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This study presents a sea urchin-like Cu2O/Cu catalyst for electrochemical CO2 reduction to C2, which is derived from rhombic dodecahedra Cu2O through one-step oxidation/etching reaction and in situ electrochemical reduction. The sea urchin-like structure provides more active sites and enhances the adsorption of the key intermediate *CO. Meanwhile the formed Cu+/Cu0 interfaces facilitate the C-C coupling reactions between C1 intermediates. As a result, the excellent C2H4 prod [Detail] ...
Download coverThe composition of biomass pyrolysis gas is complex, and the selective separation of its components is crucial for its further utilization. Metal-incorporated nitrogen-doped materials exhibit enormous potential, whereas the relevant adsorption mechanism is still unclear. Herein, 16 metal-incorporated nitrogen-doped carbon materials were designed based on the density functional theory calculation, and the adsorption mechanism of pyrolysis gas components H2, CO, CO2, CH4, and C2H6 was explored. The results indicate that metal-incorporated nitrogen-doped carbon materials generally have better adsorption effects on CO and CO2 than on H2, CH4, and C2H6. Transition metal Mo- and alkaline earth metal Mg- and Ca-incorporated nitrogen-doped carbon materials show the potential to separate CO and CO2. The mixed adsorption results of CO2 and CO further indicate that when the CO2 ratio is significantly higher than that of CO, the saturated adsorption of CO2 will precede that of CO. Overall, the three metal-incorporated nitrogen-doped carbon materials can selectively separate CO2, and the alkaline earth metal Mg-incorporated nitrogen-doped carbon material has the best performance. This study provides theoretical guidance for the design of carbon capture materials and lays the foundation for the efficient utilization of biomass pyrolysis gas.
The electrocatalytic hydrogen evolution reaction is a crucial technique for green hydrogen production. However, finding affordable, stable, and efficient catalyst materials to replace noble metal catalysts remains a significant challenge. Recent experimental breakthroughs in the synthesis of two-dimensional bilayer borophene provide a theoretical framework for exploring their physical and chemical properties. In this study, we systematically considered nine types of bilayer borophenes as potential electrocatalysts for the hydrogen evolution reaction. Our first-principles calculations revealed that bilayer borophenes exhibit high stability and excellent conductivity, possessing a relatively large specific surface area with abundant active sites. Both surface boron atoms and the bridge sites between two boron atoms can serve as active sites, displaying high activity for the hydrogen evolution reaction. Notably, the Gibbs free energy change associated with adsorption for these bilayer borophenes can reach as low as ‒0.002 eV, and the Tafel reaction energy barriers are lower (0.70 eV) than those on Pt. Moreover, the hydrogen evolution reaction activity of these two-dimensional bilayer borophenes can be described by engineering their work function. Additionally, we considered the effect of pH on hydrogen evolution reaction activity, with significant activity observed in an acidic environment. These theoretical results reveal the excellent catalytic performance of two-dimensional bilayer borophenes and provide crucial guidance for the experimental exploration of multilayer boron for various energy applications.
The chemical equilibrium equations utilized in reactive transport modeling are complex and nonlinear, and are typically solved using the Newton-Raphson method. Although this algorithm is known for its quadratic convergence near the solution, it is less effective far from the solution, especially for ill-conditioned problems. In such cases, the algorithm may fail to converge or require excessive iterations. To address these limitations, a projected Newton method is introduced to incorporate the concept of projection. This method constrains the Newton step by utilizing a chemically allowed interval that generates feasible descending iterations. Moreover, we utilize the positive continuous fraction method as a preconditioning technique, providing reliable initial values for solving the algorithms. The numerical results are compared with those derived using the regular Newton-Raphson method, the Newton-Raphson method based on chemically allowed interval updating rules, and the bounded variable least squares method in six different test cases. The numerical results highlight the robustness and efficacy of the proposed algorithm.
To enhance the fire safety and wear resistance of epoxy, phosphorus-containing nickel phyllosilicate whiskers (FP-NiPS) were synthesized using a facile hydrothermal technology, with 9,10-dihydro-9-oxa-10-phosphaphenanthrene as the organic modifier. The impacts of FP-NiPS on the thermal stability, flame retardancy, and mechanical and tribological properties of EP composites were explored. The findings demonstrated that 5 wt % FP-NiPS elevated the limiting oxygen index of the EP composite from 23.8% to 28.4%, achieving a V-0 rating during vertical burning tests. FP-NiPS could enhance the thermal stability of epoxy resin (EP) and facilitate the development of a dense and continuous carbon layer, thereby significantly improving the fire safety of the EP composites. The FP-NiPS led to an 8.2% increase in the tensile strength and a 38.8% increase in the elastic modulus of the EP composite, showing outstanding mechanical properties. Furthermore, FP-NiPS showed remarkable potential in enhancing the wear resistance of EP. The wear rate of 1 wt % FP-NiPS is 2.34 × 10−5 mm3·N–1·m–1, a decrease of 66.7% compared to EP. This work provides a novel promising modification method to enhance the fire safety, mechanical and wear resistance properties of EP.
Electrochemical CO2 reduction is a sustainable approach in green chemistry that enables the production of valuable chemicals and fuels while mitigating the environmental impact associated with CO2 emissions. Despite its several advantages, this technology suffers from an intrinsically low CO2 solubility in aqueous solutions, resulting in a lower local CO2 concentration near the electrode, which yields lower current densities and restricts product selectivity. Gas diffusion electrodes (GDEs), particularly those with tubular architectures, can solve these issues by increasing the local CO2 concentration and triple-phase interface, providing abundant electroactive sites to achieve superior reaction rates. In this study, robust and self-supported Cu flow-through gas diffusion electrodes (FTGDEs) were synthesized for efficient formate production via electrochemical CO2 reduction. They were further compared with traditional Cu electrodes, and it was found that higher local CO2 concentration due to improved mass transfer, the abundant surface area available for the generation of the triple-phase interface, and the porous structure of Cu FTGDEs enabled high formate Faradaic efficiency (76%) and current density (265 mA·cm–2) at –0.9 V vs. reversible hydrogen electrode (RHE) in 0.5 mol·L–1 KHCO3. The combined phase inversion and calcination process of the Cu FTGDEs helped maintain a stable operation for several hours. The catalytic performance of the Cu FTGDEs was further investigated in a non-gas diffusion configuration to demonstrate the impact of local gas concentration on the activity and performance of electrochemical CO2 reduction. This study demonstrates the potential of flow-through gas-diffusion electrodes to enhance reaction kinetics for the highly efficient and selective reduction of CO2, offering promising applications in sustainable electrochemical processes.
Surface engineering and Cu valence regulation are essential factors in improving the C2 selectivity during the electrochemical reduction of CO2. Herein, we present a sea urchin-like CuO/Cu2O catalyst derived from rhombic dodecahedra Cu2O through one-step oxidation/etching method where the mixed Cu+/Cu0 states are formed via in situ reduction during electrocatalysis. The combined effects of the morphology and the mixed Cu+/Cu0 states on C–C coupling are evaluated by the Faradaic efficiency of C2 and the C2/C1 ratio obtained in an H-cell. R-CuO/Cu2O exhibited 49.5% Faradaic efficiency of C2 with a C2/C1 ratio of 3.1 at −1.4 V vs. reversible hydrogen electrode, which are 1.5 and 3.2 times higher than those of R-Cu2O, respectively. Using a flow-cell, 68.0% Faradaic efficiency of C2 is achieved at a current density of 500 mA·cm−2. The formation of the mixed Cu+/Cu0 states was confirmed by in situ Raman spectra. Additionally, the sea urchin-like structure provides more active sites and enables faster electron transfer. As a result, the excellent C2 production on R-CuO/Cu2O is primarily attributed to the synergistic effects of the sea urchin-like structure and the stable mixed Cu+/Cu0 states. Therefore, this work presents an integrated strategy for developing Cu-based electrocatalysts for C2 production through electrochemical CO2 reduction.
Cerium dioxide (CeO2) photocatalysts are used in treating environmental pollution and addressing the energy crisis due to their excellent oxygen storage capacities and abundant oxygen vacancies. In this paper, CeO2 precursors were synthesized with different water-alcohol ratios via a solvothermal method, and CeO2 photocatalysts with different Ce3+/Ce4+ ratios were obtained by changing the precursor calcination atmospheres (air, Ar) as well as the calcination time. The effects of CeO2 with different Ce3+/Ce4+ ratios in photocatalytic degradations of methylene blue under visible light were investigated. X-ray photoelectron spectroscopy results showed that the surfaces of the samples calcined under Ar had higher Ce3+/Ce4+ ratios and oxygen vacancy concentrations, which reduced the band gaps of the catalysts and improved their utilization of visible light. In addition, the many Ce3+/Ce4+ redox centers and oxygen vacancies on the sample surfaces improved the separation and transfer efficiencies of the photogenerated carriers. The sample C2-Ar calcined under Ar showed a high adsorption capacity and excellent photocatalytic activity by removing 96% of the methylene blue within 120 min, which was more than twice the degradation rate of the sample (C2-air) prepared via calcination under air. Trapping experiments showed that photogenerated holes played a key role in the photocatalytic process. In addition, a synergistic photocatalytic mechanism for the Ce3+/Ce4+ redox centers and oxygen vacancies was elucidated in detail, and the sensitization of cerium dioxide by dyes aided the degradation of methylene blue.
A nitrogen-doped carbon microsphere sorbent with a hierarchical porous structure was synthesized via aggregation-hydrothermal carbonization. The Hg0 adsorption performance of the nitrogen-doped carbon microsphere sorbent was tested and compared with that of the coconut shell activated carbon prepared in the laboratory. The effect of H2S on Hg0 adsorption was also investigated. The nitrogen-doped carbon microsphere sorbent exhibited superior mercury removal performance compared with that of coconut shell activated carbon. In the absence of H2S at a low temperature (≤ 100 °C), the Hg0 removal efficiency of the nitrogen-doped carbon microsphere sorbent exceeded 90%. This value is significantly higher than that of coconut shell activated carbon, which is approximately 45%. H2S significantly enhanced the Hg0 removal performance of the nitrogen-doped carbon microsphere sorbent at higher temperatures (100–180 °C). The hierarchical porous structure facilitated the diffusion and adsorption of H2S and Hg0, while the nitrogen-containing active sites significantly improved the adsorption and dissociation capabilities of H2S, contributing to the generation of more active sulfur species on the surface of the nitrogen-doped carbon microsphere sorbent. The formation of active sulfur species and HgS on the sorbent surface was further confirmed using X-ray photoelectron spectroscopy and Hg0 temperature-programmed desorption tests. Density functional theory was employed to elucidate the adsorption and transformation of Hg0 on the sorbent surface. H2S adsorbed and dissociated on the sorbent surface, generating active sulfur species that reacted with gaseous Hg0 to form HgS.
The selective oxidation of cyclohexane to cyclohexanone and cyclohexanol (KA oil) is a challenging issue in the chemical industry. At present the industrial conversion of cyclohexane to cyclohexanone and cyclohexanol is normally controlled at less than 5% selectivity. Thus, the development of highly active and stable catalysts for the aerobic oxidation of cyclohexane is necessary to overcome this low-efficiency process. Therefore, we have developed a cobalt-nitrogen co-doped porous sphere catalyst, Co-NC-x (x is the Zn/Co molar ratio, where x = 0, 0.5, 1, 2, and 4) by pyrolyzing resorcinol-formaldehyde resin microspheres. It achieved 88.28% cyclohexanone and cyclohexanol selectivity and a cyclohexane conversion of 8.88% under Co-NC-2. The results showed that the introduction of zinc effectively alleviated the aggregation of Co nanoparticles and optimized the structural properties of the material. In addition, Co0 and pyridinic-N are proposed to be the possible active species, and their proportion efficiently increased in the presence of Zn2+ species. In this study, we developed a novel strategy to design highly active catalysts for cyclohexane oxidation.
The use of fossil fuels results in significant carbon dioxide emissions. Biofuels have been increasingly adopted as sustainable alternatives to fossil fuel to address this environmental issue. Integrating petroleum refineries into biofuel supply chains is an effective approach to mitigating greenhouse gas emissions and improving environmental sustainability. In this study, an integrated supply chain optimization framework was established, considering the carbon trade policy. In addition, a mixed-integer nonlinear programming model was developed to optimize the selection of biomass suppliers, construction of pretreatment plants and biorefineries, integration of petroleum refineries, and selection of transportation routes with the objective of minimizing the total annual cost. An example is presented to illustrate the applicability of the model. The optimization results show that integrating petroleum refineries into biofuel supply chains effectively mitigates carbon emissions. Carbon trade policies can have a direct impact on the total annual cost and carbon emissions of the supply chain.
