Catalyst System Research Articles

Optimization of Electrochemical Reduction of Biomass Derived 5-Hydroxymethylfurfural (HMF): A Volcano Plot and Bimetallic Catalysts.

2,5-bis(hydroxymethyl)furan (BHMF) derived from 5-Hydroxymethylfurfural (HMF) through a hydrogenation process has extensive applications in the production of resins, polymers, and artificial fibers. However, screening out the candidate and then modulating the active site to optimize the catalyst for high yield of BHMF are currently insufficient. In this study, Gibbs free energy diagrams of the reduction of HMF on 13 metals were presented, along with the identification of the rate-determining step (RDS) with the highest reaction barrier for each metal. We attempted to construct a volcano plot for HMFRR reaction. Additionally, a strategy was proposed to adjust the reaction barriers of RDS by combining two appropriate metals. Further experiments confirmed that Pb with the lowest energy barrier exhibited the highest HMF conversion (BHMF selectivity) among single metals. The modified catalyst by doping Ag on Pb, further boosted the HMF conversion (BHMF selectivity) from 42.1% (59.4%) to 80.8% (80.9%), respectively. These results provide an approach to rationally design and construct the catalyst system for efficient conversion of HMF.

Chemoenzymatic cascade conversion of methyl parathion to 4-aminophenol with immobilized organophosphate hydrolase onto Cu-MOF-loaded mesoporous silica

Organophosphates (OPs), essential pesticide ingredients, are highly toxic and environmentally problematic. OPs can be efficiently hydrolyzed by the enzyme organophosphorus hydrolase (OPH). However, the resulting p-nitrophenol (4-NP) is still toxic, and its chemical reduction to p-aminophenol (4-AP) can be environmentally friendly and increase economic value. We constructed a chemical-enzymatic cascade catalyst system for methyl parathion (MP) using OPH and a copper-based metal-organic framework (HKUST-1) with 4-NP reduction catalytic activity. The nano-HKUST-1 was first loaded into aminated mesoporous silica nanospheres (MSN-NH2) to construct HKUST-1@MSN-NH2, and then OPH was immobilized into the HKUST-1@MSN-NH2 pores by a covalent method to obtain OPH@HKUST-1@MSN-NH2. The resulting composite catalyst, OPH@HKUST-1@MSN-NH2, achieved chemoenzymatic cascade catalysis of MP hydrolysis to 4-NP and subsequent reduction to 4-AP. The composite nano-biocatalyst has good catalytic performance and reusability, which can rapidly convert entirely 50 μM MP to 4-AP in 8 min at a dosage of 30 mM NaBH4. Still, it has 77% activity after 10 cycles and a stable material structure. The present study provides a strategy for constructing a chemoenzymatic cascade catalytic system, and the obtained composite nano catalysts achieve the continuous degradation and resourceful conversion of organophosphorus pollutants, which has specific practical application value.

Modular Synthesis of [6,6]‐Oxaspirolactones Enabled by Palladium‐Catalyzed Carbonylative Spirolactonization

An expedient and efficient carbonylative protocol proceeded via palladium‐catalyzed tandem cyclic ketonization and carbonylative spirolactonization has been developed. This carbonylation reaction is compatible with a wide range of hydroxyalkyl ketone tethered benzyl chlorides bearing different functional groups and can be proceeded under comericially available Pd2(dba)3/BINAP catalyst system, providing a straithfowrd and practical approach to a broad range of [6,6]‐oxaspirolactones. The synthesized [6,6]‐oxaspirolactones are commonly found as core structures in natural products and can potentially serve as C2‐symmetric ligand synthons.

Copper/O2-Mediated Oxidative C-C Activation of Nitriles for Selective Acylation-Bromination of Anilines.

This study reports selective dual amino acylation and C-H bromination of aniline compounds enabled by Cu/O2 catalyst systems. This method involves crucial oxidation-induced C-CN bond cleavage of α-methylene nitriles to generate an acylcyanide intermediate that is facilely intercepted by anilines. After amino acylation, the Cu(II) precatalyst in combination with NBS generates Cu(III)-Br in situ that engages in selective electrophilic para- or ortho-C-H bromination. The substrate scope, mechanistic aspects, and late-stage functionalization of biologically active anilines are studied. This study shows the synthetic potential of oxidative C-CN bond activation of nitriles for the development of valuable reactions.

Desymmetrization of Cyclic Sulfonimidamides by Asymmetric Allylation.

Herein we report the first transition metal-catalyzed approach to the enantioenriched synthesis of cyclic sulfonimidamides relying on commercially available palladium catalysts and ligands. High-throughput experimentation (HTE) was employed to identify the optimal catalyst system and solvent. The method is applied to a variety of saturated and unsaturated rings and exhibits the highest selectivity for 2-substituted allyl electrophiles. The products are further elaborated to complex, tricyclic scaffolds. DFT experiments presented herein highlight the key ligand substrate interactions leading to the high levels of enantioselectivity.

Desymmetrization of Cyclic Sulfonimidamides by Asymmetric Allylation

Herein we report the first transition metal‐catalyzed approach to the enantioenriched synthesis of cyclic sulfonimidamides relying on commercially available palladium catalysts and ligands. High‐throughput experimentation (HTE) was employed to identify the optimal catalyst system and solvent. The method is applied to a variety of saturated and unsaturated rings and exhibits the highest selectivity for 2‐substituted allyl electrophiles. The products are further elaborated to complex, tricyclic scaffolds. DFT experiments presented herein highlight the key ligand substrate interactions leading to the high levels of enantioselectivity.

Allyl‐Allyl Coupling Promoted by Catalyst Systems with two Palladium Atoms – A Plethora of Potentially Pericyclic Processes

Allyl‐Allyl Coupling Promoted by Catalyst Systems with two Palladium Atoms – A Plethora of Potentially Pericyclic Processes

Allyl-Allyl Coupling Promoted by Catalyst Systems with two Palladium Atoms - A Plethora of Potentially Pericyclic Processes.

Recently, Huang and co-workers reported a catalytic reaction that utilizes H2 as the sole reductant for a C-C coupling of allyl groups with yields up to 96%. Here we use computational quantum chemistry to identify several key features of this reaction that provide clarity on how it proceeds. We propose the involvement of a precatalyst Pd-Pd bound dimer, demonstrate the importance of ligand π-π interactions and counterions, and identify a new, energetically viable, mechanism involving two dimerized, outer-sphere reductive elimination transition structures that determine both the rate and selectivity. Although we rule out the previously proposed transmetalation step on energetic grounds, we show it to have an unusual aromatic transition structure in which two Pd atoms support rearranging electrons. The prevalence of potential metal-supported pericyclic reactions in this system suggests that one should consider such processes regularly, but the results of our calculations also indicate that one should do so with caution.

Rational solvent selection for the preparation of industrial monolithic supported liquid-phase (SLP) olefin hydroformylation catalyst

Heterogenisation of the hydroformylation (HyFo) process converting C4 olefins and syngas (CO/H2) to n-pentanal can substantially reduce its carbon footprint by simplifying downstream processing. Current upscaling efforts include constructing a pilot plant containing a Rh-diphosphite-stabilized supported liquid-phase (SLP) catalyst. The air-sensitive nature of the catalyst requires in-situ impregnation of the porous support material with the liquid phase components (Rh-precursor, ligand, stabiliser) entailing the use of large quantities of an organic solvent. Environment, health, and safety (EHS) as well as regulatory aspects prompt the search for an alternative to dichloromethane (DCM), which was used as standard solvent for lab-scale studies. To obtain alternatives to DCM, the replacement solvent methyl tert-butyl ether (MTBE) and in-silico screening of more than 5000 solvent candidates has been performed covering boiling points and solubility predictions by COSMO-RS as well as carcinogenicity- and mutagenicity predictions by quantitative structure–activity relationship (QSAR) models. The final list of solvent candidates contained unsaturated compounds (alkenes, alkynes) in addition to ether- and ester-functionalized​ solvents, which are typically recommended as DCM replacements. Sufficiently high solubilities of ligand and stabiliser to prepare the desired SLP catalyst were experimentally determined in the following solvents: methyl propionate (MP), dimethoxymethane (DMM), MTBE, tetrahydrofuran (THF) and DCM for benchmarking, and a monolithic SLP catalyst prepared with MTBE demonstrated to perform equally well in the HyFo reaction of 1-butene as the benchmark catalyst prepared using DCM solvent. Overall, the study demonstrates a practical approach for selecting solvents with a greener profile for making catalyst systems applicable for large-scale production.

Single‐Site Heterogenized Molecular Catalysts towards CO2 Hydrogenation to Formates, Formamides and Methanol

Harnessing CO2 in conjunction with inexpensive reusable H2 for catalytic hydrogenation is a viable method for lowering the environmental impact of industrial operations while producing useful chemicals and fuels. To make the process more sustainable, particular emphasis was paid to the heterogeneous catalyst system in this regard. Intending to profit from both homogeneous and heterogeneous catalysis in real‐world circumstances for the CO2 hydrogenation reaction, heterogenized molecular catalysts are receiving a lot of attention among heterogeneous catalysts. This review is devoted to significant developments in single‐site heterogenized molecular catalysts for CO2 hydrogenation reactions. Attempting to illustrate the state‐of‐the‐art developments in this domain, the present work meticulously summarizes several recently reported heterogenized molecular catalysts for the CO2 hydrogenation process producing formic acid/formate, N‐formamide, and methanol. The fundamental structure–activity relationships and mechanistic understanding are given particular attention since they offer solid foundations for sensible catalyst architectural design. Important variables that influence catalytic activity are also emphasized, such as electron density, metal dispersion, porous nature, surface area, a robust backbone, and coordination environment of metal sites. Finally, a short assessment is given as potential directions for further research.

Novel Silver vanadate coupled semiconductor nanocomposites for effective removal of toxic organics

One of the world's most important challenges is the lack of access to clean water, and researchers are working tirelessly to find a solution. Nanotechnology-treated water is superior to conventionally treated water since it contains no hazardous microorganisms or organic dyes. In this study, the influence of light on Ag3VO4 nanocomposites doped with synthesized ZnO nanoparticles was analyzed. SEM, FTIR, XRD, XPS, and UV-vis spectroscopy were just some of the methods used to characterize the as-prepared nanocomposites. An Ag3VO4/ZnO nanocomposite was used to successfully adsorb and photodegrade Acid Green-16(AG-16), and Acid Red-72(AR-72) from an aqueous solution. Visible light dramatically accelerates the adsorption and photodegradation of the Ag3VO4/ZnO nanocomposite compared to complete darkness. 77.52%, 82.86%, and 89.56% of AG-16 and 77.11%, 82.74%, and 87.91% of AR-72 were removed by the ZnO, Ag3VO4, and Ag3VO4/ZnO nanocomposites, respectively, in less than 60 minutes. However, visible-light photodegradation is more successful than adsorption alone in removing AG-16 and AR-72. In this pioneering study, we assess the catalytic performance of newly synthesized ZnO incorporated Ag3VO4 nanocomposites for the UV-assisted degradation of organic dyes. Our study presents an innovative catalyst system that exhibits improved efficiency and holds promise for implementation in environmentally sustainable wastewater treatment methods.

Deciphering the stability mechanism of Pt-Ni/Al2O3 catalysts in syngas production via DRM

Deactivation induced by coke deposition remains the foremost challenge in using Ni-based catalysts for the production of syngas via dry reforming of methane (DRM) reaction. Herein, highly dispersed Pt-Ni/Al2O3 bimetallic catalysts prepared by atomic layer deposition (ALD) displayed remarkable stability at 650 ℃ in the DRM reaction. The Pt-Ni catalysts underwent an activation process within the initial 10 h and maintained its activity without deactivation throughout the subsequent aging testing up to 48 h. In contrast, the Ni/Al2O3 rapidly deactivated over time. Despite its high CH4 conversion rates, the Pt-Ni bimetallic catalyst produced a substantial quantity of carbon nanotubes (CNTs) analogous to the Ni/Al2O3 catalyst. The discrepancy in stability performance between two catalysts derived from disparities in the carbon sites and structural defects evolving over reaction time. Regarding the catalysts with Pt decoration on the Ni surface, CNTs exhibited increasing structural defects and gradually deposited on the Al2O3 support without fully encapsulating the metal active sites, as evidenced by CH4-TPD experiments. In the case of Ni nanoparticles on Al2O3, crystalline CNTs with fewer defects accumulated, leading to rapid deactivation. These findings enhance our understanding of coke resistance in DRM catalysts and help the development of more robust bimetallic catalyst systems.

Controlled Magnetite Grafted Poly(glycidyl methacrylates) for Heavy Metal Absorption and Recovery via SET-LRP

A versatile magnetite based stringent polymer for effective metal capture was prepared by reacting iron oxide based initiator with glycidyl methacrylate monomer via single-electron transfer living radical polymerization (SET-LRP) technique. The versatile grafted polymer was successfully synthesized by metal catalyzed living radical polymerization using the catalyst system Cu/N,N,N',N'',N'''-pentamethyldiethylenetriamine as the ligand. The structural confirmation of the initiator and the grafted polymer was analyzed by using instrumentation methods such as proton nuclear magnetic resonance spectroscopy, UV-visible, TGA, SEM and gel permeation chromatography for molecular weight measurements. As the polymerization time increased, both the conversion and the molecular weight were observed to increase linearly with time. Narrow dispersed lower polydispersity index (PDI) and dispensable magnetite-g-PGMA was utilized for the extract of toxic lead from the wastewater. Sustained binding was observed due to the presence of epoxide ring in the repeating units of the polymer and recovered by magnetic effect. The material shows good stability as evident by TGA curves and better affinity to toxic lead as observed by UV-visible and SEM techniques.

Oxidation of Alcohols and Aldehydes with Peracetic Acid and a Mn(II)/Pyridin‐2‐Carboxylato Catalyst: Substrate and Continuous Flow Studies

A homogeneous catalyst system, consisting of Mn(OAc)2 and 2‑picolinic acid was studied for alcohol oxidation using peracetic acid as the oxidant. Catalyst loadings as low as 0.01 mol% could be utilized and the system compared well to other peroxide based methods. The utilization of continuous flow allowed the fast, exothermic reactions to be carried out in a safe and scalable manner.

Plasma-Driven Efficient Conversion of CO2 and H2O into Pure Syngas with Controllable Wide H2/CO Ratios over Metal-Organic Frameworks Featuring In SituEvolved Ligand Defects.

While the mild production of syngas (a mixture of H2 and CO) from CO2 and H2O is a promising alternative to the coal-based chemical engineering technologies, the inert nature of CO2 molecules, unfavorable splitting pathways of H2O and unsatisfactory catalysts lead to the challenge in the difficult integration of high CO2 conversion efficiency with produced syngas with controllable H2/CO ratios in a wide range. Herein, we report an efficient plasma-driven catalytic system for mild production of pure syngas over porous metal-organic framework (MOF) catalysts with rich confined H2O molecules, where their syngas production capacity is regulated by the in situ evolved ligand defects and the plasma-activated intermediate species of CO2 molecules. Specially, the Cu-based catalyst system achieves 61.9 % of CO2 conversion and the production of pure syngas with wide H2/CO ratios of 0.05:1-4.3:1. As revealed by the experimental and theoretical calculation results, the in situ dynamic structure evolution of Cu-containing MOF catalysts favors the generation of coordinatively unsaturated metal active sites with optimized geometric and electronic characteristics, the adsorption of reactants, and the reduced energy barriers of syngas-production potential-determining steps of the hydrogenation of CO2 to *COOH and the protonation of H2O to *H.

Plasma‐Driven Efficient Conversion of CO2 and H2O into Pure Syngas with Controllable Wide H2/CO Ratios over Metal‐Organic Frameworks Featuring In Situ Evolved Ligand Defects

While the mild production of syngas (a mixture of H2 and CO) from CO2 and H2O is a promising alternative to the coal‐based chemical engineering technologies, the inert nature of CO2 molecules, unfavorable splitting pathways of H2O and unsatisfactory catalysts lead to the challenge in the difficult integration of high CO2 conversion efficiency with produced syngas with controllable H2/CO ratios in a wide range. Herein, we report an efficient plasma‐driven catalytic system for mild production of pure syngas over porous metal‐organic framework (MOF) catalysts with rich confined H2O molecules, where their syngas production capacity is regulated by the in situ evolved ligand defects and the plasma‐activated intermediate species of CO2 molecules. Specially, the Cu‐based catalyst system achieves 61.9 % of CO2 conversion and the production of pure syngas with wide H2/CO ratios of 0.05:1‐4.3:1. As revealed by the experimental and theoretical calculation results, the in situ dynamic structure evolution of Cu‐containing MOF catalysts favors the generation of coordinatively unsaturated metal active sites with optimized geometric and electronic characteristics, the adsorption of reactants, and the reduced energy barriers of syngas‐production potential‐determining steps of the hydrogenation of CO2 to *COOH and the protonation of H2O to *H.

Photochemical Synthesis of Chiral Heterocycles via Asymmetric Carbon‐Heteroatom Bond Formation

Chiral heterocyclic compounds play a crucial role in the pharmaceutical science, materials science, and agrochemical industries. The critical step for synthesizing chiral heterocycles is the formation of asymmetric carbon‐heteroatom bonds, which can be achieved in a chiral environment under thermal or photochemical conditions. However, photochemical asymmetric transformation has become an area of immense growth in the past 15 years. In the drug discovery and development era, chiral photochemical transformations have drawn the attention of researchers to develop new synthetic strategies for chiral heterocycles via asymmetric carbon‐heteroatom bond formation. Chiral photochemistry in the pathway of asymmetric synthesis requires a chirality source which is transferred to the products. A catalytic chiral metal complexing agent or a chiral photosensitizer that generally follows a single electron transfer (SET) or oxidative and reductive quenching cycle has been widely exploited to achieve this goal. In this review, we have demonstrated the recent development of photochemical synthesis of chiral heterocycles via asymmetric carbon‐heteroatom bond formation by using a chiral metal catalyst, asymmetric organocatalyst, or dual catalytic system based on their plausible mechanism.

Supported ruthenium phosphide as a promising catalyst for selective hydrogenation of sugars

This work demonstrates that ruthenium phosphides (RuP2) are attractive catalysts for selective production of alditols by sugar hydrogenation. In our studies, carbon supported RuP2 with a ruthenium content of 5 wt.‐% led to the highest activity in xylose hydrogenation and to nearly 100 % yield for xylitol. ICP‐OES and XRD measurements revealed the stability of this novel RuP2/C catalyst under typical hydrogenation conditions (50 barH2, 120 °C) in aqueous phase. Furthermore, STEM‐EDX illustrated the close proximity of ruthenium and phosphorous on the catalyst site and the formation of nanoparticles in the size of 2‐4 nm. The novel catalyst system was successfully applied for the selective hydrogenation of further sugar substrates, including glucose, fructose, and disaccharides, such as cellobiose and sucrose. Here, the RuP2/C revealed its bifunctional acidic/metallic character, enabling in a tandem reaction the hydrolysis of disaccharides, directly followed by a selective hydrogenation to form sugar alcohols in high yield.

Effect of Na+ migration and the component proximity on direct conversion of aromatics into aromatics over Fe-based zeolite bifunctional catalysts

Direct conversion of syngas into aromatics (STA) via Fischer-Tropsch (F-T) synthesis, using Fe-based zeolite bifunctional catalysts, has recently become a topic of great interest. The catalytic performance of the Fe-based zeolite bifunctional catalyst is influenced by the component proximity in the STA reaction, in addition to their physicochemical properties. However, the mechanism by which the component proximity affects the STA performance is still unclear. Herein, we investigate the effect of Na+ migration and the component proximity on the F-T reactivity, the aromatic distribution, and catalyst stability in a Fe-based ZSM-5 catalyst system. The correlation between the proximity of two components, the migration of alkali-metal promoters, the evolution of the Fe-based active phase, and the coke on the zeolite is analyzed using XRD, XPS, FT-IR, TG, Mössbauer spectroscopy techniques. The findings indicate that when the components are closer to each other, it encourages the formation of iron carbides and inhibits the coke deposition on the zeolite. However, the migration of alkali metals and the acidic environment of zeolite can decrease the catalyst’s stability and F-T reactivity. Moreover, by improving the hydrophobic nature of the zeolite, we can prevent the transfer of alkali-metal promoters from the Fe-based component to zeolite. This enhances the stability of Fe-based ZSM-5 catalysts in the STA reaction, suggesting a new approach to improve their STA performance.

Scalable Bioreactor Production of an O2‐Protected [FeFe]‐Hydrogenase Enables Simple Aerobic Handling for Clean Chemical Synthesis

AbstractThe enzyme CbA5H, a [FeFe]‐hydrogenase from Clostridium beijerinckii, has previously been shown to survive exposure to oxygen, making it a promising candidate for biotechnological applications. Thus far [NiFe]‐hydrogenases are typically considered for such applications, due to the superior O2‐tolerance and therefore simplified enzyme handling. However, methods for production of [FeFe]‐hydrogenases are generally more successful than for other classes of hydrogenases, therefore in this work we focus on demonstrating scalable CbA5H production, and report results with active enzyme prepared in bioreactors (up to 10 L) with >20‐fold improvement in purified enzyme yield. We then go on to confirm excellent H2/H+‐cycling activity of the air‐purified protein, highlighting that CbA5H can be prepared and isolated without the need for complex and expensive infrastructure. Next, we demonstrate good stability of the air‐purified CbA5H both in solution assays, and as a heterogenous catalyst system when immobilized on a carbon support. Finally, we successfully implement this enzyme within previously demonstrated biotechnologies for flavin and NADH recycling, highlighting its relevance in chemical synthesis, and we demonstrate production of an important API precursor, 3‐quinuclidinol at >0.4 g scale in standard benchtop hydrogenation infrastructure, with >100,000 CbA5H turnovers over 18 operational hours.