C catalyst.

Fe-N-C catalysts are considered promising substitutes for Pt-based catalysts at the cathode in direct methanol fuel cells (DMFCs) owing to their great methanol tolerance. However, Fe-N-C-based DMFCs commonly suffer from a decreased performance under extremely high methanol concentrations and exhibit poor stability, while the underlying mechanism remains controversial. In this study, a self-degradation phenomenon in a passive Fe-N-C-based DMFC was investigated in detail. The DMFC with an optimized ionomer content and catalyst loading delivered an extremely high peak power density of 28.85 mW cm-2 when fed with 3 M methanol solution, while the peak power density of the cell rapidly declined to 16.61 mW cm-2 after standing for 10 days without any discharging operation. Several electrochemical measurements were designed and conducted to explore the mechanism for this phenomenon. The results of these measurements revealed that methanol molecules are chemically adsorbed on the surface of the Fe-N-C catalyst, and the bonding cannot be reversed using simple physical methods, leading to the isolation of active sites from oxygen. Herein, we provide a new perspective on passive Fe-N-C-based DMFCs that would be significant for the technological development of portable power devices.

Electrochemical and physical properties of magnesioferrite nanomaterial and photocatalytic degradation of methylene blue

This research successfully synthesized semiconductive magnesioferrite (MgFe2O4) nanomaterials using a green chemistry method that utilizes the natural extract of Moringa olefeira serving as both a reducing and oxidizing agent. The optical characteristics and crystalline structure of the MgFe2O4 nanomaterials were analysed using photoluminescence, diffuse reflectance spectroscopy, and X-ray diffraction. Additionally, Fourier transform infrared spectroscopy provided valuable insights into the chemical bonding and composition. High-resolution transmission electron microscopy was employed to obtain extensive information on crystalline size and distribution. Furthermore, the electrochemical properties were assessed through cyclic voltammetry and electrochemical impedance spectroscopy, revealing an excellent voltametric response and pseudo-capacitive behaviour associated with faradaic reactions, as well as outstanding conductivity linked to the unique charge transport mechanisms present in the MgFe2O4 structure. The effectiveness of the MgFe2O4 nanomaterials in the photodegradation of methylene blue from aqueous solutions was evaluated under visible light irradiation. Photocatalytic experiments measured the influence of various parameters, including catalyst loading, dye concentration, and pH. The MgFe2O4 nanomaterials exhibited impressive photocatalytic degradation efficiency, achieving an 81% degradation rate at pH 5.0 within 120 min. Kinetic studies indicated that the degradation process adhered to a pseudo-first-order model, with a rate constant of 0.01533 min−1, signifying a rapid reaction under optimal conditions. This study provides a thorough understanding of the electrochemical properties and enhanced photocatalytic capabilities of MgFe2O4 nanomaterials, thereby advancing green nanotechnology for environmental remediation.

Catalytic Screening for 1,2-Diol Protection: A Saccharose-Derived Hydrothermal Carbon Showcases Enhanced Performance

A benchmarking study is reported on a series of modified carbocatalysts to efficiently promote the acetalization of 1,2-diols under heterogeneous conditions. Among the catalysts surveyed, a hydrothermal carbon generated from saccharose, a cheap, abundant, and biobased material, showed excellent performance when tested on two representative diols. All catalysts have been thoroughly characterized, focusing on surface acidity and composition. Optimal working parameters such as temperature and catalyst loading could be established. Remarkably, sonication improved the diol protection, which proceeded faster at 25 °C. The catalyst could be easily recycled and reused several times. In addition, the protocol was successfully translated from batch to continuous flow operation using a packed-bed reactor.

Mg(SPh)2 as a Catalyst for Efficient Photocatalytic Alkylation Reactions of Active Methylene Compounds with Nonactivated Alkenes

Mg(SPh)2 has been found to be a highly active catalyst in photocatalytic alkylation reactions of active methylene compounds with nonactivated alkenes. The desired reactions proceeded smoothly to afford the corresponding alkylated products in high yields with low catalyst loadings (0.2‐0.3 mol%). This protocol is applicable to a continuous‐flow system. Notably, magnesium is an earth‐abundant metal, and Mg(SPh)2 exhibits higher catalytic activity than the previously reported LiSPh.

Comparative economic analysis of batch vs. continuous manufacturing in catalytic heterogeneous processes: impact of catalyst activity maintenance and materials costs on total costs of manufacturing in the production of fine chemicals and pharmaceuticals

Abstract To evaluate the feasibility of transforming batch manufacturing processes in the fine chemicals and pharmaceutical industries to continuous synthesis, Capex, Opex and the total cost of manufacturing are estimated for production facilities for the hydrogenation of a nitro compound to its final amino counterpart. Two cases are evaluated: First, a high annual production dedicated plant, designed on the basis of processing 100,000 kg of the principal raw material per year, where raw materials cost, catalyst cost, and catalyst activity maintenance are varied over a broad range for typical industrial cases. Second, a “short campaign” model for a small volume production trial setup designed for the manufacture of only 100 kg of the final product, as a way to evaluate relevant industrial scenarios of scale-up and process development. A comparison is made between slurry batch, catalyst basket batch reactor and fixed bed continuous reactor manufacturing facilities. The hydrogenation of 2,4-dinitrotoluene was chosen as a probe reaction for the development of the manufacturing processes, with costs of the key raw material varying between $5 and $100 per kilogram, costs of catalyst varying between $100 and $1,500 per kilogram, and catalyst activity maintenances varying between 1,000 and 2,000,000 total turnovers before a change in catalyst load is necessary. For low catalyst activity maintenance, the total manufacturing costs for the fixed bed reactor process were always found to be higher than those of the two other alternatives. As catalyst activity maintenance increases, the manufacturing costs for the continuous alternative rapidly fall, reaching savings between 37 and 75% compared to the base batch reactor case, depending on the combination of costs of the key raw material and catalyst used. Graphical Abstract

Effective One-Component Organocatalysts for Eco-Friendly Production of Cyclic Carbonates

One-component or bifunctional organocatalysts are some of the most capable compounds to perform the synthesis of cyclic carbonates from epoxides and carbon dioxide (CO2) since the presence of a co-catalyst is not required. In this study, we designed, synthesized, and evaluated five halogenated compounds as bifunctional organocatalysts for this catalytic transformation. Among them, 1,3-dimethylimidazolium iodide (1) exhibited the highest catalytic efficiency, enabling the synthesis of a broad range of monosubstituted cyclic carbonates with diverse functional groups under mild conditions (80 °C, 20 bar CO2) within 1 h, using only 1 mol% catalyst loading. Remarkably, this organocatalyst also facilitated the synthesis of five internal cyclic carbonates and a carvone-derived exo-cyclic carbonate, which was obtained for the first time without the use of a metal catalyst, under more demanding conditions. A mechanistic proposal was developed through a combination of 1H-NMR studies and density functional theory (DFT) simulations. Styrene oxide and cyclohexene oxide were used as model substrates to investigate the reaction pathway, which was computed using an optimized climbing-image nudged elastic band (CI-NEB) method. The results revealed the critical role of 1,3-dimethylimidazolium iodide in key reaction steps, particularly in facilitating the epoxy ring opening process. These findings highlight the potential use of bifunctional compounds as efficient and versatile catalysts for CO2 valorization.

Structural modification of defective WO3 by g-C3N4 for photocatalytic gold recovery from non-cyanide-based plating effluent

A set of nCN/WO3 − x composites was synthesized through a simple thermal treatment for gold recovery from the simulated effluent of a non-cyanide-based plating bath. The obtained results exhibited that all nCN/WO3 − x composites demonstrated a higher photocatalytic activity for gold recovery than their pristine components due to the formation of nanocomposites which paved a convenient pathway for charge transfer. Among all synthesized composites, the 5.0CN/WO3 − x composite exhibited the highest photocatalytic activity, recovering around 69.4% of gold within 120 min under UV-vis light irradiation at an intensity of 3.45 mW/cm² and a catalyst loading of 1.0 g/L, in the absence of hole scavenger. This result can be ascribed to the presence of an optimal number of defects, which can act as electron trapping sites and thereby reduce the recombination rate of charge carriers. Gold recovery increased with repeated reuse, attributed to the decorated gold, which enhances light absorption and decreases the recombination rate of charge carriers. The feasible application of used CN/WO3 − x were also explored for H2 production, dye degradation and gold recovery. The obtained results provide a new insight about the photocatalytic recovery of gold from industrial wastewater and also shed light on the application of gold-decorated CN/WO3 − x as a catalyst for other photocatalytic applications.

Asymmetric Heck Silylation of Unactivated Alkenes.

Heck silylation of unactivated alkenes is an efficient strategy for the synthesis of useful organosilicon compounds. However, extensive efforts have been dedicated to only achieving achiral molecules. Herein, a highly regio- and enantioselective cobalt-catalyzed Heck silylation of unactivated alkenes with hydrosilanes is reported for the first time, providing access to axially chiral alkenes in good to excellent yields with 87-98% ee. Aryl and alkyl groups as well as quaternary carbon centers at the 4-position of vinylcyclohexane could be well tolerated, featuring good functional group tolerance. The gram-scale reaction proceeds smoothly under mild conditions even with 0.5 mol% catalyst loading. A possible mechanism has been proposed, in which enantioselectivity is controlled by alkene insertion. A templating strategy that enhances weak bond interaction is employed to control regioselectivity by modifying the substituents on the ligand and silane.

Enantioselective Copper-Catalyzed Three-Component Cascade Boronation-Dearomatization Reaction: Synthesis of Chiral Boron-Containing 1,4-Dihydropyridines.

A three-component cascade boronation-dearomatization reaction of alkenes, a diboron compound, and a pyridinium salt is diclosed, affording chiral boron-containing 1,4-dihyropyridines in high yields (≤98%) and diastereoselectivity (≤10:1 dr), along with excellent enantioselectivity (typically >99% ee). The catalytic system performs efficiently at low catalyst loadings (1 mol %) and was tested with >50 examples, including some biologically active molecules.

Palladium-Catalyzed Stereospecific Glycosylation Enables Divergent Synthesis of N-O-Linked Glycosides.

We present a versatile palladium-catalyzed glycosylation platform that enables facile access to structurally diverse N-O-linked glycosides with constantly excellent regio- and stereoselectivities. Importantly, this approach offers a broad substrate scope, low catalyst loadings, and outstanding chemoselectivity, allowing for the selective reaction of oximes/hydroximic acids over hydroxyl groups that would otherwise pose challenges in conventional glycosylation methods. The synthetic utility of this method is further exemplified through a range of synthetic transformations and late-stage modification of bioactive molecules. Overall, our method provides an efficient toolkit for the synthesis of N-O-linked glycosides, which will facilitate their subsequent biological evaluations.

Ni-Co doped TiO2 catalyst for efficient photocatalytic degradation of Malachite Green under UV and direct sunlight.

In the present study, combustion-synthesized TiO2 nanoparticles were wet impregnated with Ni, Co, and Ni-Co, respectively. The photocatalytic performance of synthesized catalysts was evaluated against Malachite Green dye. The synthesized materials were characterized for crystallite size, surface morphology, elemental composition, and band gap using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and ultra-violet diffused reflectance spectroscopy, respectively. The optimum parameters for maximum degradation were found by examining the effects of catalyst loading, initialdye concentration, and light intensity. A comparative analysis of Ni-doped, Co-doped, and Ni-Co-doped TiO2 photocatalysts wasconducted. The results indicate superior photocatalytic activity of Ni-Co doped TiO2 among the catalysts investigated under UV light. The degradation kinetics was studied, and the underlying degradation mechanism was proposed with the help of LC-MS analysis. Furthermore, a comparative study on the degradation under solar radiation using Ni-Co/TiO2 was conducted.

Interrupting Associative π-σ-π Isomerization Enables Z-Retentive Asymmetric Tsuji-Trost Reaction.

The asymmetric Tsuji-Trost reaction has been extensively studied due to its importance in establishing stereogenic centers, often adjacent to an E-olefin moiety in organic molecules. The generally preferential formation of chiral E-olefin products is believed to result from the thermodynamically more stable syn-π-allylpalladium intermediate. The rapid associative π-σ-π isomerization makes it challenging to synthesize chiral Z-olefin products via the transient anti-π-allylpalladium intermediate. Herein, we report a strategy for regulating associative π-σ-π isomerization by tuning the steric bulkiness of the ligands, allylic leaving groups, and counteranions. The utilization of a Pd catalyst derived from chiral phosphoramidite ligands interrupts the associative π-σ-π isomerization, enabling a highly efficient Z-retentive asymmetric Tsuji-Trost reaction toward an array of α-amino acid derivatives bearing a Z-olefin motif in high yields (up to 95%) and excellent stereoselectivity (up to 99% ee and >19:1 Z/E) with low catalyst loading (0.1 mol %). The mechanistic insights and the design strategy reported in this work pave the way for rational developments of Z-retentive asymmetric Tsuji-Trost-type reactions.

High H2 Solubility of Perfluorocarbon Solvents and Their Use in Reversible Polarization Transfer from para-Hydrogen.

This research uses perfluorocarbons (PFCs) as effective alternatives to traditional toxic solvents in reversible para-hydrogen-induced polarization (PHIP) for NMR signal enhancement. Hydrogen solubility in PFCs is shown here to be an order of magnitude higher than in typical organic solvents by determination of Henry's constants. We demonstrate how this high H2 solubility enables the PFCs to deliver substantial polarization transfer from para-hydrogen, achieving up to 2400-fold signal gains for 1H NMR detection and 67,000-fold (22% polarization) for 15N NMR detection at 9.4 T in substrates such as pyridine and nicotine. Notably, methylperfluorobutylether outperforms catalytic efficiency in methanol-d4 and dichloromethane-d2 for pyridine at low catalyst loadings. This makes PFCs particularly advantageous for applications demanding high NMR sensitivity. With high polarization efficiency and reduced toxicity, PFCs hold strong potential for expanding hyperpolarized NMR applications across the biomedical and analytical fields.

Tin(IV)Porphyrin-Based Porous Coordination Polymers as Efficient Visible Light Photocatalyst for Wastewater Remediation.

Two porphyrin-based polymeric frameworks, SnP-BTC and SnP-BTB, as visible light photocatalysts for wastewater remediation were prepared by the solvothermal reaction of trans-dihydroxo-[5,15,10,20-tetrakis(phenyl)porphyrinato]tin(IV) (SnP) with 1,3,5-benzenetricarboxylic acid (H3BTC) and 1,3,5-tris(4-carboxyphenyl)benzene (H3BTB), respectively. The strong bond between the carboxylic acid group of H3BTC and H3BTB with the axial hydroxyl moiety of SnP leads to the formation of highly stable polymeric architectures. Incorporating the carboxylic acid group onto the surface of SnP changes the conformational frameworks as well as produces rigid structural transformation that includes permanent porosity, good thermodynamic stability, interesting morphology, and excellent photocatalytic degradation activity against AM dye and TC antibiotic under visible light irradiation. The photocatalytic degradation activities of AM dye were found to be 95% by SnP-BTB and 87% by SnP-BTC within 80 min. Within 60 min of visible light exposure, the photocatalytic degradation activities of TC antibiotic were found to be 70% by SnP-BTB and 60% by SnP-BTC. The enhanced catalytic photodegradation performances of SnP-BTB and SnP-BTC were attributed to the synergistic effect between SnP and carboxylic acid groups. The carboxylic acid connectors strongly resist the separation of SnP from the surface of SnP-BTB and SnP-BTC during the photodegradation experiments. Therefore, the high degradation rate and low catalyst loading make SnP-BTB or SnP-BTC more efficient than other reported catalysts. Thus, the present investigations on the porphyrin-based photocatalysts hold great promise in tackling the treatment of dyeing wastewater.

Kaolin-supported molybdovanado phosphoric acid as green catalyst for fluoride ion removal in water

Using the impregnation approach, molybdovanado phosphoric acid (MVPA) has been immobilized onto kaolin resulting in a green heterogeneous catalyst (MVPA@Kaolin). A comprehensive physicochemical analysis was performed on the catalyst. Because of its uses in fine chemicals and medicines, this hybrid material is meant to be used as a sustainable catalyst. To investigate the catalyst, a variety of physicochemical characterization approaches were used. Through the adsorption of fluoride, the performance of the material was evaluated with temperature, pH, catalyst load, and contact time. The results demonstrated rapid and efficient fluoride removal, with a removal efficiency of more than 85 % in a little contact time. The optimum pH obtained as 1 with fluoride removal efficiency of 84 %, catalyst load 5 g/L (85 %), and temperature 50 oC (85 %). Additionally, composite material regeneration and reusability were investigated. The results aid in the creation of effective and environmentally sustainable fluoride-in water treatments.

Fe-TiO2 WITH LOW QUANTITY OF IRON EXTRACTED FROM (ILMENITE) MINING WASTE TO THE PHOTOCATALYTIC DEGRADATION OF CYANIDE IN WATER

Nanoparticles of TiO2 doped with low amount of Fe were synthesized from natural ilmenite obtained from alluvial gold mine wastes. The obtained TiO2 were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), UV-Vis diffuse reflectance, thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), N2 adsorption-desorption isotherms, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results confirm the formation of mesoporous TiO2 nanoparticles in anatase phase with 0.05 wt.% of iron possibly replacing some titanium places. All the characterizations were performed to the synthesized solid and the reference materials (TiO2 anatase and Degussa P25). The photocatalytic activity of both the synthesized solid and references were evaluated in the photo-oxidation of cyanide in aqueous medium under UV illumination. An experimental design type Box-Behnken was performed choosing three different parameters: the initial concentration of cyanide (50, 150 and 250 ppm) the catalyst load (0.1, 0.5 and 1.0 g L-1) and the oxygen source. The percentage of cyanide conversion was chosen as response in the design obtaining as optimal conditions [CN-]0 = 50 ppm, catalyst load = 0.6 g L-1 and air bubbling. Under these conditions it was reached 32, 32 and 89% of cyanide conversion for Fe-TiO2 synthesized, TiO2 anatase and Degussa P25, respectively.

Effect of catalyst synthesis of bimetallic nickel-cobalt supported iron-based catalysts on converting palm kernel oil into bio-jet fuel via deoxygenation reaction.

Bimetallic nickel-cobalt supported magnetite catalyst has been synthesized using varies techniques such as hydrothermal reactor (R), wet-impregnation (W) and co-precipitation (C) approaches in order to study the effect of preparation methods on the catalytic efficiency of NiCo/Fe3O4 catalyst in transforming the PKO into bio-jet fuel via deoxygenation (DO) reaction. Noted, co-precipitation method rendered greater changes on textural morphological changes, with NiCo/Fe3O4 (C) specific surface area were 157 m2/g followed by Fe3O4 (25 m2/g), NiCo/Fe3O4 (W) (7 m2/g) and NiCo/Fe3O4 (R) (2 m2/g ), respectively. Indeed, NiCo/Fe3O4 (C) showed highest weak+strong acidic sites (15,038.1μmol/g). The efficiency of the DO followed NiCo/Fe3O4 (C) > NiCo/Fe3O4 (W) > NiCo/Fe3O4 (R) > Fe3O4, whereby the highest hydrocarbon yield was 90% and 21% is the lowest. Noteworthy to mention, all of the liquid product exhibited selectivity of over 90% towards the kerosene range. The deoxygenation reaction was optimized using the most effective catalyst, NiCo/Fe3O4 (C) catalyst, through the OVAT technique. The results showed that the optimal conditions were achieved at a temperature of 350 °C within 3 h by using 5 wt% of catalyst loading. The reusability and stability of the NiCo/Fe3O4 (C) catalyst were examined, revealing that the catalyst may be reused for up to 8 runs. During these runs, the catalyst achieved a hydrocarbon yield of up to 55% and a BJF selectivity of over 95%. The decrease in the yield and selectivity was attributed to coking, specifically in the form of graphitic carbon.

Low-coordinate bis-phosphine and monophosphine Ni(0) complexes: synthesis and reactivity in C-S cross-coupling.

Preformed Ni(0) complexes are rarely used as precatalysts in cross-coupling reactions, although they can incorporate catalytically active nickel directly into the reaction. In this work, we focus on the preparation and the catalytic application of low-coordinate Ni(0) complexes supported by bulky monophosphine ligands in C-S cross-coupling reactions. We have prepared two families of Ni(0) complexes, bis-phosphine aducts of the type [Ni(PR2Ar')2] (Ar' = m-terphenyl group) and monophosphine derivatives of the type [Ni(PR2Ar')(DVDS)] (DVDS = divinyltetramethyldisiloxane). DFT calculations were used to account for the atypical bent structures displayed by the bis-phosphine Ni(0) complexes. Monophosphine-Ni(0) complexes display catalytic activity superior to bis-phosphine Ni(0) adducts, which suggests that the former facilitate the generation of highly reactive monoligated PNi(0) species. Furthermore, the reactivity of monophosphine-Ni(0) precatalysts outperform that observed with Ni(II) precatalysts with the same phosphine ligands, supporting a more facile activation step to the same catalytic species. This enhanced reactivity allows for the use of lower catalyst loadings (1-5 mol%) and for carrying out the challenging coupling between aryl chlorides and alkylthiols.

Asymmetric synthesis of spiro[benzofuran-pyrrolidine]-indolinedione via bifunctional urea catalyzed [3 + 2]-annulation.

In this study, we unveil a highly enantioselective [3 + 2] annulation protocol, adept at merging N-2,2,2-trifluoroethylisatin ketimines with 3-alkylidene benzofuranones under quinine-derived urea catalysis. This strategy furnishes complex spiro[benzofuran-pyrrolidine]indolinedione architectures, featuring strategically positioned trifluoromethyl groups of considerable pharmacological significance. The method distinguishes itself by employing minimal catalyst loadings while ensuring energy efficiency and accommodating a broad spectrum of substrates, resulting in excellent yields and exceptional stereocontrol (38 examples, up to 98% yield, up to >20 : 1 dr, and up to 99 : 1 er). Mechanistic investigations, underpinned by SC-XRD and NMR NOE analyses, elucidate the stereochemical pathways driving selectivity, while a comprehensive evaluation of electronic and steric substituent effects further refines the reaction's scope.