Formation Of Active Species Research Articles

Constructing efficient Ti4O7/PbO2 heterostructured photoelectrode for water remediation

Photoelectrocatalytic oxidation (PEC) technology is considered to be an efficient process for the treatment of organic wastewater, and its performance depends on the characteristics of the PEC photoanodes. Therefore, the construction of heterogeneous nanostructured photoelectrodes based on suitable semiconductor materials for fast induced carrier transfer efficiency is essential for a high-performance PEC technique. Herein, titanium suboxide/lead (IV) oxide (Ti4O7/PbO2) ceramic photoelectrode with efficient PEC performance was synthesized by coupling PbO2 nanospheres with Ti4O7 through a hydrothermal method. To maximize the PEC performance of the ceramic electrodes, the Ti4O7/PbO2 nano-heterostructures were optimized by modulating the hydrothermal temperature. The optimized ceramic electrodes possessed a low Tafel slope, a low charge-transfer resistance and a good photocurrent response. Ti4O7/PbO2-110 exhibited an efficient PEC activity (approximately 92.21%) for the degradation of reactive brilliant blue KN-R. The efficient PEC performance of Ti4O7/PbO2-110 arose from the formation of a type II heterojunction between Ti4O7 and PbO2, which achieved efficient photogenerated carrier separation and facilitated the formation of intermediate active species. This work not only validates the efficient performance of Ti4O7/PbO2-110 for PEC water purification but also provides a reference strategy for the preparation of heterostructured ceramic photoelectrodes with a high PEC efficiency.

Boosting Electrocatalytic Ethylene Epoxidation by Single Atom Modulation.

The electrochemical synthesis of ethylene oxide (EO) using ethylene and water under ambient conditions presents a low-carbon alternative to existing industrial production process. Yet, the electrocatalytic ethylene epoxidation route is currently hindered by largely insufficient activity, EO selectivity, and long-term stability. Here we report a single atom Ru-doped hollandite structure KIr4O8 (KIrRuO) nanowire catalyst for efficient EO production via a chloride-mediated ethylene epoxidation process. The KIrRuO catalyst exhibits an EO partial current density up to 0.7 A cm-2 and an EO yield as high as 92.0 %. The impressive electrocatalytic performance towards ethylene epoxidation is ascribed to the modulation of electronic structures of adjacent Ir sites by single Ru atoms, which stabilizes the *CH2CH2OH intermediate and facilitates the formation of active Cl2 species during the generation of 2-chloroethanol, the precursor of EO. This work provides a single atom modulation strategy for improving the reactivity of adjacent metal sites in heterogeneous electrocatalysts.

Boosting Electrocatalytic Ethylene Epoxidation by Single Atom Modulation

AbstractThe electrochemical synthesis of ethylene oxide (EO) using ethylene and water under ambient conditions presents a low‐carbon alternative to existing industrial production process. Yet, the electrocatalytic ethylene epoxidation route is currently hindered by largely insufficient activity, EO selectivity, and long‐term stability. Here we report a single atom Ru‐doped hollandite structure KIr4O8 (KIrRuO) nanowire catalyst for efficient EO production via a chloride‐mediated ethylene epoxidation process. The KIrRuO catalyst exhibits an EO partial current density up to 0.7 A cm−2 and an EO yield as high as 92.0 %. The impressive electrocatalytic performance towards ethylene epoxidation is ascribed to the modulation of electronic structures of adjacent Ir sites by single Ru atoms, which stabilizes the *CH2CH2OH intermediate and facilitates the formation of active Cl2 species during the generation of 2‐chloroethanol, the precursor of EO. This work provides a single atom modulation strategy for improving the reactivity of adjacent metal sites in heterogeneous electrocatalysts.

Optimizing Low-Temperature CO2 methanation with Aluminum-Doped Ni/CeO2 Catalysts: Insights into reaction pathway adjustments and strong Metal-Support interactions

Revealing the logical relationship between the structure, reaction mechanism and performance of the catalyst is a key step in the design of low-temperature CO2 methanation catalyst. The elemental Al was introduced into Ni/CeO2 using a co-precipitation method to form a composite support CeO2-Al2O3 loaded nickel-based catalyst. It was found that the incorporation of Al significantly improved the catalytic performance of low-temperature CO2 methanation. Notably, at a molar ratio of Al/Ce equal to 0.1, the catalyst exhibited optimal CO2 conversion of 88.83% and CH4 selectivity of 99.96% at 240 ℃. The addition of appropriate amounts of Al not only increases the specific surface area of the catalyst but also maintains a moderate strong interaction between metal Ni-support, thereby promoting the formation of active metal Ni species. Furthermore, the presence of Al leads to an increase in oxygen vacancy concentration, which facilitates the generation of numerous hydroxyl groups. Consequently, this alters the distribution of basic sites on the catalyst surface, resulting in a shift from the CO* pathway to a dual pathway involving both CO* and formate pathways. Remarkably, these divergent reaction pathways correspond to distinct active sites, thereby maximizing the utilization of each region within the catalyst. The diversity of reaction pathways and active sites represents pivotal factors for enhancing the catalytic performance of low-temperature CO2 methanation catalysts.

Fine-Tune the Electronic Structure of Copper Nanowire Networks by Heteroatom Doping Toward Enhanced Fenton-like Reaction

To fine-tune the configuration of electrons around metal centers is critical to enhancing the activation of peroxymonosulfate (PMS) for organic decontamination in a manner similar to the Fenton-like reaction. Herein, we systematically explored the inclusion of different heteroatoms to manipulate the electronic configuration of copper nanowire (CuNW) networks toward PMS activation. Both experimental results and theoretical simulations unveiled that doping the CuNW with boron (B) to generate CuNW-B adjusted the d orbital of CuNW, optimized the electronic density of Cu active sites and endowed a proper adsorption energy of PMS, which provided the most active oxidation capacity of the materials studied. Conversely, doping with phosphorus (P) to generate CuNW-P caused evident performance decay in terms of the activation of PMS, as strong adsorption energy hindered the effective desorption of key intermediates. Accordingly, the CuNW-B boosts the Fenton-like reaction and is nearly triple and twice as effectively at degrading bisphenol A (92.5%) as CuNW-P (36.0%) and CuNW (50.5%). Thus, it was reasonably hypothesized that electronic reconstruction played an important role in improving the Fenton-like reaction. During this process, an applied potential (AP) facilitated the catalytic process by reducing Cu2+ to Cu+, which was followed by the formation of primary active species (Cu3+). Additionally, the use of a recirculating fluid flow in the reactor provided convective mass transfer, which led to more charge transfer to the structure of electrode relative to a conventional diffusion-limited batch reactor. Moreover, tests in a variety of challenging conditions demonstrated the robustness and stability of the combined CuNW-B/PMS/AP approach. This study provides an approach to finely control the electronic structure of Cu sites and is expected to guide the design of advanced Fenton-like catalysts, which could further provide a promising technology for the treatment of actual organic wastewater in a sustainable manner.

Kinetic Insights into Boron-Based Materials Catalyzed Oxidative Dehydrogenation of Light Alkanes.

High selectivity toward alkenes in oxidative dehydrogenation (ODH) of light alkanes makes boron-based materials promising catalysts. However, many key mechanistic aspects are still debated due to the challenge of capturing fleeting reaction intermediates. Kinetic analysis, including determining reaction orders and activation energy, could be informative for reactions involving radical intermediates but has not been extensively exploited. This Review summarizes the current understanding of the apparent alkane reaction order and the apparent activation energy in the boron-catalyzed ODH. Despite varying compositions and structures, a majority of boron-based catalysts share many common features, including alkene selectivity, the evolution and the formation of active site, and the apparent kinetic properties. These common trends could be attributed to the shared gas-phase radical-mediated reaction pathways and the formation of active hydroxylated boron oxide species on boron-containing materials under ODH conditions. Values of apparent alkane reaction orders and apparent activation energies are sensitive and reliable experimental measures of the contributions of the gas-phase radical-mediated and surface-mediated pathways, suggesting the outline of a general mechanistic framework of the boron-catalyzed ODH.

Constructing Cu+ and Lewis acid sites enabling the generation of highly reactive N‑oxyl radical for the efficient aerobic oxidation of alkylarenes

Developing heterogeneous catalytic systems with high performance for the oxygenation of C(sp3)–H bonds to carbonyls using molecular oxygen as the oxidant is highly desirable. In the present research, active Cu+ sites have been efficiently constructed based on layered double hydroxides (LDHs) through in-situ reduction during the coprecipitation. Simultaneously, the formed CuZn(Mg)Al-LDH(R) catalysts demonstrated the characters of increased amount of oxygen vacancy and surface Lewis acid site. The newly synthesized catalysts exhibited higher catalytic performance than the samples prepared via conventional method, and up to 49.4% improvement in specific activity was observed in the aerobic oxidation of ethylbenzene. The mechanism study including a series of control experiments, semi-in-situ FT-IR analysis, and EPR analysis, demonstrated that reactive •O2– species generated via the acceleration of Cu+ species, and activated the NHPI (N-hydroxyphthalimide) molecule to form active PINO (phthalimide N-oxyl) species. The oxygen vacancy was verified to be able to activate O2 molecule and promote the formation of active 1O2 species. The surface Lewis acid site was proposed to interact with NHPI molecule, enabling the generation of highly active PINO species. The catalytic system also has the advantages of catalytical and structural stability, recyclability, and tolerance of wide substrate scope. We believe that the synergistic effect between the highly active sites and Lewis acid sites in catalyst can open up new opportunities for the activation of inert C–H bonds via O2/NHPI system.

Highly productive V/Zn-SiO2 catalysts for the selective oxidation of methane

The production of formaldehyde on industrial scale requires huge amounts of energy due to the involvement of reforming processes in combination with the demand in the megaton scale. Hence, a direct route for the transformation of (bio)methane to formaldehyde would decrease costs and puts less pressure on the environment. Herein, we report on the use of zinc modified silicas as possible support materials for vanadium catalysts and the resulting consequences for the performance in the selective oxidation of methane to formaldehyde. After optimization of the Zn content and reaction conditions, a remarkably high space-time yield of 12.4 kgCH2O·kgcat−1·h−1 was achieved. As a result of the extensive characterization by means of UV–vis, Raman, XANES and NMR spectroscopy it was found that vanadium is in the vicinity of highly dispersed zinc atoms which promote the formation of active vanadium species as supposed by theoretical calculations. This work presents a further step of catalyst development towards direct industrial methane conversion which may help to overcome current limitations in the future.

An energy-efficient H2 production based on urea-aided water splitting enhanced by Ru induced in-situ speciation of NiO nanosheets on porous Ni

Efficient hydrogen production by water electrolysis is primarily restrained by imperfect over-potential and poor reaction dynamics on oxygen evolution reaction (OER). Thermodynamically favourable urea oxidation reaction (UOR) is a class of promising routes for substituting sluggish OER and for coupling with cathodic hydrogen production because of smaller equilibrium potential (0.37 V) than that of OER (1.23 V). Herein, a versatile Ru-NiO/p-Ni catalyst was prepared through in-situ generating nickel hydroxide nanosheets on the surface of ordered porous Ni, then doping low Ru and annealing treatment. The optimized Ru-NiO/p-Ni displayed outstanding activity and stability towards hydrogen evolution reaction (HER), OER and UOR with potentials of −0.13 V, 1.57 V, and 1.39 V at 100 mA cm−2, respectively. Ru-NiO/p-Ni‖Ru-NiO/p-Ni can achieve 100 mA cm−2 in urea-aided water splitting at a voltage of only 1.58 V, which is prominently 170 mV smaller than the voltage of water electrolysis (1.75 V). The excellent electrocatalytic performance is owing to the outstanding inherent activity generated by cooperative effect of Ru and NiO, along with rich defect and active centre of Ru-NiO/p-Ni supplied by the large surface area of 3D porous structure. The formation of more rich Ni active species with a high valence through transport of electrons between Ru and Ni is favourable to promoting the dissociation of urea molecules, eventually improving UOR. Therefore, it can facilitate urea-aided water splitting, which provides a valuable strategy for constructing versatile catalysts for a cathodic energy-efficient hydrogen production coupled with other anodic oxidation reactions.

Quantitative characterization of the contribution of electrogenerated active species for NH+ 4-N oxidation on Ti/RuO2-IrO2 anode

The contribution of active species for ammonia nitrogen (NH4+-N) oxidation has received much attention in recent decades through electrocatalytic oxidation (EO) technology. Here we describe the strong NH4+-N removal capacity (more than 98 %) with NaCl as electrolyte of Ti/RuO2-IrO2 anode. Electrochemical tests were used to characterize the excellent NH4+-N degradation performance of Ti/RuO2-IrO2 anode in presence of chlorides. The values of electron transfer number (n = 1.02) and transfer coefficient (α = 0.42) show that the reaction is in the diffusion control stage, which is more conducive to the degradation of NH4+-N. Additionally, three active species (•OH, Cl•, and ClO•) formation is related to the adsorption energy (obtained by density functional theory (DFT) calculation) during the electrolysis process. The difference charge density and density of state (DOS) calculation indicate that the O − in ClO• is more likely to break and react with pollutants in water, which is consistent with the results of active species detection experiments. The combination of kinetics (Tafel) and thermodynamics (adsorption energy) shows that the variation of Tafel slope is affected by the coverage of active species on the electrode surface.

Ruthenium catalyzed efficient hydroformylation regulated by thiazolinyl-based phosphine

A catalytic system comprised of Ru3(CO)12, thiazolinyl-based phosphine (L1), and HBF4 enables the efficient hydroformylation, which the tautomer L1b is more favorable for the occurrence of the reaction as well as the additive HBF4 is beneficial for the formation of ruthenium hydrogen active species. The formation and stabilization of the critical Ru-complex intermediates were verified by the DFT calculations. The hydroformylation proceeds with high chemical selectivity especially for the linear, internal and cyclic olefins (conversion up to 99 %, selectivity of aldehysdes up to 92 %).

High-valence metal sites induced by heterostructure engineering for promoting 5-hydroxymethylfurfural electrooxidation and hydrogen generation

The electrocatalytic 5-hydroxymethylfurfural (HMF) oxidation reaction coupling with hydrogen evolution reaction (HER) serves as a promising strategy to generate both high-value-added products and clean energy, which is limited by the poor catalytic efficiency of bifunctional electrocatalysts and unclear electrocatalytic mechanism for HMF oxidation reaction. Herein, we fabricate a bifunctional NiSe2-NiMoO4 heterostructure nanowire electrocatalyst for the conversion of HMF to 2,5-furandicarboxylic acid (FDCA) and simultaneous H2 production. As expected, the NiSe2-NiMoO4 exhibits outstanding activity and selectivity toward HMF oxidation reaction. In particular, at a potential of 1.50 V, the yield of FDCA could reach 98 % with a faradaic efficiency of 96.5 %, as well as excellent stability. Density functional theory calculation results demonstrate that the NiSe2-NiMoO4 heterostructure could tune the adsorption energy of HMF, facilitate high-valence active species formation, and enhance electronic conductivity. Furthermore, a two-electrode electrolyzer assembled using NiSe2-NiMoO4 as a bifunctional catalyst requires 1.53 V to acquire a current density of 50 mA cm−2, which is 201 mV lower than that of water electrolysis. This work provides new insights for designing multifunctional catalysts for biomass upgrading coupled with hydrogen evolution.

SAND-ROSE SHAPED β-Ni(OH)2 MICROSPHERES: A HIGH EFFICIENT ADDITIVE IN THE THERMAL DECOMPOSITION OF AMMONIUM PERCHLORATE

Sand-rose shaped β-Ni(OH)2 submicron particles were successfully synthesized by a simple wet-chemistry process. The influence of the as-prepared material on the thermal decomposition of ammonium perchlorate (AP) was explored by thermogravimetry and differential scanning calorimetry analyses. The in-situ formation of active NiO species in the AP/β-Ni(OH)2 system is beneficial for electron transfer in the decomposition steps of AP, leading to the acceleration of its thermal decomposition. In particular, the addition of 5 wt. % β-Ni(OH)2 to AP lowers the decomposition temperature of the latter by 68.5°C and, moreover, the apparent heat of decomposition is increased almost twofold compared to that of pure AP.

Built-in electrophilic/nucleophilic domain of nitrogen-doped carbon nanofiber-confined Ni2P/Ni3N nanoparticles for efficient urea-containing water-splitting reactions.

Transferring urea-containing waste water to clean hydrogen energy has received increasing attention, while challenges are still faced in the sluggish catalytic kinetics of urea oxidation. Herein, a novel hybrid catalyst of Ni2P/Ni3N embedded in nitrogen-doped carbon nanofiber (Ni2P/Ni3N/NCNF) is developed for energy-relevant urea-containing water-splitting reactions. The built-in electrophilic/nucleophilic domain resulting from the electron transfer from Ni2P to Ni3N accelerates the formation of high-valent active Ni species and promotes favourable urea molecule adsorption. A spectral study and theoretical analysis reveal that the negatively shifted Ni d-band centre in Ni2P/Ni3N/NCNF weakens the adsorption of intermediate CO2 and facilitates its desorption, thereby improving the urea oxidation reaction kinetics. The overall reaction process is also optimized by minimizing the energy barrier of the rate-determining step. Following the stability test, the surface reconstruction of the pre-catalyst is discussed, where an amorphous layer of NiOOH as the real active phase is formed on the surface/interface of Ni2P/Ni3N for urea oxidation. Benefiting from these characteristics, a high current density of 151.11 mA cm-2 at 1.54 V vs. RHE is obtained for urea oxidation catalysed by Ni2P/Ni3N/NCNF, exceeding that of most of the similar catalysts. A low cell voltage of 1.39 V is required to reach 10 mA cm-2 for urea electrolysis, which is about 200 mV less than that of the general water electrolysis. The current work will be helpful for the development of advanced catalysts and their application in the urea-containing waste water transfer to clean hydrogen energy.

Synergy between the coordination and trace ionization of co-solvents enables reversible magnesium electroplating/stripping behavior

The synergy between coordination and trace ionization induces active ionic species formation and simultaneously alleviates electrolyte decomposition.

CoF2 coupled MXene with facile active phase reconstruction for oxygen evolution reaction.

The combined CoF2/MXene system was effective in the facile cobalt active species formation induced by surface reconstruction and charge redistribution to promote oxygen evolution reaction.

The design of high-entropy metal sulfides promising high-performance gaseous elemental mercury removal

Regulating the surface coordination environment and improving the formation of active species represent the key factor in designing high-performance metal sulfide-based sorbents for gaseous Hg0 capture. This paper reported the Hg0 adsorption by high entropy metal sulfides for the first time, and clarified the mechanisms involved in the evolutions of active species as well as the Hg0 adsorption. The multiple metal components of the high entropy metal sulfides have great significance in improving the surface chemistry. The addition of Ce helps not only the formation of chemically homogeneous structure, but also the generation of high valence state metal cations and unsaturated sulfur species, thereby improving obviously the Hg0 removal ability. The synthesized CeNiCoMnCuSx has a high Hg0 adsorption capacity of 10.52 mg·g−1 at 80 %-breakthrough, and a Hg0 adsorption rate of 4.31 μg·g−1·min−1. The high valence state metal cations (Ni3+, Co3+, Mn4+, Cu2+ and Ce4+) and unsaturated Sx2− and S22− species can directly oxidize Hg0 and convert it into HgS. In comparison, the quaternary sulfide counterpart (NiCoMnCuSx) cannot form a main phase structure, and has obviously lower percentages of high valence state metal cations and unsaturated sulfur species. This work provides a new space for developing metal sulfides for Hg0 adsorption.

Sodium Promoted FeZn@SiO2-C Catalysts for Sustainable Production of Low Olefins by CO2 Hydrogenation

A prepared FeZnNa@SiO2-C catalyst with graphitized carbon (C)-modified mesoporous SiO2 supports metal nanoparticles with the sol–gel method. The effect of adding metal Na and Zn promoters as a dispersion on the CO2 hydrogenation to low olefins was systematically studied. The results showed that Zn–Na, as a combination, could promote the absorption of CO2 and improved the conversion rate of CO2. Na as an alkaline substance can improve the absorption of more acidic CO2, which could increase the conversion rate of CO2 to 59.03%. Meanwhile, the addition of secondary metal Zn to Fe-based catalysts to form a surface alloy could alter the adsorption of CO2 and the activation of C-O bonds, inhibit the subsequent hydrogenation of olefins to paraffins, and facilitate the reduction of Fe2O3 and the formation of active Fe5C2 species. The formation of active Fe5C2 species was found in TEM and XRD, and the selectivity of the target product was 41.07%. The deep hydrogenation of olefins was inhibited, and the space–time yield (STY) of low olefins was raised again by inhibiting their deep hydrogenations, up to 0.0436. However, the corresponding STY did not increase infinitely with the increase of Na doping, and higher catalytic performance for CO2 hydrogenation could be exhibited when the Na doping reached 6.4%. Compared with Fe@SiO2-C catalyst, Na- and Zn-promoted Fe-based catalysts, prepared by the modified sol-gel method, can be used directly for highly efficient CO2 hydrogenation to low olefins and thus has a more promising application prospect in the future.

The synthesis of propanol from ethylene over homogeneous Rh/amine catalytic system via auto-tandem reductive hydroformylation

Here we report our investigation on auto-tandem reductive hydroformylation of ethylene, which allows to obtain propanol in a single technological step. The effect of pressure, ligand structure, temperature, solvent type, ratio of components, and gas supply on the process was studied. It was found that ethylene could be successfully converted to propanol by reductive hydroformylation on a homogeneous Rh/NR3 catalytic system with productivity per Rh atom up to 1299 h−1 (9.0 MPa, 110 ℃). Under milder conditions, low ethylene concentrations and constant syngas supply should be applied. Noteworthy, by using atmospheric distillation as a separation procedure, the system can be used for multiple consecutive reactions without significant activity loss. Probable pathways for the formation of active species and the transformation of rhodium complexes during the distillation process are discussed.

Cu-promoted Ni-LaCeOx/SBA-15 catalysts for ethanol steam reforming

Hydrogen is a globally recognized high-energy, clean, and ecofriendly fuel that is currently produced by means of electrocatalysis, biomass conversion, coal gasification, and thermal decomposition of hydrocarbons, with the steam reforming showing high potential. The present work is focused on Cu-promoted SBA-15-supported Ni-LaCeOx catalysts for ethanol steam reforming (ESR). The catalysts were prepared by incipient wetness impregnation and characterized by XRF, N2 adsorption-desorption, IR spectroscopy, SAXS, XRD, H2-TPR, Raman, and STA methods. The support features caused by the distribution of LaCeOx NPs and Cu promoter in proper ratios affect the conditions of formation of active dispersed Ni species to determine the catalyst performance and its reducibility. At 800 оС, the NiСu-LaCeOx/SBA-15 (1:1) catalyst demonstrates a 100 % ethanol conversion and 55 % hydrogen yield. Thus, the role of the Cu-containing promoter comprises both a significant decrease of carbon deposits on the catalyst surface and redirecting of the intermediate interactions towards the formation of the desired gaseous products.