Reduction Products Research Articles

Fe-MOF-74 Reactivity Explored: Comprehensive Computational Assessment of O and S Atom Influence on CO2 and CO Reduction Reactions

The conversion of carbon dioxide (CO2) and carbon monoxide (CO) into higher-value materials is crucial for addressing escalating levels of greenhouse gases in Earth’s atmosphere. Employing first-principles methods, we investigated the electrocatalytic reduction of CO2 and CO on two Fe-based MOFs: Fe2DOBDC and Fe2DSBDC. By directly comparing these MOFs, we aimed to discern the impact of introducing S atoms into the framework without changing the topological framework. Several chemical properties such as electronegativity, atomic radius, polarizability, and charge density are expected to lead to significant changes for the reduction reactions upon the replacement of O atoms with S atoms. CM5 atomic charge analysis highlights some of these differences by showing the equatorial Fe-O/S bonds of Fe2DSBDC are less polarized and result in smaller positive and negative charges on the Fe and O/S atoms, respectively. Additionally, the larger S atoms are expected to weaken adsorbate binding due to less favorable van der Waals interactions near the open-metal Fe site. Consequently, the less electropositive Fe site and the larger S atoms of Fe2DSBDC impede the adsorption of reduced CO2 and CO products, while the more electropositive Fe site and smaller O atoms of Fe2DOBDC strongly favor product adsorption. This implies that CO2 and CO reduction on Fe2DSBDC is likely to yield only 2e- products (HCOOH and CH2O, respectively), whereas Fe2DOBDC is expected to produce deeper reduction products (CH2O and CH4, respectively). This insight offers a foundation for constructing novel MOFs with tunable reaction behaviors by strategically replacing O atoms with heavier S atoms in the MOF scaffold.

(Invited) Understanding Electrochemical Reaction Mechanisms of Sulfur in All-Solid-State Batteries through Operando and Theoretical Studies

All-solid-state lithium-sulfur batteries (ASLSBs) have been considered a promising next-generation energy storage technology due to their remarkable safety and high energy density. In ASLSBs, the electrochemical pathways are intrinsically different from conventional Li-S batteries using liquid electrolytes. However, the mechanism still lacks clear identification and deep understanding. Herein, for the first time, we investigated the chemistries and explored the electrochemical reaction mechanism in ASLSBs through coupling operando Raman spectroscopy and ex-situ X-ray absorption spectroscopy. We proved that no long-chain lithium polysulfides (Li2Sn, 4≤n≤8) were formed during the redox reactions, but a short-chain polysulfide (Li2S2) intermediate phase formation was identified in the conversion between active material S8 and reduction product Li2S. This evidence explains the electrochemical behavior differences of Li-S batteries when using liquid and solid electrolytes. Moreover, there are partial S8 and Li2S2 remaining at the cathode even at fully lithiation stage, suggesting the sluggish reaction kinetics in the ASLSBs. This study revealed the generation of Li2S2 intermediates in ASLSBs, inspiring future research to further improve the performance of ASLSBs through completing the conversions and promoting reaction kinetics in ASLSBs.

Rational Modulation of Interface Microenvironment and Design of the Flow Electrolyzer for COx Electroreduction to Alcohol.

The electrocatalytic reduction of COx (including CO2 and CO) into value-added fuels and chemicals, particularly multi-carbon (C2+) alcohols, presents a significant opportunity to close the manmade carbon cycle and support sustainable energy systems. The catalytic performance of electrochemical reduction reactions of CO2 and CO (COxRR)is strongly correlated with the local microenvironments, the flow electrolyzer, and the catalysis approaches with flow electrolyzers, which contribute to the kinetic and thermodynamic landscape of the reaction, ultimately determining the efficiency and selectivity of the COxRR toward desired reduction products. However, controllable microenvironment construction, rationally designed flow electrolyzers, and matchable flow electrolyzers derived catalysis approaches chosen for improving COxRR-to-alcohol performance still face challenges. Building upon the foundation laid by previous research, this review article will provide an in-depth summary of the regulation of the catalytic reaction interface microenvironment, the design of flow electrolyzers, and the development of derived stepwise catalysis approaches with the flow electrolyzers, which provide a comprehensive and strategic approach to enhancing the COxRR process for alcohol production, offering valuable insights and innovative solutions that can significantly impact the field of COxRR conversion to alcohol and contribute to the development of more sustainable chemical production methods.

Valorizing polymeric wastes and biomass through optimized co-pyrolysis for upgraded pyrolysis oil: A study on TG-FTIR and fixed bed reactor

The co-pyrolysis of biomass and polymeric wastes offers a promising approach for waste reduction and valuable product recovery while decreasing fossil fuel dependence. This study aimed to investigate the synergistic effects of blending waste tire (WT) or polystyrene (PS) with sawdust (SD) at varying effective hydrogen/carbon ratio (H/Ceff) on liquid product distribution. Thermal degradation behavior was analyzed using TGA-FTIR, followed by fixed-bed reactor pyrolysis experiments at different temperatures. The devolatilization of SD primarily occurred between 185 and 390°C, while WT and PS decomposed between 250 and 500°C and 350–460°C, respectively. Results showed that SD addition to WT accelerated degradation at lower temperatures. Optimal H/Ceff ratios were 0.42 for WT/SD and 0.64 for PS/SD blends at 500°C, maximizing valued hydrocarbons, reducing pollutants, and yielding the highest liquid fraction. TGA-FTIR analysis revealed the presence of various functional groups, including C-H, CC, CO2, and O-H. The pyrolytic oil showed improved stability with significantly fewer undesired compounds. This research provides theoretical and practical insights into the control and application potential as well as the limitations of high-value energy products derived from the co-pyrolysis of SD, WT, and PS.

A High Capacity Gas Diffusion Electrode for Li-O2 Batteries.

The very high theoretical specific energy of the lithium-air (Li-O2) battery (3500Wh kg-1) compared with other batteries makes it potentially attractive, especially for the electrification of flight. While progress has been made in realizing the Li-air battery, several challenges remain. One such challenge is achieving a high capacity to store charge at the positive electrode at practical current densities, without which Li-air batteries will not outperform lithium-ion. The capacity is limited by the mass transport of O2 throughout the porous carbon positive electrode. Here it is shown that by replacing the binder in the electrode by a polymer with the intrinsic ability to transport O2, it is possible to reach capacities as high as 31 mAh cm-2 at 1mA cm-2 in a 300µm thick electrode. This corresponds to a positive electrode energy density of 2650Wh L-1 and specific energy of 1716Wh kg-1, exceeding significantly Li-ion batteries and previously reported Li-O2 cells. Due to the enhanced oxygen diffusion imparted by the gas diffusion polymer, Li2O2 (the product of O2 reduction on discharge) fills a greater volume fraction of the electrode and is more homogeneously distributed.

GOLD MICROFLOWER MODIFIED SCREEN‐PRINTED CARBON ELECTRODE FOR THE ELECTROCHEMICAL DETECTION OF LACTIC ACID IN BLOOD AND SWEAT

A nonenzymatic electrochemical lactic acid sensor was fabricated by electrodepositing gold microflowers on a screen‐printed carbon electrode and used to determine lactic acid in human serum and sweat quantitatively. Extensive voltammetric studies with lactic acid in phosphate‐buffer saline (PBS) and the analysis of the reduction product proved beyond doubt that lactic acid undergoes two‐electron reduction to form lactaldehyde. The reduction current increased quantitively with lactic acid concentration from 0.5 to 8.5 mM in 0.1 M PBS. The sensor showed excellent sensitivities of 1243 µA mM‐1 cm‐2 and 2752 µA mM‐1 cm‐2 in two linear ranges, 0.5 to 2.5 mM and 2.5 to 8.5 mM, respectively with a detection limit of 0.012 ± 0.0014 mM. The performance of the sensor was validated by estimating lactic acid in human serum and the sweat generated through physical exercise. The estimated lactic acid concentrations are in good agreement with clinical analysis data.This indicates the potential applicability of the sensor in the point‐of‐care detection of lactic acid.

2D/2D Bi2WO6/C3N5 S-scheme heterojunction for highly selective production of CH4 by photocatalytic CO2 reduction under visible light

Photocatalytic CO2 reduction is a practical solution to the energy dilemma and environmental damage caused by greenhouse gases, and it is very important to explore high-efficiency photocatalysts. In this study, a novel Bi2WO6/C3N5 step(S)-scheme heterojunction was successfully constructed and applied for CO2 photoreduction. The 2D/2D structure showed excellent photocatalytic properties, with methane production reaching 1.976 μmol·g−1·h−1 and selectivity reaching 100 % under 5 hours of visible light irradiation. The result indicates that combining Bi2WO6 and C3N5 can promote interfacial charge separation and maintain the optimal reducing ability of photogenerated electrons. Based on experimental and theoretical calculations, we characterized the reaction mechanism and heterojunction formation mechanism. This study offers a novel approach to improve the selectivity and photocatalytic efficiency of CO2 reduction products.

Preparation of cementing material and recovery of iron resources using converter slag

This study aims to optimize the modification of blast furnace slag and converter slag using dust removal ash as a reducing agent, with the dual goals of enriching cementitious materials and recovering iron resources. The results show that the pulverization effect of the modified slag is optimized when the dust removal ash addition ratio is 14 wt%, the reduction temperature is 1450 °C, and the reduction time is 30 min. Under these conditions, the pulverization and iron recovery rates reached 65.23 % and 60.85 %, respectively. The composition of the reduction-modified product is influenced by the particle size of the reduction product, which in turn affects its phase composition. The main phases of small particles (particle size < 0.150 mm) identified were magnesium rose pyroxene (Ca3Mg(SiO4)2, C3MS2) and dicalcium silicate (γ-Ca2SiO4, γ-C2S). The main phases of large particles (particle size > 0.150 mm) identified were dicalcium silicate (β-Ca2SiO4, β-C2S) and Ca2Fe2O5. Iron primarily exists in the form of an alloy and cementite, while P is dispersed in the iron beads in the form of Fe3P, Fe2P, and Mn2P in a striped configuration.

Molecular Electrochemical Catalysis of CO-to-Formaldehyde Conversion with a Cobalt Complex.

Formox, a highly energy-intensive process, currently serves as the primary source of formaldehyde (HCHO), for which there is a crucial and steadily growing chemical demand. The alternative electrochemical production of HCHO from C1 carbon sources such as CO2 and CO is still in its early stages, with even the few identified cases lacking mechanistic rationalization. In this study, we demonstrate that cobalt phthalocyanine (CoPc) immobilized on multiwalled carbon nanotubes (MW-CNTs) constitutes an excellent electrocatalytic system for producing HCHO with productivity through the direct reduction of CO, the two-electron reduction product of CO2. By carefully adjusting both the pH and the applied potential, we identified conditions that enable the production of HCHO with a partial current density of 0.64 mA cm-2 (17.5% Faradaic efficiency, FE) and a total FE of 61.2% for the liquid products (formaldehyde and methanol). A reduction mechanism is proposed.

Metal–Organic Framework Supported Low‐Nuclearity Cluster Catalysts for Highly Selective Carbon Dioxide Electroreduction to Ethanol

AbstractIt is still a great challenge to achieve high selectivity of ethanol in CO2 electroreduction reactions (CO2RR) because of the similar reduction potentials and lower energy barrier of possible other C2+ products. Here, we report a MOF‐based supported low‐nuclearity cluster catalysts (LNCCs), synthesized by electrochemical reduction of three‐dimensional (3D) microporous Cu‐based MOF, that achieves a single‐product Faradaic efficiency (FE) of 82.5 % at −1.0 V (versus the reversible hydrogen electrode) corresponding to the effective current density is 8.66 mA cm−2. By investigating the relationship between the species of reduction products and the types of catalytic sites, it is confirmed that the multi‐site synergism of Cu LNCCs can increase the C−C coupling effect, and thus achieve high FE of CO2–to–ethanol. In addition, density functional theory (DFT) calculation and operando attenuated total reflectance surface‐enhanced infrared absorption spectroscopy further confirmed the reaction path and mechanism of CO2–to–EtOH.

Metal-Organic Framework Supported Low-Nuclearity Cluster Catalysts for Highly Selective Carbon Dioxide Electroreduction to Ethanol.

It is still a great challenge to achieve high selectivity of ethanol in CO2 electroreduction reactions (CO2RR) because of the similar reduction potentials and lower energy barrier of possible other C2+ products. Here, we report a MOF-based supported low-nuclearity cluster catalysts (LNCCs), synthesized by electrochemical reduction of three-dimensional (3D) microporous Cu-based MOF, that achieves a single-product Faradaic efficiency (FE) of 82.5 % at -1.0 V (versus the reversible hydrogen electrode) corresponding to the effective current density is 8.66 mA cm-2. By investigating the relationship between the species of reduction products and the types of catalytic sites, it is confirmed that the multi-site synergism of Cu LNCCs can increase the C-C coupling effect, and thus achieve high FE of CO2-to-ethanol. In addition, density functional theory (DFT) calculation and operando attenuated total reflectance surface-enhanced infrared absorption spectroscopy further confirmed the reaction path and mechanism of CO2-to-EtOH.

Assessing the impact of carbon quota allocation in enhancing supply chain members emission reduction and advertising efforts

Carbon quota allocation, a precise implementation approach within the cap-and-trade policy, exerts an enduring impact on the production and economic activities of supply chain members. Recognizing the dynamic fluctuations in product goodwill, this study formulates differential game models involving both the manufacturer and retailer within the supply chain. Subsequently, differences in carbon emission reduction efforts, advertising expenditures, product goodwill, and profitability among supply chain members within each contractual framework are comprehensively compared and analyzed. Numerical illustrations are then utilized to validate the theoretical findings and strengthen the subsequent key insights. First, the implementation of carbon quotas allocation, especially those grounded in the benchmarking-based contract, enhances carbon reduction and advertising efforts by supply chain members. Second, both grandfathering-based and benchmarking-based regulations improve the product goodwill, with the latter yielding more substantial improvements. Third, the escalation in unit emission permit price positively impacts the dedication and profitability of supply chain members, although variations in profit enhancements between the manufacturer and retailer hinge on the specific carbon quota allocation methods employed. Lastly, the grandfathering-based total carbon quotas exclusively benefit the manufacturer's profitability, whereas the per-unit carbon quotas under benchmarking-based contract fosters enhanced individual efforts and profitability for all supply chain members.

Efficient reduction-oxidation coupling degradation of nitroaromatic compounds in continuous flow processes

Nitroaromatic compounds (NACs) with electron-withdrawing nitro (-NO2) groups are typical refractory pollutants. Despite advanced oxidation processes (AOPs) being appealing degradation technologies, inefficient ring-opening oxidation of NACs and practical large-scale applications remain challenges. Here we tackle these challenges by designing a reduction-oxidation coupling (ROC) degradation process in LaFe0.95Cu0.05O3@carbon fiber cloth (LFCO@CFC)/PMS/Vis continuous flow system. Cu doping enhances the photoelectron transfer, thus triggering the -NO2 photoreduction and breaking the barriers in the ring opening. Also, it modulates surface electronic configuration to generate radicals and non-radicals for subsequent oxidation of reduction products. Based on this, the ROC process can effectively remove and mineralize NACs under the environmental background. More importantly, the LFCO catalyst outperformed most of the recently reported catalysts with lower cost (13.72 CNY/ton) and higher processing capacity (3600 t/month). Furthermore, the high scalability, material durability, and catalytic activity of LFCO@CFC under various realistic environmental conditions prove the potential ability for large-scale applications.

Green Synthesis of Pure Superparamagnetic Fe3O4 Nanoparticles Using Shewanella sp. in a Non-Growth Medium

Conventional wet chemical methods for the synthesis of superparamagnetic magnetite nanoparticles (MNPs) are energy-intensive and environmentally unsustainable. Green synthesis using bacteria is a less-explored approach to MNP production. Large-scale biosynthesis of MNPs has heretofore been conducted using extremophilic bacteria that exhibit low growth rates and/or require strict temperature control. However, a decrease in material and energy costs would make such bioprocesses more sustainable. In this study, Shewanella putrefaciens CN-32, an iron-reducing bacterium, was employed to reduce amorphous iron oxyhydroxide and synthesize MNPs in a non-growth medium at ambient temperature and pressure. The synthesis was conducted using plain saline solution (0.85% NaCl) to avoid impurities in the products. X-ray diffraction and transmission electron microscopy indicated that the reduction products were MNPs with a pseudo-spherical shape and 6 ± 2 nm average size. Magnetometry showed that the particles were superparamagnetic with maximum saturation magnetization of 73.8 emu/g, which is comparable to that obtained via chemical synthesis methods. Using less than a quarter of the raw materials employed in a typical chemical co-precipitation method, we obtained a maximum yield of 3.473 g/L (&gt;5-fold increase). These findings demonstrate that our simple and ecofriendly process can help overcome the current barriers for large-scale synthesis of high-purity magnetic nanopowders.

Direct quantification of electrochemical CO2 reduction products with an improved DEMS setup

Direct quantification of electrochemical CO2 reduction products with an improved DEMS setup

High-purity ethylene production via indirect carbon dioxide electrochemical reduction

High-purity ethylene production from CO2 electroreduction (CO2RR) is a coveted, yet arduous feat because the product stream comprises a blend of unreacted CO2, H2, and other off-target CO2 reduction products. Here we present an indirect reduction strategy for CO2-to-ethylene conversion, one that employs 2-bromoethanol (Br-EO) as a mediator. Br-EO is initially generated from CO2RR and subsequently undergoes reduction to ethylene without the need for energy-intensive separation steps. The optimized AC-Ag/C catalyst with Cl incorporation reduces the energy barrier of the debromination step during Br-EO reduction, and accelerates the mass-transfer process, delivering a 4-fold decrease of the relaxation time constant. Resultantly, AC-Ag/C achieved a FEethylene of over 95.0 ± 0.36% at a low potential of −0.08 V versus reversible hydrogen electrode (RHE) in an H-type cell with 0.5 M KCl electrolyte, alongside a near 100% selectivity within the range of −0.38 to −0.58 V versus RHE. Through this indirect strategy, the average ethylene purity within 6-hour electrolysis was 98.00 ± 1.45 wt%, at −0.48 V (vs RHE) from the neutralized electrolyte after CO2 reduction over the Cu/Cu2O catalyst in a flow-cell.

Photoredox Cascade Catalysts for Solar Hydrogen Production from Sustainable Hydrogen Sources.

Visible-light-driven photocatalytic hydrogen (H2) production has been extensively studied as a clean and sustainable energy resource. Although sacrificial electron donors (SEDs) are commonly used to evaluate photocatalytic activity, their irreversible decomposition forces charge separation, which disrupts the inherent dual productivity of photocatalysis, that is, the formation of both the reduction and oxidation products. To achieve highly efficient photoinduced charge separation without SED decomposition, the layer-by-layer assembly of redox-active photosensitizing dyes and electron mediators through Zr4+-phosphonate bonds has been extensively studied as an artificial mimic of the electron transport chain in natural photosynthesis. This concept paper presents an overview of photoredox cascade catalytic (PRCC) systems comprising multiple Ru(II)-trisbipyridine-type dyes and mediator layers on Pt-loaded TiO2 nanoparticles for H2 production from redox reversible electron donors (RREDs). The PRCC structure-activity relationship for photocatalytic H2 production is briefly discussed in terms of layer thickness, surface structure and modification, and cooperativity with molecular oxidation catalysts. Finally, new insights into the design of efficient dual-production photocatalysts based on the PRCC structure are presented.

Kinetics study on the temperature-dependent reduction of aqueous U(VI) by natural pyrite

Previous studies have indicated that acid-washed pyrite is inert toward aqueous U(VI) under most pH conditions at ambient temperature, even though insoluble UO2 is the thermodynamically predicted product for the reduction of U(VI) by pyrite. Considering the exothermic nature of nuclear waste, the interaction between uranyl nitrate/acetate and natural pyrite was studied at temperatures ranging from 25 °C to 85 °C and at pH values between ∼4.0 and ∼9.5, to simulate the scenarios encountered in a high-level radioactive waste repository. The results revealed that the reactivity of pyrite toward aqueous U(VI) significantly increased with rising temperature, and the reaction could be described by a pseudo-first-order kinetic equation. Activation energies were calculated to be 79.4 ± 10.6 and 45.7 ± 3.8 kJ⋅mol−1 for the reduction of uranyl nitrate, and 78.2 ± 5.2 and 42.2 ± 5.8 kJ⋅mol−1 for the reduction of uranyl acetate, at pH values of ∼4.5 and ∼5.0, respectively. These values indicate that the reaction is controlled by the surface chemical processes. In addition, the complete reduction of aqueous U(VI) to UO2 product was first observed for the reactions at pH ∼4.0 to ∼5.5 when the temperature was ≥75 °C. Conversely, non-stoichiometric UO2+x(s) (0 < x ≤ 0.67) was found at lower temperatures within the same pH range, and also at 85 °C with a reaction pH of ∼9.5. Moreover, the ratio of reduced U(IV/V) on pyrite surfaces increased gradually over time, indicating that reaction time played a significant role in the reduction products. The findings are essential not only for the safety assessment of the high-level radioactive waste repository, but also for understanding the metallogenic mechanism of U(IV)-bearing ore deposits under the relevant anaerobic and hydrothermal conditions.

Efficient removal of U(VI) by graphene-based electrode modified with amidoxime: Performance and mechanism

The burgeoning interest in nuclear energy as a sustainable power source brings to the fore significant environmental and human health concerns associated with wastewater from uranium mining. This study presented the successful synthesis of amidoxime modified graphene-based electrode materials (PAO-N-rGO/CF) designed for treating uranium containing wastewater. The influencing factors of PAO-N-rGO/CF during the electrokinetic restoration process were systematically investigated, exploring the mechanisms of adsorption and electrochemical reduction from the perspectives of establishing adsorption theoretical models, evaluating electrochemical performance, and characterizing reduction products. According to the results, the optimal removal efficiency for U(VI) by PAO-N-rGO/CF reached 99.93 % under conditions of an applied voltage of 5 V, an electrification duration of 20 min, and a pH of 7. Compared to Ca2+, K+, and Mg2+, PAO-N-rGO/CF exhibited strong selectivity for UO22+. Whether dissolved oxygen was present or not, PAO-N-rGO/CF maintained its excellent electrochemical performance. After undergoing 10 cycles of reuse, the removal efficiency for U(VI) only decreased by 8.75 %. The establishment of the adsorption model demonstrated the presence of a chemical bond between uranium and amidoxime groups. The electrochemical performance tests evidenced that PAO-N-rGO/CF exhibited superior electron transfer capability. The reduction of (UO2)3(OH+)5 to UO2 in wastewater at a pH = 7 was verified by analysis of the reduction products. The successful development and mechanistic study of the novel and efficient electrode material provide theoretical support for the control of radioactive nuclide pollution and possess practical value for engineering applications in treating uranium containing wastewater.

The role of oxidants in the intensive cyanidation of gold. 1. Gold dissolution

In the intensive cyanidation of gravity gold concentrates, sodium m-nitrobenzene sulfonate (NBS) is often used to supplement dissolved oxygen as the oxidant in the process. This paper presents the results of a largely electrochemical study of the behaviour of NBS during cyanidation. The results have confirmed that NBS acts as an oxidant in the cyanidation of gold and that the mixed potential model can be applied to describe the mechanism of its action.The mixed potential is a good initial indicator of the rate of gold dissolution and, as expected, the anodic dissolution of pure gold in cyanide solutions is characterized by passivation at potentials above about −0.35 V.The reduction of oxygen under the conditions of the present study occurs in two 2-electron steps with peroxide as an intermediate. Dissolution of gold occurs at potentials in the diffusion-controlled region for the first step. The cathodic reduction of NBS occurs in the same potential region as the reduction of oxygen. The reaction is first order in the concentration of NBS and is largely independent of the pH. The stoichiometry of the reaction involves six moles of gold per mole of NBS confirming that the amine is the final product of reduction of NBS.Rates of gold dissolution in various solutions have been measured using a calibrated linear polarisation method. The rate increases approximately linearly with increasing NBS concentration and is independent of pH. The rate in 0.5 g/L NBS is approximately the same as in oxygenated solutions.A relatively simple titration has been adapted for use in determining NBS concentrations.