Recent Understanding of Water‐Assisted CO2 Hydrogenation to Alcohols

Posted on 8 March 2024 by

Continuously removing water is desired to alleviate thermodynamic barriers during CO₂ hydrogenation. However, at low concentrations, water can enhance alcohol productivity. Here, we discuss the main findings that led to an atomic-level understanding of water promotional effects in CO₂ hydrogenation to alcohols.

Abstract

Alcohol production from CO₂ hydrogenation is a cutting-edge process in sustainable chemistry that holds vast promise for addressing climate change by recycling and repurposing emissions. Many strategies have been proposed to improve the process efficiency. In-situ generated, and trace amounts of water added to the feed stream have recently proved to be determinant to promote key reaction steps, increasing alcohol selectivity and yield. Here, we discuss the main findings that led to an atomic-level understanding of water promotional effects in CO₂ hydrogenation to alcohols. H₂O and the products resultant from its dissociation (OH and O) can act in different ways, stabilizing intermediates and active sites or participating in the hydrogen transfer mechanisms during the reaction. Gaining insights into the mechanisms underlying water promotion offers a cost-effective strategy for enhancing alcohol production efficiency.

Pushing the Efficiency of the Selective and Base‐free Air‐Oxidation of HMF by Varying the Properties of Carbon‐based Supports

Posted on 8 March 2024 by

Support for base-free: Pt supported on various activated carbon and carbon black materials was prepared and tested for the base-free, selective air-oxidation of 5-(Hydroxymethyl)furfural to 2,5-Furandicarboxylic acid. Depending on the chemical properties (graphitization degree, O-containing functional groups) of the supports as determined by comprehensive characterization, highly active and selective catalysts were found due to the active role of the support.

Abstract

The selective oxidation of 5-(Hydroxymethyl)furfural (HMF) to 2,5-Furandicarboxylic acid (FDCA) is highly attractive for the production of renewable monomers as substitute for fossil-based monomers. To achieve a sustainable synthesis, we report on advances for a base-free approach, reducing waste from the process, using air as oxidant and heterogeneous catalysts. Various Carbon-based supports, which can be bio-sourced and cost-efficient, for Pt particles were investigated as they allow for an easy reuse and at the end-of-life Pt can be recycled to enable a closed cycle. Commercially available supports with varying properties, which might replace the base, were studied with Pt particles of similar size and loading. Significant differences in the catalytic activity were observed, which were correlated with the O-functionalities and graphitization degree of the supports derived from Raman spectroscopy, temperature-programmed desorption, and X-ray photoelectron spectroscopy. An activated carbon (Norit ROX) rich in quinone/pyrone-type groups and a carbon black-based catalyst with graphene-layers pushed the efficiency with enhanced FDCA-yields enabling the complete substitution of the homogeneous base. This allows to circumvent the base in this process which together with high selectivity, air as oxidant, a reusable catalyst, and the use of bio-based feedstock contributes to the sustainability of the production of renewable monomers.

Unlocking the Mysteries of Technical Catalyst Deactivation: A View from Space

Posted on 8 March 2024 by nShweta Sharma, nFlorian Maurer, nPatrick Lott, nThomas L. Sheppardn

The paper highlights spatially–resolved characterization techniques for investigating deactivation of technical catalysts. Employing advanced analytical tools, such studies can provide deep insights into the heterogeneous nature of catalyst deactivation. The importance of spatial mapping and scale–bridging analyses is clear to connect observations and understanding of catalyst deactivation from model to technical scale.

Abstract

Modern analytical techniques enable researchers to study heterogeneous catalytic systems at extended length scales and with local probing methods which were previously impractical. Such spatially–resolved analyses are ideal for exploring the complex dynamics governing catalytic activity, and more specifically, deactivation. Here we highlight significant experimental concepts and milestones in the spatially–resolved analysis of technical catalysts, where it is now possible to study catalyst behavior even up to industrially relevant scale. At such extended length scales and in contrast to many model systems, spatial heterogeneities in solid catalyst bodies may play a crucial role in controlling catalytic properties and may be closely linked to catalyst deactivation. Spatially–resolved studies can therefore provide a unique source of information about such local phenomena. Researchers can gain a deeper insight into the operational life of a catalyst by understanding deactivation patterns, which are one of many factors influencing the dynamics of catalytic reactions. In turn, this information promotes the design of more robust and sustainable catalytic systems. We therefore outline the current state of spatially–resolved characterization, together with its role in deconvoluting the complexity of technical catalysts and their deactivation.

Acid‐Free Intermolecular Hydroarylation of Acetylene Catalyzed by Dicationic Palladium(II) and Platinum(II) Ethylene Complexes

Posted on 8 March 2024 by

The hydroarylation of acetylene is catalyzed by dicationic palladium and platinum pincer complexes [M(PNP)(C₂H₄)](SbF₆)₂ (M=Pd and Pt; PNP=2,6-bis(diphenylphosphinomethyl)pyridine). After optimization of reaction conditions, a benchmark of TON 200 is achieved for the catalytic addition of pentamethylbenzene to acetylene with 0.5% [Pd(PNP)(C₂H₄)](SbF₆)₂ at room temperature in 24 h under acid-free conditions. Water in small amounts serves as co-catalyst.

Abstract

Four dicationic palladium and platinum ethylene complexes of the type [M(PNP)(C₂H₄)]X₂ (M=Pd, Pt; X=BF₄, SbF₆, PNP=2,6-bis(diphenylphosphinomethyl)pyridine) were studied as pre-catalysts for the intermolecular hydroarylation of acetylene under acid-free conditions. The palladium complex [Pd(PNP)(C₂H₄)](SbF₆)₂ was found to be the most active catalyst for the addition of pentamethylbenzene to acetylene at room temperature. In a ³¹P NMR spectroscopic study the impact of the counter anion on the rate determining step was demonstrated. Various reaction parameters were screened to optimize the catalytic efficiency. The presence of small amounts of water were beneficial and increased the reaction rate. Water acts as co-catalyst assisting in proton transfer during the catalytic reaction. After optimization of the reaction conditions, a benchmark for the palladium(II) catalyzed hydroarylation of acetylene was achieved with TON 200 at room temperature in 24 h under acid-free conditions. However, this catalytic system has a very limited substrate scope.

Assembly of Titanium‐oxo Clusters from Embonic Acid‐Modified {Ti2} Molecular Building Blocks with Efficient Sulfur‐Catalyzed Oxidation Activities

Posted on 8 March 2024 by

A family of titanium-oxo clusters were assembled from large-size ligand embonic acid-modified {Ti₂} molecular building blocks under solvothermal conditions and Ti₂₀ with a large nuclear number has been used as a stable and heterogeneous catalyst to catalyze sulfur oxidation reactions efficiently.

Abstract

To design and synthesize high-nucleated titanium-oxo clusters rationally based on molecular building blocks with potential coordination ability is still a great challenge. In this work, a family of titanium-oxo clusters, including Ti₂ , Ti₆ , Ti₁₂ , and Ti₂₀ clusters, have been assembled from large-size ligand embonic acid-modified {Ti₂} molecular building blocks under solvothermal conditions. By modulating auxiliary linkers and solvent types, the {Ti₂} building blocks exhibit varying degrees of polymerization to form high-nuclear titanium-oxo clusters. Notably, Ti₂₀ with high nucleation, as the decamer containing {Ti₂} building blocks, can act as a stable and heterogeneous catalyst to efficiently catalyze the oxidation of sulfides to sulfones and sulfoxides when using H₂O₂ as the green oxidant. This study provides a new approach for the design and synthesis of highly nucleated and homometallic TOCs based on {Ti₂} units.

Securing Reversibility of UVO2+/UVIO22+ Redox Equilibrium in [emim]Tf2N‐Based Liquid Electrolytes towards Uranium Redox‐Flow Battery

Posted on 8 March 2024 by

Reversibility of a U^VO₂ ⁺/U^VIO₂ ²⁺ redox equilibrium in a [emim]Tf₂N-based liquid electrolyte was successfully established after addition of DMF and Cl⁻ appropriately. The former was employed to reduce viscosity of the system for improving diffusivity of the U-based electrode active materials, while the latter is also essential to stabilize both U^VO₂ ⁺ and U^VIO₂ ²⁺ as tetrachloro complexes.

Abstract

We studied electrochemical behavior of U^VO₂ ⁺/U^VIO₂ ²⁺ in non-aqueous liquid electrolytes to clarify what is required to attain its reversibility for utilizing depleted U in a redox-flow battery. To transfer knowledge from former pyrochemical systems in high temperature molten salts, 1-ethyl-3-methylimidazolium bis(trifluoromethyl)sulfonylamide ([emim]Tf₂N) ionic liquid was employed here. As a result, a reversible redox reaction of the U^VO₂ ⁺/U^VIO₂ ²⁺ was successfully observed on a glassy carbon working electrode under presence of Cl⁻ in [emim]Tf₂N, where [U^VIO₂Cl₄]²⁻+e⁻=[U^VO₂Cl₄]³⁻ occurs after stabilization of both U oxidation states by the Cl⁻ coordination. The observed electrochemical responses are rather sensitive to an electrode material, so that cyclic voltammograms on a Pt working electrode were actually irreversible. To improve diffusivity of solutes, viscosity (η) of [emim]Tf₂N diluted with an auxiliary molecular solvent, N,N-dimethylformamide (DMF), was examined under absence and presence of Cl⁻. When the mole fraction of DMF (x _DMF) is 0.769, η of the mixture becomes sufficiently low to be utilized as a liquid electrolyte. Finally, we have succeeded in demonstrating a reversible redox reaction of [U^VIO₂Cl₄]²⁻+e⁻=[U^VO₂Cl₄]³⁻ in the [emim]Tf₂N-DMF (50 : 50 v/v, x _DMF=0.769) liquid electrolyte containing [Cl⁻]=0.519 M, where η=6.2 mPa ⋅ s.

Chair vs. Boat: Conformational Impacts on DNA Binding Capacity in Cu(II) Complexes Featuring cis‐1,4‐Cyclohexanedicarboxylate

Posted on 8 March 2024 by

This work reports the syntheses of two new Cu(II) coordination complexes using cis-1,4 cyclohexanedicarboxylic acid (cis-1,4-H₂chdc) linker; and 4,4′-dimethyl-2,2′-bipyridine (1)/5,5′-dimethyl-2,2′-bipyridine (2) auxiliary ligands, wherein, cis-1,4-chdc adopts chair form in 1 and boat conformation in 2. Intriguingly, this conformational change impacts the DNA binding capacities of the complexes as revealed by spectrophotometry, circular dichroism spectroscopy and docking studies.

Abstract

Two new coordination complexes were synthesized, which are formulated as [Cu₂(cis-1,4-chdc)(4,4′-Me₂bpy)₄] ⋅ 2(ClO₄ ⁻) ⋅ H₂O (1) and [Cu₂(cis-1,4-chdc)(5,5′-Me₂bpy)₄] ⋅ 2(ClO₄ ⁻) ⋅ H₂O (2), using cis-1,4-cyclohexanedicarboxylic acid (cis-1,4-H₂chdc), 4,4′-dimethyl-2,2′-bipyridine (4,4′-Me₂bpy), 5,5′-dimethyl-2,2′-bipyridine (5,5′-Me₂bpy). Interestingly, cis-1,4-chdc adopts chair form in 1 and boat conformation in 2. This conformational change impacts the DNA binding capacities of the complexes as revealed by spectrophotometry, circular dichroism (CD) spectroscopy and docking studies. The complex 1 having the chair conformation shows higher affinity towards the DNA base pairs due to anti-alignment of the planar aromatic pyridyl rings of 4,4′-Me₂bpy, which strongly intercalates with the adenosine base pairs of DNA by formation of three π–π stacking and two extra π-positive stacking interactions between adenosine bases and positively charged nitrogen. Conversely, 5,5′-Me₂bpy with planar aromatic pyridyl rings of complex 2 shows bis-intercalation with weak affinities toward base pairs by formation of two π–π stacking and one π-positive stacking interactions.

Efficient CO2 Electroreduction to CO Facilitated by Porous Ag(111)‐dominant Ag Nanofoams and Cooperative Ionic Liquid Electrolytes

Posted on 8 March 2024 by

The application of electrochemical CO2 reduction reaction (CO2RR) to generate value-added products, including carbon monoxide (CO), represents a sustainable strategy for addressing the global carbon balance. Silver (Ag) has gained significant attention as an attractive and cost-effective electrocatalyst for CO2RR-to-CO due to high activity. Here, the porous Ag nanofoam catalysts with Ag(111)-dominant were prepared by in-situ electrolysis-deposition method in the ionic liquid (IL) electrolyte. The Ag nanofoam catalysts exhibited exceptional activity in converting CO2 to CO, with a high Faradaic efficiency (> 95%) in a wide range of -1.9 ~ -2.4 V vs. Ag/Ag+ in the 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) electrolyte. The maximum CO partial current density of -125.40 mA cm-2 was obtained on this Ag nanofoam catalyst, representing 62% improvement over Ag(110)-dominant Ag electrode (-77.35 mA cm-2) at -2.4 V vs Ag/Ag+ in the [Bmim][BF4] electrolyte. Density functional theory calculations demonstrate that the Ag(111) crystal facet formed by in-situ electrolysis-deposition method prefers to adsorb [Bmim][BF4] which can stabilize the reaction intermediate, thereby weakening the reaction free energy and promoting CO2 electroreduction.

DNA Logic Gates Integrated on DNA Substrates in Molecular Computing

Posted on 8 March 2024 by

A new generation of DNA computers is evolving to solve biological and medical problems. DNA logic gates are used to create integrated circuits with biocompatibility and programmability. This minireview highlights the efforts in the development of DNA circuits by integration of DNA logic gates into long chains localized on DNA substrates. This approach of all-DNA integrated circuits (DNA ICs) has the advantage of biocompatibility, increased circuit response due to precise gate localization, increased circuit density, reduced unit concentration, and facilitated cell uptake.

Abstract

Due to nucleic acid's programmability, it is possible to realize DNA structures with computing functions, and thus a new generation of molecular computers is evolving to solve biological and medical problems. Pioneered by Milan Stojanovic, Boolean DNA logic gates created the foundation for the development of DNA computers. Similar to electronic computers, the field is evolving towards integrating DNA logic gates and circuits by positioning them on substrates to increase circuit density and minimize gate distance and undesired crosstalk. In this minireview, we summarize recent developments in the integration of DNA logic gates into circuits localized on DNA substrates. This approach of all-DNA integrated circuits (DNA ICs) offers the advantages of biocompatibility, increased circuit response, increased circuit density, reduced unit concentration, facilitated circuit isolation, and facilitated cell uptake. DNA ICs can face similar challenges as their equivalent circuits operating in bulk solution (bulk circuits), and new physical challenges inherent in spatial localization. We discuss possible avenues to overcome these obstacles.

Aldehyde Reductase Activity of Carboxylic Acid Reductases

Posted on 8 March 2024 by nMargit Winkler, nHannah G. Breuer, nLukas Schobern

The synthesis of aldehydes from carboxylic acids is a challenge that the enzyme carboxylic acid reductase (CAR) is mastering. The R-domains of CARs, however, can additionally catalyze carbonyl reduction. This activity is a minor side reaction for many substrate/enzyme pairs but may be significant for others.

Abstract

Carboxylic acid reductase enzymes (CARs) are well known for the reduction of a wide range of carboxylic acids to the respective aldehydes. One of the essential CAR domains - the reductase domain (R-domain) - was recently shown to catalyze the standalone reduction of carbonyls, including aldehydes, which are typically considered to be the final product of carboxylic acid reduction by CAR. We discovered that the respective full-length CARs were equally able to reduce aldehydes. Herein we aimed to shed light on the impact of this activity on aldehyde production and acid reduction in general. Our data explains previously inexplicable results and a new CAR from Mycolicibacterium wolinskyi is presented.