Search

Gas diffusion electrode (GDE)-based setups have shown promising performance for CO2 electrocatalysis and further development of these systems will be important on the path to industrial feasibility. In this article, we model an effective catalyst pore within a GDE-based flow-cell to study the influence of the catalyst structure and operating conditions on the reaction environment for CO2 electrocatalysis at practically relevant current densities. Using a generalized modified Poisson-Nernst-Planck (GMPNP) 3D model of the nanoporous catalyst layer, we show that the length of the catalyst pore as well as the boundary conditions at the gas-electrolyte and electrolyte-electrolyte interfaces across this length are highly influential parameters for determining the conditions within the catalyst pore. Pores with the same catalytic surface area can have very different reaction environments depending primarily on the pore length and not the pore radius. Properties such as electrolyte pH and buffer breakdown, ionic strength and CO2 concentration are also highly-sensitive to the catalyst layer thickness, gas pressure, electrolyte flow rate and the flow-channel geometry. The applied potential impacts the concentration of ionic species in the pore, which in turn determines the solubility of CO2 available for the reaction. Our results underline the need to understand and manage transport within GDE-based electrocatalysis systems as an essential means to control catalyst performance. Benchmarking of GDE-based electrocatalytic systems against their structural and operational parameters will be important for achieving improvements in performance that can be ultimately translated to large-scale operation.

In this study, we construct a 193 nm ultraviolet laser dissociation high-resolution mass spectrometry (HRMS) platform to produce Pt

The formation of M–Zn-intermetallic species (M = Ni, Pd) in the course of the Negishi reaction in THF solvent and their potential impact on in situ catalyst inhibition were investigated by DFT calculations carried out at two levels of theory. The solvent coordination to the transition metal centers was explicitly accounted for in the calculations. Two model PR3 ligands (PR3 = PMe3 and PPh3), as well as a model NHC-type ligand (1,3-diisopropylimidazol-2-ylidene), were selected. The formation of the intermetallic species during the catalytic process effectively removes the key in-cycle cross-coupling intermediates M(0)L2, cis-[L2PhM(II)X], and trans-[L2PhM(II)X] from the main Negishi catalytic cycle. The reaction between the ZnX2 by-product of the cross-coupling and the M(0)L2 species yields bi-metallic adducts with M–Zn dative bonds. The nature of these bonds in the resulting complexes was analyzed with QTAIM. ZnX2 coordination to [L2PhM(II)X] intermediates prevents the binding of alkylzinc halide (RZnX) reagents and blocks the cross-coupling process. Based on these findings, we consider LiX additives as agents that passivate the Lewis-acidic ZnX2 by-product and therefore limit the product inhibition. This work highlights the profound effect of a system view on catalytic cross-coupling reactions, where interactions between components of catalytic systems are taken into account explicitly, and discourage the use of single-cycle-only models.

Herein we report our efforts to control the size of colloidal Ni nanoparticles (NiNPs) via a seed-mediated approach and to produce supported Ni catalysts that are sinter-resistant. NiNPs are prepared using a mild capping ligand and an external reducing agent at 90 °C to obtain seeds of 3-4 nm, followed by NiNP growth at 220 °C to vary the final size up to 8 nm. These NiNPs were either introduced onto high surface area silica via direct deposition in organic solvents, or encapsulated in mesoporous silica. Encapsulation was determined to be the most promising approach to support the particles. A range of such encapsulated NiNP catalysts were evaluated for CO2 hydrogenation between 200-400 °C: they were comparably active as catalysts reported in the literature, and thermally stable and sinter-resistant for 70 h at 350 °C. Nevertheless, it was found that the Ni phase was redistributed throughout the mesoporous silica network, resulting in Ni catalysts with nearly identical particle size of 4-5 nm, determined by the size of the support pores, after a combination of oxidative and reductive pretreatments. Our approach provides a route to obtain Ni@SiO2 catalysts with a narrow particle size distribution from a range of colloidal NiNP precursors.

Coke deposition is one of the main challenges in the commercialization of dry reforming of methane over supported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for the catalyst lifetime. Accordingly, in this study, we analysed the effect of different metal promoters on both these variables over Ni/ ZrO2 catalysts. Alkali metals are known to block the most active coke forming sites already at low loading, leading to an investigation of Na, K and Cs. To analyse the possible contributions of coke gasification activity of the alkali metals, Mn was additionally used as a comparison. While the conversion is barely affected by the type of promoter, it has profound effect on the amount and the composition of carbon deposits formed during reaction: Addition of K or Mn reduces the coke content to a similar degree but with less carbon fibres observed in the case of K. Promotion by Cs and Na results in the lowest coke content, which is attributed to enhanced coke gasification via carbonate species

The foremost requirement for any catalyst to beimplemented in practice is its efficiency and stability. Thisrequirement is particularly valid for manganese hydrogenation catalysts representing more sustainable alternatives to conventional noble metal-based systems. Herein, we report a highly efficient Mn(I)-CNP pre-catalyst featuring phosphine arm hemilability, which gives rise to the excellent productivity (TOF° up to 41 000 h-1) and outstanding stability (TON up to 200 000) in hydrogenation catalysis. This system enables near-quantitative hydrogenation of ketones, imines, aldehydes, and esters at the catalyst loadings as low as 5-200 ppm. Our analysis points to the crucial role of the phosphine hemilability for the catalyst activation step and the stability of the reactive species under the catalytic conditions. Unprecedented inmanganese hydrogenation catalysis, this unusual coordination behavior might have general utility for improving catalysis by Mn complexes and bringing them yet another competitive advantage.

We describe the synthesis and properties of a new composite material based on heparin and MIL-101(Fe) metal-organic framework. The intrinsic instability of MIL-101(Fe) towards hydrolysis enables binding of heparin molecules to the framework structure as is evidenced by DFT calculations and adsorption experiments. The de novo formed heparin-MOF composites showed good biocompatibility in in vitro and demonstrated pronounced anticoagulant activity. The specific interaction between the bioactive molecule and the carrier is critical for the selective degradation of the complex in the body fluids and for the enhanced activity. Hep_MIL-101(Fe) composite could serve as a drug-releasing depot for nanofabrication and to introduce anticoagulant activity to medical devices and biocoatings. Addition of Hep_MIL-101(Fe) to a sol-gel derived thrombolytic matrix allowed the combination of anticoagulant and thrombolytic activities in a single hybrid nanomaterial that could be applied as a bioactive nanocoating for PTFE vein implants.

We demonstrate herein an all-optical switch based on stimuli-responsive and photochromic-free metal-organic framework (HKUST-1). Ultrafast near-infrared laser pulses stimulate a reversible 0.4 eV blue shift of the absorption band with up to 200 s-1 rate due to dehydration and concomitant shrinking of the structure-forming [Cu2 C4 O8 ] cages of HKUST-1. Such light-induced switching enables the remote modulation of intensities of photoluminescence of single crystals of HKUST-1 as well visible radiation passing through the crystal by 2 order of magnitude. This opens up the possibility of utilyzing stimuli-responsive MOFs for all-optical data processing devices.

Ag is a promising catalyst for the production of carbon monoxide (CO) via the electrochemical reduction of carbon dioxide (CO2ER). Herein, we study the role of the formate (HCOO−) intermediate *OCHO, aiming to resolve the discrepancy between the theoretical understanding and experimental performance of Ag. We show that the first coupled proton-electron transfer (CPET) step in the CO pathway competes with the Volmer step for formation of *H, whereas this Volmer step is a prerequisite for the formation of *OCHO. We show that *OCHO should form readily on the Ag surface owing to solvation and favorable binding strength. In situ surface-enhanced Raman spectroscopy (SERS) experiments give preliminary evidence of the presence of O-bound bidentate species on polycrystalline Ag during CO2ER which we attribute to *OCHO. Lateral adsorbate interactions in the presence of *OCHO have a significant influence on the surface coverage of *H, resulting in the inhibition of HCOO− and H2 production and a higher selectivity towards CO.

Structural heterogeneity defines the properties of many functional polymers and it is often crucial for their performance and ability to withstand mechanical impact. Such heterogeneity, however, poses a tremendous challenge for characterization of these materials and limits our ability to design them rationally. Herein we present a practical methodology capable of resolving the complex mechanical behavior and tracking mechanical impact in discrete phases of segmented polyurethane—a typical example of a structurally complex polymer. Using direct optical imaging of photoluminescence produced by a small‐molecule organometallic mechano‐responsive sensor we observe in real time how polymer phases dissipate energy, restructure, and breakdown upon mechanical impact. Owing to its simplicity and robustness, this method has potential in describing the evolution of complex soft‐matter systems for which global characterization techniques fall short of providing molecular‐level insight.

Metal-organic frameworks comprise a class of crystalline porous coordination polymers with unique chemical and physical properties. On the one hand, due to high specific surface area, biocompatibility and stability in biological media, framework materials are ideal candidates for the development of new dosage forms, in particular, for drug delivery systems. On the other hand, the modular structure of frameworks provides an opportunity for computational screening and predictive calculations. This opens new prospects for the design of modern functional materials. The computational screening and simulation of adsorption – desorption processes play a key role in the development of drug delivery systems, as they provide data that are difficult to obtain solely from experiments. These data can greatly assist in the development of drug delivery systems. The first part of the review gives a brief overview of the metal-organic frameworks which have already proved to be potential drug carriers as well as frameworks which are currently being extensively studied and gain attention in this area. The second part addresses the concept of rational design and computer-aided design of such systems. The bibliography includes 216 references.

Periodic density functional theory (DFT) calculations were carried out to investigate the mechanism of methane oxidation with H2O2 over the defined Fe sites in Fe/ZSM-5 zeolite. The initial Fe site is modeled as a [(H2O)2-Fe(III)-(μO)2-Fe(III)-(H2O)2]2+ extraframework cluster deposited in the zeolite pore and charge-compensated by two anionic lattice sites. The activation of this cluster with H2O2 gives rise to the formation of a variety of Fe(III)-oxo and Fe(IV)-oxo complexes potentially reactive toward methane dissociation. These sites are all able to promote the first C-H bond cleavage in methane by following three possible reaction mechanisms: namely, (a) heterolytic and (b) homolytic methane dissociation as well as (c) Fenton-type reaction involving free OH radicals as the catalytic species. The C-H activation step is followed by formation of MeOH and MeOOH and regeneration of the active site. The Fenton-type path is found to proceed with the lowest activation barrier. Although the barriers for the alternative heterolytic and homolytic pathways are found to be somewhat higher, they are still quite favorable and are expected to be feasible under reaction conditions, resulting ultimately in MeOH and MeOOH products. H2O2 oxidant competes with CH4 substrate for the same sites. Since the oxidation of H2O2 to O2 and two [H+] is energetically more favorable than the C-H oxofunctionalization, the overall efficiency of the latter target process remains low.

Transition metal-zeolite composites are versatile catalytic materials for a wide range of industrial and lab-scale processes. Significant advances in fabrication and characterization of well-defined metal centers confined in zeolite matrixes have greatly expanded the library of available materials and, accordingly, their catalytic utility. In this review, we summarize recent developments in the field from the perspective of materials chemistry, focusing on synthesis, postsynthesis modification, (operando) spectroscopy characterization, and computational modeling of transition metal-zeolite catalysts.

This paper reports for the first time a computational analysis of the redox properties of graphene-supported Ru-porphyrins as potential catalytic materials for electrochemical CO2 reduction. Density functional theory reveals that such catalytic ensembles can efficiently activate both CO2 and CH4 molecules indicating their generic utility as C1-functionalization catalysts. The charge transfer from the graphene surface to the catalytic Ru centers influences the thermodynamic stability of the key reaction intermediates and therefore determines the selectivity of the electrochemical process. The electrochemical reduction of CO2 can yield CO or methane, depending on the applied potential and reaction conditions. Calculations also identified alternative paths towards methanol and formic acid.

Peptide-based nanostructures are very promising for nanotechnological applications because of their excellent self-assembly properties, biological and chemical flexibility, and unique multifunctional performance. However, one of the limiting factors for the integration of peptide assemblies into functional devices is poor control of their alignment and other geometrical parameters required for device fabrication. In this work, we report a novel method for the controlled deposition of one of the representative self-assembled peptides - diphenylalanine (FF) - using a commercial inkjet printer. The initial FF solution, which has been shown to readily self-assemble into different structures such as nano- and microtubes and microrods, was modified to be used as an efficient ink for the printing of aligned FF-based structures. Furthermore, during the development of the suitable ink, we were able to produce a novel type of FF conformation with high piezoelectric response and excellent stability. By using this method, ribbonlike microcrystals based on FF could be formed and precisely patterned on different surfaces. Possible mechanisms of structure formation and piezoelectric effect in printed microribbons are discussed along with the possible applications.

Stability is the key property of functional materials. In this work we investigate computationally the degradative potential of a model Mn-BTC (BTC = benzene-1,3,5-tricarboxylate) metal–organic framework (MOF) building block in aqueous solutions under oxidative conditions. Model density functional theory calculations have shown that the direct hydrolysis of the Mn-containing moieties is more difficult than their decomposition via oxidation-induced paths. While the interaction with H2O2 species is of non-covalent nature and requires O–O-bond breaking to initiate Mn-center oxidation, open-shell O2 species readily oxidize radical Mn-centers and form bonds of σ-, π-, or δ-symmetry with the metal. The oxidative transformations of di-Mn paddle-wheel carboxylate structure-forming units are accompanied with substantial distortions of the coordination polyhedra that, together with the increased Lewis acidity of the oxidized metal centers, facilitates the hydrolysis leading to the degradation of the structure at a larger scale. Whereas such a mechanism is expected to hamper the catalytic applications of such Mn-MOFs, the associated structural response to oxidizing and radical species can create a basis for the construction of Mn-MOF-based drug delivery systems with increased bio-compatibility.

A series of substituted, pyridyl-functionalized 2,4,6-triarylpyrylium salts were prepared and investigated for their light absorption and emission properties. After reaction with P(SiMe3)3, the corresponding λ3-phosphinines were obtained, which carry on the 4- or 6-aryl ring ±I and ±M substituents. Supported by DFT calculations, a systematic evaluation of the σ-donor and π-donor as well as π-acceptor properties of these low-coordinate P,N-hybrid ligands was performed. The modular synthetic approach allowed us at the same time to synthesize the structurally related bipyridine derivatives for comparison reasons. Reaction of the chelating ligands with [W(CO)6] in THF afforded the corresponding [(P^N)W(CO)4] and [(N^N)W(CO)4] complexes. A crystallographic characterization of selected coordination compounds revealed significant structural differences between the pyridyl-phosphinine- and the bipyridine-based compounds. Their characterization by means of IR-spectroscopy gave experimental insight into the electronic properties of the respective ligands.

Non‐oxidative dehydroaromatization of methane (MDA) is a promising catalytic process for direct valorization of natural gas to liquid hydrocarbons. The application of this reaction in practical technology is hindered by a lack of understanding about the mechanism and nature of the active sites in benchmark zeolite‐based Mo/ZSM‐5 catalysts, which precludes the solution of problems such as rapid catalyst deactivation. By applying spectroscopy and microscopy, it is shown that the active centers in Mo/ZSM‐5 are partially reduced single‐atom Mo sites stabilized by the zeolite framework. By combining a pulse reaction technique with isotope labeling of methane, MDA is shown to be governed by a hydrocarbon pool mechanism in which benzene is derived from secondary reactions of confined polyaromatic carbon species with the initial products of methane activation.

The catalytic Diels–Alder cycloaddition–dehydration (DACD) reaction of furanics with ethylene is a promising route to bio‐derived aromatics. The reaction can be catalyzed by alkali‐metal‐exchanged faujasites. Herein, the results of periodic DFT calculations based on accurate structural models of alkali‐metal‐exchanged zeolites are presented, revealing the fundamental roles that confinement and the nature of the exchangeable cations in zeolite micropores have in the performance of faujasite‐based catalysts in the DACd reaction. Special attention is devoted to analyzing the effect of functional substituents on furanic substrates (furan, 2,5‐dimethylfuran, 2,5‐furandicarboxylic acid) on the catalyst behavior. It is demonstrated that the conventional reactivity theories of the Diels–Alder chemistry based on simplistic single‐site Lewis acidity and substituent effects do not apply if catalytic processes in the multiple‐site confined environment of zeolite nanopores are considered. The nature and cooperativity of the interactions between the multiple exchangeable cations and the substrates determine the reaction energetics of the elementary steps involved in the DACD process.

The [4+2] cycloaddition reaction between 2-pyrone and Me3 Si-C≡P gives the corresponding 2-(trimethylsilyl)-λ3 -phosphinine in good yields as a rather air and moisture stable, colorless oil. Insight into the regioselectivity of the pericyclic reaction was obtained with the help of deuterium-labeling experiments. The silyl-phosphinine acts as a ligand for the preparation of a Cu(I) and the first crystallographically characterized phosphinine-Ag(I) complex. The title compound was further used as a starting material for an alternative preparation of the parent phosphinine C5 H5 P by means of protodesilylation with HCl. C5 H5 P reacts with CuBr⋅S(CH3 )2 to give an infinite Cu(I)Br coordination polymer. DFT calculations shed light on the influence of the -Si(CH3 )3 group on the electronic properties of the aromatic phosphorus heterocycle.

The alkylation of isobutane with light alkenes plays an essential role in modern petrochemical processes for the production of high-octane gasoline. In this study we have employed periodic DFT calculations combined with microkinetic simulations to investigate the complex reaction mechanism of isobutane–propene alkylation catalyzed by zeolitic solid acids. Particular emphasis was given to addressing the selectivity of the alkylate formation versus alkene formation, which requires a high rate of hydride transfer in comparison to the competitive oligomerization and deprotonation reactions resulting in catalyst deactivation. Our calculations reveal that hydride transfer from isobutane to a carbenium ion occurs via a concerted C–C bond formation between a tert-butyl fragment and an additional olefin, or via deprotonation of the tert-butyl fragment to generate isobutene. A combination of high isobutane concentration and low propene concentration at the reaction center favor the selective alkylation. The key reaction step that has to be suppressed to increase the catalyst lifetime is the deprotonation of carbenium intermediates that are part of the hydride transfer reaction cycle.

The addition of Re to Ni on TiO2 yields efficient catalysts for the hydrogenation of acids and esters to alcohols under mild conditions. Rhenium promotes the formation of atomically dispersed and sub-nanometre-sized bimetallic species interacting strongly with the oxide support.

Surface atomic arrangement and coordination of photocatalysts highly exposed to different crystal facets significantly affect the photoreactivity. However, controversies on the true photoreactivity of a specific facet in heterogeneous photocatalysis still exits. Herein, we exemplified well-defined BiOBr nanosheets dominating with respective facets, (001) and (010), to track the reactivity of crystal facets for photocatalytic water splitting. The real photoreactivity of BiOBr-(001) were evidenced to be significantly higher than BiOBr-(010) for both hydrogen production and oxygen evolution reactions. Further in situ photochemical probing studies verified the distinct reactivity is not only owing to the highly exposed facets, but dominated by the co-exposing facets, leading to an efficient spatial separation of photogenerated charges and further making the oxidation and reduction reactions separately occur with different reaction rates, which ordains the fate of the true photoreactivity.

Lead-free inorganic halide perovskites have triggered appealing interests in various energy-related applications including solar cells and photocatalysis. However, why perovskite-structured materials exhibit excellent photoelectric properties and how the unique crystalline structures affect the charge behaviors are still not well elucidated but essentially desired. Herein, taking inorganic halide perovskite Cs3 Bi2 Br9 as a prototype, the significant derivation process of silver atoms incorporation to induce the structural transformation from Cs3 Bi2 Br9 to Cs2 AgBiBr6 , which brings about dramatic differences in photoelectric properties is unraveled. It is demonstrated that the silver incorporation results in the co-operated orbitals hybridization, which makes the electronic distributions in conduction and valence bands of Cs2 AgBiBr6 more dispersible, eliminating the strong localization of electron-hole pairs. As consequences of the electronic structures derivation, exhilarating changes in photoelectric properties like band structure, exciton binding energy, and charge carrier dynamics are verified experimentally and theoretically. Using photocatalytic hydrogen evolution activity under visible light as a typical evaluation, such crystalline structure transformation contributes to a more than 100-fold enhancement in photocatalytic performances compared with pristine Cs3 Bi2 Br9 , verifying the significant effect of structural derivations on the exhibited performances. The findings will provide evidences for understanding the origin of photoelectric properties for perovskites semiconductors in solar energy conversion.

Coke deposition is one of the main challenges in the commercialisation of dry reforming of methane over supported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for the catalyst lifetime. Accordingly, in this study, we analysed the effect of Na, K, and Cs promoters on both these variables over Ni/ ZrO2 catalysts. Besides blocking the most active coke-forming sites already at low loading, the promoting effect of the alkali metals is also contributed by their coke gasification activity. To evaluate the additional impact of the latter, the behaviour of alkali-doped catalysts was compared to that for Mn-doped catalysts, exclusively featuring the site-blocking promotion mechanism. While the conversion is barely affected by the type of promoter, it has a profound effect on the amount and the composition of carbon deposits formed during the reaction. Promoting with K or Mn reduces the coke content to a similar degree but with less carbon fibres observed in the case of K. The promotion by Cs and Na results in the lowest coke content. The superior performance of Cs and Na-doped Ni/ZrO2 catalysts is attributed to the enhanced coke gasification via carbonate species on top of the site blocking effects.

The viability of the Power-to-Gas (PtG) concept is strongly dependent on the development of highly active and stable methanation catalysts obtained from cheap and abundant elements. In this paper, the promotional effect of MnO on Ni catalysts supported on silica-modified γ-Al2O3 (SA) was investigated in CO2 and CO methanation on catalysts with Mn/Ni atomic ratios between 0 and 0.25. Significantly higher methanation rates and CH4 selectivities were obtained for Mn-promoted compositions compared to Ni-only catalysts. The optimal NiMn/SA (Mn/Ni = 0.25) catalyst exhibited improved stability compared with unpromoted Ni/SA at 20 bar. The nature of the catalyst precursor and active catalyst was studied with STEM-EDX, XPS, and X-ray absorption spectroscopy (XAS). Evidence of a mixed Ni-Mn oxide in the catalyst precursor was obtained by EXAFS. EXAFS measurements revealed that the reduced catalyst consisted of metallic Ni particles and small oxidic Mn2+ species. Moreover, Mn addition improved the Ni dispersion and enhanced the Ni2+ reducibility by weakening the interaction between the Ni-oxide precursor and the support. A mechanistic study involving IR spectroscopy and steady-state isotopic (13CO2) transient kinetic analysis (SSITKA) showed that the presence of Mn enhanced CO2 adsorption and activation.

The influence of the model and method choice on the DFT predicted 13C NMR chemical shifts of zeolite surface methoxide species has been systematically analyzed. Twelve 13C NMR chemical shift calculation protocols on full periodic and hybrid periodic-cluster DFT calculations with varied structural relaxation procedures are examined. The primary assessment of the accuracy of the computational protocols has been carried out for the Si-O(CH3)-Al surface methoxide species in ZSM-5 zeolite with well-defined experimental NMR parameters (chemical shift, δ(13C) value) as a reference. Different configurations of these surface intermediates and their location inside the ZSM-5 pores are considered explicitly. The predicted δ value deviates by up to ±0.8 ppm from the experimental value of 59 ppm due to the varied confinement of the methoxide species at different zeolite sites (model accuracy). The choice of the exchange-correlation functional (method accuracy) introduces ±1.5 ppm uncertainty in the computed chemical shifts. The accuracy of the predicted 13C NMR chemical shifts for the computational assignment of spectral characteristics of zeolite intermediates has been further analyzed by considering the potential intermediate species formed upon methane activation by Cu/ZSM-5 zeolite. The presence of Cu species in the vicinity of surface methoxide increases the prediction uncertainty to ±2.5 ppm. The full geometry relaxation of the local environment of an active site at an appropriate level of theory is critical to ensure a good agreement between the experimental and computed NMR data. Chemical shifts (δ) calculated via full geometry relaxation of a cluster model of a relevant portion of the zeolite lattice site are in the best agreement with the experimental values. Our analysis indicates that the full geometry optimization of a cluster model at the PBE0-D3/6-311G(d,p) level of theory followed by GIAO/PBE0-D3/aug-cc-pVDZ calculations is the most suitable approach for the calculation of 13C chemical shifts of zeolite surface intermediates.

In this study, we construct a 193 nm ultraviolet laser dissociation high-resolution mass spectrometry (HRMS) platform to produce Pt+ cations with high efficiency, which is in situ applied for monitoring the "Pt+ + alkanes"reactions (where alkanes include methane, ethane, and propane). The conversion intermediates and products could be accurately determined by an orbitrap detector with high resolution (up to 150â»000). Importantly, methane conversion by Pt+ cations yields [Pt + ethane]+ and [Pt + ethylene]+ as the sole products formed via the cross-coupling reaction of the Pt-CH2 intermediate with gaseous methane. However, the Pt+ cations promote only the nonoxidative dehydrogenation of ethane and propane to give the corresponding [Pt + alkenes]+ and [Pt + alkynes]+. The details of the reaction mechanism are corroborated by density functional theory (DFT) calculations. These results highlight the power of HRMS with the laser dissociation of metal clusters in the generation and reaction characterization of metal ions.

Transitioning from fossil fuels to sustainable and green energy sources in mobile applications is a difficult challenge and demands sustained and highly multidisciplinary efforts in R&D. Liquid organic hydrogen carriers (LOHC) offer several advantages over more conventional energy storage solutions, but have not been yet demonstrated at scale. Herein we describe the development of an integrated and compact 25 kW formic acid-to-power system by a team of BSc and MSc students. We highlight a number of key engineering challenges encountered during scale-up of the technology and discuss several aspects commonly overlooked by academic researchers. Conclusively, we provide a critical outlook and suggest a number of developmental areas currently inhibiting further implementation of the technology.

Weak noncovalent interactions are responsible for structure and properties of almost all supramolecular systems, such as nucleic acids, enzymes, and pharmaceutical crystals. However, the analysis of their significance and structural role is not straightforward and commonly requires model studies. Herein we describe an efficient and universal approach for the analysis of noncovalent interactions and determination of vdW radii using the Line-of-Sight (LoS) concept. The LoS allows to unambiguously identify and classify the “direct” interatomic contacts in complex molecular systems. This approach not only provides an improved theoretical base to molecular “sizes” but also enables the quantitative analysis of specificity, anisotropy and steric effects of intermolecular interactions.

Energy storage solutions are a vital component of the global transition toward renewable energy sources. The power-to-gas (PtG) concept, which stores surplus renewable energy in the form of methane, has therefore become increasingly relevant in recent years. At present, supported Ni nanoparticles are preferred as industrial catalysts for CO2 methanation due to their low cost and high methane selectivity. However, commercial Ni catalysts are not active enough in CO2 methanation to reach the high CO2 conversion (>99%) required by the specifications for injection in the natural gas grid. Herein we demonstrate the promise of promotion of Ni by Mn, another low-cost base metal, for obtaining very active CO2 methanation catalysts, with results comparable to more expensive precious metal-based catalysts. The origin of this improved performance is revealed by a combined approach of nanoscale characterization, mechanistic study, and density functional theory calculations. Nanoscale characterization with scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDX) and X-ray absorption spectroscopy shows that NiMn catalysts consist of metallic Ni particles decorated by oxidic Mn2+ species. A mechanistic study combining IR spectroscopy of surface adsorbates, transient kinetic analysis with isotopically labeled CO2, density functional theory calculations, and microkinetics simulations ascertains that the MnO clusters enhance CO2 adsorption and facilitate CO2 activation. A macroscale perspective was achieved by simulating the Ni and NiMn catalytic activity in a Sabatier reactor, which revealed that NiMn catalysts have the potential to meet the demanding PtG catalyst performance requirements and can largely replace the need for expensive and scarce noble metal catalysts.

The environment of a CO2 electroreduction (CO2ER) catalyst is intimately coupled with the surface reaction energetics and is therefore a critical aspect of the overall system performance. The immediate reaction environment of the electrocatalyst constitutes the electrical double layer (EDL) which extends a few nanometers into the electrolyte and screens the surface charge density. In this study, we resolve the species concentrations and potential profiles in the EDL of a CO2ER system by self-consistently solving the migration, diffusion and reaction phenomena using the generalized modified Poisson-Nernst-Planck (GMPNP) equations which include the effect of volume exclusion due to the solvated size of solution species. We demonstrate that the concentration of solvated cations builds at the outer Helmholtz plane (OHP) with increasing applied potential until the steric limit is reached. The formation of the EDL is expected to have important consequences for the transport of the CO2 molecule to the catalyst surface. The electric field in the EDL diminishes the pH in the first 5 nm from the OHP, with an accumulation of protons and a concomitant depletion of hydroxide ions. This is a considerable departure from the results obtained using reaction-diffusion models where migration is ignored. Finally, we use the GMPNP model to compare the nature of the EDL for different alkali metal cations to show the effect of solvated size and polarization of water on the resultant electric field. Our results establish the significance of the EDL and electrostatic forces in defining the local reaction environment of CO2 electrocatalysts.

Catalytic reductions of carbonyl‐containing compounds are highly important for the safe, sustainable, and economical production of alcohols. Herein, we report on the efficient transfer hydrogenation of ketones catalyzed by a highly potent Mn(I)−NHC complex. Mn−NHC 1 is practical at metal concentrations as low as 75 ppm, thus approaching loadings more conventionally reserved for noble metal based systems. With these low Mn concentrations, catalyst deactivation is found to be highly temperature dependent and becomes especially prominent at increased reaction temperature. Ultimately, understanding of deactivation pathways could help close the activity/stability‐gap with Ru and Ir catalysts towards the practical implementation of sustainable earth‐abundant Mn‐complexes., A little is enough: Mn(I)−NHC complex 1 is a highly active and robust catalyst for the transfer hydrogenation of ketones. Catalysis with 1 proceeds efficiently at unprecedented catalyst loadings as low as 75 ppm, thus approaching levels more conventionally reserved for privileged Ru‐based catalysts.

Quantum chemistry-based codes and methods provide valuable computational tools to estimate reaction energetics and elucidate reaction mechanisms. Electronic structure methods allow directly studying the chemical transformations in molecular systems involving breaking and making of chemical bonds and the associated changes in the electronic structure. The link between the electronic structure and chemical bonding can be provided through the crystal orbital Hamilton population (COHP) analysis that allows quantifying the bond strength by computing Hamilton-weighted populations of localized atomic orbitals. Another important parameter reflecting the nature and strength of a chemical bond is the bond order that can be assessed by the density derived electrostatic and chemical (DDEC6) method which relies on an electron and spin density-partitioning scheme. Herein, we describe a linear correlation that can be established between the DDEC6-derived bond orders and the bond strengths computed with the COHP formalism. We demonstrate that within defined boundaries, the COHP-derived bond strengths can be consistently compared among each other and linked to the DDEC6-derived bond orders independent of the used model. The validity of these correlations and the effective model independence of the electronic descriptors are demonstrated for a variety of gas-phase chemical systems, featuring different types of chemical bonds. Furthermore, the applicability of the derived correlations to the description of complex reaction paths in periodic systems is demonstrated by considering the zeolite-catalyzed Diels-Alder cycloaddition reaction between 2,5-dimethylfuran and ethylene. ©

A range of Sn-modified MWW, MFI, MOR and Beta zeolites were prepared by a post-synthetic Sn functionalization method and their catalytic properties for sugar conversions were evaluated. The focus of this work was to understand the effect of micropore dimensions and additional mesoporosity on the Sn incorporation and on the catalytic properties. The post-synthetic approach, which involves acid-dealumination of the parent zeolite followed by SnCl4 grafting, is highly efficient for the selective incorporation of lattice Sn sites in wide-pore Beta and MOR zeolites. The modification of the medium-pore MWW and MFI is impaired by the more difficult dealumination and hence the lower efficiency of the Sn incorporation. Hierarchical structuring of the zeolites allows the increase of the Sn loading in the final zeolites. The catalytic properties were assessed in the isomerization and retro-aldolization reactions of glucose and the conversion of 1,3-dihydroxyacetone to methyl lactate. The catalytic results depend strongly on the structural and topological properties of the catalysts as well as on the reactant. Glucose isomerization carried out at a relatively low temperature is mainly limited by strong adsorption of carbohydrates to the active sites. This explains why zeolite nanostructuring had little effect on the catalyst activity, which instead depends mainly on the zeolite topology and the nature of the reactive Sn centers. The influence of pore size is most pronounced for Sn-MWW and Sn-MFI zeolites which are inactive in glucose-to-fructose isomerization, but perform in the higher-temperature retro-aldolization of carbohydrates with an activity similar to that of Sn-Beta. Because of the limited accessibility of the Sn sites inside the 1D MOR pore system, Sn-MOR catalysts were only moderately active in all probe reactions considered.

The origin of the high Brønsted acidity of Ni-SMM (Ni-substituted synthetic mica-montmorillonite; beidellite structure) clays was investigated. Ni-SMM clays with varying F content, SMM with F and Ni-SMM without F in the structure were synthesized under hydrothermal conditions. Ni-SMM clays with intermediate F content contained very strong Brønsted acid sites. The optimum Ni-SMM sample outperformed zeolites such as H-ZSM-5 and H-USY (ultrastabilized Y) in alkane hydroisomerization. Infrared spectroscopy with different probe molecules shows that Ni-SMM contains two types of BAS. In addition to acid sites also observed in other clays and amorphous silica-alumina, Ni-SMM contains a small number of acid sites that are stronger than the acid sites in zeolites. The number of such sites does not depend on Ni-SMM reduction. A small amount of strongest Brønsted acid sites positions the catalytic activity of Ni-SMM clay beyond that of zeolites. Periodic density functional theory calculations show that the substitution of octahedral [Al3+-O]+ by [Ni2+-F]+ causes high acidity of the interlayer proton connected to the aluminium-occupied tetrahedron. This explains why Ni-SMM (no F in the structure) and SMM with F (no Ni in the structure; F replaces only structural OH) exhibit conventional clay acidity. The presence of Ni in the octahedral layer leads to isomorphous substitution of bridging O anions that connect the octahedral with the tetrahedral layer by F. The electron-withdrawing nature of the bridging F induces the unusually high acidity of the interlayer protons in Ni-SMM.

The depolymerization of lignin model compounds and soda lignin by super Lewis acidic metal triflates has been investigated in a mixture of ethanol and water at 400 °C. The strong Lewis acids convert representative model compounds for the structure-forming linkages in lignin, namely α–O–4, 5–O–4 (C–O–C ether bridge), and α–1 (methylene bridge). Only the 5–5′ C–C linkage in biphenyl was unaffected under the given reaction conditions. Full conversion of soda lignin was achieved without char formation. Lignin was converted into a wide range of aliphatic and aromatic hydrocarbons. Ethanol was involved in the alkylation of the lignin depolymerization products. These alkylation reactions increased the product yield by inhibiting repolymerization of the products. The resulting organic phase consisted of aliphatic hydrocarbons (paraffins and olefins), aromatic hydrocarbons (extensively alkylated non-oxygenated mono-aromatics, mainly alkylbenzenes as well as mono-aromatic oxygenates, mainly phenolics), condensation products (mainly naphthalenes) and saturated oxygenates (ketones and carboxylic acids). Although complete product analysis was not possible, the data suggest that the dominant fraction of lignin was converted into monomeric units with a small fraction with molecular weights up to 650 g/mol.

Periodic density functional theory (DFT) calculations were carried out to investigate the mechanism of glucose to fructose isomerization over tungstite (WO3·H2O). The isomerization reaction is catalyzed by undercoordinated W6+ sites. The reaction mechanism proceeds through an H-shift from C2 to C1 and involves a cooperative action of Lewis acidic tungsten sites with neighboring proton donors, which form a hydrogen-bonding surface network. Dopants of group IV-VI transition metals stabilize the preactivated complex, which is the deprotonated open form of glucose adsorbed to the surface. In particular, calculations reveal that doping the tungstite structure with Nb5+ and Ti4+ ions is effective in lowering the overall barrier for glucose isomerization.

In this Perspective, we highlight the main challenges to be addressed in the development of heterogeneous catalysts for the direct functionalization of methane. Along with our personal view on current developments in this field, we outline the main mechanistic, engineering, and catalyst design issues that have hampered implementation of new technologies and highlight possible paths to overcome these problems.

Mo/ZSM-5 is one of the most studied and efficient catalysts for the dehydroaromatization of methane (MDA), but the mechanism of its operation remains controversial. Here, we combine an ab initio thermodynamic analysis with a comprehensive mechanistic density functional theory study to address Mo-speciation in the zeolite and identify the active sites under the reaction conditions. We show that the exposure of Mo/ZSM-5 to the MDA conditions yields a range of reduced sites including mono- and binuclear Mo-oxo and Mo-carbide complexes. These sites can catalyze the MDA reaction via two alternative reaction channels, namely, the C-C coupling (ethylene) and the hydrocarbon-pool propagation mechanisms. Our calculations point toward the binuclear Mo-carbide species operating through the hydrocarbon-pool mechanism to be the most catalytically potent species. Although all other Mo sites in the activated catalyst can promote C-H activation in methane, they fail to provide a successful path to the desirable low-molecular-weight products.

Optimization and execution of chemical reactions are to a large extend based on experience and chemical intuition of a chemist. The chemical intuition is rooted in the phenomenological Le Chatelier's principle that teaches us how to shift equilibrium by manipulating the reaction conditions. To access the underlying thermodynamic parameters and their condition‐dependencies from the first principles is a challenge. Here, we present a theoretical approach to model non‐standard free energies for a complex catalytic CO2 hydrogenation system under operando conditions and identify the condition spaces where catalyst deactivation can potentially be suppressed. Investigation of the non‐standard reaction free energy dependencies allows rationalizing the experimentally observed activity patterns and provides a practical approach to optimization of the reaction paths in complex multicomponent reactive catalytic systems., Operando modeling: Optimization and execution of chemical reactions are to a large extend based on experience and chemical intuition of a chemist. Herewith we present a practical computational approach to investigate condition‐dependencies of reaction free energies in reactive multicomponent multiphase solutions. This method can be readily used to rationally select starting parameters for experimental catalyst tests.

Producing aromatics directly from the smallest hydrocarbon building block, methane, is attractive because it could help satisfy increasing demand for aromatics while filling the gap created by decreased production from naphtha crackers. The system that catalyzes the direct methane dehydroaromatization (MDA) best so far is Mo supported on zeolite. Mo has shown to outperform other transition metals (TMs). Here we attempt to explain the superiority of Mo by directly comparing Fe and Mo supported on HZSM-5 zeolite. To determine the most important parameters responsible for the superior performance of Mo, detailed characterization using X-ray absorption spectroscopy (XAS) techniques combined with catalytic testing and theoretical calculations are performed. The higher abundance of mono- and dimeric sites for the Mo system, their ease of carburization in methane, as well as intrinsically lower activation energy barriers of breaking the methane C-H bond over Mo explain the better catalytic performance. In addition, a pretreatment in CO is presented to more easily carburize Fe and thereby improve its catalytic performance.

Here we report the methodology for nanocomposite fabrication based on the inkjet printing technique. Doped TiO2 nanoparticles with Sc contents up to 10 wt.% were synthesized and adapted towards a facile fabrication of microscale structures and thin film printing. Implementation of the state-of-the-art low-temperature synthesis allowed to us successfully incorporate high concentrations of Sc3+ ions into the TiO2 lattice and improve the light absorption characteristics of the resulting materials. Without affecting the anatase structure substantially, Sc doping gave rise to an intensified absorbance capacity and provided the means for the efficient fabrication of Sc-TiO2 microarchitectures via the inkjet printing technique. The changes in the spectral and structural characteristics of the Sc-TiO2 composites were observed by Energy Dispersive X-Ray spectroscopy (EDX), X-ray diffraction (XRD), and UV-vis methods. The rheological parameters of the colloidal suspension based on the synthesized Sc-TiO2 nanoparticles were adapted for inkjet printing in terms of the optimal viscosity, morphology, and surface tension. The developed individual ink characteristics allowed us to produce a close coherence between the enhanced optical properties of the Sc-TiO2 prepared the sol&ndash, gel method and the inkjet-printed films. The introduced methodology features the possibility to inkjet-print doped and pure TiO2 robust films for potential large-scale fabrication.

A recently discovered photodecarboxylase from Chlorella variabilis NC64A ( CvFAP) bears the promise for the efficient and selective synthesis of hydrocarbons from carboxylic acids. CvFAP, however, exhibits a clear preference for long-chain fatty acids thereby limiting its broad applicability. In this contribution, we demonstrate that the decoy molecule approach enables conversion of a broad range of carboxylic acids by filling up the vacant substrate access channel of the photodecarboxylase. These results not only demonstrate a practical application of a unique, photoactivated enzyme but also pave the way to selective production of short-chain alkanes from waste carboxylic acids under mild reaction conditions.

Cu-exchanged zeolites are known to be active in the selective oxidation of methane to methanol at moderate temperatures. Among them, Cu-exchanged mordenite (MOR) is the system that has so far shown the highest methanol yield per Cu atom. This high efficiency is attributed to the ability of MOR to selectively stabilize an active tricopper cluster with a [Cu3(μ-O)3]2+ structure when activated in the presence of O2 at high temperatures. In this study, we investigate the elementary steps in the formation of [Cu3(μ-O)3]2+ by in situ X-ray absorption spectroscopy and ultraviolet-visible spectroscopy. We demonstrate that the Cu cations undergo a series of thermally driven steps during activation that precede the formation of the active oxidizing species. We hypothesize that the thermal formation of highly mobile Cu+ species by autoreduction of Cu2+ in an inert gas is essential to enable the reorganization of Cu ions in MOR, which is necessary for the formation of a reduced precursor of [Cu3(μ-O)3]2+. Such a precursor can be oxidized in the presence of strong oxidants - such as O2 and N2O - to form active [Cu3(μ-O)3]2+ at temperatures as low as 50 °C.