Catalytic Active Sites Research Articles

Tuning the catalytic active sites of TiO2/CeO2 interactions to improve oxygen vacancy and lattice parameters for CO2 conversion to green fuel additive

In recent years, the conversion of carbon dioxide (CO2) to value-added products has become an area of great interest, both from an industrial and environmental perspective. Here we have successfully synthesized TiO2/CeO2-based catalysts by exo- and endo-template and use for direct conversion of CO2 to dimethyl carbonate (DMC). It was found that the catalytic activity of TiO2/CeO2 catalysts depends on the acidic and basic sites present in the catalyst. The study also investigated the optimization of reaction conditions in a batch reactor. It was found that the catalytic activity of TiO2/CeO2-based catalysts significantly enhances the CO2 conversion and achieves a high DMC yield compared to the performance of pure CeO2 and TiO2. The reusability of the TiO2/CeO2 catalysts was examined as well. Additionally, the heat of the reaction and Gibbs free energy were calculated using chemical equilibrium models. The experimental response data was validated using artificial neural networks (ANN). The R2 values between the expected and experimental results for DMC yield and CO2 conversion were 0.9953 and 0.9969, respectively. The developed ANN model successfully predicts the percentage of CO2 conversion and DMC yield under the given reaction conditions, with prediction accuracy MSE of 0.0013 and 0.0008, respectively.

Understanding the Reverse Water Gas Shift Reaction over Mo2C MXene Catalyst: A Holistic Computational Analysis

AbstractPristine Mo2C MXene has been proposed as an heterogeneous catalysis of the reverse water gas shift (RWGS) reaction. The present computational study aims at understanding its catalytic performance and reaction mechanisms tackling its thermodynamics, kinetics, and surface dynamic effects, combining Gibbs free energy profiles gained by density functional theory (DFT), mean‐field kinetics by microkinetic modeling, and rare‐event steps by kinetic Monte Carlo (kMC). The RWGS endergonicity goes for the use of high temperatures and reactants partial pressures to make the reaction exergonic. Gibbs free energy profiles show a preference for redox mechanism, whereas microkinetic simulations favor a low‐temperature preference of formate mechanism. The kMC reveals simultaneous operating redox and formate pathways, where surface coverage disfavors redox favoring the formate pathway. A peak performance is found at 700 K, in line with reported experiments, where the formation of surface O2* is found to be key, acting as a reservoir for O* adatoms while freeing surface sites upon O2* formation. Even though high turnover frequencies are predicted, the system could benefit from swing operando conditions, alternating CO production steps with H2 reduction regeneration steps, and/or ways to reduce the surface O2* and so to have more active catalytic sites.

Revealing Local and Directional Aspects of Catalytic Active Sites by the Nuclear and Surface Electrostatic Potential

Revealing Local and Directional Aspects of Catalytic Active Sites by the Nuclear and Surface Electrostatic Potential

Role of oxophilic metal ions (Mo, Zr, Ti) impregnated Ni/γ-Al2O3 catalysts for hydrothermal liquefaction of kraft lignin

In this study, the effect of oxophilic metal ions (Mo, Zr, and Ti) loaded Ni/γ-Al2O3 (Al) catalysts was explored for the first time for the hydrothermal liquefaction of kraft lignin using IPA for 30 min/280 °C. The liquefaction of lignin was noticed to be 65.4 wt% with 10 wt% loaded Ni/Al with an 81.3% total conversion. The performance of Ni/Al was enhanced remarkably by using the oxophilic metal ions as promoters owing to an increase in the Lewis character of the catalyst's surface. The bio-oil yield was a maximum of 72 wt% with a 91.5% conversion using 3 wt% loaded Ti–10Ni/Al. The different alcoholic solvents such as methanol, ethanol, and IPA were also examined for the same. However, the best liquefaction was noticed with IPA owing to better H-donor tendency. Additionally, a series of IPA-water co-solvent examinations attributed to a significant improvement in the liquefaction to 74.8 wt% (50:50) IPA-water system. The optimum catalyst 10Ni–3Ti/Al was tested for four catalytic cycles, which indicated a slight loss in the catalytic activity because of blockage of the catalytic active site by char deposition. The GC-MS investigation of optimum catalytic bio-oil showed the highest selectivity of acetosyringone (68.5%) and 2-methoxy-phenol (22.8%), which was observed to be only 30.1 and 5.1% for non-catalytic bio-oil. The 1H NMR and FT-IR investigation of raw lignin and bio-oil proved the breakage of lignin's 3D structure into respective G-and S-type monomeric compounds. Additionally, catalysts were characterized using the XRD, BET, and XPS analysis.

Room-temperature sulfur doped NiMoO4 with enhanced conductivity and catalytic activity for efficient hydrogen evolution reaction in alkaline media

Transition metal oxides have been acknowledged for their exceptional water splitting capabilities in alkaline electrolytes, however, their catalytic activity is limited by low conductivity. The introduction of sulfur (S) into nickel molybdate (NiMoO4) at room temperature leads to the formation of sulfur-doped NiMoO4 (S-NiMoO4), thereby significantly enhancing the conductivity and facilitating electron transfer in NiMoO4. Furthermore, the introduction of S effectively modulates the electron density state of NiMoO4 and facilitates the formation of highly active catalytic sites characterized by a significantly reduced hydrogen absorption Gibbs free energy (ΔGH*) value of −0.09 eV. The electrocatalyst S-NiMoO4 exhibits remarkable catalytic performance in promoting the hydrogen evolution reaction (HER), displaying a significantly reduced overpotential of 84 mV at a current density of 10 mA cm−2 and maintaining excellent durability at 68 mA cm−2 for 10 h (h). Furthermore, by utilizing the anodic sulfide oxidation reaction (SOR) instead of the sluggish oxygen evolution reaction (OER), the assembled electrolyzer employing S-NiMoO4 as both the cathode and anode need merely 0.8 V to achieve 105 mA cm−2, while simultaneously producing hydrogen gas (H2) and S monomer. This work paves the way for improving electron transfer and activating active sites of metal oxides, thereby enhancing their HER activity.

Catalytic properties of 3D flower-likeMgCo2O4/MXene composites for the thermal decomposition of ammonium perchlorate by one-pot synthesis

The catalytic active sites of the materials have a major role in the catalytic activity of nanocatalytic materials for the heat thermal decomposition of ammonium perchlorate. By adopting one-pot strategy to load MgCo2O4 onto MXene nanosheets, we were able to create highly dispersed MgCo2O4/MXene composites that improved the dispersion of the nanoparticles and increased the catalytic active sites. The MgCo2O4/MXene catalytic active sites were clearly optimized (Specific surface area increased from 115.4 of MgCo2O4 to 168.8 m2·g−1), according to the BET results. The performance tests demonstrated that the MgCo2O4/MXene composite effectively decreased the thermal decomposition temperature of AP, and the MgCo2O4/MXene composite significantly reduced the peak decomposition temperature of AP by 208.3 °C (from 471.2 °C of pure AP to 262.9 °C). The decomposition heat of AP increased from 782 J·g−1 of pure AP to 1453 J·g−1. In addition, the apparent activation energy of AP dropped from 296.19 kJ·mol−1 to 119.48 kJ·mol−1. Application of MgCo2O4/MXene composite to AP/HTPB-based composite solid propellants (CSPs) for combustion experiments resulted in an appreciable reduction in ignition delay time of ∼ 45 ms (from ∼ 51 ms to ∼ 6 ms). The highly dispersed MgCo2O4/MXene composite was a positive catalyst for AP-based composite solid propellant.

Valorisation of alkali from tungsten leaching solution using diffusion dialysis and selective electrodialysis for anion-exchange membrane water electrolysis

Currently, tungsten mining procedures discharge a large amount of alkali wastewater, necessitating the development of sustainable approaches to valorise valuable bases for further utilization. In this study, diffusion dialysis (DD) and selective electrodialysis (SED) were utilized to recycle the alkali from a simulated tungsten leaching solution; the recycling base was further subjected to anion-exchange membrane water electrolysis (AEMWE) for H2 production. The results indicate that DD is capable of recycling 0.447 mol/L NaOH base with negligible leakage of WO42−, while the SED process enables the recycling of 1.63–2.01 mol/L NaOH but contains 0.11–0.14 mol/L WO42−. The AEMWE experiment showed that the water electrolyser with SED recycling alkali had a current density of 580.26 mA·cm−2 at 1.8 V, which is much greater than 374.16 mA·cm−2 with DD treatment solution and 352.81 mA·cm−2 without any treatment. The WO42− impurities could adsorb on the surface of the catalyst, which further occupied the catalytic active site of the electrode catalyst and reduced the active specific surface area of the catalyst. This work demonstrated the ability of the SED and DD approaches to recycle alkali for hydrogen production, creating a new pathway for the valorisation of alkali from the tungsten mining industry.

Effect of potassium in copper catalysts on selective C–O bond activation of furfuryl alcohol

Selective C-O bond activation in biomass-derived furanic compounds is essential for biomass upgrading. Hydrogenolysis of furfuryl alcohol (FFA) provides two value-added chemicals 1,5-pentanediol (1,5-PDO) and 1,2-pentanediol (1,2-PDO), the generation of both involve selective C-O bond cleavage of FFA, but the respective catalytic active sites still remain obscure. Here we prepared a series of potassium-modified basic oxide supported Cu catalysts and found the product distribution of 1,2-PDO/1,5-PDO selectivity ratio decreased with the rise of K loadings. Various characterization techniques show that the Cu/MgO mainly consists of Cu nanoparticles, while the 2 K-Cu/MgO is dominant by oxidized Cu species especially Cu+. It is proposed that the selective C-O bond cleavage of the furan ring of FFA to 1,5-PDO over basic oxide supported Cu catalysts is attributed to Cu+ species, while the formation of 1,2-PDO is dependent on Cu nanoparticles. This work sheds light on the selective C-O bond activation in the biomass-derived furanic compounds.

Synergistically accelerating capture and catalytic conversion of polysulfides by Co@NCNT-MoSe2 nanocomposite modified separator for advanced Lithium-Sulfur batteries

Lithium-sulfur (Li-S) battery with a high theoretical energy density (2600 Wh·kg−1) is considered as a promising energy storage system. However, the shuttle effect and the sluggish redox kinetics of lithium polysulfides (LiPSs) lead to low sulfur utilization. A multifunctional layer modified on separator, as a collaborator of capturer-catalyst-conductor, is be regarded as an effective strategy to solve these problems. Herein, the Co@NCNT-MoSe2 nanocomposite as a modified layer is synthesized with a mesoporous structure by the hydrothermal reaction, in which a large number of transparent MoSe2 nanosheets grow outside NCNT embedded with Co nanoparticles, forming a flower-like outer walls of tube. The modified layer displays the significant features of capturing and catalytic conversion toward LiPSs, attributing to strong adsorption abilities, abundant catalytic active sites, and efficient transferring pathway of electron/Li+. Benefitting from these alluring properties, the results demonstrate that the modified separator offers a high discharge capacity of 983.2 mAh·g−1 at 0.2C after 200 cycles. Even at 2C, after long-term 1000 cycles, it still shows a superb capacity of 725 mAh·g−1 accompanied by a low capacity fading of 0.042 % per cycle. More notably, at 0.2C, the modified separator can realize an ideal areal capacity of 5.24 mAh·cm−2 under high S load (5 mg·cm−2) and poor electrolyte (7.5 μL·mg−1). Therefore, this work will provide a new insight on the development of multifunctional separators to achieve a long-life battery with high sulfur utilization by restraining shuttle effect and accelerate redox kinetics of LiPSs.

A Ce-CuZn catalyst with abundant Cu/Zn-OV-Ce active sites for CO2 hydrogenation to methanol

CO2 hydrogenation to chemicals and fuels is a significant approach for achieving carbon neutrality. It is essential to rationally design the chemical structure and catalytic active sites towards the development of efficient catalysts. Here we show a Ce-CuZn catalyst with enriched Cu/Zn-OV-Ce active sites fabricated through the atomic-level substitution of Cu and Zn into Ce-MOF precursor. The Ce-CuZn catalyst exhibits a high methanol selectivity of 71.1% and a space-time yield of methanol up to 400.3 g·kgcat−1·h−1 with excellent stability for 170 h at 260 °C, comparable to that of the state-of-the-art CuZnAl catalysts. Controlled experiments and DFT calculations confirm that the incorporation of Cu and Zn into CeO2 with abundant oxygen vacancies can facilitate H2 dissociation energetically and thus improve CO2 hydrogenation over the Ce-CuZn catalyst via formate intermediates. This work offers an atomic-level design strategy for constructing efficient multi-metal catalysts for methanol synthesis through precise control of active sites.

Rational design of cuprofullerene bipyridine nanozyme with high peroxidase-like activity for colorimetric sensing of bleomycin.

The high catalytic activity of Cu-based nanozymes mainly depends on the efficient Fenton-like reaction of Cu+/ H2O2, but Cu+ cannot exist stably. Trying to find a material that can stably support Cu+ while promoting the electron cycle of Cu2+/Cu+ still faces serious challenges. C60 is expected to be an ideal candidate to solve this problem due to its unique structure and rich physicochemical properties. Here, we designed and synthesized a C60-doped Cu+-based nanozyme (termed as C60-Cu-Bpy) by loading high catalytic active site Cu+ onto C60 and coordinating with 2,2'-bipyridine (Bpy). The single crystal diffraction analysis and a series of auxiliary characterization technologies were used to demonstrate the successful preparation of C60-Cu-Bpy. Significantly, the C60-Cu-Bpy exhibited superior peroxidase-like activity during the catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Then, the catalytic mechanism of C60-Cu-Bpy as peroxidase was elucidated in detail, mainly benefiting from the dual function of C60. On the one hand, C60 acted as a carrier to directly support Cu+, which has the ability to efficiently decompose H2O2 to produce reactive oxygen species. The other was that C60 acted as an electron buffer, contributing to promoting the Cu2+/Cu+ cycle to facilitate the reaction. Furthermore, a colorimetric sensor for the quantitative analysis of bleomycin was established based on the principle of bleomycin specific inhibition of C60-Cu-Bpy peroxidase-like activity, with satisfactory results in practical samples. This study provides a new strategy for the direct synthesis of Cu+-based nanozymes with high catalytic performance.

A C3‐Symmetric Amino Organocatalyst for Asymmetric Synthesis of Warfarin and Analogues: Mechanistic Insight from ESI‐MS Spectrometry and Computational Calculations

AbstractA novel C3‐symmetric multi–amino catalyst was synthesized and evaluated in the asymmetric Michael addition to produce warfarin and its analogues. The multi–amino catalyst turned out to be efficient up to 1 % molar without the use of acidic additives providing the desired product in 82 % yield and maintaining good level of enantioselectivity. ESI‐MS experiments together with data supplied by theoretical models allowed us the understand the operating mechanism of the catalyst, clarifying the role of the amine functions and confirming the catalyst's multifunctionality. The presence of three active catalytic sites makes it easy its anchoring to silica as solid support for applications in heterogeneous phase catalysis.

Electronic structure-modulated NiFe-metal–organic framework nanosheets for enhance electrochemical oxygen Evolution

Oxygen Evolution Reaction (OER) is a critical half-reaction that hinders water decomposition due to its sluggish kinetics. Developing efficient, stable electrocatalysts for OER is crucial for addressing the challenges in energy crisis and green hydrogen production. Compared to single-metal Metal-Organic Frameworks (MOFs), synergistic interactions between metal ions in bimetallic MOFs provide sufficient space for tuning the electronic structure and oxygen-containing intermediate adsorption energies, and therefore bimetallic MOFs shows great potential in enhancing the OER kinetics. In this work, NiFe-MIL-88A nanosheets were synthesized on nickel foam via a facile one-step hydrothermal method. The catalyst exhibited exceptional OER performance in 1.0 M KOH solution. Notably, it achieved a current density of 50 mA cm−2 at a low overpotential of 220 mV and displayed a Tafel slope of 43.2 mV/dec. Furthermore, it had impressive electrocatalytic durability suitable for commercial applications. This work elucidates the performance enhancement of NiFe bimetallic MOF from the perspective of electron migration. In-situ Raman spectroscopy was adopted to investigate the structural reconfiguration of the catalyst to reveal the true catalytic active sites. First-principle calculation demonstrate that introduction of Ni atoms with low electronegativity is conducive to optimizing the catalytic d-band center and ƒe value. This work provides insights for the designing bimetallic MOFs with superior OER performance.

Fabrication of a laser-directed electrochemical paper analytical device and its deployment for multi-functional electrochemical sensing

The demand for eco-friendly, disposable, and affordable electrochemical sensors stimulates the fabrication of laser-directed paper-based electrodes. This work reports the fabrication of laser-derived patterns on the paper substrate and its multi-functional sensing applications. For this, a computer-aided design (CAD) software-driven computer numerical control (CNC) manufacturing method was developed to engrave a three-electrode design on a paper substrate. The fabricated Laser-Directed electrochemical Paper Analytical Device (LD-ePAD) was thoroughly characterized by Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), contact angle analysis, electrochemical impedance spectroscopy (EIS), and the cyclic voltammetry (CV). After that, we demonstrated the multi-functional sensing ability of the LD-ePADs by detecting diverse model analytes, including small molecules (i.e., lead ions [Pb2+]), free radicals (i.e., peroxide [H2O2]), and macromolecules (i.e., Alkaline phosphatase [ALP]). Upon investigation, it exhibits a fair detection limit of 5.19 (±0.21) µM for Pb2+, 48.66 (±0.31) µM for H2O2, and 0.48 (±0.02) U/L for ALP. The LD-ePADs' outstanding repeatability, stability, abundance of catalytic active sites, remarkable tunability, and potential for nano-bioengineering emphasized their tremendous commercial feasibility. To the best of our knowledge, this is the first study to use controlled one-step laser direct engraving to fabricate a three-electrode setup on a paper-substrate that can sense three heterogeneous molecules electrochemically.

Nitrogen-doped carbon aerogel supported SnO2 anode for electrocatalytic degradation of phenol: Enhanced generation of free radicals

To obtain a high-efficiency and low-cost electrocatalytic anode for environmental pollutant degradation, a nitrogen doped graphene aerogel supported tin oxide (SnO2-NGA) composite catalyst was prepared and SnO2-NGA/Ti anode was fabricated. The influence of nitrogen doping content on electrocatalytic activity of the catalysts was investigated. The effects of current density and initial solution pH on degradation efficiency were studied. The SnO2-N3.0GA/Ti anode shows good catalytic activity for phenol degradation. The conversion of phenol and COD removal by SnO2-N3.0GA/Ti reached 83.6% and 61.2% within 4 h when applied current density was 5.00 mA/cm2 and initial pH was 3.0. The SnO2-N3.0GA/Ti electrode has higher specific surface area, and lower charge transfer resistance. The nitrogen atoms doping increased the content of pyridinic N species, which is beneficial for providing more in-situ catalytic active sites and enhancing the production of reactive oxygen species, especially hydroxyl radical (•OH). This work provides a novel strategy for synthesis of electrocatalytic anode with enhanced activity for degradation of refractory organic pollutants in water.

Abstract A014: ClpP drives efficacy and mediates acquired resistance with imipridones ONC201 and ONC206 in glioma in vitro

Abstract A014: ClpP drives efficacy and mediates acquired resistance with imipridones ONC201 and ONC206 in glioma <i>in vitro</i>

Increasing the Accessibility of Internal Catalytic Sites in Covalent Organic Frameworks by Introducing a Bicontinuous Mesostructure.

Introducing continuous mesochannels into covalent organic frameworks (COFs) to increase the accessibility of their inner active sites has remained a major challenge. Here, we report the synthesis of COFs with an ordered bicontinuous mesostructure, via a block copolymer self-assembly-guided nanocasting strategy. Three different mesostructured COFs are synthesized, including two covalent triazine frameworks and one vinylene-linked COF. The new materials are endowed with a hierarchical meso/microporous architecture, in which the mesochannels exhibit an ordered shifted double diamond (SDD) topology. The hierarchically porous structure can enable efficient hole-electron separation and smooth mass transport to the deep internal of the COFs and consequently high accessibility of their active catalytic sites. Benefiting from this hierarchical structure, these COFs exhibit excellent performance in visible-light-driven catalytic NO removal with a high conversion percentage of up to 51.4 %, placing them one of the top reported NO-elimination photocatalysts. This study represents the first case of introducing a bicontinuous structure into COFs, which opens a new avenue for the synthesis of hierarchically porous COFs and for increasing the utilization degree of their internal active sites.

Simultaneously Regulating charge separation and proton supply-demand in polyphenol amine for hydrogen peroxide photosynthesis

In the H2O2 photosynthesis, apart from the charge separation, the balance of proton supply and demand was also required between the kinetically faster oxygen reduction reaction (ORR) (μs ∼ ms) and the sluggish kinetics of water oxidation reaction (WOR) (s). Faced by this challenge, the article designed the heterojunction photocatalyst formed by in-situ polymerization of polyphenol amine on the surface of CdS under alkaline conditions. As a result, the synthesized CdS-Poly(catechol-hexamethylenediamine) (PCHA) produced 6.1 mM H2O2 after 8 h of visible light irradiation, which is 29 times that of CdS. The experimental results evidenced that the coating of PCHA increased the charge separation and mobility, inhibited the photocorrosion of CdS, and thus enhanced the stability and photoactivity. Moreover, the catechol units of PCHA could function as a proton supplier and regulate local protons concentrations around the catalytic active sites to balance the proton supply–demand in the ORR and WOR at different reaction time scales.

Effect of ligand structure and metal center on ethylene oligomerization with N, N′ Schiff base late transition complexes: experiments and calculations

A series of N, N’ bis(pyridine-imine) Schiff base late transition metal (Fe, Co, and Ni) complexes with different ligand structures and catalytic active sites were synthesized. Ethylene oligomerization results showed that bis(pyridine-imine) iron complex had the highest catalytic activity (10.8 × 105 g/mol Fe h), and the catalytic activity of cobalt complex was the lowest (2.5 × 105 g/mol Co h); nickel complex had the highest selectivity toward high carbon olefins (28.6%), while the iron complex had the lowest (0.2%). The structure-activity relationship between the catalyst structure and catalytic properties for ethylene oligomerization was further studied by density functional theory (DFT) calculations. The bis(pyridine-imine) iron complex had the highest energy gap value and the most stable catalyst structure, which was more conducive to oligomerization; and the N–M–N bond of the nickel complex had the smallest bond angle, which was beneficial for chain growth. Based on the Cossee mechanism, a mechanism for ethylene oligomerization catalyzed by bis(pyridine-imine) metal complexes was proposed. To further study the micro reaction process of ethylene oligomerization, a molecular model of pyridine imine nickel complex and its catalytic ethylene oligomerization reaction path were proposed. The structure and energy of the reaction intermediate and transition state were calculated using DFT. The molecular model of the nickel complex had a lower ethylene insertion barrier and β-H elimination of energy barriers, indicating that the molecular model of the pyridine imine nickel complex had ethylene oligomerization active centers.

B–F dual-doped carbon nanotubes for multi-site and high-rate two-electron oxygen reduction reaction electrocatalysis

Electrocatalytic two-electron oxygen reduction reaction (2e−-ORR) to produce hydrogen peroxide (H2O2) is a promising green way to replace the conventional anthraquinone reaction. Non-metallic catalysts are considered as low-cost catalysts due to their excellent stability and versatile surface chemistry. The performance of non-metallic electrocatalysts is usually limited by the limited catalytic active sites on the surface. Here, we report fluorine and boron dual-doped carbon nanotubes (B–F–C) as a metal-free electrocatalyst for H2O2 production, fabricated via a fast microwave treatment. With the synergistic effect of F and B, this strategy can effectively convert carbon and boron atoms on carbon nanotubes into highly active sites. As a result, an H2O2 yield up to 24.3 mol g−1 L−1 is achieved over B–F–C with a stable selectivity of above 90% within 0.2–0.7 V vs. RHE in 0.1 M KOH. Density functional theory (DFT)calculations further confirm that the multiple active sites created by the dual doping of fluorine and boron are the key factor in improving the performance of 2e−-ORR electrocatalysis. Therefore, this work offers a promising prospect for the design and preparation of catalysts with high catalytic activity for H2O2 production and other catalytic areas of industrial significance.