Catalyst Molecules Research Articles

Facile Synthesis of 3D Sea Urchin-like CuO Microspheres Structures and its Higher Photocatalytic Properties

The three-dimensional (3D) sea urchin-like CuO microspheres structures were successfully synthesized by a simple hydrothermal method. With the hydrothermal temperature increases, the morphology of CuO micro-/nanostructures has changed: When the hydrothermal temperature reaches above 40 °C, the irregular CuO particles transform into a 3D sea urchin-like CuO microspheres. X-ray diffraction spectrum and Raman scatting spectra confirm that the obtained 3D sea urchin-like CuO microspheres at hydrothermal temperature of 60 °C are composed of a high purity and single-phase monoclinic CuO. It is found that the 3D sea urchin-like CuO microspheres structures exhibit the better photocatalytic property for degradation of methylene blue (MB) solution under the visible light irradiation compared to the irregular CuO particles, which duo to the relatively larger specific surface area of the sea urchin-like CuO microspheres structures, exposing more active sites and increasing the contact area between the catalyst and dye molecule. This remarkable photocatalytic performance of the 3D sea urchin-like CuO microspheres structures might has a promising application in waste water treatment.

In situ activation of therapeutics through bioorthogonal catalysis.

Bioorthogonal chemistry refers to any chemical reactions that can occur inside of living systems without interfering with native biochemical processes, which has become a promising strategy for modulating biological processes. The development of synthetic metal-based catalysts to perform bioorthogonal reactions has significantly expanded the toolkit of bioorthogonal chemistry for medicinal chemistry and synthetic biology. A wide range of homogeneous and heterogeneous transition metal catalysts (TMCs) have been reported, mediating different transformations such as cycloaddition reactions, as well as bond forming and cleaving reactions. However, the direct application of 'naked' TMCs in complex biological media poses numerous challenges, including poor water solubility, toxicity and catalyst deactivation. Incorporating TMCs into nanomaterials to create bioorthogonal nanocatalysts can solubilize and stabilize catalyst molecules, with the decoration of the nanocatalysts used to provide spatiotemporal control of catalysis. This review presents an overview of the advances in the creation of bioorthogonal nanocatalysts, highlighting different choice of nano-scaffolds, and the therapeutic and diagnostic applications.

Heterogeneous Molecular Catalysts of Metal Phthalocyanines for Electrochemical CO2 Reduction Reactions.

ConspectusMolecular catalysts, often deployed in homogeneous conditions, are favorable systems for structure-reactivity correlation studies of electrochemical reactions because of their well-defined active site structures and ease of mechanistic investigation. In pursuit of selective and active electrocatalysts for the CO2 reduction reactions which are promising for converting carbon emissions to useful fuels and chemical products, it is desirable to support molecular catalysts on substrates because heterogeneous catalysts can afford the high current density and operational convenience that practical electrolyzers require. Herein, we share our understanding in the development of heterogenized metal phthalocyanine catalysts for the electrochemical reduction of CO2. From the optimization of preparation methods and material structures for the electrocatalytic activity toward CO2 reduction to CO, we find that molecular-level dispersion of the active material and high electrical conductivity of the support are among the most important factors controlling the activity. The molecular nature of the active site enables mechanism-based optimization. We demonstrate how electron-withdrawing and -donating ligand substituents can be utilized to modify the redox property of the molecule and improve its catalytic activity and stability. Adjusting these factors further allows us to achieve electrochemical reduction of CO2 to methanol with appreciable activity, which has not been attainable by conventional molecular catalysts. The six-electron reduction process goes through CO as the key intermediate. Rapid and continuous electron delivery to the active site favors further reduction of CO to methanol. We also point out that, in homogeneous electrocatalysis where the catalyst molecules are dissolved in the electrolyte solution, even if the molecular structure remains intact, the actual catalysis may be dominated by molecules permanently adsorbed on the electrode surface and is thus heterogeneous in nature. This account uses our research on CO2 electroreduction reactions catalyzed by metal phthalocyanine molecules to illustrate our understanding about heterogeneous molecular electrocatalysis, which is also applicable to other electrochemical systems.

CAT-COSMO-CAMPD: Integrated in silico design of catalysts and processes based on quantum chemistry

Catalysts are of paramount importance as most chemical processes would be uneconomical without suitable catalysts. Consequently, the identification of appropriate catalysts is a key step in chemical process design. However, the number of potential catalysts is usually vast. To suggest promising candidates for experimental testing, in silico catalyst design methods are highly desirable. Still, such computational methods are in their infancy. Moreover, simple performance indicators are commonly employed as design objective instead of evaluating the actual process performance enabled by considered catalysts. Here, we present the CAT-COSMO-CAMPD method for integrated in silico design of homogeneous molecular catalysts and processes. CAT-COSMO-CAMPD integrates design of molecular catalysts with process optimization, enabling a process-based evaluation of every designed candidate catalyst. Reaction kinetics of catalytic reactions are predicted by advanced quantum chemical methods. We demonstrate for a catalytic carbamate-cleavage process that CAT-COSMO-CAMPD successfully identifies catalyst molecules maximizing the predicted process performance.

Heterogeneous C-H Functionalization in Water via Porous Covalent Organic Framework Nanofilms: A Case of Catalytic Sphere Transmutation.

Heterogeneous catalysis in water has not been explored beyond certain advantages such as recyclability and recovery of the catalysts from the reaction medium. Moreover, poor yield, extremely low selectivity, and active catalytic site deactivation further underrate the heterogeneous catalysis in water. Considering these facts, we have designed and synthesized solution-dispersible porous covalent organic framework (COF) nanospheres. We have used their distinctive morphology and dispersibility to functionalize unactivated C-H bonds of alkanes heterogeneously with high catalytic yield (42-99%) and enhanced regio- and stereoselectivity (3°:2° = 105:1 for adamantane). Further, the fabrication of catalyst-immobilized COF nanofilms via covalent self-assembly of catalytic COF nanospheres for the first time has become the key toward converting the catalytically inactive homogeneous catalysts into active and effective heterogeneous catalysts operating in water. This unique covalent self-assembly occurs through the protrusion of the fibers at the interface of two nanospheres, transmuting the catalytic spheres into films without any leaching of catalyst molecules. The catalyst-immobilized porous COF nanofilms' chemical functionality and hydrophobic environment stabilize the high-valent transient active oxoiron(V) intermediate in water and restricts the active catalytic site's deactivation. These COF nanofilms functionalize the unactivated C-H bonds in water with a high catalytic yield (45-99%) and with a high degree of selectivity (cis:trans = 155:1; 3°:2° = 257:1, for cis-1,2-dimethylcyclohexane). To establish this approach's "practical implementation", we conducted the catalysis inflow (TON = 424 ± 5) using catalyst-immobilized COF nanofilms fabricated on a macroporous polymeric support.

SiCaSMA: An Alternative Stochastic Description via Concatenation of Markov Processes for a Class of Catalytic Systems

The Chemical Master Equation is a standard approach to model biochemical reaction networks. It consists of a system of linear differential equations, in which each state corresponds to a possible configuration of the reaction system, and the solution describes a time-dependent probability distribution over all configurations. The Stochastic Simulation Algorithm (SSA) is a method to simulate sample paths from this stochastic process. Both approaches are only applicable for small systems, characterized by few reactions and small numbers of molecules. For larger systems, the CME is computationally intractable due to a large number of possible configurations, and the SSA suffers from large reaction propensities. In our study, we focus on catalytic reaction systems, in which substrates are converted by catalytic molecules. We present an alternative description of these systems, called SiCaSMA, in which the full system is subdivided into smaller subsystems with one catalyst molecule each. These single catalyst subsystems can be analyzed individually, and their solutions are concatenated to give the solution of the full system. We show the validity of our approach by applying it to two test-bed reaction systems, a reversible switch of a molecule and methyltransferase-mediated DNA methylation.

Co-improvement of –COOH group and –SO3H group densities in carbon-based solid acid by a simple strategy

High-performance carbon-based solid acid was prepared by a simple method. The effects of carbonization temperature and mixing ratio on the structure and performance of carbon catalysts were explored. The participation of borax increases both –COOH group and –SO3H group densities. In addition, graphitization and specific surface area of the catalyst increase by this co-carbonization method. Higher –COOH group density and aromaticity facilitate the adsorption between catalyst and substrate molecule through hydrogen bonding and CH-π interaction respectively. These improvements of structural significantly increase the hydrolysis activity of the catalyst.

Theory-Driven Design of Electrocatalysts for the Two-Electron Oxygen Reduction Reaction Based on Dispersed Metal Phthalocyanines

Theory-Driven Design of Electrocatalysts for the Two-Electron Oxygen Reduction Reaction Based on Dispersed Metal Phthalocyanines

Rapid hyperpolarization and purification of the metabolite fumarate in aqueous solution

Hyperpolarized fumarate is a promising biosensor for carbon-13 magnetic resonance metabolic imaging. Such molecular imaging applications require nuclear hyperpolarization to attain sufficient signal strength. Dissolution dynamic nuclear polarization is the current state-of-the-art methodology for hyperpolarizing fumarate, but this is expensive and relatively slow. Alternatively, this important biomolecule can be hyperpolarized in a cheap and convenient manner using parahydrogen-induced polarization. However, this process requires a chemical reaction, and the resulting solutions are contaminated with the catalyst, unreacted reagents, and reaction side-product molecules, and are hence unsuitable for use in vivo. In this work we show that the hyperpolarized fumarate can be purified from these contaminants by acid precipitation as a pure solid, and later redissolved to a desired concentration in a clean aqueous solvent. Significant advances in the reaction conditions and reactor equipment allow for formation of hyperpolarized fumarate at 13C polarization levels of 30-45%.

The catalytic effects of H2O, basic and acidic catalysts on the gas‐phase hydrolysis mechanism of carbonyl fluoride (CF2O)

AbstractThe carbonyl fluoride (CF2O) is one of the significant atmospheric molecules, and its hydrolysis reaction has been considered the most potential removal process in the earth's troposphere. In this article, the hydrolysis reaction of CF2O assisted by H2O, basic (NH3 and CH3NHCH3), and acidic (H2SO4, HCOOH, and CF3COOH) catalysts have theoretically investigated using quantum chemical methods. These catalysts significantly decrease the hydrolysis reaction of barrier height by 20.4–28.8 kcal mol−1. Here two H‐transfer mechanisms have been identified in these catalyzed hydrolytic reactions as asynchronous collaborative caused by base molecules and the synchronous collaborative led by H2O and acid molecules. In addition, the rate coefficient and relative rate of all catalytic reactions have calculated using conventional transition state theory (TST) over a temperature range of 280–320 K. The results show that H2SO4 has the best catalytic effect without considering the concentration of catalyst molecules in the atmosphere. On the contrary, a high concentration of HCOOH (10 ppbv) is dominant in the catalytic reaction when considered the concentrations of catalyst molecules. In this work, it was identified that the catalytic efficiencies of H2O, acid and base molecules upon addition reaction between CF2O and H2O is not only related to their catalytic mechanisms but also depending upon their concentrations in the atmosphere.

In-situ block copolymerization of 1,3-butadiene with cyclohexene oxide and trimethylene carbonate via combination of coordinative chain transfer polymerization and ring opening polymerization by neodymium-based catalyst system

Incorporating polar segment or polar block to non-polar polybutadiene is eye-catching as they can modify the interfacial energy and adhesion between polybutadiene matrix and polar materials. Herein, we report the in-situ preparation of well-defined polybutadiene-based block copolymers (poly(1,3-butadiene)-b-poly(cyclohexene oxide) and poly(1,3-butadiene)-b-poly(trimethylene carbonate)) using a commercially available neodymium-based catalytic system Nd(vers)3/AliBu2H/Me2SiCl2. First, the polybutadiene block was conveniently and highly efficiently synthesized via Coordinative Chain Transfer Polymerization (CCTP), yielding 5–11 polymer chains per catalyst molecule. This system revealed a high catalytic efficiency and well-controlled fashion, narrowly distributed together with well-regulated molecular weights were also resulted. Then, taking advantage of the living metal-capped polybutadienyl chain that were produced during the CCTP reaction in the first step, in-situ Ring Opening Polymerization of cyclohexene oxide, trimethylene carbonate were assessed. All the products were carefully characterized by combination of GPC, FTIR, 1H NMR, 2D DOSY NMR and DSC analysis, providing advantages and limitations for this method to prepare nonpolar-polar block copolymers.

Electrostatic Interactions Accelerating Water Oxidation Catalysis via Intercatalyst O-O Coupling.

Intercatalyst coupling has been widely applied in the functional mimics for binuclear synergy in natural metal enzymes. Herein, we introduce two facile and effective design strategies, which facilitate the coupling of two catalytic units via electrostatic interactions. The first system is based on a catalyst molecule functionalized with both a positively charged and a negatively charged group in the structure being able to pair with each other in an antiparallel manner arranged by electrostatic interactions. The other system consists of a mixture of two different of catalysts modified with either positively or negatively charged groups to generate intermolecular electrostatic interactions. Applying these designs to Ru(bda) (H2bda = 2,2'-bipyridine-6,6'-dicarboxylic acid) water-oxidation catalysts improved the catalytic performance by more than an order of magnitude. The intermolecular electrostatic interactions in these two systems were fully identified by 1H NMR, TEM, SAXS, and electrical conductivity experiments. Molecular dynamics simulations further verified that electrostatic interactions contribute to the formation of prereactive dimers, which were found to play a key role in dramatically improving the catalytic performance. The successful strategies demonstrated here can be used in designing other intercatalyst coupling systems for activation and formation of small molecules and organic synthesis.

Efficient ORR activity of N-doped porous carbon encapsulated cobalt electrocatalyst derived from a novel bimetal-organic framework

Transition metal nitrogen-doped carbon catalysts have been feasible substitutes for Pt-based electrocatalysts for oxygen reduction reaction (ORR). Herein, porous cobalt N-doped carbon materials with core-shell nanostructure were synthesized by direct carbonization of bimetal-organic framework CoxZn100-x(adeninate)4(biphenyldicarboxylate)6 (x = 0, 3, 5, 8) precursors at various temperatures (800, 900, 1000 °C) in Ar atmosphere. The as-prepared catalysts present core-shell nanostructure and highly graphitic hollow carbon-ring structure. Meanwhile, Co nanoparticles are evenly distributed in the nitrogen-doped carbon matrix. The effects of different molar ratios of Co/Zn and pyrolysis temperatures on ORR catalytic performance were evaluated. After replacement of 5 % Zn in the precursor by Co, the Co5-N-C-900 exhibited superior oxygen reduction activity to that of 20 wt% commercial Pt/C catalyst in 0.1 M KOH, as evidenced by higher half-wave potential (0.86 V vs. 0.85 V) and diffusion-limited current density (−5.79 mA cm−2 vs.−5.26 mA cm−2) vs. RHE. Additionally, the catalyst has long-time stability than that of Pt/C catalyst. Co core-shell nanostructure, large surface area, porous structure and Co-Nx active sites of Co5-N-C-900 were beneficial to the oxygen reduction property, which enlarged the contact area between catalyst and oxygen molecules, exposed sufficient active sites, and elevated mass diffusion and electron transfer rates. Overall, this study provides an appropriate strategy for the synthesis and application of bimetal-organic framework-derived transition metal nitrogen-doped carbon materials as oxygen reduction electrocatalysts.

Highly Active Cooperative Lewis Acid—Ammonium Salt Catalyst for the Enantioselective Hydroboration of Ketones

AbstractEnantiopure secondary alcohols are fundamental high‐value synthetic building blocks. One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe a new concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5–3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule. Control experiments reveal that both catalytic centers are essential for the observed activity. Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via a concerted mechanism, in which hydride at Boron is continuously displaced by iodide, reminiscent to an SN2 reaction. The catalyst, which is accessible in high yields in few steps, was found to be stable during catalysis, readily recyclable and could be reused 10 times still efficiently working.

Highly Active Cooperative Lewis Acid-Ammonium Salt Catalyst for the Enantioselective Hydroboration of Ketones.

Enantiopure secondary alcohols are fundamental high‐value synthetic building blocks. One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe a new concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5–3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule. Control experiments reveal that both catalytic centers are essential for the observed activity. Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via a concerted mechanism, in which hydride at Boron is continuously displaced by iodide, reminiscent to an SN2 reaction. The catalyst, which is accessible in high yields in few steps, was found to be stable during catalysis, readily recyclable and could be reused 10 times still efficiently working.

Reshaping the Cathodic Catalyst Layer for Anion Exchange Membrane Fuel Cells: From Heterogeneous Catalysis to Homogeneous Catalysis.

In anion exchange membrane fuel cells, catalytic reactions occur at a well-defined three-phase interface, wherein conventional heterogeneous catalyst layer structures exacerbate problems, such as low catalyst utilization and limited mass transfer. We developed a structural engineering strategy to immobilize a molecular catalyst tetrakis(4-methoxyphenyl)porphyrin cobalt(II) (TMPPCo) on the side chains of an ionomer (polyfluorene, PF) to obtain a composite material (PF-TMPPCo), thereby achieving a homogeneous catalysis environment inside ion-flow channels, with greatly improved mass transfer and turnover frequency as a result of 100 % utilization of the catalyst molecules. The unique structure of the homogeneous catalysis system comprising interconnected nanoreactors exhibits advantages of low overpotential and high fuel-cell power density. This strategy of reshaping of the catalyst layer structure may serve as a new platform for applications of many molecular catalysts in fuel cells.

Reshaping the Cathodic Catalyst Layer for Anion Exchange Membrane Fuel Cells: From Heterogeneous Catalysis to Homogeneous Catalysis

AbstractIn anion exchange membrane fuel cells, catalytic reactions occur at a well‐defined three‐phase interface, wherein conventional heterogeneous catalyst layer structures exacerbate problems, such as low catalyst utilization and limited mass transfer. We developed a structural engineering strategy to immobilize a molecular catalyst tetrakis(4‐methoxyphenyl)porphyrin cobalt(II) (TMPPCo) on the side chains of an ionomer (polyfluorene, PF) to obtain a composite material (PF‐TMPPCo), thereby achieving a homogeneous catalysis environment inside ion‐flow channels, with greatly improved mass transfer and turnover frequency as a result of 100 % utilization of the catalyst molecules. The unique structure of the homogeneous catalysis system comprising interconnected nanoreactors exhibits advantages of low overpotential and high fuel‐cell power density. This strategy of reshaping of the catalyst layer structure may serve as a new platform for applications of many molecular catalysts in fuel cells.

A high-efficiency dye-sensitized Pt(II) decorated metal-organic cage for visible-light-driven hydrogen production

Platinum (Pt) complexes have been tremendously exploited as efficient catalysts for producing hydrogen from water due to their high work function and redox potential, yet maximum utilization remains challenging. Herein, we have synthesized and characterized a novel Zr-Bpydc-PtCl2 MOCs material by immobilization a platinum complex in 2,2'-bipyridyl-5,5'-dicarboxylic acid-based metal-organic cages (MOCs) for the first time. In the presence of photosensitizer (Rhodamine B), the functionalized Zr-Bpydc-PtCl2 MOCs exhibits good stability and a high photocatalytic H2 evolution rate (10,466 μmol g−1 h−1) in aqueous solution, which are 6 times of Bpy-PtCl2 and 1.8 times of Bpydc-PtCl2 under visible light irradiation (λ > 420 nm), respectively. Compared with reference experiments, the good performance of Zr-Bpydc-PtCl2 MOCs indicated that integrating catalyst molecules into MOCs is a promising approach for stabilizing the catalytic center and improving the photocatalytic efficiency of H2 production in water.

Study of Esterification Reaction Between Ethanol and Acetic Acid Using Homogeneous and Heterogeneous Catalyst

The Ethyl acetate is the final product of esterification reaction between ethanol and acetate acid which usually used as a solvent. Catalysts are used to boost the esterification reaction rate, mostly the homogenous catalyst (acid liquid catalyst) is used. The use of homogeneous catalyst needs quite long process to separate, that is the reason why using the heterogeneous catalyst is the alternate way. The purpose of this research is to compare the performance of homogeneous catalyst (sulphuric acid) and heteregenous catalyst (natural zeolite from Bayah) by variating the factors that has an impact on reaction. The reaction was happened in batch reactor by variating the speed of agitation speed in range 500-700 rpm and the catalyst molecules size 60 mesh and 100 mesh for the solid catalysts. The goal of the variation is to maximize the reactant mass transfer to the active site of the catalyst. The result of this research shows that on the agitation speed of 700 rpm and 100 mesh Bayah natural zeolite is able to yield bigger conversion of acetate acid compared to using the sulphuric acid catalyst, which are 45.03% and 15.19% .

A simple Cu(II) complex of phenolic oxime: synthesis, crystal structure, supramolecular interactions, DFT calculation and catecholase activity study

A copper (II) complex [Cu(4-MeO-salox)2](1) based on saloxime ligand was synthesized and characterized using single crystal X-ray diffraction studies. The geometry was further emphasized by DFT optimization. The complex was found to be pseudo-macrocyclic mononuclear having square planer geometry. The complex 1 shows two types of supramolecular hydrogen bonding interactions and forms the multi-dimensional framework with the help of CH∙∙∙O, OH∙∙∙O and π∙∙∙π(chelate) interactions. The complex 1 performs as efficient catalyst in catecholase activiy having good turnover number (TON), kcat = 22.97 h−1 where TON is the number of catechol molecules converted into quinone by catalyst molecule i.e 1 in a unit time.