EES catalysis最新文献

Sequestering greenhouse gases (CO₂ and CH₄) in biogas into carbon nanofibers (CNF) offers a promising route to mitigate carbon emissions and create value-added solid carbon materials. Coupling non-thermal plasma with a thermocatalytic reactor in a tandem setup is a promising approach for tandem reactions of dry reforming of methane to synthesis gas and its subsequent conversion to CNF. Various parameters were studied to determine their effects on CNF growth. Decreasing the total flow rate resulted in an increase in CNF growth. Increasing the plasma power input or the plasma zone length also enhanced the production of CNF. These results illustrate that plasma-thermal tandem reactors can be used to synthesize CNF from biogas with tunable parameters that may be further optimized in future studies.

Scaling up gas-phase heterogeneous photocatalysis requires the development of high-efficiency, cost-effective photoreactors that maximize photon capture while minimizing parasitic light losses. The integration of photocatalysis with fluidized bed technology enhances light penetration, improves particle–light interactions, and facilitates mass and heat transfer. To elucidate the mechanisms behind enhanced light absorption in a photofluidized bed reactor (PFBR), we employed CFD-DEM simulations and ray tracing to model the absorption characteristics of fluidized particles. Compared to fixed-bed systems, fluidized beds demonstrated significantly improved light absorption, particularly for particles with lower intrinsic absorptivity. The effects of particle size and gas flow rate on light absorption were also analyzed. Experimental validation was conducted using a solar-driven reverse Boudouard reaction, demonstrating the photochemistry of fluidized carbon particles in a carbon dioxide flow within an annular quartz tube reactor, and facilitating carbon monoxide production. At experimentally low gas flow rates, the PFBR exhibited enhanced photocatalytic performance. Furthermore, a comparative analysis of thermochemical and photochemical performance between fluidized and fixed beds highlighted the remarkable solar advantages of PFBRs. The results underscore the advantages of fluidized bed reactors in achieving uniform mixing of reactant gases, particles, and light under isothermal, isobaric, and isophotonic reaction conditions, demonstrating their potential for scalable solar-driven catalytic processes.

Anion-exchange-membrane water electrolyzers (AEMWE) for hydrogen production have attracted interest because cost-effective Ni- and Fe-based catalysts can be used for the oxygen evolution reaction (OER). Although NiFe oxide/hydroxide-based catalysts have been extensively studied, the role of Fe and its chemical state during OER are not well understood, with inconsistent findings across different studies. In this work, we combined in situ⁵⁷Fe Mössbauer (MS) and X-ray absorption spectroscopy (XAS) to investigate the chemical states of Fe and Ni and elucidate their synergy during the OER. A NiFe (8 : 1 molar ratio) aerogel catalyst with high surface area, nano crystallinity, and high performance in AEMWE was used. We show that both Fe and Ni are oxidized during anodic polarization, and the potential for the change of oxidation states correlates well with the onset of the OER. In situ MS shows that 80–90% of Fe³⁺ becomes tetravalent at OER potentials and remains so even after the potential is lowered below OER onset. Analysis of in situ XAS results suggests full Fe incorporation into Ni hydroxide. At OER potentials, lattice contraction indicates high oxidation states for both Ni and Fe. Upon returning to lower potentials, a portion of the Fe remains in its more oxidized form which corroborates the in situ MS findings. Results from this work affirm the importance of high-valent Ni and Fe in promoting the OER. Ni and Fe exhibit synergy during OER and the aerogel's unique nanomorphology leads to high OER activity.

CoO, as a typical water oxidation electrocatalyst, has gradually entered the bottleneck stage of performance modulation through composition optimization. Herein, the N, Fe co-bonded CoO was achieved by N plasma, which suggests further potential to be enhanced by a magnetic field during oxygen evolution reaction (OER) electrocatalysis. N atoms are a bridge for bonding Fe and Co centers, which serve as a fast channel for electron transfer. N, Fe co-doping decreases the electron density around Co²⁺ centers, which increases the unpaired electrons for electron acceptors. As a result, the intrinsic OER activities are boosted, which is further beneficial for amplifying the magnetic enhancement effect. The best performance emerges under a parallel magnetic field with 420 mT intensity, which results in a lowered overpotential of 217 mV and a Tafel slope of 25.1 mV dec⁻¹ in alkaline media. The magnetic enhancement comes from the magnetohydrodynamic effect and the escape energy barrier reduction of the paramagnetic triplet state of O₂. The magnetic enhancement effect would be amplified when the catalytic current becomes larger (magnetic current is 8 mA and 22 mA under 500 mA and 1000 mA total current, respectively). This work provides an in-depth insight into the magnetic enhancing mechanism and a highly feasible strategy for coupling heteroatoms with the magnetic field to operate and break through the bottleneck of non-noble electrocatalysis performance.

Electroreduction of carbon dioxide and carbon monoxide to organic compounds is considered a promising way for (i) exploring a source of carbon alternative to fossil carbon; (ii) storing electrical energy as stable chemical energy; and (iii) producing useful e-chemicals and e-fuels for the chemical industry. While it is generally considered that only Cu-based catalysts facilitate the formation of multicarbon compounds, which are mainly limited to ethylene and ethanol, recent studies have challenged this assumption. In this review, we provide exhaustive, structural and mechanistic analyses of the solid materials that have been reported as catalysts for electroreduction of CO₂ and CO to more complex molecules. This review elucidates that besides copper, metals such as nickel, iron and molybdenum have the potential to favor C–C coupling reactions to form important molecules in the chemical industry, such as propane, propanol, and butanol, along with offering substantial faradaic efficiencies. Thus, this review offers fresh perspectives on CO₂R and COR.

The direct electrolysis of liquid anhydrous ammonia (NH₃(l), >99.99% of NH₃, free of water and solvent) is demonstrated using a 25 cm² zero-gap electrolyzer, consisting of a Ru/C anode and a Pt/C cathode, with the two electrodes spatially separated by a cation exchange membrane. This system, supplied by NH₃(l) and NH₄Br as the supporting electrolyte, continuously produces high-purity and pressurized hydrogen (H₂, >99.99%, >5.5 bar) at a temperature of 10 °C and a pressure of 6.2 bar, without requiring H₂/N₂ separation and compression processes. The direct NH₃(l) electrolyzer exhibits a cell potential of 1.1 V at 0.1 A cm⁻², presenting a faradaic efficiency of >99.3% for H₂ production. The developed system achieves a H₂ production rate of >18.8 mol-H₂ g_cat⁻¹ h⁻¹ at 0.5 A cm⁻², which is 4.7-fold higher than the highest H₂ production rate reported to date for NH₃(g) thermolysis at temperatures of over 500 °C.

Electrochemical CO₂ reduction reaction (CO₂RR) has emerged as a promising strategy to convert CO₂ into value-added chemicals and fuels. While methane is especially desirable owing to its extensive use as a fuel, existing infrastructure, and large global market, the direct electroreduction of CO₂ to CH₄ is hindered by challenges such as low product purity and high overpotentials. In this study, an efficient cascade electrolysis and thermocatalysis system for the high-purity production of CH₄ from CO₂ has been demonstrated. Electrochemical syngas production was carried out using CO₂RR-active electrocatalysts, including Au₂₅ and Ag₁₄ nanoclusters (NCs). While both NCs exhibited high CO₂-to-CO activity in alkaline media, Ag₁₄ NCs enabled syngas production with a varying ratio (H₂/CO) by adjusting the CO₂ flow rate, achieving near-theoretical single-pass conversion efficiency (SPCE) of over 45% (theoretical limit = 50%). Electrokinetic analysis revealed that the strong CO₂ binding affinity and exceptional CO selectivity of Ag₁₄ NCs contribute to superior syngas tunability and carbon conversion efficiency. Electrochemically generated syngas (H₂/CO = 3) at 800 mA cm⁻² was directly fed into a thermocatalysis reactor, producing CH₄ with a purity exceeding 85%.

Perovskite oxides (ABO₃) are widely studied in oxygen electrocatalysis due to their simple synthesis routes, rich compositions, adjustable crystal/electronic structures, and high intrinsic activities. Despite these advantages, high calcination temperatures usually lead to agglomeration of perovskite materials, greatly reducing atomic utilization. Moreover, the different element features of A/B cations generally make easy enrichment of surface A-sites, and such surface deviation from the ideal structure would impede the precise illustration of structure–activity relationships for electrocatalysis. Up to now, various strategies have been developed to tackle the above issues, through which significant progress in both catalytic performance and underlying catalytic mechanisms has been achieved. Here we summarize those optimization methods as “disassembling and reassembling perovskites” and concisely review related studies and findings in terms of the fundamental understanding of approaches and the applications in oxygen electrocatalysis. Three typical methods, including physical, chemical, and electrochemical, are introduced with their effects on perovskite structures/catalytic mechanisms thoroughly discussed. Finally, four scientific issues regarding disassembling and reassembling perovskites are proposed for future studies. We aim to raise the community's awareness of this emerging approach and hope it could contribute to material design for applications beyond oxygen electrocatalysis.

Despite extensive efforts to optimize the single-step production of syngas, hydrocarbons, and oxygenates via plasma catalysis, several challenges remain unresolved. In particular, understanding the various reaction pathways is hindered by the complexity of the reactions and the diverse range of chemical products formed. In this study, our main objective is to evaluate and compare the influence of zirconia on reaction pathways, methane (CH₄) and carbon dioxide (CO₂) conversions (%), and syngas selectivity (%) relative to the plasma-only route. Experiments were conducted at a low radio-frequency plasma power of 50 Watts without external heating. The results demonstrated significantly enhanced conversions of carbon dioxide and methane when the reaction chamber was packed with zirconia (ZrO₂). Methane conversion was observed to be the highest at a rich CO₂ feed [CO₂ : CH₄ (2 : 1)], while plasma only revealed conversion of 20.1%. After packing with zirconia, the conversion increased to 71.2% (3.5 times increment). On the other hand, carbon dioxide conversions were also observed to be the highest at a feed composition of CO₂ : CH₄ (2 : 1), with plasma only (13.6%) vs. with zirconia packing (60.9%) revealing a 4.4 times increase. Interestingly, at the rich CO₂ feed composition, the syngas product (CO + H₂) selectivity increased after packing ZrO₂ by 1.1 times for CO and 1.2 times for H₂. Optical emission spectroscopy (OES) analysis revealed important insights into the gas phase, with signatures of atomic oxygen (O) being the dominant plasma species in the gas phase under plasma-only conditions, while their intensities plummeted when zirconia was introduced, indicating active oxygen diffusion onto the surface of zirconia. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed important surface alterations after plasma exposure and most importantly provided experimental proof on zirconia's oxygen mobility. These findings provided an integral perspective into the design of catalytic materials that enhance oxygen mobility, enabling low-temperature and energy-efficient dry methane reforming for a sustainable future.

Ni and Mo atom pairs as single sites supported on N-doped graphitic carbon was prepared by pyrolysis of a mixture of Ni(NO₃)₂, (NH₄)₆Mo₇O₂₄, glucose, and melamine at 800 °C and subsequent washing with HCl. Coulombic association between Ni²⁺ and Mo₇O₂₄⁶⁻ is key for the formation of the Ni–Mo pairs (distance: 0.23 nm), whose presence was determined by atomic resolution aberration-corrected STEM and EXAFS. The dual NiMo-DASC exhibits better performance for urea formation by simultaneous electrochemical CO₂ and NO₃⁻ reduction reactions than the Ni- or Mo-single atom catalysts on N-doped graphitic carbon prepared analogously at similar total metal loadings and surface areas. Using pulsed electrochemical reduction of −0.5 V vs. RHE for NO₃RR and −0.7 V vs. RHE to promote CO₂RR, urea was formed with a faradaic efficiency of 31.8% and a yield of 11.3 mmol h⁻¹ g⁻¹. The sources of C and N were confirmed by isotopic ¹³C and ¹⁵N labelling experiments using NMR spectroscopy. In situ surface enhanced IR spectroscopy shows the appearance of adsorbed *CO (1937 cm⁻¹), *NH species (1636 cm⁻¹) and C–N (1597 cm⁻¹) vibration bands. DFT calculations of the Ni–Mo pair on N-doped graphene model predict a distance of 0.22 nm between the two metal atoms and suggest that the synergistic effect is derived from co-the adsorption of CO₂, preferentially on the Ni atom, and NO₃⁻ on the Mo atom, with the crucial C–N bond formation occurring between neighbor CO (on Ni) and NH (on Mo), thereby showing the synergistic effect arising from the presence of Ni and Mo at the catalytic site.