One-Step Reforming of CO2 and CH4 into High-Value Liquid Chemicals and Fuels at Room Temperature by Plasma-Driven Catalysis

Solution-plasma interaction for synthesizing highly active Pt-Ni alloy oxygen reduction nanocatalysts for PEMFCs

A highly active PtNi-alloy catalyst (p-PtNi/KB) is synthesized using solution-plasma interaction. The plasma effect results in a substantial increase of active sites on the support surface. This facilitates the alloying and functionalization of supports, enabling achievement of enhanced catalytic activity and effective resolution of cost-related challenges in fuel cells.

Non-thermal plasma-catalytic processes for CO2 conversion toward circular economy: fundamentals, current status, and future challenges

Practical and energy-efficient carbon dioxide (CO2) conversion to value-added and fuel-graded products and transitioning from fossil fuels are promising ways to cope with climate change and to enable the circular economy. The carbon circular economy aims to capture, utilize, and minimize CO2 emissions as much as possible. To cope with the thermodynamic stability and highly endothermic nature of CO2 conversion via conventional thermochemical process, the potential application of non-thermal plasma (NTP) with the catalyst, i.e., the hybrid plasma catalysis process to achieve the synergistic effects, in most cases, seems to promise alternatives under non-equilibrium conditions. This review focuses on the NTP fundamentals and comparison with conventional technologies. A critical review has been conducted on the CO2 reduction with water (H2O), methane (CH4) reduction with CO2 to syngas (CO + H2), CO2 dissociation to carbon monoxide (CO), CO2 hydrogenation, CO2 conversion to organic acids, and one-step CO2-CH4 reforming to the liquid chemicals. Finally, future challenges are discussed comprehensively, indicating that plasma catalysis has immense investigative areas.

Long-Chain Hydrocarbons from Nonthermal Plasma-Driven Biogas Upcycling

The burgeoning necessity to discover new methodologies for the synthesis of long-chain hydrocarbons and oxygenates, independent of traditional reliance on high-temperature, high-pressure, and fossil fuel-based carbon, is increasingly urgent. In this context, we introduce a nonthermal plasma-based strategy for the initiation and propagation of long-chain carbon growth from biogas constituents (CO2 and CH4). Utilizing a plasma reactor operating at atmospheric room temperature, our approach facilitates hydrocarbon chain growth up to C40 in the solid state (including oxygenated products), predominantly when CH4 exceeds CO2 in the feedstock. This synthesis is driven by the hydrogenation of CO2 and/or amalgamation of CHx radicals. Global plasma chemistry modeling underscores the pivotal role of electron temperature and CHx radical genesis, contingent upon varying CO2/CH4 ratios in the plasma system. Concomitant with long-chain hydrocarbon production, the system also yields gaseous products, primarily syngas (H2 and CO), as well as liquid-phase alcohols and acids. Our finding demonstrates the feasibility of atmospheric room-temperature synthesis of long-chain hydrocarbons, with the potential for tuning the chain length based on the feed gas composition.

Plasma-Assisted Reforming of Methane

Methane (CH4 ) is inexpensive, high in heating value, relatively low in carbon footprint compared to coal, and thus a promising energy resource. However, the locations of natural gas production sites are typically far from industrial areas. Therefore, transportation is needed, which could considerably increase the sale price of natural gas. Thus, the development of distributed, clean, affordable processes for the efficient conversion of CH4 has increasingly attracted people's attention. Among them are plasma technology with the advantages of mild operating conditions, low space need, and quick generation of energetic and chemically active species, which allows the reaction to occur far from the thermodynamic equilibrium and at a reasonable cost. Significant progress in plasma-assisted reforming of methane (PARM) is achieved and reviewed in this paper from the perspectives of reactor development, thermal and nonthermal PARM routes, and catalysis. The factors affecting the conversion of reactants and the selectivity of products are studied. The findings from the past works and the insight into the existing challenges in this work should benefit the further development of reactors, high-performance catalysts, and PARM routes.

One-step direct conversion of methane to methanol with water in non-thermal plasma

Achieving methane-to-methanol is challenging under mild conditions. In this study, methanol is synthesized by one-step direction conversion of CH₄ with H₂O at room temperature under atmospheric pressure in non-thermal plasma (NTP). This route is characterized by the use of methane and liquid water as the reactants, which enables the transfer of the methanol product to the liquid phase in time to inhibit its further decomposition and conversion. Therefore, the obtained product is free of carbon dioxide. The reaction products include gas and liquid-phase hydrocarbons, CO, CH₃OH, and C₂H₅OH. The combination of plasma and semiconductor materials increases the production rate of methanol. In addition, the addition of Ar or He considerably increases the production rate and selectivity of methanol. The highest production rate of methanol and selectivity in liquid phase can reach 56.7 mmol g_cat^-1 h^-1 and 93%, respectively. Compared with the absence of a catalyst and added gas, a more than 5-fold increase in the methanol production rate is achieved.

Excess CO2 Reductions during CH3COOH Formation from CH4 and CO2 under Periodic Operation: Downhill Side Reactions in an Uphill Target Reaction under Unsteady Conditions

Acetic acid (CH3COOH) formation from methane (CH4) and carbon dioxide (CO2) is an ideal reaction for chemical production, whereas this reaction possesses a severe thermodynamic limitation. To address this issue, it has been reported that periodic operation allowing a non-equilibrium condition can overcome the thermodynamic limitation. However, although an intrinsic issue of uphill reactions in non-equilibrium conditions generally is occurrence of unfavorable downhill reactions, this issue has seldom been discussed for the CH3COOH formation under periodic operation. Herein, excess CO2 reductions were found to be the unfavorable downhill reactions possibly occurring in the reaction aiming at CH3COOH formation under periodically operated CH4 and CO2 feeds. The reaction using an isotopic reactant (i.e., 13CH4 ) unveiled that excess CO2 reductions to CO and even to CH3 moiety could occur, indicating importance of catalyst development. Furthermore, it was proposed that H2 O vapor introduction into the CO2 feed, which increased the CH3COOH product, most likely facilitated the reverse reaction of the excess CO2 reductions and thereby is effective to hamper the unfavorable side reaction.

High-Performance Plasma-Enabled Biorefining of Microalgae to Value-Added Products

Conversion of renewable biomass by time- and energy-efficient techniques remains an important challenge. Herein, plasma catalytic liquefaction (PCL) is employed to achieve rapid liquefaction of microalgae under mild conditions. The choice of the catalyst affects both the liquefaction efficiency and the yield of products. The acid catalyst is more effective and gave a liquid yield of 73.95 wt % in 3 min, as opposed to 69.80 wt % obtained with the basic catalyst in 7 min. Analyses of the thus-formed products and the processing environment reveal that the enhanced PCL performance is linked to the rapid increase in temperature under the effect of plasma-induced electric fields and the generation of large quantities of reactive species. Moreover, the obtained solid residue can be simply upgraded to a carbon product suitable for supercapacitor applications. Therefore, the proposed strategy may provide a new avenue for fast and comprehensive utilization of biomass under benign conditions.

Direct Conversion of Methane with Carbon Dioxide Mediated by RhVO3 - Cluster Anions

Direct conversion of methane with carbon dioxide to value-added chemicals is attractive but extremely challenging because of the thermodynamic stability and kinetic inertness of both molecules. Herein, the first dinuclear cluster species, RhVO₃ ^- , has been designed to mediate the co-conversion of CH₄ and CO₂ to oxygenated products, CH₃ OH and CH₂ O, in the temperature range of 393-600 K. The resulting cluster ions RhVO₃ CO^- after CH₃ OH formation can further desorb the [CO] unit to regenerate the RhVO₃ ^- cluster, leading to the successful establishment of a catalytic cycle for methanol production from CH₄ and CO₂ (CH₄ +CO₂ →CH₃ OH+CO). The exceptional activity of Rh-V dinuclear oxide cluster (RhVO₃ ^- ) identified herein provides a new mechanism for co-conversion of two very stable molecules CH₄ and CO₂ .

Selective light absorber-assisted single nickel atom catalysts for ambient sunlight-driven CO2 methanation

Ambient sunlight-driven CO₂ methanation cannot be realized due to the temperature being less than 80 °C upon irradiation with dispersed solar energy. In this work, a selective light absorber was used to construct a photothermal system to generate a high temperature (up to 288 °C) under weak solar irradiation (1 kW m⁻²), and this temperature is three times higher than that in traditional photothermal catalysis systems. Moreover, ultrathin amorphous Y₂O₃ nanosheets with confined single nickel atoms (SA Ni/Y₂O₃) were synthesized, and they exhibited superior CO₂ methanation activity. As a result, 80% CO₂ conversion efficiency and a CH₄ production rate of 7.5 L m⁻² h⁻¹ were achieved through SA Ni/Y₂O₃ under solar irradiation (from 0.52 to 0.7 kW m⁻²) when assisted by a selective light absorber, demonstrating that this system can serve as a platform for directly harnessing dispersed solar energy to convert CO₂ to valuable chemicals.

While light-driven CO₂ methanation provides a renewable means to upgrade waste emissions, the sunlight is insufficient to drive high temperature CO₂ methanation. Here, authors prepare single-atom Ni on Y₂O₃ with a selective light absorber for ambient-sunlight-driven photothermal CO₂ methanation.

Activation of CO2 in Photoirradiated CO2-H2O Clusters: Direct Ab Initio Molecular Dynamics (MD) Study

Carbon dioxide (CO₂) is one of the stable and inactive molecules that contribute to greenhouse gases. The development of new reactions of CO₂ activation, chemical fixation, and conversion is a very important issue. In this report, the reactions of CO₂-H₂O binary clusters were investigated using a direct ab initio molecular dynamics (AIMD) method to find a new reaction of CO₂ activation. Clusters composed of carbon dioxide and water molecules, CO₂(H₂O) _n ( n = 2-5), were utilized as a model of the binary cluster. The reaction dynamics of [CO₂(H₂O) _n]⁺ following the ionization of parent neutral clusters were also investigated. Two electronic states of [CO₂(H₂O) _n]⁺ were examined for direct AIMD surfaces: CO₂[(H₂O) _n]⁺ (ground state) and (CO₂)⁺(H₂O) _n (excited charge transfer (CT) state). After the ionization of the clusters, a proton-transfer (PT) reaction occurred within the (H₂O) _n⁺ moiety at the ground state, whereas the reactive HCO₃ radical was formed at the CT state for OH addition to CO₂⁺: CO₂⁺(H₂O) _n → HCO₃ + H⁺(H₂O) _n-1. The mechanisms of the PT process and the HCO₃ radical formation were discussed based on the theoretical results.