Mn–graphene single-atom catalyst evaluated for CO oxidation by computational screening

CO oxidation reactions on 3-d single metal atom catalysts/MgO(100)

The present work deals with a comprehensive computational theoretical study of the molecular CO and O2 adsorption on 3d single atoms (M/MgO(100)). The study is based on the chemical elements of the 3d row, as they represent an economic advantage compared with the so-called noble metals. The present study has been performed employing density functional theory calculations. Through the representation of the metastable states, we perform a synergetic analysis of the CO oxidation reaction to find trends that suggest the possible use of new candidates such as Ni/MgO(100) or Cu/MgO(100) single-atom catalysts, for this type of redox reaction. We found that Ni and Cu produce energetically viable CO to CO2 reactions. Ni and Cu atoms show the greatest diffusion barrier and are the best candidates due to their low sintering capability. The energetic and electronic properties of the single Cu and Ni atoms on MgO (100) give them the best characteristics to help in the CO oxidation process.

Pyridinic-N Coordination Effect on the Adsorption and Activation of CO2 by Single Vacancy Iron-Doped Graphene

Graphene doped with different transition metals has been recently proposed to adsorb CO2 and help reduce the greenhouse effect. Iron-doped graphene is one of the most promising candidates for this task, but there is still a lack of full understanding of the adsorption mechanism. In this work, we analyze the electronic structure, geometry, and charge redistribution during adsorption of CO2 molecules by single vacancy iron-doped graphene by DFT calculations using the general gradient approximation of Perdew, Burke, and Ernzernhof functional (PBE) and the van der Waals density functional (vdW). To understand the impact of the pyridinic-N coordination of the iron atom, we gradually replaced the neighboring carbon atoms by nitrogen atoms. The analysis indicates that chemisorption and physisorption occur when the molecule is adsorbed in the side-on and end-on orientation, respectively. Adsorption is stronger when pyridinic-N coordination increases, and the vdW functional describes the chemical interactions and adsorption energy differently in relation to PBE without significant structural changes. The development of the chemical interactions with the change of coordination in the system is further investigated in this work with crystal overlap Hamilton population (COHP) analysis.

Review of Carbon Support Coordination Environments for Single Metal Atom Electrocatalysts (SACS)

This topical review focuses on the distinct role of carbon support coordination environment of single-atom catalysts (SACs) for electrocatalysis. The article begins with an overview of atomic coordination configurations in SACs, including a discussion of the advanced characterization techniques and simulation used for understanding the active sites. A summary of key electrocatalysis applications is then provided. These processes are oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), and carbon dioxide reduction reaction (CO2 RR). The review then shifts to modulation of the metal atom-carbon coordination environments, focusing on nitrogen and other non-metal coordination through modulation at the first coordination shell and modulation in the second and higher coordination shells. Representative case studies are provided, starting with the classic four-nitrogen-coordinated single metal atom (MN4 ) based SACs. Bimetallic coordination models including homo-paired and hetero-paired active sites are also discussed, being categorized as emerging approaches. The theme of the discussions is the correlation between synthesis methods for selective doping, the carbon structure-electron configuration changes associated with the doping, the analytical techniques used to ascertain these changes, and the resultant electrocatalysis performance. Critical unanswered questions as well as promising underexplored research directions are identified.

Nb2S2C Monolayers with Transition Metal Atoms Embedded at the S Vacancy Are Promising Single-Atom Catalysts for CO Oxidation

Single atoms anchored on stable and robust two-dimensional (2D) materials are attractive catalysts for carbon monoxide (CO) oxidation. Here, 3d (Fe-Zn), 4d (Ru-Cd), and 5d (Os-Hg) transition metal-decorated Nb2S2C monolayers were systematically studied as potential single-atom catalysts for low-temperature CO oxidation reactions by performing first-principles calculations. Sulfur vacancies are essential for stabilizing the transition metals anchored on the surface of defective Nb2S2C. After estimating the structure stability, the aggregation trend of the embedded metal atoms, and adsorption strength of reactants and products, Zn-decorated defective Nb2S2C is predicted to be a promising catalyst to facilitate CO oxidation through the Langmuir-Hinshelwood (LH) mechanism with an energy barrier of only 0.25 eV. Our investigation indicates that defective carbosulfides can be promising substrates to generate efficient and low-cost single-atom catalysts for low-temperature CO oxidation.

Fe@χ3-borophene as a promising catalyst for CO oxidation reaction: A first-principles study

A novel single-atom catalyst of Fe adsorbed on χ₃-borophene has been proposed as a potential catalyst for CO oxidation reaction (COOR). Quantitative pictures have been provided of both the stability of Fe@χ₃-borophene and various kinetic reaction pathways using first-principles calculations. Strong adsorption energy of -3.19 eV and large diffusion potential of 3.51 eV indicates that Fe@χ₃-borophene is highly stable. By exploring reaction mechanisms for COOR, both Eley-Ridel (E-R) and trimolecule E-R (TER) were identified as possible reaction paths. Low reaction barriers with 0.49 eV of E-R and 0.57 eV of TER suggest that Fe@χ₃-borophene is a very promising catalyst for COOR. Charge transfer between the χ₃-borophene and CO, O₂ and CO₂ gas molecules plays a key role in lowering the energy barrier during the reactions. Our results propose that Fe@χ₃-borophene can be a good candidate of single-atom catalyst for COOR with both high stability and catalytic activity.

Single-Atom (Iron-Based) Catalysts: Synthesis and Applications

Supported single-metal atom catalysts (SACs) are constituted of isolated active metal centers, which are heterogenized on inert supports such as graphene, porous carbon, and metal oxides. Their thermal stability, electronic properties, and catalytic activities can be controlled via interactions between the single-metal atom center and neighboring heteroatoms such as nitrogen, oxygen, and sulfur. Due to the atomic dispersion of the active catalytic centers, the amount of metal required for catalysis can be decreased, thus offering new possibilities to control the selectivity of a given transformation as well as to improve catalyst turnover frequencies and turnover numbers. This review aims to comprehensively summarize the synthesis of Fe-SACs with a focus on anchoring single atoms (SA) on carbon/graphene supports. The characterization of these advanced materials using various spectroscopic techniques and their applications in diverse research areas are described. When applicable, mechanistic investigations conducted to understand the specific behavior of Fe-SACs-based catalysts are highlighted, including the use of theoretical models.

Research Progress and Application of Single-Atom Catalysts: A Review

Due to excellent performance properties such as strong activity and high selectivity, single-atom catalysts have been widely used in various catalytic reactions. Exploring the application of single-atom catalysts and elucidating their reaction mechanism has become a hot area of research. This article first introduces the structure and characteristics of single-atom catalysts, and then reviews recent preparation methods, characterization techniques, and applications of single-atom catalysts, including their application potential in electrochemistry and photocatalytic reactions. Finally, application prospects and future development directions of single-atom catalysts are outlined.

Small Transition-Metal Mixed Clusters as Activators of the C-O Bond. FenCum-CO (n + m = 6): A Theoretical Approach

Binding of carbon monoxide, CO, and its activation on the surface of the Fe_nCu_mCO (n + m = 6) clusters are studied in this work. Using the BPW91/6-311 + G(2d) method, we have found that adsorption of the CO molecule on the surface of Fe_nCu_m (n + m = 6) clusters is thermochemically favorable. Atop and bridge CO cluster coordinations appear for pure, Fe₆ and Cu₆, and mixed, Fe₂Cu₄ and Fe₄Cu₂, clusters. Threefold coordination takes place for Fe₃Cu₃-CO where the CO bond length, d_CO, suffers a largest increase from 1.128 ± 0.014 Å for bare CO up to 1.21 Å. The CO stretching, ν_CO, as an indicator for the CO bond weakening is redshifted, from 2099 ± 4 cm^-1 for isolated CO up to 1690 cm^-1 for Fe₃Cu₃CO and 1678 cm^-1 for Fe₆CO. In addition, in Cu₆CO, the strongest CO bond is slightly weakened as it has a bond length of 1.15 Å and a ν_CO of 2029 cm^-1. There is a correlation between the CO bond weakening and the increase of CO coordination in Fe_nCu_mCO, which in turns promotes the transference of charges from the metal core into the antibonding orbitals of CO. Substitution of up to three Cu atoms in Fe₆ increases the adsorption energies and the activation of CO. Indeed, Fe_nCu_m (n + m = 6) are promising clusters to catalyze CO dissociation, particularly Fe₃Cu₃, Fe₅Cu, and Fe₆, which have large CO bond lengths and CO adsorption energies. The Bader analysis of the electronic density indicates that Fe_nCu_mCO species with threefold coordination show a rise in the C-O covalent character due to the less electronic polarization. They also show important M → CO charge transfer, which favors the weakening of the CO bond.

Application of a blast furnace slag carrier catalyst in flue gas denitration and sulfur resistance

It is an urgent need to develop a new catalyst with high efficiency and low cost. In the present study, we successfully prepared bimetallic-supported denitration catalysts using the blast furnace slag as the main material and calcium bentonite as the binder. The as-prepared catalyst was characterized via X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Besides, the mechanism of denitration was further determined with the help of the denitration and sulfur resistance of the catalyst. The results indicated that when the Mn load was 5%, and the second metal reactive component was loaded at 3%, Mn-Cu/GGBS (catalyst prepared by loading Mn and Cu on the blast furnace slag) had the best effects on low temperature denitration. Moreover, the conversion rate of NO was up to 97%, and it possessed the capability of specific sulfur resistance; when the third metal reactive component, Ce, was introduced with 1% load, the sulfur resistance of the Mn-Cu-Ce/GGBS (catalyst prepared by loading Mn, Cu, and Ce on the blast furnace slag) catalyst was further improved compared with that of the Mn-Cu/GGBS catalyst.

An asymmetric Salamo-based Zn complex supported on Fe3O4 MNPs: a novel heterogeneous nanocatalyst for the silyl protection and deprotection of alcohols under mild conditions

In this study, a magnetic asymmetric Salamo-based Zn complex (H2L = salen type di-Schiff bases)-supported on the surface of modified Fe3O4 (Fe3O4@H2L-Zn) as a new catalyst was designed and characterized via numerous analytical techniques such as FT-IR spectroscopy, XRD, EDS, ICP-AES, SEM, TEM, TGA and VSM. An efficient and sustainable synthetic protocol has been presented for the synthesis of silyl ether substructures via the silyl protection of alcohols under mild conditions. The synthetic protocol involves a two-component solvent-free reaction between various hydroxyl-bearing substrates and hexamethyldisilazane (HMDS) as an inexpensive silylating agent using Fe3O4@H2L-Zn MNPs as a magnetically separable, recyclable and reusable heterogeneous catalyst. Fe3O4@H2L-Zn MNPs were also applied for the removal of silyl protecting groups from hydroxyl functions using water in CH2Cl2 under green conditions. The catalyst demonstrated good to excellent catalytic yield efficiency for both the reactions compared to the commercial metal-based catalysts under green conditions for a wide range of substrates.

Research on the deactivation mechanism of a denitration catalyst WO3-V2O5/TiO2 at a coal-fired power plant

The spent and fresh V₂O₅–WO₃/TiO₂ monolith catalysts were collected from a coal-fired power plant. The de-NO_x efficiency dropped by 20% after the fresh catalyst was used for 30 000 h. Then, the catalysts and the fly ash attached to spent catalysts were collected and analyzed. It was found that the relative amount of Si and Al increased by 80.84% and 2.26 times, respectively, which indicated that a lot of sediments deposited on the surface of the catalyst. Moreover, the content of Na, K, Ca and Fe increased in different degrees. A few new elements, such as Cl, Zn and Pb, appeared on the surface of the deactivated catalyst, and all of these elements had bad effects on the activity. Some kinds of ammonium salts and sulfates emerged on the fly ash, which showed that the catalysts were poisoned by SO₂. The special area decreased only by 4.39 m² g⁻¹. The V³⁺/(V⁴⁺ + V⁵⁺) ratio in the catalyst increased from 0.09 to 0.45 after deactivation, and V⁴⁺ decreased by about 39.54%, which caused the deactivation of the catalyst. The surface acidity of the deactivated catalyst decreased a lot, which might be the immediate cause of deactivation. The particle size of TiO₂ increased due to sintering. The main causes for the deactivation may be described as active sites decreased, poisoned and covered.

The active sites were washed away. The active sites were poisoned. The active sites were covered by substances.

Carbon Monoxide Activation on Small Iron Magnetic Cluster Surfaces, FenCO, n = 1-20. A Theoretical Approach

The chemical activation of the carbon monoxide (CO) molecule on the surface of iron clusters Fe_n (n = 1-20) is studied in this work. By means of density functional theory (DFT) all-electron calculations, we have found that the adsorption of CO over the bare magnetic Fe_n (n = 1-20) clusters is thermochemically favorable. The Fe_n-CO interaction increases the C-O bond length, from 1.128 ± 0.014 Å, for isolated CO, up to 1.251 Å, for Fe₉CO. Also, the calculated wavenumbers associated with the stretching modes ν_CO are decreased, or red-shifted, as another indicator of the CO bond weakening, passing from 2099 ± 4 to 1438 cm^-1. Markedly, wavenumbers of vibrational modes ν_CO agree admirably well in comparison with experimental results reported for Fe_nCO (n = 1, 18-20), getting small errors below 2.6%. The C-O bond is enlarged on the Fe_nCO (n = 1-20) composed systems, as the CO molecule increases its bonding, charge transference, and coordination with the iron cluster. Therefore, small bare iron particles Fe_n (n = 1-20) can be proposed to promote the CO dissociation, especially Fe₉CO, which has been proven to obtain the most prominent activation of the strong C-O bond by means of the charge transference from the metal core.

Theoretical Understandings of Graphene-based Metal Single-Atom Catalysts: Stability and Catalytic Performance

Research on heterogeneous single-atom catalysts (SACs) has become an emerging frontier in catalysis science because of their advantages in high utilization of noble metals, precisely identified active sites, high selectivity, and tunable activity. Graphene, as a one-atom-thick two-dimensional carbon material with unique structural and electronic properties, has been reported to be a superb support for SACs. Herein, we provide an overview of recent progress in investigations of graphene-based SACs. Among the large number of publications, we will selectively focus on the stability of metal single-atoms (SAs) anchored on different sites of graphene support and the catalytic performances of graphene-based SACs for different chemical reactions, including thermocatalysis and electrocatalysis. We will summarize the fundamental understandings on the electronic structures and their intrinsic connection with catalytic properties of graphene-based SACs, and also provide a brief perspective on the future design of efficient SACs with graphene and graphene-like materials.

Theoretical Calculation of Different Reaction Mechanisms for CO Oxidation on MnN3-Doped Graphene

In recent decades, great expectation has always been placed on catalysts that can convert toxic CO into CO₂ under mild conditions. The catalytic mechanism of CO oxidation by Mn-coordinated N-doped graphene with a single vacancy (MnN₃-SV) and a double vacancy (MnN₃-DV) was studied by density functional theory (DFT) calculations. Molecular dynamics simulations showed that CO₂ on MnN₃-SV could not be desorbed from the substrate and MnN₃-SV was not suitable for use as a CO oxidation catalyst. MnN₃-DV was more suitable for CO oxidation (COOR) and from the electronic structure it was found that the Mn atom was the main active site, which was the reaction site for CO oxidation. At temperatures of 0 and 298.15 K, CO oxidation on MnN₃-DV via the Langmuir-Hinshelwood (LH) mechanism was the best reaction pathway. The rate-determining step using MnN₃-DV as the catalyst for CO oxidation through the LH mechanism was O₂ + CO → OOCO, and the energy barrier was 0.861 eV at 298.15 K. MnN₃-DV was suitable as a catalyst for CO oxidation in terms of both thermodynamics and kinetics. This study provides a comprehensive understanding of the various reaction mechanisms of CO oxidation on MnN₃-DV, which is conducive to guiding the development and design of efficient catalysts for CO oxidation.

Density functional study on the CO oxidation reaction mechanism on MnN2-doped graphene

The CO oxidation mechanisms over three different MnN2-doped graphene (MnN2C2: MnN2C2-hex, MnN2C2-opp, MnN2C2-pen) structures were investigated through first-principles calculations. The vacancy in graphene can strongly stabilize Mn atoms and make them positively charged, which promotes O2 activation and weakens CO adsorption. Hence, CO oxidation activity is enhanced and the catalyst is prevented from being poisoned. CO oxidation reaction (COOR) on MnN2C2 along the Eley-Rideal (ER) mechanism and the Langmuir-Hinshelwood (LH) mechanism will leave one O atom on the Mn atom, which is difficult to react with isolated CO. COOR on MnN2C2-opp along the ER mechanism and termolecular Eley-Rideal (TER) mechanism need overcome low energy barriers in the rate limiting step (RLS), which are 0.544 and 0.342 eV, respectively. The oxidation of CO along TER mechanism on MnN2C2-opp is the best reaction pathway with smallest energy barrier. Therefore, the MnN2C2-opp is an efficient catalysis and this study has a guiding role in designing effective catalyst for CO oxidation.

A new class of organoplatinum-based DFNS for the production of cyclic carbonates from olefins and CO2

We studied the potential application of an efficient, reusable, and easily recoverable catalyst of dendritic fibrous nanosilica (DFNS)-supported platinum(ii) complexes (DFNS/Pt(ii) NPs) to form cyclic carbonates in the presence of epoxides by converting carbon dioxide. Cyclic carbonates from epoxides and carbon dioxide is proposed as the most appropriate way to synthesis this C1 building block. We performed FE-SEM, TEM, TGA, BET, VSM, and ICP-MS to thoroughly characterize DFNS/Pt(ii) NPs.

We studied the potential application of an efficient, reusable, and easily recoverable catalyst of dendritic fibrous nanosilica (DFNS)-supported platinum(ii) complexes (DFNS/Pt(ii) NPs) to form cyclic carbonates in the presence of epoxides by converting carbon dioxide.

Release kinetics study and anti-corrosion behaviour of a pH-responsive ionic liquid-loaded halloysite nanotube-doped epoxy coating

This study focuses on the release kinetics of inhibitor-loaded nanocontainers and the anti-corrosive properties of epoxy coatings doped and undoped with the nanocontainers. In this work, 1-butyl-3-methylimidazolium chloride [Bmim][Cl] was loaded into halloysite nanotubes (HNTs), and the loaded HNTs were encapsulated with polyethyleneimine (PEI)/polyacrylic acid (PAA) and poly(diallyldimethylammonium chloride) (PDADMAC)/polyacrylic acid (PAA) to allow controlled release upon pH stimuli. The polyelectrolyte layer deposition was characterized using zeta potential analysis, and the release profiles were evaluated in neutral, acidic, and alkaline media. The release kinetics was studied and found to conform to the Ritger-Peppas and Korsmeyer-Peppas model, and the results proved that the combination of weak polyelectrolytes (PEI and PAA) provided a good response for up to 50% release of [Bmim][Cl] in acidic and alkaline media after 72 hours. The loaded HNTs encapsulated with the PEI/PAA combination were incorporated into an epoxy coating matrix and applied on an X52 steel substrate. The corrosion resistance of the coated and uncoated substrates was evaluated using electrochemical impedance spectroscopy (EIS) after immersion in a 3.5 wt% NaCl solution up to 72 hours. An artificial defect was created on the coating prior to immersion to evaluate the active corrosion inhibition ability. The coating doped with the smart pH-responsive halloysite nanotubes showed promising results in corrosion protectiveness even after 72 hours of exposure to a salt solution through EIS and SEM.

Enantioselective hydrosilylation of unsaturated carbon-heteroatom bonds (C[double bond, length as m-dash]N, C[double bond, length as m-dash]O) catalyzed by [Ru-S] complexes: a theoretical study

A detailed theoretical study on the mechanism of enanthioselective hydrosilylation of imines and ketones catalyzed by the ruthenium(ii) thiolate catalyst [Ru–S] ([L*-Ru(SDmp)]⁺[BAr₄^F]⁻) with a chiral monodentate phosphine ligand is carried out in this work. We elucidate all the pathways leading to the main products or by products mediated by the [Ru–S] complex in order to have deep understanding of the chemoselectivity and enantioselectivity. The DFT (Density Functional Theory) calculations show that the reaction mechanism including: (1) Si–H bond cleavage by the dual activity of Ru–S bond; (2) the generation of a sulfur-stabilized silane cation; (3) the electrophilic attack of silane cation to NC/OC; (4) hydrogen transfer from Ru to carbon cation. The hydrosilylation products are found to be the final products rather than the dehydrogenative ones, which is consistent with the experimental results. The dehydrogenative silylation reaction pathways which give N- or O-silylated enamine/enol ether are reversible according to our calculations. The computational results also show that the electrophilic attack of silicon to NC/OC is the rate-determining step and the ee value can be improved significantly with more bulky model phosphine ligand based on the same calculation methods.

A detailed theoretical study on the mechanism of enanthioselective hydrosilylation of imines and ketones catalyzed by the ruthenium(ii) thiolate catalyst with a chiral monodentate phosphine ligand is carried out in this work.

Asymmetric catalysis in direct nitromethane-free Henry reactions

This review summarizes the current state and applications of catalytic Henry reactions involving complex nitroalkanes coupling with various carbonyl compounds to generate chiral β-nitro alcohol scaffolds with four adjacent stereogenic centers.

Catalytic oxidation mechanisms of carbon monoxide over single- and double-vacancy Mn-embedded graphene

CO oxidation on MnC₃ and MnC₄ has fast kinetics and a low energy barrier.

Reduction of 4-nitrophenol and 2-nitroaniline using immobilized CoMn2O4 NPs on lignin supported on FPS

In the present work, fibrous phosphosilicate (FPS) is functionalized by using octakis[3(3-aminopropyltriethoxysilane)propyl]octasilsesquioxane (APTPOSS) groups.

Palladium/graphene oxide nanocomposites with carbon nanotubes and/or magnetite for the reduction of nitrophenolic compounds

Graphene oxide (GO) was synthesised via the oxidation of graphite and was characterised using ATR FTIR, PXRD, SEM, TEM and TGA. These techniques confirmed the presence of characteristic oxygen-containing functional groups and the resulting increase in interlayer spacing in the nanostructure. GO is used as the support to form nanocomposites composed of combinations of the following: iron oxide nanoparticles (Fe₃O₄), carbon nanotubes (CNT) and palladium nanoparticles (Pd). The four final nanocomposites formed are: Pd/GO, Pd/Fe₃O₄/GO, Pd/CNT/GO, and Pd/CNT/Fe₃O₄/GO. Key intermediates were analysed using ATR FTIR for the confirmation of the modification. Additionally, all composites and their precursors underwent electron microscopic analysis to visually assess composite morphologies and the size distribution of deposited nanoparticles. The Fe₃O₄ and Pd nanoparticles were indistinguishable from each other in their spherical shape and particle diameters, which were no bigger than 32 nm. From the TGA, incorporation of Fe₃O₄, CNT and finally Pd into the nanocomposites increased total thermal stability in terms of mass percentage lost over the temperature programme. GO showed significant decomposition, with all nanocomposites remaining relatively stable up to 120 °C. ICP OES results showed total Pd content by mass percentage for each final composite, varied from 7.9% to 9.1% mass Pd/collective mass. XPS confirmed the expected elemental compositions of composites according to their structures and the Pd⁰ : Pd^II ratios are obtained. The nanocomposites were tested for the catalytic reduction of nitrophenols. Pd/CNT/Fe₃O₄/GO gave the highest TOF′ for the reduction of 4-NP and 2-NP. For the reduction of 3-NP, Pd/GO showed the highest TOF′. Nitrophenol's pK_a and catalyst TOF′ correlated in a direct proportional relationship for Pd/GO and Pd/Fe₃O₄/GO. It was found that Pd⁰ surpassed Pd^II in catalytic activity. Reduction of Pd^II to Pd⁰ took place during the first catalytic cycle.

Comparison of the catalytic activity for the reduction of nitrophenol over palladium-supported graphene oxide nanocomposites modified with iron oxide nanoparticles and/or carbon nanotubes.

A molecular electron density theory study of the mechanism, chemo- and stereoselectivity of the epoxidation reaction of R-carvone with peracetic acid

The epoxidation reaction of R-carvone 8 with peracetic acid 9 has been studied within the molecular electron density theory at the B3LYP/6-311(d,p) computational level. The chemo- and stereoisomeric reaction paths involving the two C-C double bonds of R-carvone 8 have been studied. DFT calculations account for the high chemoselectivity involving the C-C double bond of the isopropenyl group and the low diastereoselectivity, in complete agreement with the experimental outcomes. The Baeyer-Villiger reaction involving the carbonyl group of R-carvone 8 has also been analysed. A bonding evolution theory analysis of the epoxidation reaction shows the complexity of the bonding changes taking place along this reaction. Formation of the oxirane ring takes place asynchronously at the end of the reaction by attack of anionic oxygen on the two carbons of the isopropenyl C-C double bond.

Environmentally friendly nanocrystalline magnesium hydride decorated with metallic glassy-zirconium palladium nanopowders for fuel cell applications

A new solid-state hydrogen storage system of magnesium hydride (MgH₂) doped with 5 wt% of metallic glassy (MG) zirconium palladium (Zr₂Pd) nanopowder was fabricated using a high-energy ball milling technique. The end-product obtained after 50 h of milling was consolidated into bulk buttons, using a hot-pressing technique at 350 °C. The results have shown that this consolidation step, followed by the repetitive pressing at ambient temperature did not affect the nanocrystalline characteristics of pressed powders. Recycling pressing demonstrated beneficial effects of plastic deformation and lattice imperfections on Mg, leading to its enhanced hydrogenation/dehydrogenation kinetics and cycle-life-time performance compared with untreated samples. The results elucidated that spherical, hard, nanopowder of MG-Zr₂Pd were forced to penetrate the Mg/MgH₂ matrix to create micro/nanopore structures upon pressing for 50 cycles. These ultrafine spherical metallic glassy particles (∼400 nm in diameter) acted as a micro-milling media for reducing the particle size of MgH₂ powders into submicron particles. In addition, they played a vital role as grain growth inhibitors to prevent the undesired growth of Mg grains upon the application of a moderate temperature in the range of 50 °C to 350 °C. The apparent activation energy for the decomposition of this new consolidated nanocomposite material was measured to be 92.2 kJ mol⁻¹, which is far below than the measured value of pure nanocrystalline MgH₂ powders (151.2 kJ mol⁻¹) prepared in the present study. This new binary system possessed superior hydrogenation kinetics, indicated by the rather low temperature (200 °C) required to uptake 6.08 wt% H₂ within 7.5 min. More importantly, the system revealed excellent dehydrogenation kinetics at 225 °C as implied by the limited time needed to release 6.1 wt% H₂ in 10 min. The MgH₂/5 wt% MG-Zr₂Pd system showed a high performance for cyclability, implied by the achievement of continuous cycles (338 cycles) at 225 °C without degradation over 227 h.

A new solid-state hydrogen storage system of magnesium hydride (MgH₂) doped with 5 wt% of metallic glassy (MG) zirconium palladium (Zr₂Pd) nanopowder was fabricated using a high-energy ball milling technique.

Visible-light-switched electron transfer over single porphyrin-metal atom center for highly selective electroreduction of carbon dioxide

External fields are introduced to catalytic processes to improve catalytic activities. The light field effect plays an important role in electrocatalytic processes, but is not fully understood. Here we report a series of photo-coupled electrocatalysts for CO₂ reduction by mimicking the structure of chlorophyll. The porphyrin-Au catalyst exhibits a high turnover frequency of 37,069 h^-1 at -1.1 V and CO Faradaic efficiency (FE) of 94.2% at -0.9 V. Under visible light, the electrocatalyst reaches similar turnover frequency and FE with potential reduced by ~ 130 mV. Interestingly, the light-induced positive shifts of 20, 100, and 130 mV for porphyrin-Co, porphyrin-Cu, and porphyrin-Au electrocatalysts are consistent with their energy gaps of 0, 1.5, and 1.7 eV, respectively, suggesting the porphyrin not only serves as a ligand but also as a photoswitch to regulate electron transfer pathway to the metal center.

First-Principles Investigations of Single Metal Atoms (Sc, Ti, V, Cr, Mn, and Ni) Embedded in Hexagonal Boron Nitride Nanosheets for the Catalysis of CO Oxidation

We evaluated isolated transition metal atoms (Sc, Ti, V, Cr, Mn, and Ni) embedded in hexagonal-BN as novel single atom catalysts for CO oxidation. We predicted that embedded Ni atoms should have superior performance for this task. Ti, V, and Mn bind CO2 too strongly and so the reaction will not proceed smoothly. We studied the detailed reaction processes for Sc, Cr, and Ni. The Langmuir–Hinshelwood (LH), Eley–Rideal (ER), and the new termolecular Eley–Rideal (TER) processes for CO oxidation were investigated. Sc was not effective. Cr primarily used the ER process, although the barrier was relatively large at 1.30 eV. Ni was the best of the group, with a 0.44 eV barrier for LH, and a 0.47 eV barrier for TER. Therefore, we predicted that the LH and TER processes could operate at relatively low temperatures between 300 and 500 K.

Nano-kaolin/Ti4+/Fe3O4: a magnetic reusable nano-catalyst for the synthesis of pyrimido[2,1-b]benzothiazoles

Herein, nano-kaolin/Ti⁴⁺/Fe₃O₄ as a new magnetic nano-catalyst was synthesized, and its structural properties were characterized using various techniques such as Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), a vibrating sample magnetometer (VSM), thermogravimetric analysis (TGA) and energy-dispersive X-ray spectroscopy (EDX). This catalyst was used for the synthesis of pyrimido[2,1-b]benzothiazoles via the one-pot condensation of 2-aminobenzothiazole, an aldehyde and β-keto ester under solvent-free conditions at 100 °C. This simple protocol has many advantages such as easy workup, high product yields, short reaction times and reusability of the catalyst.

Herein, nano-kaolin/Ti⁴⁺/Fe₃O₄ as a new magnetic nano-catalyst was synthesized, and its structural properties were characterized using various techniques such as FTIR spectroscopy, FE-SEM, TEM, XRD, VSM, TGA and EDX.

Hydration of phenylacetylene on sulfonated carbon materials: active site and intrinsic catalytic activity

A series of sulfonated carbon materials (sulfonated glucose-derived carbon, carbon nanotubes, activated carbon and ordered mesoporous carbon, denoted as Sglu, SCNT, SAC and SCMK, respectively) were synthesized and applied as acid catalysts in phenylacetylene (PA) hydration reactions. The sulfonic acid groups (-SO3H) were identified to be the only kind of active sites and were quantified with XPS and a cation exchange process. Mechanistic studies revealed that the catalytic PA hydration reaction follows pseudo first order reaction kinetics. Sglu exhibits a higher reaction rate constant (k) and lower apparent activation energy (E a) in the hydration reactions than SCNT catalysts. NH3-temperature programmed desorption measurement results revealed that the relatively high catalytic activity of Sglu was attributed to both the stronger acidity and larger number of -SO3H active sites. This work exhibited the performance of carbon materials without any extra acidic additives in PA hydration reaction and investigated the intrinsic catalytic activity by kinetics. The present work provides the possibility for acid catalytic applications of carbon materials, which sheds light on the environmentally friendly and sustainable production strategy for aldehyde ketone compounds via the catalytic alkyne hydration reactions.