CO Conversion Rate Research Articles

Exploiting Co-C interface and graphitic carbon belts for enhanced structural stability of a porous layered Co-C catalyst for CO2 hydrogenation

Addressing the urgent need for efficient CO2 reduction, a novel Co@C catalyst was synthesized through the pyrolysis of a unique layered metal–organic framework (MOF), featuring tunable thickness, pore sizes. The CO2 hydrogenation performance demonstrates an enhancement by an optimized structure that significantly improves stability, maintaining a 25% CO2 conversion rate over an extended 80-hour period. The catalyst's composite structure exhibits a dual-confinement effect, where the Co-C interface and graphitic carbon belt stabilize Co nanoparticles, preventing sintering during reaction cycles. This study delves into the structural modifications necessary for catalytic optimization in CO2 hydrogenation, offering valuable insights for designing efficient catalysts for CO2 reduction and advancing sustainable energy solutions.

Coupling electron donors with proton repulsion via Pt-N3-S sites to boost CO2 reduction in CO2/H2 fuel cell

A fuel cell involving CO2/H2 is an appealing energy system to convert CO2 into synthetic fuels as well as to generate electricity using only waste heat. However, overcoming the inherent activation barrier of CO2 to improve the CO2 conversion rate in CO2/H2 fuel cell is still challenging. Herein, we report a synergistic electron-donor and proton-repulsion group composed of Pt-N3-S-C sites to simultaneously modulate the electronic structure and CO2-protonation ability of Ru nanoclusters (RuNC) in RuNC/Pt-N3-S-C catalyst. Experiments combined with theoretical calculations indicate that Pt-N3-S sites not only function as electron donors to Ru nanoclusters to cooperatively induce the orbital hybridization of Ru 3d and the antibonding orbitals of CO2, affording the dissociation of CO bonds in CO2, but also as electronic structure “modulator” to create new active sites on the surface of RuNC to effectively activate molecular CO2. More importantly, an internal polarization field between Pt-N3-S-C and RuNC additionally makes single atom Pt sites repel protons while Ru atoms serve as proton capturers via hydrogen spillover effect, resulting in accelerated protonation of CO2. Consequently, the catalyst exhibits highly improved catalytic activities for CO2 reduction with a conversion rate of 559.1 μmol gcat−1 h−1. This approach helps with fine tuning the electronic structures and catalytic CO2 protonation ability of catalysts for thermal-coupled electrocatalysis.

Optimization of syngas production via methane bi-reforming using CeO2 promoted Cu/MnO2 catalyst

Currently, syngas plays an important role in renewable and sustainable energy production. The idea of manufacturing syngas via bi-reforming methane, which involves the combination of methane (CH4), carbon dioxide (CO2), and steam, appears very promising. As a result, the goal of this research is to improve syngas output by improving process parameters in methane bi-reforming using a 3%Ce-15%Cu/MnO2 catalyst. Optimization analysis was performed using response surface methodology (RSM). The ultrasonic impregnation (UI) method was employed to synthesize the catalysts used in this study. Following that, the catalyst was characterized using several techniques such as Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption (TPD), and temperature programmed oxidation (TPO). The findings of the characterization show that the presence of CeO2 promoters has a dual effect on the size of CuO crystallites. Firstly, it reduces the size from 19.07 nm to 13.66 nm because to the dilutive effect generated by the inclusion of CeO2. Second, the presence of CeO2 promoter accelerates the transition from CuO to Cu0 metallic phase. Furthermore, the addition of CeO2 boosts the CH4 and CO2 conversion rates by 23.65% and 24.93%, respectively. As a result, the H2 yield increases significantly when compared to the unpromoted catalyst. The study investigates the influence of process parameters, specifically the reaction temperature (700–900℃), CO2 ratio (0.2–1), and gas hourly space velocity (GHSV) (16–36 L g cat−1 hr−1), on the conversion of CH4 and CO2, as well as the H2/CO ratio. The optimization study finds that the highest conversion rates for CH4 and CO2 are 78.32% and 72.45%, respectively, when the reaction temperature is 800 °C, the CO2 ratio is 0.6, and the gas hourly space velocity (GHSV) is 26 L g cat−1 hr−1. The optimum conditions result in the highest syngas ratio of 1.77. The results of the optimization are then assessed using the mean errors. The H2/CO ratio, as well as the average errors for CH4 and CO2 conversions, are discovered to be 0.15%, 0.95%, and 0%, respectively.

Non-Photochemical Origin of Selectivity Difference between Light and Dark Catalytic Conditions.

The interest in introducing light into heterogeneous catalysis is driven not only by the urgent need of replacing fossil energy but also by the promise of controlling product selectivity by light. The product selectivity differences observed in recent studies between light and dark reactions are often attributed to photochemical effects. Here, we report the discovery of a non-photochemical origin of selectivity difference, at essentially the same CO2 conversion rate, between photothermal and thermal CO2 hydrogenation reactions over a Ru/TiO2-x catalyst. While the presence of the photochemical effect from ultraviolet light is confirmed, it merely enhances the catalytic activity. Systematic investigation reveals that the gradual formation of an adsorbate-mediated strong metal-support interaction under catalytic conditions is responsible for the variation in the catalytic selectivity. We demonstrate that differences in product selectivity under light/dark reactions do not necessarily originate from photochemical effects. Our study refines the basis for determining photochemical effects and highlights the importance of excluding non-photochemical effects in mechanistic studies of light-controlled product selectivity.

Enhanced Methane Dry Reforming with Ni/SiO2 Catalysts Featuring Hierarchical External Nanostructures

Global energy demand escalates the interest in effective and durable catalytic systems for the dry reforming of methane (DRM), a process that converts CO2/CH4 into H2/CO syngas. Porous silica-supported nickel (Ni) catalysts are recognized as a promising candidate due to robust DRM activity associated with the confinement of Ni particles in the mesopores that reduces the catalyst deactivation by carbon byproduct deposits and sintering of active Ni sites. However, the small-sized pore configurations in the mesoporous catalysts hinders the fast mass transfer of reactants and products. A unique combination of the hierarchical nanostructure with macro–mesoporous features of the support is adopted to enhance the catalytic performance via the dual effect of the efficient mass transfer and minimized sintering issue. This study delves into the influence of SiO2 geometry and pore structure on the catalytic performance of Ni-based catalysts. Three types of porous silica supports were synthesized through various methods: (a) hydrothermal-assisted sol–gel for dendritic mesoporous silica (DMS), (b) spray-pyrolysis-assisted sol–gel for spray evaporation-induced self-assembly (EISA) silica, and (c) oven-assisted sol–gel for oven EISA silica. Among the prepared catalysts the hierarchical external nanostructured Ni/DMS showed the superior CH4 and CO2 conversion rates (76.6% and 82.1%), even at high space velocities (GHSV = 360 L∙g−1·h−1). The distinctive macro–mesoporous geometry effectively prevents the sintering of Ni particles and promotes the smooth diffusion of the reactants and products, thus improving catalytic stability over extended reaction periods (24 h). This research highlights the significant impact of macro–mesoporosity revealed in DMS support catalysts on the physicochemical properties of Ni/DMS and their crucial role in enhancing DRM reaction efficiency.

Defect-Induced All-Solid-State Frustrated Lewis Pair on Metal-Organic Monolayer Accelerating Photocatalytic CO2 Reduction with H2O Vapor.

Understanding the structure-performance relationships of a frustrated Lewis pair (FLP) at the atomic level is key to yielding high efficiency in activating chemically "inert" molecules into value-added products. A sound strategy was developed herein through incorporating oxygen defects into a Zr-based metal-organic layer (Zr-MOL-D) and employing Lewis basic proximal surface hydroxyls for the in situ formation of solid heterogeneous FLP (Zr4-δ-VO-Zr-OH). Zr-MOL-D exhibits a superior CO2 to CO conversion rate of 49.4 μmol g-1 h-1 in water vapor without any sacrificing agent or photosensitizer, which is about 12 times higher than that of pure MOL (Zr-MOL-P), with extreme stability even after being placed for half a year. Theoretical and experimental results reveal that the introduction of FLP converts the process of the crucial intermediate COOH* from an endothermic reaction to an exothermic spontaneous reaction. This work is expected to provide new prospects for developing efficient MOL-based photocatalysts in FLP chemistry through a sound defect-engineering strategy.

Surface tailoring on bifunctional CuOx/MnO2 catalyst to promote the selective catalytic reduction of NO with NH3 and oxidation of CO with O2

NO and CO are two primary pollutants in the sintering flue gas emission, posing significant challenges for the treatment. Under oxygen-enriched conditions, CO was easily oxidized to CO2 before participating in CO-SCR reaction as a reducing agent. Consequently, NH3-SCR technology coupled with CO oxidation reaction is a promising approach for simultaneous NO and CO removal. In this study, a series of bifunctional CuOx/MnO2 catalysts were synthesized using a combine of hydrothermal and wet impregnation methods, and their catalytic performance for simultaneous removal of NO and CO was assessed. CuOx/α-MnO2 catalyst displayed outstanding catalytic activity for both NO and CO, achieving over 80 % NO removal efficiency and 96 % CO conversion rate at 150 °C, while CuOx/β-MnO2 catalyst exhibited poor catalytic activity in the entire temperature range. Moreover, the interplay between the NH3-SCR and CO catalytic oxidation reactions was also explored. XPS results revealed that the concentration of Mn4+ and Cu+ species significantly influenced the catalytic activity of the catalysts for the simultaneous removal of NO and CO. Particularly, the presence of Mn4+ species promoted “fast SCR” reaction, whereas Cu+ species demonstrated higher reactivity for both NO reduction and CO oxidation. In situ DRIFTS analysis of transient reactions revealed that the L-H mechanism was followed over CuOx/α-MnO2 catalyst in the NH3-SCR reaction, while both the M-K and L-H mechanisms were observed in CO catalytic oxidation reaction.

Investigations on the Influence of Catalyst Geometry on Emission Reduction in Small‐Scale Combustion System

Legal regulations for exhaust gas treatment in small‐scale combustion systems demand both emission and dust reduction. Simultaneously removing both pollutants using catalysts presents a significant challenge due to constraints on the very low allowed pressure drop over the catalyst. It can be demonstrated that the total oxidation of CO, as one of the main pollutants in the combustion of biogenic materials, in small‐scale combustion systems can be quantitatively achieved using precious metal‐based catalysts based on Pt/CeO2/TiO2. The highest CO conversion rate can be observed with a 233 cpsi honeycomb catalyst, whereas the foam ceramic catalysts with 30, 20, and 10 ppi show progressively decreasing activity. However, concerning dust reduction, it can be demonstrated that the ceramic foam with 10 ppi is superior, as evidenced in real‐world experiments conducted on an Leda Novia W small‐scale combustion device with 8 kW combustion capacity. Particle deposition on the catalysts is observed with all catalysts, whereby catalysts with small pores show rapid pore blockage. It is observed that only with the 10 ppi foam catalyst, dust deposition does not lead to pore blockage, allowing a reduction in dust of more than 50% over the measurement cycle.

S-scheme heterojunction Cu-porphyrin/TiO2 nanosheets with highly efficient photocatalytic reduction of CO2 in ambient air

Directly capturing CO2 in ambient air and converting it into value-added fuels using photocatalysis is a potentially valuable technology. In this study, Cu-porphyrin (tetrakis-carboxyphenyl porphyrin copper, CuTCPP) was innovatively anchored on the surface of TiO2 (titanium dioxide) nanosheets to form an S-scheme heterojunction. Based on this, a photocatalytic reaction system for stably converting CO2 in ambient air into value-added fuels at the gas–solid interface was constructed without addition of sacrificial agents and alkaline liquids. Under the illumination of visible light and sunlight, the evolution rate of CO is 56 μmol·g−1·h−1 and 73 μmol·g−1·h−1, respectively, with a potential CO2 conversion rate of 35.8 % and 50.4 %. The enhanced of photocatalytic performance is attributed to the introduction of CuTCPP, which provides additional active sites, significantly improves capture capacity of CO2 and the utilization of electrons. Additionally, the formation of S-scheme heterojunction expands the redox range and improves the separation efficiency of photo-generated charges.

CO2 methanation over low-loaded Ni-M, Ru-M (M = Co, Mn) catalysts supported on CeO2 and SiC

The concentration of the major greenhouse gas CO2 is rapidly increasing in the atmosphere, leading to global warming and a range of environmental issues. An efficient circulation and utilization of CO2 is critical in the current environmental context. Methanation, an exothermic process, emerges as a critical strategy for effective CO2 utilization. On this front, there is a significant demand for rational design of catalysts that maintain high activity and methane selectivity over a wide temperature range (250–550 °C). The catalyst that can promise a consistent reaction even at 500 °C under an atmospheric pressure is thus obliged. The present study investigated bimetallic catalysts with SiC, which is known for its exceptional thermal conductivity, and CeO2, which is characterized by its CO₂ affinity, as base materials. We incorporated Ni-M and Ru-M (M = Co and Mn) as the active metals, each loaded at 2 %. Impressively, with merely 20 mg, the Ni-Co/SiC catalyst achieved a CO2 conversion rate of 77 % and CH₄ selectivity of 88 % at 500 °C, in a fixed-bed tubular reactor system with conditions of H2/CO2 = 4, a total flow rate of 70 ml min−1, and a steady GHSV of 12,000 h−1. Moreover, 2Ni-2Co/CeO2 catalyst demonstrated exceptional performance with a 76 % conversion of CO2 and a 83 % selectivity for CH4, all under identical conditions. The catalyst's durability was confirmed by a subsequent 40-hour stability test, which showed only a 3–5 % degradation. The developed catalysts were comprehensively characterized by BET/BJH, CO pulse chemisorption, H2-TPR, HAADF-STEM-EDS, SEM-EDS and XRD etc. to unveil their physicochemical and surface traits. It was found that Co and Mn, when integrated, effectively restrained the agglomeration of Ni and Ru particles, ensuring optimal metal dispersion on the support. In conclusion, our synthesized bimetallic catalysts shown a sustained catalytic capability, even in the high-temperature environment.

Study on the Catalytic Effect of Converter Dust on In Situ Online Reforming of Metallurgical By‐Product Gas and Thermochemical Energy Storage Analysis

In situ online reforming of converter gas and coke oven gas is realized by injecting coke oven gas into converter flue. This process utilizes methane dry reforming reaction to achieve heat energy recovery and CO2 capture and utilization. Moreover, the converter flue provides an excellent thermodynamic, kinetic, and catalytic environment. Experiments show that converter dust greatly improves the conversion rate of CH4 and CO2, and increases with the increase of the addition of converter dust. The conversion of CH4 reaches above 80% at 1150 °C, which is about 40% higher than that without catalyst. The CO2 conversion is more than 85% at 1150 °C, while it is only about 50% without catalysis. In addition, through the study of the main components of converter dust, the order of promoting CH4 decomposition is: Fe > Fe3O4≈CaO > FeO; the order of promoting effect on C–CO2 reaction is: Fe3O4 > CaO > FeO > Fe. Finally, the reforming energy storage is calculated by thermodynamic calculation and experimental data. The reforming energy storage of tonne crude steel is about 159.589 MJ, accounting for 44.5% of the total physical heat energy of converter flue gas, and CO2 emission reduction in converter flue gas is more than 50%.

Electro-assisted photocatalytic reduction of CO2 in ambient air using Ag/TNTAs at the gas-solid interface

The direct conversion of atmospheric CO2 into fuel via photocatalysis exhibits significant practical application value in advancing the carbon cycle. In this study, we established an electro-assisted photocatalytic system with dual compartments and interfaces, and coated Ag nanoparticles on the titanium nanotube arrays (TNTAs) by polydopamine modification. In the absence of sacrificial agent and alkali absorption liquid conditions, the stable, efficient and highly selective conversion of CO2 to CO at the gas-solid interface in ambient air was realized by photoelectric synergy. Specifically, with the assistance of potential, the CO formation rates reached 194.9 μmol h−1 m−2 and 103.9 μmol h−1 m−2 under ultraviolet and visible light irradiation, respectively; the corresponding CO2 conversion rates in ambient air were 30% and 16%, respectively. The excellent catalytic effect is mainly attributed to the formation of P–N heterojunction during the catalytic process and the surface plasmon resonance effect. Additionally, the introduction of solid agar electrolytes effectively inhibits the hydrogen evolution reaction and improves the electron utilization rate. This system promotes the development of photocatalytic technology for practical applications and provides new insights and support for the carbon cycle.

Dynamic response characteristics of solid oxide cell stacks for seawater/CO2 co-electrolysis under strong fluctuation electricity

This work focused on the intermittent characteristics of renewable energy and studied the dynamic response characteristics of seawater/CO2 co-electrolysis on solid oxide cell stacks to produce syngas under strong fluctuation electricity conditions. The results showed that when using a strong fluctuating current density of 58.2–658.1 mA/cm2 to simulate wind turbines, the power variation of the solid oxide cell stack was almost in line with the simulated wind turbine power variation curve. The theoretical conversion rate of solid oxide cell stack electrolysis products is linearly related to the current density. The measured H2O+CO2 conversion rate is similar to the theoretical value, and the current variation hardly changes the H2/CO ratio in the exhaust gas. Therefore, solid oxide electrolysis cell stacks have strong adaptability to fluctuating electricity.

ZnO–ZrO2 coupling nitrogen-doped carbon nanotube bifunctional catalyst for co-production of diesel fuel and low carbon alcohol from syngas

Catalytic syngas conversion to liquid fuel is pivotal for biomass utilization, enhancing energy security, reducing carbon emissions and curbing reliance on petroleum imports. Herein, bifunctional catalysts comprising zinc-zirconium dioxide (ZnZrO2) dispersed on nitrogen-doped multi-walled carbon nanotubes (NCNT) (ZnZrO2/NCNT) were successfully designed, enabling the simultaneous production of both diesel fuels (C9–C16 hydrocarbon) and methanol through direct syngas conversion. Operating at 450 °C, 4.5 MPa, a gas hourly space velocity (GHSV) of 4800 mL h−1·gcat−1, the ZnZrO2/NCNT catalyst, featuring 2.6% nitrogen doping, exhibited exceptional performance, achieving a 50.3% selectivity for C9–C16 hydrocarbons and a 26.4% selectivity for methanol, while maintaining a 52.5% single-pass CO conversion rate. The C9+ selectivity significantly surpasses the bottleneck predicted by the ASF distribution theory (C9+ selectivity <36%). This starkly contrasts that of ZnO/NCNT (1.7% C9–C16 and 6.3% methanol) and ZrO2/NCNT (32.5% C9–C16 and 25.4% methanol) catalysts. Moreover, the ZnZrO2/NCNT catalyst still retained C9+ 51.5% selectivity and 25% methanol selectivity after 100 h of continuous operation. The synergistic effects resulting from the amalgamation of highly active nanostructured units with a well-encapsulation structure efficiently hinder active component migration during catalysis. This significantly enhances both the catalyst's activity and stability. Furthermore, nitrogen introduction serves as a key electron donor to ZnZrO2, thereby catalyzing the activation of CO dissociation. This activation step emerges as a pivotal factor crucial for enhancing selectivity in liquid fuel production.

Effects of HCO3− and CO2 conversion rates on carbon assimilation strategies in marine microalgae: Implication by stable carbon isotope analysis of fatty acids

Marine microalgae are an essential component of marine plankton and critical primary producers, playing a vital role in marine ecosystems. The seawater carbonate system is a dynamic equilibrium system, and changes in any component can alter the carbonate balance. In CO2-concentrating mechanisms (CCMs), carbonic anhydrase (CA) regulates CO2 concentration by catalyzing the interconversion between CO2 and HCO3−. Therefore, limiting the activity of extracellular carbonic anhydrase (exCA) alters the rate at which carbonate equilibrium is reached and further affects the carbon assimilation process in microalgae. In this study, two different microalgae, Phaeodactylum tricornutum and Nannochloropsis oceanica, were selected to investigate the effects of changes in the carbonate system on photosynthetic carbon assimilation in microalgae by inhibiting exCA activity with acetazolamide (AZ). Inhibition of exCA activity reduces specific growth rates and photosynthetic efficiency of microalgae. The total alkalinity, HCO3− concentration, and CO2 concentration of the cultures increased with the decrease of pH, but the changes of the ribulose 1,5- bisphosphate carboxylase/oxygenase (Rubisco) activities of the two microalgae were different. In addition, the two microalgae possessed different lipid and carbohydrate synthesis strategies, but both restricted triacylglycerol (TAG) synthesis. Meanwhile, the microalgal cells had to utilize more 13CO2 when HCO3− and CO2 conversion rates were limited and restricted. This led to the continuous accumulation of 13C in fatty acids and the elevation of δ13CFAs. In conclusion, our study provides a new perspective on the role of microalgae in correlating carbonate changes with photosynthetic carbon assimilation strategies under mechanistic constraints on inorganic carbon utilization.

The influence of Mg/Al molar ratio on the performance of CuMgAl-x catalysts for CO2 hydrogenation to methanol.

The CuMgAl-x catalysts derived from hydrotalcite precursors with different Mg/Al molar ratios were synthesized and applied to CO2 hydrogenation to methanol reaction. In this study, the effects of Mg/Al molar ratio on the structure and surface properties of CuMgAl-x catalysts were investigated by XRD, N2 adsorption-desorption, SEM, TEM, H2-TPR, CO2-TPD, XPS, and in situ DRIFTS characterization methods. The results showed that an appropriate Mg/Al molar ratio can enhance the Cu-MgO interaction, increasing the basic sites and obtaining suitable acid sites. The dispersion of active Cu on the CuMgAl-x catalysts can be improved by strong Cu-MgO interaction, which enhances the adsorption capacity of CO2 and makes H2 activation easier, accelerates the conversion of intermediate species CO3 * and HCO3 *to HCOO*, and facilitates further conversion to CH3O* and CH3OH. The strong interaction between Cu and MgO was conducive to the formation of Cu+, which can inhibit the desorption of CO in the reverse water gas shift reaction. The CuMgAl-3 catalyst showed the highest CO2 Conversion rate (14.3%), methanol selectivity (94.5%), and STY of methanol (419.3g⋅kgcat. -1⋅h-1) at 240°C and 2.5MPa. The results obtained in this paper can provide a new idea for the design of high-performance catalysts for CO2 hydrogenation to methanol.

Reducing the impact of biomass combustion in residential units on local air quality by using innovative low-loading Pt-based heterogeneous catalyst

There are several published studies evaluating the potential of platinum and palladium-based catalysts for real flue gas purification, however, the need to reduce the mass fraction of precious metals and the effect of this process is often neglected. This study aimed to assess the influence of two catalysts on the overall flue gas composition formed during combustion in a pellet burner operated to mimic the operation of a real wood log stove. Commercial Pt–Pd-based (CAT A) and Pt-based (CAT B) catalysts with innovative sol-gel coatings and a reduced amount of active substance were used. The CO, OGC and PM conversion rates of CAT A reached 87.8%, 37.0% and 25.2%, while the removal efficiency of CAT B reached 85.8%, 37.8% and 18.8%, respectively. The decrease of organic carbon by the catalysts ranged from 28% to 49% in the case of CAT A and from 13% to 60% in the case of Cat B. The concentrations of PAHs emitted seem to indicate a less carcinogenic composition when catalytic converters are used than without these flue gas treatment units.

Impact of varied zeolite materials on nickel catalysts in CO2 methanation

Ni catalysts supported on 4A, 5A, 13X, ZSM-5, and BEA zeolites were prepared using the vacuum-heating method for CO2 methanation. These support materials play a pivotal role in shaping the catalysts' properties and their catalytic performance. High-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectroscopy (EDS) mappings suggest a significant concentration of Ni nanoparticles situated on the external surfaces of catalysts with low Si/Al ratios zeolites (Ni-4A, Ni-5A, and Ni-13X). These Ni nanoparticles exhibit characteristics of weaker metal-support interaction, lower metal reduction temperatures, and moderate H2 adsorption activity. Moreover, these low Si/Al ratio zeolites demonstrate robust CO2 adsorption activity. These properties endow Ni-5A and Ni-13X catalysts with heightened CO2 conversion (70.4–70.9%) and methane selectivity (92.4–96.4%). In contrast, high Si/Al ratio zeolite-based catalysts (Ni-ZSM-5 and Ni-BEA) exhibit smaller Ni particles, strong metal-support interaction and weaker CO2 adsorption activity, resulting in reduced CO2 methanation activity and decreased methane selectivity (71.2–73.4%). The normalized CO2 conversion rate presents a correlation with the average Ni particle size.

Variable frequency microwave induced CO2 Boudouard reaction over biochar

The Boudouard reaction presents promising application prospects as a straightforward and efficient method for CO2 conversion. However, its advancement is hindered primarily by elevated activation energy and a diminished conversion rate. This study employed a microwave reactor with a variable frequency as the initial approach to catalyze the CO2 Boudouard reaction over biochar, with the primary objective of producing renewable CO. The study systematically investigated the influence of various variables, including the heating source, microwave frequency, microwave power, gas hourly space velocity (GHSV), and carrier gas, on the conversion of CO2 and the selectivity towards CO. The experimental findings indicate that under static conditions, with a fixed microwave frequency set at 2450 MHz and 100 W microwave power, the Boudouard reaction did not initiate. Conversely, a CO2 conversion rate of 8.8% was achieved when utilizing a microwave frequency of 4225 MHz. Under this unique frequency, further elevating the microwave power to 275 W leads to the complete conversion of CO2. Furthermore, a comparative analysis between microwave and electrical heating revealed that the CO production rate was 37.7 μmol kJ−1 for microwave heating, in stark contrast to the considerably lower rate of 0.2 μmol kJ−1 observed for electric heating. Following the reaction, the biochar retained its robust 3D skeleton structure and abundant pore configuration. Notably, the dielectric constant increased by a factor of 1.8 compared to its initial state, rendering it a promising microwave-absorbing material.Graphical

Coupling and electronic synergistic effects of Fe/CeO2 composite to achieve high efficiency and selectivity for RWGS reaction

Transition metal iron, because of its high oxygen mobility, excellent thermal stability and low price, is often used in the study of RWGS reaction. However, the bottleneck problem of iron-based catalysts is the poor CO2 conversion rate. Herein, the Fe/CeO2 composite catalyst with Fe-O-Ce was successfully constructed, which has both high CO2 conversion and high CO selectivity for the low-temperature RWGS reaction. Furthermore, the influence of Fe0 contents is studied, and the result indicated that the CO2 conversion rate and CO selectivity are up to 50.05% and 100% at 500 ºC by the use of 20Fe/CeO2. Moreover, CeO2 is the best catalyst holder than the others. The physical and chemical properties of the catalysts are investigated by in-situ XPS, XRD, low-temperature N2 absorption-desorption (BET) and CO2-TPD. Nano zero-valent iron (Fe0) is the main active center for the RWGS reaction, which easily releases the outer electrons to activate reactant molecules. The introduction of the CeO2 is conducive to the high dispersion of Fe0 nanoparticles and the formation of abundant active centers. With the increase of Fe loading, the electron-rich Fe0 induces a strong electronic effect on the electron-deficient CeO2. The regularity of catalyst are changed by a large amount of zero-valent iron entering into the CeO2 lattice, then formed a lot of Fe-O-Ce solid solution. A large amount of zero-valent iron enter into the CeO2 lattice, inhibiting the grain growth and aggregation of monometallic species, and promoting nano Fe species highly dispersed on CeO2 carriers, leading more active centers exposure. Meanwhile, the abundant oxygen vacancy on xFe/CeO2 surface is advantage for the adsorption and activation of H2 and CO2 molecules. Therefore, the coupling and electronic synergistic effects of the active component Fe0 and the carrier CeO2 make xFe/CeO2 becoming a promising candidate catalyst for RWGS reaction.