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High entropy materials (HEM) have been attracting much attention as emerging catalysts for electrochemical water splitting. HEM catalysts have unique properties such as an interesting cocktail effect, broad design space, customizable electronic structure, and excellent entropy stabilization effect compared with single-digit catalysts. This paper provides a comprehensive overview of the use of HEM as a catalyst for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and water splitting. HEM design strategies including phase structure modulation, defect engineering, electrode configuration engineering, and computational aids are discussed to develop HEM catalysts with high performance and stability. In particular, the importance of density functional theory, high-throughput screening techniques, and machine learning for the discovery and design of HEM catalysts is emphasized. Finally, the challenges and imminent difficulties are prospected, and the corresponding strategies to deal with these challenges are put forward to promote the development of HEM catalysts in the field of electrochemical water splitting. [ABSTRACT FROM AUTHOR]

The development of efficient non-noble metal electrocatalysts for the oxygen evolution reaction (OER) under acidic conditions remains a critical challenge. Herein, we report a N-doped carbonaceous component-engineered Co3O4 (NCEC) catalyst synthesized via the sol-gel method. Dopamine hydrochloride (DA)-derived nitrogen-doped carbonaceous components were found to boost the OER performance of Co3O4. The optimized catalyst can reach an overpotential as low as 330 mV in 1 M H2SO4 at a current density of 10 mA cm-2 and maintains a good long-term stability of 60 hours. In particular, we found that the thermodynamic overpotential was inversely proportional to the content of oxidized N and pyridinic N, whereas it was directly proportional to the pyrrolic-N content. Our experiments and density functional theory (DFT) calculations confirm that the optimized catalyst exhibits enhanced charge transfer and the oxidized N species on Co3O4 is responsible for the high catalytic activity. Our study suggests that the performance of NCEC in acidic media can be further optimized by enhancing the content of oxidized N species. [ABSTRACT FROM AUTHOR]

This study employs density functional theory at the SMD/B3LYP-D3/6-311+G(2d,p),def2-TZVPP//SMD/B3LYP-D3/6-31G(d),SDD level of theory to explore the mechanistic details of O2 generation from tBuOOH, using H218O as the solvent, in the presence of the Mn(II) catalyst [Mn2(mcbpen)2(H2O)2]2+. Since this chemistry was reported to occur through the reaction of Mn(III)(μ-O)Mn(IV)–O˙ with water, we first revaluated this proposal and found that it occurs with an activation barrier greater than 36 kcal mol−1, ruling out the functioning of such a dimer as the active catalyst. Experimental evidence has shown that the oxidation of [Mn2(mcbpen)2(H2O)2]2+ by tBuOOH in H218O produces the Mn(IV) species [Mn(18O)(mcbpen)]+. Our investigations revealed a plausible mechanism for this observation in which [Mn (18O)(mcbpen)]+ acts as the active catalyst, generating the tert-butyl peroxyl radical (tBuOO˙) through its reaction with tBuOOH. In this proposed mechanism, the O–O bond is formed through the interaction of tBuOO˙ with another [Mn(18O)(mcbpen)]+, finally leading to the formation of the 16O＝18O product. Our findings underscore the pivotal role of [Mn(18O)(mcbpen)]+ in both generating the active species tBuOO˙ and consuming it to produce 16O＝18O. With activation barriers as low as about 9 kcal mol−1, these elementary steps highlight the feasibility of our proposed mechanism. Moreover, this mechanism elucidates why, experimentally, one of the oxygen atoms in the released O2 comes from water, while the other originates from tBuOOH. This research broadens our understanding of high oxidation state manganese chemistry, setting the stage for the development of more efficient Mn-based catalysts, aimed at improving processes in both renewable energy and synthetic chemistry. [ABSTRACT FROM AUTHOR]

Biomass provides a promising source of carbon for obtaining environment-friendly carbon materials, but obtaining heteroatom-doped carbon materials (HDCMs) from biomass directly by a green method still remains challenging. This study successfully synthesized nitrogen and phosphorus co-doped porous carbon materials (Y-NPC) by the simple in situ pyrolysis of renewable yeast mixed with water from 800 to 950 °C. Various characterization methods show that nitrogen and phosphorus are doped into the carbon skeleton and mainly exist in the forms of graphite-N, pyridine-N, C–P, P–N, and P–O states. The catalyst Y-NPC-900 °C with a 3D hierarchical porous structure and high P–N content exhibited superior nitro hydrogenation performance and reaction stability using molecular hydrogen and hydrazine hydrate as hydrogen sources under mild conditions. Density functional theory (DFT) calculations and experiments attributed the exceptional catalytic performance to hydrogen activation and the good adsorption ability of substrates over N, P co-doped carbon (NPC). Therefore, this research proposes an eco-friendly and simple synthesis strategy for in situ N, P co-doping metal-free carbon catalysts derived from biomass, showing the significance of N, P co-doping and single N- or P-monodoping in the charge distribution of carbon materials. [ABSTRACT FROM AUTHOR]

This density functional theory (DFT) study explores the efficacy of cooperative catalytic systems in enabling the ionic hydrogenation of N2 with H2, leading to NH3 formation. A set of N-heterocyclic carbene-based pincer tungsten/molybdenum metal complexes of the form [(PCP)M1(H)2] (M1 = W/Mo) were chosen to bind N2 at the respective metal centres. Simultaneously, cationic rhodium/iridium complexes of type [Cp*M2{2-(2-pyridyl)phenyl}(CH3CN)]+ (Cp* = C5(CH3)5 and M2 = Rh/Ir), are employed as cooperative coordination partners for heterolytic H2 splitting. The stepwise transfer of protons and hydrides to the bound N2 and intermediate NxHy units results in the formation of NH3. Interestingly, the calculated results reveal an encouraging low range of energy spans ranging from ∼30 to 42 kcal mol−1 depending on different combinations of ligands and metal complexes. The optimal combination of pincer ligand and metal center allowed for an energy span of unprecedented 29.7 kcal mol−1 demonstrating significant potential for molecular catalysts for the N2/H2 reaction system. While exploring obvious potential off-cycle reactions leading to catalyst deactivation, the computed results indicate that no increase in energy span would need to be expected. [ABSTRACT FROM AUTHOR]

The quantitative structure-property relationship (QSPR) of constrained geometry catalysts (CGCs) has been analyzed by combining density functional theory (DFT) and multivariate linear regression (MLR). QSPR models for determining the reaction energy barriers of ethylene and 1-octene and molecular descriptors were established and validated with a testing set. At the initiation stage, the quaternary QSPR models for ethylene and 1-octene feature R² values of 0.90 and 0.82, respectively, while the corresponding leave-one-out Q² values for ethylene and 1-octene are determined to be 0.82 and 0.69. Using the generated QSPR models, the electronic effect was proven to be more critical for determining the energy barriers of ethylene and 1-octene insertion processes. At the propagation stage, the quaternary QSPR models for ethylene and 1-octene feature R² values of 0.97 and 0.96, respectively, while the corresponding leave-one-out Q² values for ethylene and 1-octene are determined to be 0.93. Particularly, the impact of the steric effect on the energy barriers of ethylene and 1-octene insertion is more pronounced. Furthermore, the correlation between the corresponding energy barriers and experimental activities with three series of CGCs was discussed, which revealed that theoretical calculations are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

The design of low-cost and high-performance bifunctional catalysts for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is of great significance for overall water splitting. Herein, RuNi single atom alloy (SAA) decorated on reduced graphene oxide (RuNi@rGO) was synthesized by a facile strategy for use as a bifunctional HER/OER catalyst. The as-obtained RuNi@rGO catalyst exhibits outstanding electrocatalytic activities with an ultralow overpotential for the HER (15 mV) and the OER (240 mV) at a current density of 10 mA cm−2. Density functional theory (DFT) calculations demonstrate that the introduction of Ru single atoms can evidently change the electron distribution and coordination environment around Ni, and reduce the intermediate's adsorption free energy of RuNi@rGO, thus facilitating the HER/OER catalytic rate. Moreover, when used as the cathode and anode of a two-electrode system, the RuNi@rGO-based water splitting device exhibits a low potential of 1.52 V at a current density of 10 mA cm−2, as well as a high faradaic efficiency almost up to 100%, making RuNi@rGO bifunctional electrocatalysts attractive for energy storage and conversion. [ABSTRACT FROM AUTHOR]

Hydrogen (H2) is a new type of renewable energy that can meet people's growing energy needs and is environmentally friendly. In order to improve the industrial application prospects and electrochemical performance of hydrogen evolution catalysts, extensive research on transition metal materials has been carried out. Among the many catalytic materials, cobalt is an element with potential for the hydrogen evolution reaction (HER) due to its abundant reserves, low cost, and small energy barrier for H adsorption. This review classifies the latest research on cobalt-based catalysts according to the types of compound, including cobalt-based sulfides, phosphides, carbides, borides, oxides, etc., and summarizes the latest research progress of cobalt-based compound catalysts in acidic and alkaline media. Strategies to tune the properties of cobalt-based compound catalysts for high catalytic activity for HER are focused on, including structural engineering, defect engineering, and doping, etc. The advantages and limitations of each modified approach are reviewed. Not only that, but also the catalytic activity and advantages of the catalyst are evaluated by using density functional theory (DFT) calculation-related descriptors, activity evaluation parameters, etc. Finally, limitations and challenges of cobalt-based materials for HER are presented, as well as prospects for future research. This paper aims to understand the chemical and physical factors that affect cobalt-based catalysts, and to find directions for future research on cobalt-based catalysts. [ABSTRACT FROM AUTHOR]

Investigation of catalytic hydrogenation of CO2 to CO via the reverse water-gas shift (RWGS) was undertaken using Ni/SiO2-based catalysts. Among the array of catalysts tested, the Ni/SiO2 catalyst derived from the reduction of silicalite-1-encapsulated, ligand-protected Ni2+ (Ni0.2@S-1-red) exhibited promising performance. This catalyst demonstrated a CO2 conversion rate approaching the equilibrium conversion of RWGS, a selectivity for CO exceeding 99%, and a high space time yield of CO (9.7 mol gNi -1 h-1). The outcomes observed can be attributed to several factors, such as the highly dispersed Ni0 and Niδ+ species, as well as the presence of bridging oxygen of the Ni-O-Si structure, on which CO2 can be adsorbed moderately. The moderately bonded CO2 on Ni0.2@S-1-red allows for the efficient desorption of its reduced intermediate, i.e. *CO, resulting in the generation of gaseous CO at a rapid rate, consequently preventing its deep hydrogenation to CH4. Complementary Density Functional Theory (DFT) calculations were performed and revealed that CO molecules have poor adsorption and higher adsorption energy on the Ni@S-1 surface compared to the S-1 surface. This supports the rapid desorption of *CO and the observed high selectivity of CO. Moreover, the structure-activity correlation analysis further supports the claim of Ni0.2@S-1-red as a promising RWGS catalyst. [ABSTRACT FROM AUTHOR]

Hydrodeoxygenation (HDO) is an indispensable approach to produce renewable biofuels and value-added chemicals using natural biomass and its derivatives. 2,5-Dimethylfuran (DMF) is considered to be a very promising liquid biofuel, and it can be fabricated by HDO of the biomass derivative 5-hydroxymethylfurfural (HMF). Herein, a highly efficient bifunctional catalyst, Co/HAP(Ce), was fabricated by anchoring highly dispersed Co on Ce-doped hydroxyapatite (HAP(Ce)). Co/HAP(Ce) displayed excellent HDO catalytic activity to convert HMF to DMF, and 99% HMF conversion and 96% DMF selectivity can be obtained under 150 °C, 2 MPa H2 conditions for 5 h. Density functional theory calculations revealed that H2 can be more easily activated by Co/HAP(Ce). Systematic studies confirmed that the high activity of Co/HAP(Ce) can be ascribed to the desired acid–alkali properties, highly dispersed cobalt species and strong metal–support interactions. This research provides a cost effective approach for designing efficient catalysts for HDO of biomass and its derivatives. [ABSTRACT FROM AUTHOR]

Developing highly efficient electrocatalysts is crucially significant for the application of advanced energy conversion. The Fe–N–C single-atom catalyst is promising for CO2 electroreduction reaction (CO2RR) but suffers from insufficient intrinsic activity and inferior conductivity, which could be addressed by redistributing the electron density via heteroatom doping. Herein, we synthesized S-doped Fe–N–C (Fe–SN–C) as an advanced electrocatalyst for CO2RR using a simple trapping–pyrolysis strategy. Density functional theory calculations and experimental results indicate that S doping increases the d-band electrons and conductivity of Fe–SN–C by electron donating, and thus boosts *CO desorption during the CO2RR process and suppresses the competing hydrogen evolution reaction. Consequently, Fe–SN–C exhibits the maximum CO faradaic efficiency of 93% at −0.5 V and the highest partial current density of 10.1 mA cm−2 at −0.8 V for 2e− CO2RR. This finding provides a feasible and controllable method to achieve advanced electrocatalysts for efficient energy conversion. [ABSTRACT FROM AUTHOR]

Electrocatalytic water splitting, which is driven by renewable energy input to produce oxygen, has been widely regarded as a promising strategy in the future energy portfolio. The two-dimensional structure based on CoOOH nanosheets is easy to handle in the preparation process, low in cost, and has a small overpotential during water decomposition. Therefore, CoOOH two-dimensional materials have been widely used as electrocatalysts for the oxygen evolution reaction (OER). In this paper, we summarize the application of two-dimensional CoOOH nanosheets in the field of oxygen production from electrocatalytic water splitting. First, the different preparation methods of two-dimensional CoOOH nanosheets are briefly introduced. The structure–activity relationship of the two-dimensional CoOOH catalyst was analyzed from different viewpoints, such as doping, defects, etc. Finally, different catalytic mechanisms of CoOOH-based catalysts are discussed, and studies at the density functional theory (DFT) level are also provided to support the above mechanisms. To improve the readability of this review, a concise overview at the end of each section is given to illustrate some of the characteristics and trends of the studies in the corresponding part. The opportunities and challenges of two-dimensional CoOOH as an electrocatalyst in the future are summarized in the Conclusion section. This work will provide new insights and perspectives to the readers to understand the role of CoOOH nanosheets in the OER process. [ABSTRACT FROM AUTHOR]

Direct synthesis of 2,1-benzisoxazole and its related N-heterocyclic compounds via a chemoselective reductive heterocyclization route, which involves hydrogenation and subsequent intramolecular cyclodehydration steps, is a viable and attractive approach. However, the efficient transformation of the feedstocks using hydrogen as a hydrogen source at ambient temperature and atmospheric hydrogen pressure remains a great challenge. Herein, we reported a MgO-incorporated porous carbon composite (MgO@C) stabilized subnanometric Pt cluster (Pt/MgO@C) catalyst prepared by annealing a Mg-containing metal–organic framework, Mg-MOF-74, followed by impregnation of a Pt precursor and further reduction treatment strategy. The as-prepared Pt/MgO@C with ultralow Pt loading (0.078 wt%) exhibited superior catalytic performance for synthesizing 2,1-benzisoxazole derivatives by the reductive heterocyclization methodology. Excellent catalytic activity (conversion ≥ 99%), high chemoselectivity (≥92%), good stability (8 cycles), and broad functional group tolerance (10 substrates) were achieved under very mild conditions (1 bar hydrogen pressure at 303 K) over the developed Pt/MgO@C. Control experiments indicated that a proper amount of basic sites, subnanometric Pt clusters, and a close contact between them synergistically contributed to the extraordinary performance of Pt/MgO@C. Density functional theory calculations showed that the high activity and chemoselectivity of Pt/MgO@C stemmed from the active interfacial sites of Pt/MgO@C simultaneously activating the H2 and substrate, where the formed stable hydroxyl groups contributed to the enhancement of activity. The combined experimental and theoretical approach identified the formation of the –NO and –NHOH groups during the hydrogenation process, and the former corresponds to the rate-determining step. [ABSTRACT FROM AUTHOR]

The oxidation of CO by N2O over M–porphyrin (M = Ti, Fe, Co, Ni, Cu, and Zn) catalysts has been investigated via density functional theory calculations. The whole reaction process is divided into two steps: the catalytic decomposition of N2O that breaks the N–O bond resulting in O–M active species, and the carbon atoms of the CO molecule reaction with O–M to form CO2. For the rate-controlled step of the reaction, the porphyrins of different metal centers appear in different positions. The barrier height of N2O decomposition on Ti–porphyrin is 3.8 kcal mol−1, and the barrier height of CO oxidation is 21.9 kcal mol−1. The rate-controlled step appears in the process of oxidation of CO. However, for Fe–porphyrin, the barrier height of N2O decomposition is 24.2 kcal mol−1, and the barrier height of CO oxidation is 11.4 kcal mol−1. The rate-controlled step appears in the process of N2O decomposition. For the catalytic decomposition of N2O, the Ti–porphyrin has a low activation energy barrier, which may be due to the smaller gap between the highest occupied molecular orbital (HOMO) of the metal porphyrin and the lowest unoccupied molecular orbital (LUMO) of N2O for Ti–porphyrin compared to Fe–porphyrin. [ABSTRACT FROM AUTHOR]

Dimethyldichlorosilane, which is the most important organic silicon monomer, can be prepared using a novel core–shell catalyst. However, the debate continues regarding its redistribution mechanism. In the current study, the redistribution mechanism catalyzed by the ZSM-5(5T)@MIL-53(Al) catalyst was theoretically studied via density functional theory on the level of M06-2X/def2-TZVP. Then, the catalytic performances of different active centers modified with AlCl3 were evaluated. The results showed that the active center of the former was Brønsted acid, while that of the latter modified by AlCl3 was Lewis acid. In addition, Lewis acid increased the catalytic activity in comparison with Brønsted acid. The calculations of activation energy, frequency vibrational analysis, bond order analysis, frontier molecular orbital theory, electronic localization function, and localized orbital locator analyses were in agreement with the said mechanism and results. [ABSTRACT FROM AUTHOR]

Ru(bda)(py)2 (bda = 2,2′-bipyridine-6,6′-dicarboxylate, py = pyridine) has been a significant milestone in the development of water oxidation catalysts. Inspired by Ru(bda)(py)2 and aiming to reduce the use of noble metals, iron (Fe) was introduced to replace the Ru catalytic center in Ru(bda)(py)2. In this study, density functional theory (DFT) calculations were performed on Fe- and Ru(bda)(py)2 catalysts, and a more stable 6-coordinate Fe(bda)(py)2 with one carboxylate group of bda disconnecting with Fe was found. For the first time, theoretical comparisons have been conducted on these three catalysts to compare their catalytic performances, such as reduction potentials and energy profiles of the radical coupling process. Explanations for the high potential of [FeIII(bda)(py)2–H2O]+ and reactivity of [FeV(bda)(py)2–O]+ have been provided. This study can provide insights on Fe(bda)(py)2 from a computational perspective if it is utilized as a water oxidation catalyst. [ABSTRACT FROM AUTHOR]

The effects of Zr single atom modification on the hydrogenation mechanism of CO2 to methanol on the Cu(111) surface were investigated by density functional theory (DFT). In the HCOO pathway, 11 elementary steps were involved, which were analyzed from the aspects of kinetics and thermodynamics of each elementary reaction. bi-HCOO*, HCOOH*, H2COO*, H2COOH*, H2CO* and H3CO* are the key intermediates that are most likely to be generated. The elementary reactions of H2COO*, H2CO* and H3CO* hydrogenation have relatively high activation barriers of about 1 eV, and they are the rate-limiting steps in this pathway. The desorption barriers of HCOOH* and H2CO* are much higher than the energy barriers required for continued hydrogenation; therefore, the formation of by-products is inhibited on the Zr1–Cu single atom catalyst surface. In the COOH pathway, the hydrogenation product trans-COOH* of CO2 can further hydrogenate to t,t-COHOH* through the formation of O-H bonds; then, it facilely dissociates into COH*, and COH* continues to hydrogenate into HCOH*, H2COH* and the final product of CH3OH. The last step is the rate-limiting step, with an activation energy of 1.48 eV. In the RWGS pathway, trans-COOH* transforms to cis-COOH*, and its continued hydrogenation is more favorable than dissociation in terms of kinetics and thermodynamics. The generated HCOOH is incorporated into the HCOO pathway. The results show that the HCOO pathway is more likely to occur and has higher selectivity on Zr-modified Cu-based catalysts. [ABSTRACT FROM AUTHOR]

The removal of sulfur in diesel fuel requires efficient hydrodesulfurization catalysts during the upgrading process. However, although the traditionally prepared CoMoS catalyst is effective for hydrodesulfurization, it often is associated with problems such as a poor activity and deactivation susceptibility at high temperatures. In this work, chemical exfoliation and hydrothermal methods were employed to prepare MoS2 for modification with isolated Co atoms. The results showed that the prepared catalyst had a higher catalytic activity and could be used at lower temperatures. Subsequently, periodic density functional theory (DFT) calculations were used to discuss the effect of isolated Co doping on the catalytic performances of single-layer MoS2. DFT calculations revealed that the electronic structure of the MoS2 basal surface was changed by Co atom doping, making the originally inert basal surface catalytically active. Based on the energetic analysis, the influence of isolated Co atom doping on the adsorption performance, hydrogenolysis activity, and hydrodesulfurization performance of the basal surface is discussed. This work paves a new path for improving HDS catalytic activity via synergistic structure and charge characteristics. [ABSTRACT FROM AUTHOR]

Generation of molecular hydrogen by electrochemical water splitting is a promising approach, and its efficiency strictly depends on the electrocatalyst used. Therefore, it is an ongoing challenge to design materials having improved the electrocatalytic behaviour towards hydrogen evolution reaction. Here, using Co-MOF [Co4(BTC)3(BIm)6] as starting precursor, graphitic carbon encapsulated CoSe2 nanorods have been prepared through a single step selenization method. The carbon network in the CoSe2/C hybrid nanostructure forms channels, facilitating the accessibility of the electrolyte ions and maximizing the utilization of catalytic active centers. This makes the hybrid to show higher electrochemical accessible surface area, lower charge transfer resistance, and improved catalytic durability towards the electrocatalytic hydrogen evolution reaction with respect to the non-noble metal (graphite rod) counter electrode. Specifically, it needs only 253 mV of overpotential to reach the benchmarked current density (10 mA cm−2) with a lower Tafel slope. Further, the experimental findings have been supported by the theoretical analysis of the structure and electronic properties of CoSe2 and CoSe2/C hybrid by density functional theory (DFT) simulations. The interaction between CoSe2 and C is due to charge transfer from Co 3d orbital and Se 4p orbital of CoSe2 to the 2p orbital of carbon. Also, populated electronic states near Fermi level for C doped CoSe2 may infer towards increased conductivity of the material. Computed overpotentials for HER activities show a qualitative order of CoSe2/C < CoSe2, matching nicely with the experimental data. The synergic effect of increased conductivity, improved surface area, and superior electrocatalytic activity due to C doping is responsible for the superior HER catalytic performance. [ABSTRACT FROM AUTHOR]

Excessive CO2 emission has caused severe greenhouse problems. CO2 reduction reaction (CO2RR) is considered to be a promising strategy to effectively reduce CO2 emission, which not only captures CO2 in large quantity, but also produces high value-added chemicals. Herein, CO2RR on the CuPc/graphene single-atomic catalyst has been studied via density functional theory (DFT) calculations. It shows that CO2 is inclined to convert to CH3OH, followed by HCOOH and CH4. The most favored pathway to produce CH3OH is *CO2 → *COOH → *CO → *CHO → *OCH2 → *OCH3 → *OHCH3, for which the potential-limiting step is *CO2 → *COOH (endothermic by 1.41 eV). Both density of states and differential charge further indicate the high reactivity of single atomic Cu, and uncover the effect of electrostatic interaction on the hydrogenation pathway. This study can provide an insight into the structure–reaction relationship for CO2RR on CuPc/graphene, and help guide the design of highly effective catalysts. [ABSTRACT FROM AUTHOR]

5-Hydroxymethylfurfural (HMF) is a versatile furanic compound used for producing various value-added chemicals, including 2,5-dihydromethylfuran (DHMF) and 2,5-dihydromethyltetrahydrofuran (DHMTHF), via selective hydrogenation of HMF. In order to reduce the cost of highly efficient noble metal catalysts, nickel (Ni) and copper (Cu) have been developed as cheaper catalysts for this reaction. These two catalysts show good efficiency but have different selectivity towards HMF hydrogenation products. This work applied plane-wave based density functional theory (DFT) to understand the different activity and selectivity of the Ni and Cu catalysts. The interaction of precursors/products on the Ni(111), Ni(100), Cu(111) and Cu(100) facets was investigated via the adsorption calculation in gas and aqueous phases. The temperature effect was also investigated. Our results revealed that not only the energetic properties but the structural and electronic charge properties are also important for describing the different catalytic behaviors in HMF hydrogenation. [ABSTRACT FROM AUTHOR]

To date, organoseleniums are pre-eminent for peroxide decomposition and radical quenching antioxidant activities. On the contrary, here, a series of Janus-faced aminophenolic diselenides have been prepared from substituted 2-iodoaniline and selenium powder using copper-catalyzed methodology. Subsequently, condensation with substituted salicylaldehyde afforded the Schiff base, which on reduction, yielded the desired substituted aminophenolic diselenides in 72%–88% yields. The generation of reactive oxygen species (ROS) from oxygen gas by the synthesized aminophenolic diselenides was studied by analyzing the oxidation of dichlorofluorescein diacetate (DCFDA) dye and para-nitro-thiophenol by fluorescence and UV-Visible spectroscopic methods. Furthermore, density functional theory calculations and crystal structure analysis revealed the role of functional amine and hydroxyl sites present in the Janus-faced organoselenium catalyst for the activation of molecular oxygen, where NH and phenolic groups bring the oxygen molecule close to the catalyst by N–H⋯O and O–H⋯O intermolecular interactions. Additionally, these functionalities stabilize the selenium-centered radical in the formed transition states. Antioxidant activities of the synthesized diselenides have been explored as the catalyst for the decomposition of hydrogen peroxide using benzenethiol sacrificial co-reductant by a well-established thiol assay. Radical quenching antioxidant activity was studied by the quenching of DPPH radicals at 516 nm by UV-Visible spectroscopy. The structure activity correlation suggests that the electron-rich phenol and electron-rich and sterically hindered selenium center enhance the oxidizing property of the aminophenolic diselenides. Janus-faced diselenides were also evaluated for their cytotoxic effect on HeLa cancer cells via MTT assay, which suggests that the compounds are effective at 15–18 μM concentration against cancer cells. Moreover, the combination with therapeutic anticancer drugs Erlotinib and Doxorubicin showed promising cytotoxicity at the nanomolar concentration (8–28 nM), which is sufficient to suppress the growth of the cancer cells. [ABSTRACT FROM AUTHOR]

The present report focuses on the solvent effect on furfural production from xylose in biphasic systems with methods including combined experiments, molecular dynamics (MD) simulations and density functional theory (DFT) calculations. Six most effective and commonly used biphasic solvents for furfural production were comparatively analyzed and discussed based on the kinetic study, partition coefficient, degradation behavior of furfural in organic solvents, distribution of solvent molecules around xylose/furfural molecules, hydrogen bonding, moving trajectories of xylose/furfural, and the solvation free energy. During the hydrothermal reaction of xylose to furfural in biphasic systems, it was found that the conversion efficiency of biphasic systems can be ordered as DCM/H2O > 2-MTHF/H2O > 2-butanol/H2O ≈ MIBK/H2O > CPME/H2O > toluene/H2O according to the xylose conversion and furfural yield, which are dominated by the solvation free energy (ΔGsol) of furfural in organic solvents, and also be affected by three other factors, namely, the maximum solubility of furfural in organic solvents, the ΔGsol value of organic solvents in water, and the side reaction of furfural in organic solvents. The degradation rate of furfural in 2-butanol was detected to be the fastest, and molecular dynamics simulation data showed that the hydrogen bonding between furfural and 2-butanol may accelerate the degradation of furfural. DCM has excellent extraction ability for furfural, and the maximum furfural yield in the DCM/H2O system (81.64%) is much higher than that in other systems during the hydrothermal reaction without additional catalysts. [ABSTRACT FROM AUTHOR]

The design and synthesis of hybrid core–shell catalysts is of great significance for obtaining an excellent performance of hydrogen evolution reaction (HER). However, it remains a challenge to explore the exact active sites and research the catalytic mechanism for HER. Here, a series of Ni3S2@MOOH/NF (M = Fe, Ni, Cu, Mn and Co) hybrid structures is firstly in-site grown on Ni foam by the typical hydrothermal and electrodeposition methods. The Ni3S2@NiOOH/NF catalyst with a core–shell structure exhibits a relatively low overpotential of 79 mV for HER at a current density of 10 mA cm−2, which is one of the best catalytic activities reported so far. Moreover, it also shows good stability in the long-term durability test. Various spectral analysis and density functional theory calculations demonstrate that NiOOH is favorable for the adsorption of water molecules, and the S atom at the interface between Ni3S2 and NiOOH is favorable for the adsorption of H intermediates, which strongly accelerates the HER process in alkaline solution. This work provides a general strategy for the synthesis of electrocatalytic materials, which can be used for efficient electrocatalytic water splitting reactions. [ABSTRACT FROM AUTHOR]

Density functional theory computations revealed a pivalic acid assisted C–H bond activation mechanism for rhodium catalyzed formation of α-branched amines with C–C and C–N bond couplings. The reaction energies of the [Cp*RhCl2]2 dimer and silver cations indicate that the Cp*RhCl+ cation is the active catalyst. The essential role of pivalic acid is a co-catalyst for the activation of the ortho-C(sp2)–H bond in phenyl(pyrrolidin-1-yl)methanone, while the reaction of NaHCO3 and HCl reduces the overall barrier of the catalytic cycle. In the presence of both pivalic acid and NaHCO3 in the reaction, the C(sp2)–H bond is activated through a concerted metallation deprotonation process, and the C–C bond coupling is the rate-determining step with a total free energy barrier of 23.9 kcal mol−1. Without pivalic acid and NaHCO3, the C(sp2)–H bond can only be activated through a σ-bond metathesis process and the free energy barrier increases to 32.2 kcal mol−1. We also investigated the mechanisms of a side reaction for β-branched amine formation and the reaction without styrene and found that their free energy barriers are 33.4 and 30.5 kcal mol−1, respectively. [ABSTRACT FROM AUTHOR]

Over the past century, the global concentration of environmental nitrate has increased significantly from human activity, which has resulted in the contamination of drinking water and aquatic hypoxia around the world, so the development of effective nitrate-reducing agents is urgent. This work compares three potential macrocycle-based nitrate reduction electrocatalysts: [Co(DIM)]3+, [Co(cyclam)]3+ and [Co(TIM)]3+. Although all three complexes have similar structures, only [Co(DIM)]3+ has been experimentally determined to be an active electrocatalyst for selective nitrate reduction to produce ammonia in water. While [Co(cyclam)]3+ can reduce aqueous nitrate to ammonia and hydroxylamine at heavy metal electrodes, [Co(TIM)]3+ is inactive for the reduction of nitrate. As an initial step to understanding what structural and electronic properties are important for efficient electrocatalysts for nitrate reduction, density functional theory (DFT) was employed to investigate the electronic structure of the three Co complexes, with the reduction potentials calibrated to experimental results. Moreover, DFT was employed to explore four different reaction mechanisms for the first steps of nitrate reduction. The calculated reaction barriers reveal how a combination of electron transfer in a redox non-innocent complex, substrate binding, and intramolecular hydrogen bonding dictates the activity of Co-based catalysts toward nitrate reduction. [ABSTRACT FROM AUTHOR]

Sustainable fuel production from CO2 through electrocatalytic reduction is promising but challenging due to high overpotential and poor product selectivity. Herein, we computed the reaction free energies of electrocatalytic reduction of CO2 to CO and HCOO- using the density functional theory method and screened transition metal(M)--cyclam(L) complexes as molecular catalysts for CO2 reduction. Our results showed that pKa of the proton adduct formed by the protonation of the reduced metal center can be used as a descriptor to select the operating pH of the solution to steer the reaction toward either the CO or hydride cycle. Among the complexes, [LNi]2+ and [LPd]2+ catalyze the reactions by following the CO cycle and are the CO selective catalysts in the pH ranges 1.81-7.31 and 6.10 and higher, respectively. Among the complexes that catalyze the reactions by following the hydride cycle, [LMo]2+ and [LW]3+ are HCOO- selective catalysts and have low limiting potentials of -1.33 V and -1.54 V, respectively. Other complexes, including [LRh]2+, [LIr]2+, [LW]2+, [LCo]2+, and [LTc]2+ catalyze the reactions resulting in either HCOO- from CO2 reduction or H2 from proton reduction; however, HCOO- formation is always thermo-dynamically more favorable. Notably, [LMo]2+, [LW]3+, [LW]2+ and [LCo]2+ have limiting potentials less negative than -1.6 V and are based on Earth-abundant elements, making them attractive for practical application. [ABSTRACT FROM AUTHOR]

To upgrade methane to more valuable products, the non-oxidative coupling of methane (NOCM) is a hopeful method. This work investigates the mechanism and evaluates the feasibility of silica-supported single-site niobium (Nb) catalysts for NOCM by density functional theory (DFT) calculations. Two catalyst candidates were studied, namely, the silica-supported Nb(III)–methyl catalyst (denoted as (≡SiO)2Nb–CH3) and the silica-supported Nb(III)–hydride catalyst (denoted as (≡SiO)2Nb–H). The catalytic cycle working with (≡SiO)2Nb–CH3 contains 5 elementary steps, and the one working with (≡SiO)2Nb–H contains 6 elementary steps. (≡SiO)2Nb–CH3 is much more effective in catalyzing NOCM than (≡SiO)2Nb–H on the basis of the energetic span value. Interestingly, the silica-supported Nb(III)–CH3 catalyst can have an increase of 2 orders of magnitude in the turnover frequency (TOF) for NOCM compared to the silica-supported Ta(III)–CH3 catalyst, the latter having been experimentally used for NOCM catalysis. This work provides further insights into the mechanism of single-site metal catalysts for NOCM, and provides a direct guide for catalyst design for NOCM as well. [ABSTRACT FROM AUTHOR]

Umbrella-sampling density functional theory molecular dynamics (DFT-MD) has been employed to study the full catalytic cycle of the allylic oxidation of cyclohexene using a Cu(II) 7-amino-6-((2-hydroxybenzylidene)amino)quinoxalin-2-ol complex in acetonitrile to create cyclohexenone and H2O as products. After the initial H-atom abstraction step, two different reaction pathways have been identified that are distinguished by the participation of alkyl hydroperoxide (referred to as the "open" cycle) versus the methanol side-product (referred to as the "closed" cycle) within the catalyst recovery process. Importantly, both pathways involve dehydrogenation and re-hydrogenation of the –NH2 group bound to the Cu-site – a feature that is revealed from the ensemble sampling of configurations of the reactive species that are stabilized within the explicit solvent environment of the simulation. Estimation of the energy span from the experimental turnover frequency yields an approximate value of 22.7 kcal mol−1 at 350 K. Whereas the closed cycle value is predicted to be 26.2 kcal mol−1, the open cycle value at 16.5 kcal mol−1. Both pathways are further consistent with the equilibrium between Cu(II) and Cu(III) that has previously been observed. In comparison to prior static DFT calculations, the ensemble of both solute and solvent configurations has helped to reveal a breadth of processes that underpin the full catalytic cycle yielding a more comprehensive understanding of the importance of radical reactions and catalysis recovery. [ABSTRACT FROM AUTHOR]

It has been reported that either the boryl formate (HCOOBR2), bis(boryl)acetal (R2BOCH2OBR2), or methoxy borane (R2BOCH3) product of CO2 reduction is selectively afforded adopting the nickel (Ni) pincer catalyst by changing the properties of borane reductants. To obtain an insight into the influence of borane reductants on the selectivity of hydroboration of CO2 catalyzed by (tBuPCP)NiH , a density functional theory (DFT) computational study is performed with three different boranes (HBcat (catecholborane), 9-BBN (9-borabicyclo [3.3.1] nonane), and HBpin (pinacolborane)). The detailed formation and conversion of four-electron product R2BOCH2OBR2 were considered for the first time, combining with the three sequential catalytic cycle mechanism, and the calculated results demonstrate that the distinctions of the electronic process in some key intermediates and transition states lead to the selectivity on products for different borane reductants. [ABSTRACT FROM AUTHOR]

Herein, we report the first-ever neutral noble-metal free metal oxide cluster catalysts for multiple CO oxidation reactions. The electronic structure and catalytic activity of neutral transition metal-doped cobalt oxide (TMCoO2, TM = Sc–Zn) clusters have been investigated using density functional theory. Among the studied clusters, VCoO2–4 and CrCoO2–4 clusters can oxidize two CO molecules consecutively in the CO oxidation reaction. The V (in VCoO2–4) and Cr (in CrCoO2–4) atoms behave like noble-metal atoms to store and release electrons during the oxidation reaction process. Since neutral metal oxide clusters are challenging for experimental studies, our study will be helpful to understand the catalytic activities of neutral metal oxide clusters. [ABSTRACT FROM AUTHOR]

In this study, a series of high-activity imidazole-based dicationic ionic liquids (DILs) were designed and prepared as efficient catalysts for balancing the reactivity between the endo-hydroxyl group (endo-OH) and the exo-hydroxyl group (exo-OH) of isosorbide (ISO) to synthesize high molecular weight poly(isosorbide carbonate) (PIC). Meanwhile, the thermal performance of PIC was precisely optimized by regulating the chain configuration. The results showed that when the trace amounts (4.5 × 10−5 based on the ISO molar amount) of bis-(3-methyl-1-imidazole)-ethylene dibromide ([C2(Min)2][Br]2) were used, the weight average molecular weight (Mw) of PIC reached 98 700 g mol−1. It could be concluded from the results of the experiment and the stimulation that the high catalytic activity of DILs was attributed to the strong electrostatic interaction between the cation and the substrate and the effective balance of the reactivity of the endo-OH and the exo-OH. Furthermore, we found that the reduction of hydroxyl groups in the terminal groups and the increase of endo–endo (a1) structure in the repeating unit improved the thermal properties of PIC. Finally, 1H NMR, Fourier infrared spectroscopy, and density functional theory (DFT) calculations were used to verify the reaction process through anion and cation multi-site synergistic effect and a possible electrophilic–nucleophilic reaction mechanism was successfully obtained. [ABSTRACT FROM AUTHOR]

In this work, we report the syntheses and physicochemical characterization of new chloro and aqua complexes of Ru(II) with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) and 2,2′-bipyridines substituted with donor and acceptor groups in the 4,4′-positions. The aqua complexes behave as precursors for water oxidation catalysts at pH = 1 using Ce(IV) as a sacrificial oxidant. Besides, the oxidized forms Ru(IV) and Ru(V) have been characterized at different pH values by electrochemistry, UV-Visible spectroscopy and spectroelectrochemistry. The reaction mechanisms were studied by combining mixing and stopped-flow experiments with spectrophotometric monitoring in the UV-visible region and all the rate constants were determined together with the corresponding TON and TOF values at pH = 1. Calculations based on Density Functional Theory (DFT and TD-DFT) were performed to support the experimental data. [ABSTRACT FROM AUTHOR]

Based on density functional theory (DFT) calculations, the adsorption geometries, stability and catalytic properties of single-atom Ru and Mo anchored on graphenylene sheets (gra-Ru and gra-Mo) are comparatively investigated. Compared with isolated gas molecules, different kinds of coadsorbed gas reactants (2NO, 2CO, CO–O2 and NO–O2) exhibit high stability on gra-Ru and gra-Mo sheets, and the coadsorbed configurations of gas reactants are considered as initial states for the NO and CO oxidation reactions. According to the calculated energy barriers, NO oxidation reactions on the gra-Ru sheet through the Langmuir–Hinshelwood (LH) mechanism have relatively large energy barriers than CO oxidation reactions. In addition, the preadsorbed 2NO reacting with 2CO (2NO + 2CO → 2CO2 + N2) on gra-Ru and gra-Mo sheets through the Eley–Rideal (ER) mechanism (<0.5 eV) are energetically more favorable reactions. Therefore, different kinds and adsorption geometries of gas reactants have a close relationship with the reaction mechanism and energy barriers for the NO and CO oxidation, which provide an important reference for designing novel graphenylene-based catalysts for the removal of toxic gases. [ABSTRACT FROM AUTHOR]

A Co(II) complex with a stable structure was designed and synthesized with quinalic acid and Co (OAc)2·4H2O. The single crystal structure of the complex was characterized by X-ray diffraction. A dehydrogenative coupling of aromatic diamines and primary alcohols was developed by using the Co(II) complex as the catalyst to synthesize 2-substituted benzimidazole. A series of 2-substituted benzimidazoles were obtained with good to excellent yields under mild reaction conditions. In addition, a compound with inhibitory Parkinson's activity was synthesized on a gram-scale by using this method. Finally, the reaction mechanism was proposed and the energy changes in the reaction process were simulated by density functional theory (DFT). [ABSTRACT FROM AUTHOR]

Oxygen atom transfer (OAT) reactions employing transition metal–oxo species have tremendous significance in homogeneous catalysis for industrial use. Understanding the structural and mechanistic aspects of OAT reactions using high-valent metal–oxo species is of great importance to fine-tune their reactivity. Herein we examine the reactivity of a non-heme high-valent oxo-manganese(IV) complex, [MnIVH3buea(O)]− towards a variety of substrates such as PPh2Me, PPhMe2, PCy3, PPh3, and PMe3 using density functional theory as well as ab initio CASSCF/NEVPT2 methods. We have initially explored the structure and bonding of [MnIVH3buea(O)]− and its congener [MnIVH3buea(S)]−. Our calculations affirm an S = 3/2 ground state of the catalyst with the S = 5/2 and S = 1/2 excited states predicted to be too high lying in energy to participate in the reaction mechanism. Our ab initio CASSCF/NEVPT2 calculations, however, reveal a strong multi-reference character for the ground S = 3/2 state with many low-lying quartets mixing significantly with the ground state. This opens up various reaction channels, and the admixed wave-function evolves during the reaction with the excited triplet dominating the ground state wave-function at the reactant complex. Our calculations predict the following pattern of reactivity, PCy3 < PMe3 < PPh3 < PPhMe2 < PPh2Me for the OAT reaction with the MnIV＝O species which correlates well with the experimental observations. Detailed electronic structure analysis of the transitions states reveal that these substrates react via an unusual low-energy δ-type pathway where a spin-up electron from the substrate is transferred to the δ*x2−y2 orbital of the MnIV＝O facilitated by its multi-reference character. The unusual reactivity observed here has implications in understanding the reactivity of [Mn4Ca] species in photosystem II. [ABSTRACT FROM AUTHOR]

Taking into account that the transformation of biomass-derived 2,5-dimethylfuran (DMF) to p-xylene involves Diels–Alder (DA) cycloaddition as the limiting step, the use of an ITQ-2 zeolite obtained by direct synthesis (DS-ITQ-2) as a catalyst for this reaction is proposed based on the fact that the organic molecule employed for its synthesis mimics the size and shape of the DA oxanorbornene cycloadduct intermediate. Periodic Density Functional Theory (DFT) calculations reveal a better stabilization of the oxanorbornene intermediate within the external hemicavities or "cups" of the DS-ITQ-2 zeolite (MWW-framework) than in other zeolites employed for this reaction, such as FAU and Beta. Interestingly, experimental results also show improved catalytic conversion values for the DS-ITQ-2 zeolite compared to FAU and Beta, in good agreement with the stabilization energies calculated by DFT. The "ab initio" catalyst design presented here to enhance the catalytic performance for the transformation of biomass-derived products is a valuable example that could be employed for the rationalization of other chemical processes catalyzed by zeolites. [ABSTRACT FROM AUTHOR]

The conversion of alkynyl epoxides to furans is an unusual tandem catalytic process in which two different oxidation states of palladium are employed. In this study, we used density functional theory calculations to establish the mechanistic details of the catalytic cycles for all the individual processes in this conversion. The results showed that the use of Pd(0) or Pd(II) alone as the catalyst leads to high reaction barriers. This finding is consistent with experimental observations of low furan yields and the need for high temperatures in the presence of either catalyst alone. However, a combination of Pd(0) and Pd(II) lowers the reaction barriers considerably. Our key finding is that the reaction pathway involves epoxide ring opening catalyzed by Pd(0), followed by tautomerization of an enol to generate an allenyl ketone in conjunction with Pd(0), with a subsequent Pd(II)-catalyzed cyclization to yield the furan. [ABSTRACT FROM AUTHOR]

The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) using the η4-(2,3,4,5-tetraphenylcyclopentadienone) ruthenium tricarbonyl precursor of the well-known Shvo catalyst and H2 pressure was established under solvent-free conditions to achieve 100% conversion and 100% selectivity within 5 hours. Kinetic reaction curves were measured in order to deduce the optimal reaction conditions, which were further evaluated by means of density functional theory (DFT) calculations, and compared with catalytic concepts that consume formic acid or isopropyl alcohol as hydrogen donor. Ultimately, this alternative reaction procedure was subjected to a life cycle assessment (LCA) in comparison with the transfer hydrogenation methodologies, in order to verify its contribution towards a practice of environmentally benign chemistry. [ABSTRACT FROM AUTHOR]

Cu can prevent carbon deposition on a surface due to weak adsorption, but it exhibits a high energy barrier to C–H bond activation, which means that it is not practical. Here, inspired by the catalytic properties of Pt and the strategy of single-atom alloys, a Pt1Cu single-atom alloy (SAA) catalyst is built and studied. The primary goal is to understand the alloy's catalytic activity and coke-resistant properties during the partial oxidation of methane (POM) using density functional theory (DFT). Based on the wide application of Ni-based catalysts in POM, a parallel sample using a Pt1Ni SAA catalyst is also studied. C–H bond activation and coke resistance are quantified by the activation energy barrier of CH4 dissociation and the energy barrier of C2 formation, respectively. It is shown that the Pt1Cu SAA catalyst can promote activation of the C–H bond of CH4, without affecting the excellent coke resistance. The first C–H cleavage is promoted by the introduction of a Pt single atom, and the activation energy barrier is 1.73 eV on the Cu(111) surface, while it is 1.16 eV on the Pt1Cu(111) surface. The activation energy barrier of C2 formation is 2.08 eV on the Cu(111) surface and 1.89 eV on the Pt1Cu(111) surface. The properties of the Pt single-alloy Cu catalyst are obviously enhanced compared with reactions on commercial Ni-based catalysts. The activation energy barrier is 1.10 eV for CH4 dissociation and 1.35 eV for C2 formation with the Pt1Ni SAA catalyst. Coke resistance is further elucidated by the method of changes of partial density of states (PDOS) and Mulliken charges in this work. The results on the electronic properties are consistent with the thermodynamic results. A reference strategy is provided in this work to promote the activation of the C–H bond and the coke-resistant performance during POM. [ABSTRACT FROM AUTHOR]

The discrete anionic structure of polyoxometalates (POMs) at the interface is more like a separate small “island”, which effectively prevents the diffusion of single atoms and prohibits the agglomeration and generation of metal particles; thus, POMs can enhance the sintering-resistant behavior and increase metal loading on the surface of single-atom catalysts (SACs). To explore the catalytic performance of POM-supported SACs for CO oxidation, we employed density functional theory (DFT) calculations to gain an understanding of some important aspects, including the CO adsorption, the formation of oxygen vacancies, and the activity of the surface oxygen species, of the catalytic system. Compared to previous theoretical studies, in which the catalytic behavior of POMs has been investigated based on the anionic unit with the highest negative charge, herein, we have constructed a model of the POM-supported SACs, which are neutral species. Our DFT calculations indicated that in the series of the SACs studied herein, (1) upon anchoring of a single metal atom on the POM surface, four key surface oxygen atoms were lifted from the POM surface to form a new interface, and thus, the surface oxygen species were activated; (2) CO adsorbed more strongly on the Ir, Os, Rh, Pt, and Ru sites than on the Fe, Mn, and Co sites; (3) it was easy to form an oxygen vacancy on the POM surface in the case of the Pt system when compared with the other systems; (4) the difference in the surface oxygen species for CO oxidation was remarkable, and the Oc atom at the catalyst interface had higher reactivity for CO oxidation as compared to the Ob atom in the Pt system studied herein; and (5) the single Pt atom served as an electron reservoir in the CO oxidation along the reaction pathway. [ABSTRACT FROM AUTHOR]

The mechanism of the ruthenium carboxylate-catalyzed hydrogenation of carboxylic acids was investigated by using density functional theory (DFT) calculations. The novel mechanism including two hydrogenation cycles was proposed for this reaction. The first cycle is the hydrogenation of the carboxylic acid to an aldehyde, while the second cycle is the hydrogenation of the aldehyde to an alcohol. These two catalytic cycles share similar elementary steps, including H2 heterolysis, hydride migration of the carboxylic acid or aldehyde, and catalyst regeneration. In this hydrogenation mechanism, the carboxylic acid is not only a reactant, but also an important proton source. Furthermore, the noncovalent interaction (e.g. hydrogen bonding interaction) between the ligand and carboxylic acid substrate could promote the hydrogenation of the carboxylic acid through stabilizing the transition state of the most energy-demanding step (i.e., hydride migration in the first catalytic cycle). Besides, the strong electron-donating ability of the dppb ligand could also facilitate the hydride migration. [ABSTRACT FROM AUTHOR]

Quenched-flow data for propene polymerization with rac-Me2Si(2-Me-4-Ph-1-indenyl)2ZrCl2/MAO support a picture where removal of MAO qualitatively changes the kinetic profile from a mainly enthalpic to a mainly entropic barrier. DFT studies suggest that a not previously recognized singly-bridged end-on coordination mode of Me6Al2 to catalytically active centers may be kinetically relevant as a resting state. In contrast, the more traditional doubly-bridged complex of Me3Al is proposed to be more relevant to chain transfer to cocatalyst. [ABSTRACT FROM AUTHOR]

The protolytic cleavage of the O–H bond in water and alcohols is a very important reaction, and an important method for producing dihydrogen. Full quantum chemical studies with density functional theory (DFT) reveal that germanium based complexes, such as HC{CMeArB}2GeH (Ar = 2,6-iPr2C6H3), with the assistance of silicon based compounds such as SiF3H, can perform significantly better than the existing state-of-the-art post-transition metal based systems for catalyzing dihydrogen generation from water and alcohols through the protolysis reaction. [ABSTRACT FROM AUTHOR]

A recent DFT study of the ruthenium pincer benzoate complex [Ru(PNP)(PhCOO)2] I (PNP = 2,6-bis- (diphenylphosphanyl)lutidine) in its meridional form has revealed mer-I to be a promising catalyst lead structure for the direct insertion of CO2 into the C-H bonds of arenes, such as benzene. After the successful synthesis of I, its solid state structure interestingly and unexpectedly showed the pincer ligand to adopt the facial rather than the meridional coordination mode. Recalculation of the catalytic cycle with fac-I including all relevant local minima and transition states revealed (a) fac-I to be significantly more stable (6.1 kcal mol-1) than mer-I, (b) that the energetic span (ES; i.e. the effective activation barrier) for the cycle with fac-I amounts to 38.8 kcal mol-1, while the cycle with mer-I has an ES of 25.5 kcal mol-1 only. These results are a hint that fac-I is catalytically inactive. Experimental testing of fac-I showed indeed no product formation, which is in full accordance with the computations. To reduce the spatial flexibility of the pincer ligand, its CH2 groups were replaced by O atoms. The resulting complex [Ru(PONOP)(PhCOO)2] II (PONOP = 2,6-bis(diphenylphosphinito)pyridine) was used for the calculation of the catalytic cycle in benzene as the solvent. Gratifyingly, the starting complex mer-II is more stable than fac-II by 1.9 kcal mol-1 in benzene as the solvent. Consequently, mer-II should be available experimentally. As with fac-I, also fac-II generates a catalytic cycle with a high ES (37.1 kcal mol-1), while mer-II generates a cycle with a significantly lower ES (27.2 kcal mol-1) indicating mer-II to be a potentially active catalyst. A possible explanation of the much lower ES in the case of the meridionally coordinated species is found in the stronger interaction of the substrate with the metal center in the arene-s-bond complex. As a result the issue that is created by the mer/fac isomerism can be resolved by creating spatially less flexible structures. [ABSTRACT FROM AUTHOR]

In this study, a density functional theory (DFT) method was utilised to predict the reaction mechanism of N-heterocyclic carbene (NHC)-catalysed remote N–H activation in indole aldehydes for the synthesis of enantiomerically enriched oxazinoindole derivatives. Simulation results indicate that the mechanism involves six energetically feasible stages: (a) chemo-selective nucleophilic addition of NHC to indole aldehydes, (b) N,N-diisopropylethylamine (DIEA) and protonated DIEA-assisted simultaneous proton shifts for the generation of Breslow intermediates, (c) oxidation of Breslow intermediates, (d) another DIEA-assisted intermolecular proton shift for the formation of reactive aza-o-quinone methide (aza-o-QM) analogues, (e) stereo-selective [4+2]-cycloaddition of aza-o-QM to a ketonic moiety, and (f) regeneration of NHC with simultaneous formation of the desired product. Chemo- and stereo-selectivity of the titled reaction was analysed by adopting several well-known DFT tools. Conceptual DFT-derived reactivity indices and the frontier molecular orbitals (FMOs) were analysed comprehensively to unravel the real role of NHC in this proposed catalytic cycle. Besides NHC, DIEA and DIEA–H+ were found to play crucial roles in lowering the activation energy barrier of different proton transfer stages. This investigation may help in the rational designing of other NHC-catalysed novel organic transformations. [ABSTRACT FROM AUTHOR]

Electrochemical nitrogen reduction reactions (NRR) under ambient conditions are a promising and attractive way to ammonia (NH3) synthesis. It is significant to develop efficient and low-cost electrocatalysts for nitrogen reduction. Herein, an investigation of single B atom doped C5N2 as a metal-free electrocatalyst for NRR was carried out using density functional theory (DFT) calculations. The results show that the boron atom is preferentially doped into the interstitial site of C5N2. The formed B-interstitial (Bint)-doped C5N2 sufficiently activates the nitrogen (N2) molecule through the "acceptance–donation" process. In particular, N2 can be effectively reduced via an alternating mechanism with a low overpotential (0.38 V). Thus, by carefully controlling the doping sites, the B-doped C5N2 can be an ideal candidate for an efficient NRR, which may provide a new idea in the design of NH3 synthesis catalysts. [ABSTRACT FROM AUTHOR]

The homopolymerization of ethene (ET), propene (PP), 1-butene (BT), 1-hexene (HX), and styrene (ST) by the rac-[Zr{1-Me2Si(3-Pr-(η5-C9H5))(3-H-(η5-C9H5))Cl2}] ansa-zirconocene catalyst was investigated using Density Functional Theory (DFT) calculations. This study unveiled the following: (i) ansa-zirconocene is a regio- and stereoselective catalyst for PP, BT, HX, ST polymerization; (ii) the regio- and stereoselectivities depend on the orientation of the growing chain and the incoming olefin monomers; (iii) primary (1,2)-insertion is preferred over secondary (2,1)-insertion for linear olefins (PP, BT, and HX) while it is the opposite for ST; (iv) the activity of olefin polymerization by ansa-zirconocene is controlled by the thermodynamics of π-complex formation and the kinetics of insertion. Our results revealed that the regio- and stereoselectivity of the catalyst can be described by the steric interaction between the incoming monomer and the isobutyl group of the growing chain. For ET polymerization, the effect of the catalyst structure on the productivity of the process was examined and QSPR models were constructed based on experimental activities and theoretical calculations. The model suggests that potent ansa-zirconocene catalysts should have a lower dipole moment and a more positive charge on the Zr metal atom. This information will provide clues for the design of more potent ansa-zirconocene catalysts for ethylene polymerization. [ABSTRACT FROM AUTHOR]

Recent years have witnessed an upsurge in the development of non-precious catalysts (NPCs) for alkaline water electrolysis (AWE), especially with the strides made in experimental and computational techniques. In this contribution, the most recent advances in NPCs for AWE were systematically reviewed, emphasizing the application of in situ/operando experimental methods and density functional theory (DFT) calculations in their understanding and development. First, we briefly introduced the fundamentals of the anode and cathode reaction for AWE, i.e., the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), respectively. Next, the most popular in situ/operando approaches for characterizing AWE catalysts, including hard and soft XAS, ambient-pressure XPS, liquid and identical location TEM, electrochemical mass spectrometry, and Raman spectroscopy were thoroughly summarized. Subsequently, we carefully discussed the principles, computational methods, applications, and combinations of DFT with machine learning for modeling NPCs and predicting the alkaline OER and HER. With the improved understanding of the structure–property–performance relationship of NPCs for AWE, we proceeded to overview their current development, summarising state-of-the-art design strategies to boost their activity. In addition, advances in various extensively investigated NPCs for AWE were evaluated. By conveying these methods, progress, insights, and perspectives, this review will contribute to a better understanding and rational development of non-precious AWE electrocatalysts for hydrogen production. [ABSTRACT FROM AUTHOR]

Converting CO2 into useful fuels and chemicals offers a promising strategy for mitigating the issues of energy crisis and global warming. However, it is still a fundamental challenge to find highly efficient catalysts for the CO2 electrochemical reduction (CO2ER) reaction. In this work, the catalytic performance of heteroatom (B, P, Si, and S)-doped C3N materials as metal-free CO2ER electrocatalysts was investigated by means of density functional theory (DFT) calculations. The results reveal that these heteroatom-doped C3N materials exhibit high stability. On the basis of the calculated Gibbs free energies, BN-doped C3N exhibits superior CO2ER catalytic activity for CO2 reduction to HCOOH with a low overpotential of 0.14 V vs. RHE. The present work demonstrates the promising potential of BN-doped C3N as an active and selective CO2ER catalyst, and provides an effective strategy for electrochemical applications. [ABSTRACT FROM AUTHOR]