CO CO2 Research Articles

Dolomite-derived catalyst-free dual function materials pellets for integrating calcium-looping and reverse–water–gas–shift reaction

Integrated CO2 capture and utilization via reverse water–gas shift reaction (ICCU-RWGS) for syngas production is a promising step contributing to carbon neutrality. Naturally occurring Ca-rich ores are potential candidates of dual function materials (DFMs) for ICCU-RWGS, while the practical circulating operation in twin fluidized-bed reactors necessitates DFMs pellets with high reactivity and good mechanical properties, to overcome powder elutriation and to withstand particle attrition. Dolomite (DM)-derived catalyst-free DFMs pellets are synthesized via the extrusion-spheronization (ES) and graphite-casting (GC) methods. Pelletization will result in pore structure blockage while the decline in textural properties has been remedied to some extent, due to the decomposition of CaMg(CO3)2. The hydration activation of Ca species in molding has benefited the DFMs pellets with uniform dispersion of CaO with smaller grain size. The dolomite-derived DFMs pellets outperform the pristine dolomite and the calcined dolomite DFMs regarding the ICCU-RWGS performance. Promoters such as Al2O3, ZrO2 or aluminate cement (AC) are incorporated to enhance the mechanical strength of the DM-GC pellets. The formed Ca3Al2O6, CaAl2O4, CaZrO3, and Ca2Al2SiO7 due to the interaction between CaO and the promoter, act as supporting skeleton for reinforced mechanical strength and physical barrier for retarding crystal sintering and particle agglomeration. Upon doping 10 wt% ZrO2, the compressive strength of the DM-GC pellets increases remarkably from 0.13 to 1.35 MPa. The desired DM-GC-Zr5 DFMs pellets exhibit excellent ICCU-RWGS performance with high and stabilized CO2 capture capacity (6.01 mmol CO2/g) and CO yield (5.01 mmol CO/g) within 10 cycles, demonstrating as a good DFMs candidate for cost-effective CO2 capture and conversion.

Enhanced sintering resistance of NiFe‐based RWGS catalysts through Cu doping

AbstractThe reverse water‐gas shift (RWGS) reaction offers an effective method for mitigating CO2 emissions. Due to its affordability and physicochemical stability, iron has garnered significant attention as a potential catalyst for RWGS. The incorporation of nickel and copper promoters can enhance CO2 conversion and CO selectivity in Fe‐based catalysts. This study focuses on modifying the strength of the Strong Metal‐Support Interaction (SMSI) through particle size optimization. Doping Cu into NiFe‐based catalysts restricts particle size, which influences the curvature of the Ni0@FeOx interface. This curvature enhances the electron coupling between Ni0 and FeOx, promoting the formation of a denser and thicker Ni0 and FeOx layer. This results in a nearly 90% increase in the CO2 reaction rate during the sintering resistance test by anchoring Ni0 and facilitating electron transfer to active sites. Such morphological evolution improves high‐temperature resistance to sintering during RWGS. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Amyloid-Like Protein-Modified Carbon Nitride as a Bioinspired Material for Enhanced Photocatalytic CO2 Reduction.

Modification of g-C3N4 with metal-free biomaterials through an environmentally friendly, low-energy, facile, and rapid single-step method is desired for the preparation of photocatalysts with efficient activity and high selectivity of CO2 reduction but remains a great challenge. Herein, we develop a phase-transitioned protein modification strategy for photocatalysts through superfast amyloid-like protein assembly on surfaces using a one-step sequential coating method. Metal-free carbon nitride/protein heterojunction composite photocatalysts (the phase-transitioned lysozyme (PTL), phase-transitioned bovine serum albumin (PTB), and phase-transitioned ovalbumin (PTO)-coated carbon nitride@SiO2 (CN@SiO2) and bioinspired carbon nitride hollow nanospheres (CN-HS) obtained by etching of CN@SiO2) are prepared using lysozyme, bovine serum albumin, and ovalbumin. The insulator-semiconductor heterojunctions formed at the protein-carbon nitride interface promote the migration and separation of photogenerated charges. The exposed hydrophobic alkyl and aryl groups of the surface-modified protein enable the formation of a CO2-aqueous solution-photocatalyst three-phase interface on the catalyst surface and the exposed -NH2 groups provide sites for CO2 adsorption, which effectively increases CO2 mass transfer and its adsorption as well as hydrophobicity, promoting CO2 reduction and inhibiting hydrogen production. Therefore, protein modification effectively improves the CO2 reduction activity and CO selectivity. For instance, compared to CN-HS, the CO yield of the PTL-modified CN-HS (1346.5 μmol g-1) increased by 24.5 times and the CO selectivity reached 90.5%. These findings represent a critical advancement in the surface modification of carbon nitride for CO2 reduction and the design of bioinspired materials for various applications.

Pivotal copper bimetallic oxide in hierarchical Calcium magnesium materials for low-temperature carbon capture and utilization

Carbon removal from anthropogenic greenhouse gas emissions is essential to achieve net-zero emissions and mitigate climate change, and integrated carbon capture and utilisation (ICCU) has been studied for subsequent in-situ chemical production. However, high temperature and CaO sintering remain critical issues, highlighting the need for improved, low-cost CO2 adsorbents that can be regenerated at lower temperatures. Herin, we innovatively introduce the low-temperature ICCU coupled with reverse water gas shift reactions (RWGS) using dual functional materials (DFMs), exemplifying a range of potential transition metals doped over CaO with or without the MgO support. Among all the prepared DFMs, D-Cu showed desirable enhanced catalytic activity at a comparatively low-temperature performance (550°C) and still maintained a stable CO2 capture capacity (7.0mmol g−1) and CO yield (8.0mmol g−1) with an exceptional CO2 conversion (94.4 %) and CO selectivity (97.6 %) after cyclic hydrogenation. The mechanism study revealed that Ca2CuO3 bimetalliccatalyst in the hierarchical porous 2CaO/MgO matrix of D-Cu plays a crucial role in retaining its cyclic stability, surpassing that of noble D-Pt. Given the ICCU-RWGS performance and cyclic stability of cost-effective D-Cu at reduced operating temperatures, the findings would minimise energy and cost consumption.

Hydrogen purification via hydrate-based methods: Insights into H2-CO2-CO hydrate structures, thermodynamics, and kinetics

Hydrate-based H2 purification is promising for removing impurities owing to the cage-like structures formed by water molecules. Understanding the competition mechanism of multicomponent gas molecule in hydrate is critical for improving gas purification efficiency. This study investigated the hydrate structure, thermodynamics, and kinetics of ternary gas mixture (H2–CO2–CO) from natural gas reforming products. The results identified H2–CO2–CO hydrate as type sI and determined the lattice parameters using X-ray diffraction. Raman spectroscopy results confirmed the presence of H2, CO2, and CO gas molecules in the hydrate phase. Increasing pressure, compared to cooling, enhanced CO2 content in hydrate phase. The phase equilibrium conditions and average hydrate dissociation enthalpy (53.47 J/g) were determined using a high-pressure microcalorimeter. Gas chromatography identified that the content of CO2 in the hydrate was the highest, followed by H2, and CO was the least abundant. The molecule dynamics simulation results show CO2 molecule numbers reflected trends in 51262 cages, H2 numbers correlated with changes in 512 cages, while CO numbers showed insignificant variation. Under the gas composition studied, the ability of gas molecules to be incorporated within hydrates decreases in the following order: CO2, H2, and CO.

Unraveling the role of reducing atmospheres on Fe-Zn-Al catalysts for highly selective carbon dioxide hydrogenation to light olefins

This study investigates the carbon dioxide (CO2) hydrogenation performance of Fe-Zn-Al catalysts pretreated under four distinct reducing atmospheres (H2, H2/N2, H2/CO, and CO/N2), elucidating their impact on CO2 conversion, CO selectivity, and light olefins selectivity. Combined with the characterization results, it was found that various catalyst components were obtained after activation in different atmospheres, but Fe5C2 was observed in all the catalysts after the CO2 hydrogenation reaction. The catalytic performance is intricately linked to the type of surface species produced after reduction and the Fe5C2 content. In a comparative perspective, the catalytic activity of the same catalyst in the four atmospheres followed the sequence H2>H2/N2>CO/N2>H2/CO. Notably, catalyst pretreatment with H2 yielded the highest CO2 conversion rate at 31.6 % and light olefins selectivity at 40.2 %. These results can be attributed to the highest electron density detected by XPS for the iron species on the spent catalyst and to the largest concentration of Fe5C2 formed during the reaction in the hydrogen reduced sample.

An estimate of chlorine fugacity in the low water fluid of the system С-О-(Н)-NaCl in the cumulus of ultrabasic-basic intrusions

At high PT parameters of the cumulates of ultramafic-mafic intrusions at low fO2 (below the QFM buffer), platinum dissolves in the fluid with CO as a carbonyl complex of the native metal. The high solubility of platinum as PtCl2 in brines with NaCl, which is associated with the formation of low-sulfide PGE deposits, is achieved at high oxygen fugacity (above the NNO buffer). It is assumed that at low oxygen fugacity in the low water CO–CO2 fluid, native Pt can also be converted into a cation-soluble form by chlorination. Experimental data (Р = 200 MPa, Т = 950oC, fO2 QFM and fluid CO–CO2) on the reaction of NaCl with magnetite and chromite, accessor minerals of mafic-ultramafic intrusions, with the formation of iron and chromium chlorides are presented. As shown by thermodynamic calculations, the equilibrium in the FeCl3–FeCl2 pair provides the high chlorine fugacity (fCl2). This fugacity is only 3–4 orders of magnitude lower than fCl2 in the Pt–PtCl2 equilibrium and 2.5–3 orders of magnitude higher than in the aqueous fluid 1 M HCl at the same P–T–fO2 parameters.

Transition-Metal-Doped CeO2 for the Reverse Water-Gas Shift Reaction: An Experimental and Theoretical Study on CO2 Adsorption and Surface Vacancy Effects.

Transition metal-doped ceria (M-CeO2) catalysts (M = Fe, Co, Ni and Cu) with multiple loadings were experimentally investigated for reverse water gas shift (RWGS) reaction. Density functional theory (DFT) calculations were performed to benchmark the properties that impact catalytic activity of CO2 reduction. Temperature-programmed desorption (TPD) was conducted to study the CO2 binding strength on doped CeO2 surfaces; the trend of the energy along increasing metal loading agrees with the DFT calculations. Notably, CO2 dissociative adsorption energy and oxygen vacancy (OV) formation energy are key descriptors obtained from both DFT and experiments, which can be used to evaluate catalytic performance. Results show the effectiveness of transition metal doping in enhancing CO2 adsorption and reducibility of the surfaces, with Fe showing particularly promising results, i.e., CO2 conversion higher than 56% at 600 °C and 100% selectivity to CO. Cu exhibits 100% selectivity to CO but low CO2 conversion, while Co and Ni showed notable ability of methanation, particularly at high loadings. This study finds that an effective CeO2 based RWGS catalyst corresponds to OV sites that have low OV formation energies for surface reduction, and moderate CO2 adsorption energies for strong interaction with the surface to promote C-O bond scission.

Highly Active Cerium Oxide Supported Solution Combustion Cu/Mn Catalysts for CO-PrOx in a Hydrogen-Rich Stream

Mono- and di-substituted cerium oxide catalysts, viz. Ce0.95Cu0.05O2-δ, Ce0.90Cu0.10O2-δ, Ce0.90 Cu0.05Mn0.05O2-δ, Ce0.85Cu0.10Mn0.05O2-δ, and Ce0.80Cu0.10Mn0.10O2-δ, were synthesized via a one-step urea-assisted solution combustion method. The elemental composition and textural and structural properties of the catalysts were determined by various physical, electronic, and chemical characterization techniques. Hydrogen temperature-programmed reduction showed that co-doping of copper and manganese ions into the CeO2-δ lattice improved the reducibility of copper. Powder XRD, XPS, HR-TEM, and Raman spectroscopy showed that the catalysts were a singled-phased, solid-solution metal oxide with a cerium oxide cubic fluorite (cerianite) structure, and evidence of oxygen vacancies was observed. Catalytic results in the preferential oxidation of CO in a hydrogen-rich stream showed that complete CO conversion occurred between 150 and 180 °C. Furthermore, at 150 °C, Ce0.90Cu0.05Mn0.05O2-δ, Ce0.90 Cu0.10O2-δ, and Ce0.85Cu0.10Mn0.05O2-δ catalysts were the most active, achieving complete CO conversion and CO2 selectivity of 81, 79, and 71%, respectively. The catalysts performed moderately in the presence of CO2 and water, with the Ce0.90Cu0.05Mn0.05O2-δ catalyst giving a CO conversion of 80% in CO2, which decreased to about 60% when water was added.

Zinc oxide morphology-dependent CuOx-ZnO interactions and catalysis in CO oxidation and CO2 hydrogenation

CuO/ZnO catalysts with different ZnO morphologies, i.e. nanoplates (p-ZnO) and nanorods (r-ZnO), have been prepared to test for CO oxidation and CO2 hydrogenation. Strong morphology-dependent CuOx-ZnO interactions were observed, which are tightly associated with the ZnO morphology. p-ZnO predominantly exposing polar {002} facets greatly promote the CuOx-ZnO interactions, contributing to the stabilities of CuOx/ZnO catalysts in both reactions. Experimental evidences reveal that CuO-ZnO interfaces act as the active sites in CO oxidation. CuO/p-ZnO catalyst with stronger CuO-ZnO interactions can facilitate the generations of fine CuO and interfacial Cu(I) species, responsible for the adsorption and reactivity of CO and subsequently the high (intrinsic) activity in CO oxidation. However, CuO/ZnO catalysts undergo in situ restructuring to generate Cu/ZnO in CO2 hydrogenation, whose catalytic performance is determined by the key step of CO2 activation. Consequently, Cu/r-ZnO catalyst possessing more surface basic sites exhibits better catalytic performance. These results greatly deepen the fundamental understanding of Cu-based catalysts in both reactions and broaden the concept of morphology-dependent catalysis of oxide-based nanocrystal catalysts that varies with the reactions catalyzed.

Influence of cerium addition and redox state on silicate structure and viscosity

AbstractThe viscosities of Ce‐free and Ce‐bearing (∼1.3 mol%, ∼6.5 wt.% Ce2O3) soda lime silicate (window glass) melts were measured with respect to oxidation state. Experiments were performed isothermally using a concentric‐cylinder viscometer on melts equilibrated with successively reducing CO–CO2 gas mixtures within a gas tight vertical tube furnace at 1 atm. Viscosity measurement and sampling were performed at the end of each melt reduction step. Further, viscosities in the glass transition temperature range were estimated using the shift factor method applied to glass transition temperature values determined using differential scanning calorimetry (DSC) measurements on quenched glasses. The Ce speciation at each stepwise melt reduction was probed using Ce L3‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy, while structural information upon Ce addition and reduction was provided by Raman spectroscopy. The viscosities of these materials remain constant at this level of Ce addition and do not vary significantly with redox state at high temperature. Conversely, viscosity values in the glass transition temperature range increase upon both Ce addition and reduction. Our analysis, based on the glass composition analyses obtained via electron probe microanalyzer (EPMA), viscosity calculations, and observations of silicate structural changes, leads to the conclusion that the observed viscosity increase around the glass transition temperature is explained by the high ionic field strength of Ce ions as well as the polymerization behavior of the silicate matrix occurring during reduction of Ce. Because of its low concentration, resulting from its low solubility, Ce redox changes exert only minimal effects on the viscosity of this melt.

Fabrication of double modified electrocatalyst by dual flame synthesis for enhancing electrochemical reduction of carbon dioxide

A rapid dual flame synthesis is developed for one-step preparation and modification of double modified ZnO catalysts with carbon doping and oxygen vacancies. The growth mechanism and nanostructure evolution are also investigated. The double modified ZnO with carbon doping and oxygen vacancies exhibies excellent performance in CO2 reduction to syngas, with a high current density of 14.02 mA/cm2 at −1.1 V vs. RHE and a maximum Faradaic efficiency of 71% for CO production. The maximum adjustable range of the CO/H2 ratio from 0.5 to 2.7. In a flow cell, the double modified ZnO exhibits a large current density of 126.8 mA/cm2 at −1.2 V vs. RHE. The maximum Faradaic efficiency for CO2 reduction to CO is 74.8% at 50 mA/cm2. Double modified ZnO maintains stable potential and Faradaic efficiency for over 5 h of electrolysis. Operando X-ray absorption spectroscopy and density functional theory calculations reveal that the active site is the Zn–Zn configuration, and that carbon dopant and oxygen vacancy promote CO2 activation and CO desorption, and reduce reaction overpotential of CO2RR.

Modulation Excitation Spectroscopy: A Powerful Tool to Elucidate Active Species and Sites in Catalytic Reactions.

ConspectusA rational design of catalysts requires a knowledge of the active species and sites. Often, catalyst surfaces are dominated by spectators, which do not participate in the reaction, while the catalytically active species and sites are hidden. Modulation-excitation spectroscopy (MES) allows discrimination between active and spectator species by applying a concentration modulation, which is translated into the active (that is, actively responding) species by phase-sensitive detection (PSD).While MES has been known for a while, its combination with infrared spectroscopy (IR-MES) has been applied to the detailed mechanistic analysis of a wide range of supported metal and metal oxide catalysts only recently, used for catalytic reactions such as CO2 hydrogenation, water-gas shift, and CO and selective oxidation. The applicability of IR-MES is not limited to catalysis but has started to expand into other areas of research (e.g., gas sensing).In the context of renewable energy, CO2 hydrogenation has been a matter of intense mechanistic debate, despite its great importance for synthesis gas production and further processing to fuels and chemicals. Applying IR-MES to supported Cu and Au catalysts enabled us to discriminate between redox and associative mechanisms. While CO2 hydrogenation to CO and water follows an associative pathway with sequential H2 activation via hydrides and formation of carbon- and oxygen-containing intermediates, such as carbonates and formates, the reverse reaction, that is, the water-gas shift reaction, was shown to proceed via a redox mechanism including oxygen vacancy formation followed by reoxidation of the catalyst by CO2.Recent IR-MES studies on (supported) metal oxides have provided direct spectroscopic insight into the catalytically active sites during the selective oxidation of alkanes and alcohols. By further expanding the potential of IR-MES by transient isotopic exchange experiments, we were able to resolve the nuclearity-dependent vanadium and adsorbate dynamics of supported vanadia catalysts during oxidative dehydrogenation, highlighting the intimate interplay between the surface vanadia species and the support. The strong influence of the support material (ceria and titania) on the sequence of reaction steps provides an explanation for the different catalytic performance. Based on these mechanistic insights, the rational design of improved catalysts has been possible.Expanding the application of IR-MES to the area of gas sensing, as recently demonstrated for doped SnO2, provides access to enhanced mechanistic insight, including previously undetected surface species. Methodical challenges arising from background features associated with semiconductor metal oxides have been successfully tackled, supporting further expansion of IR-MES in the gas sensing community. Mechanistically, the application of IR-MES allows identification of the actively participating OH groups and adsorbed species (e.g., alkoxy, CO, carbonate) and monitoring of reaction sequences based on their temporal behavior, providing a level of understanding typically not accessible by steady-state methods.As outlined above, the combination of MES/PSD with IR spectroscopy constitutes a powerful approach for the identification of catalytically active species and sites, which is essential for a profound mechanistic understanding of surface reactions, greatly facilitating the rational design of catalysts and other functional materials.

LaCoO3 is a promising catalyst for the dry reforming of benzene used as a surrogate of biomass tar.

Tar build-up is one of the bottlenecks of biomass gasification processes. Dry reforming of tar is an alternative solution if the oxygen chemical potential on the catalyst surface is at a sufficient level. For this purpose, an oxygen-donor perovskite, LaCoO3, was used as a catalyst for the dry reforming of tar. To circumvent the complexity of the tar and its constituents, the benzene molecule was chosen as a model compound. Dry reforming of benzene vapor on the LaCoO3 catalyst was investigated at temperatures of 600, 700, and 800 °C; at CO2/C6H6 ratios of 3, 6, and 12; and at space velocities of 14,000 and 28,000 h-1. The conventional Ni(15 wt.%)/Al2O3 catalyst was also used as a reference material to determine the relative activity of the LaCoO3 catalyst. Different characterization techniques such as X-ray diffraction, N2 adsorption-desorption, temperature-programmed reduction, and oxidation were used to determine the physicochemical characteristics of the catalysts. The findings demonstrated that the LaCoO3 catalyst has higher CO2 conversion, higher H2 and CO yields, and better stability than the Ni(15 wt.%)/γ-Al2O3 catalyst. The improvement in activity was attributed to the strong capacity of LaCoO3 for oxygen exchange. The transfer of lattice oxygen from the surface of the LaCoO3 catalyst facilitates the oxidation of carbon and other surface species and leads to higher conversion and yields.

Short-stage synthesis of metal–ceramics composites as precursors for high performance catalytic applications

NiAl, NiCoAl, and CoCuAl intermetallics on ceramic TiC and TiCrC supports were produced by self-propagating high-temperature synthesis (SHS) from granular mixtures and used as precursors for preparation of catalysts for CO and propane deep oxidation and CO2 hydrogenation. The precursors were converted into catalysts by aluminum leaching and stabilization with hydrogen peroxide solution. Prepared supported catalysts were characterized by XRD, SEM/EDS, and BET methods and tested in the processes of deep oxidation of CO and propane and methanation of CO2. It was revealed that 100 % CO conversion is observed in TiC-supported catalysts at 250 °C. Catalysts containing NiCo active phase on both ceramic supports were shown to be the most active in propane oxidation. In CO2 methanation, Ni/TiCrC sample showed the highest CO2 conversion (58.9 % at 350 °C) with 100 % methane selectivity.

Surface oxygen vacancy regulation and active metal doping for Cu-Al based spinel catalysts synthesis toward high-efficiency reverse water-gas shift reaction

The reverse water-gas shift (RWGS) reaction is of great significance to convert CO2 to valuable feedstocks. Reasonable design and preparation of catalysts is necessary to achieve high CO2 conversion and CO selectivity. In this study, a series of Cu-Al based spinel catalysts were synthesized by coprecipitation-calcination method or A-site doped with active metal (Co, Zn, Mg, and Fe) for the RWGS reaction. The results indicated that the surface oxygen vacancies and crystal structure of CuAl2O4 can be regulated by calcination temperature. Remarkably, the CuAl-800 catalyst exhibits the highest CO2 conversion rate (62.7 %) with 100 % CO selectivity at 500 °C. Excessive calcination temperatures (> 800 °C) resulted in a well-defined spinel structure, but decreased surface oxygen vacancies and CO2 conversion rate. At calcination temperatures < 800 °C, surface oxygen vacancies increased, but the formation of CuO impurities which irreversibly converted to Cu2O during reduction, decreased catalytic activity. Compared with Zn, Mg and Fe, Co doping can significantly improved the reactivity of CuAl2O4 catalyst in RWGS reaction at 500 °C, increasing the CO2 conversion rate by 8 % while maintaining 100 % CO selectivity. The main reason is that Co doping not only effectively improves the integrity and stability of spinel structure of CuAl2O4, but also enhances its ability to dissociate and activate H species through interfacial sites of CuO-OV-CuXCo1-XAl2O4, thus further enhancing its catalytic conversion ability of CO2 to CO. These results enrich the understanding of surface chemistry of CuAl2O4 spinel and lay an important theory foundation for design of spinel-based catalysts for RWGS reaction.

Optimization of Cu/MnO2 catalyst for enhanced methane bi-reforming: a response surface methodology approach for sustainable syngas production

Hydrogen or syngas, valued for its clean and high-energy properties, stands as a promising solution to future energy shortages by converting CO2 and CH4 waste into renewable syngas through a reaction known as methane bi-reforming. Hence, the purpose of this current research is to examine the effectiveness of Cu/MnO2 catalyst in methane bi-reforming (MBR) using response surface methodology (RSM). The synthesis of the 15%Cu/MnO2 catalyst was accomplished using the ultrasonic impregnation method, followed by a comprehensive analysis and characterization of the catalyst using CO2-TPD, BET, H2-TPR, TPO, and XRD evaluation. The effect of reaction parameters was investigated using RSM analysis, including temperature, CO2/CH4 ratio, and gas hourly space velocity (GHSV) (700–900 °C, 0.2–1.0, and 16–36 L g cat−1 h−1, respectively). According to the analysis of variance and three-dimensional response surface plots, it was determined that CH4 conversion and H2 yield were largely influenced by temperature, whereas CO2 conversion and CO yield could be manipulated through CO2/CH4 feed ratio. Meanwhile, the GHSV appeared to have a significant influence on the H2/CO ratio and CH4 conversion. From the experimental data, it was found that the 15%Cu/MnO2 catalyst performed best under specified optimal conditions of 800 °C, a CO2/CH4 ratio of 0.6, and a GHSV of 26 L g cat−1 h−1. These optimal conditions resulted in the maximum conversion of CH4 (54.67%), CO2 conversion (47.52%), H2 yield (43.81%), CO yield (36.29%), and H2/CO ratio (1.384). Despite the inevitability of carbon formation resulting from the breakdown of CH4 and CO at high temperatures, the examination of the spent catalysts under optimal conditions yielded a smaller quantity of carbon of approximately 28.27% in comparison to the suboptimal conditions with 55.37%.

The performance of CO2 reduction by dielectric barrier discharge plasma coupled Cu-Ni binary silicon-based composites

As a major greenhouse gas, the rational conversion and utilization of CO2 can help reduce carbon emissions and mitigate the greenhouse effect. In this study, mesoporous SiO2 as a carrier, with CuO and NiO employed to construct a binary metal composite silica-based catalyst, coupled with dielectric barrier discharge (DBD) plasma, for the conversion of CO2. Physicochemical analysis confirmed the successful introduction of CuO into the mesoporous SiO2. NiO and CuO bimetals were dispersed on SiO2 surfaces with large specific surface areas, ensuring an optimal distribution of metal oxide. Gas chromatography was utilized to investigate the performance of DBD-coupled x%CuO-3 %NiO/Si for CO2 conversion. The results indicated that the CuO-NiO binary composite silica catalysts significantly improved CO2 conversion, CO yield, and energy efficiency compared to the monometallic 3 %NiO/Si materials. Further microstructural analysis of the 9 %CuO-3 %NiO/Si catalyst revealed near-elliptic particles with dimensions of 200 by 500 nm and a large number of irregular fine particles attached to the surface. When the CuO loading reached an optimal level and the input power was set at 30 W, the energy efficiency of the 9 %CuO-3 %NiO/Si catalyst increased by 119.6 %. The CuO-NiO binary composite Si-based catalyst developed in this study boasts simple operation and environmental friendliness, making it highly significant for CO2 treatment.

High efficient CuCeO2‐δ/SiO2 catalyst for RWGS reaction: impact of Ce content and loading sequence

AbstractThe extensive use of fossil energy leads to wanton emission of CO2 and serious environmental problems. The exploration of high‐performance catalysts plays a pivotal role in CO2 resource utilization. In this paper, CuCeyK catalysts are prepared by wet impregnation method using ordered mesoporous SiO2 as support for the reverse water gas shift (RWGS) reaction. The physicochemical properties of the prepared catalysts are characterized by H2‐TPR, BET, XRD, Quasi in‐situ XPS, H2‐TPD, and CO2‐TPD techniques. The results demonstrate thatthe Cu0 species can form synergistic effects with oxygen vacancies (Ov) to enhance the CuCeyK catalytic performance. Additionally, the electronic effects between Ce and Cu not only enhances the adsorption and activation performances of the catalyst towards CO2 and H2 molecules, but also effectively suppresses the sintering of Cu0 species, thereby enhancing the stability of the corresponding catalyst. It is worth mentioning that the Ce content also directly affects the catalytic performances of the CuCeyK catalyst. The CuCe15K catalyst with a Ce content of 15% displays excellent CO2 hydrogenation performances, and the CO2 conversion and CO selectivity up to 41 % and 100 % at 420 °C, respectively. © 2024 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Understanding the Temperature Effect on Carbon‐Carbon Coupling during CO2 and CO Electroreduction in Zero‐Gap Electrolyzers†

Comprehensive SummaryCu‐catalyzed electrochemical CO2 reduction reaction (CO2RR) and CO reduction reaction (CORR) are of great interest due to their potential to produce carbon‐neutral and value‐added multicarbon (C2+) chemicals. In practice, CO2RR and CORR are typically operated at industrially relevant current densities, making the process exothermal. Although the increased operation temperature is known to affect the performance of CO2RR and CORR, the relationship between temperatures and kinetic parameters was not clearly elaborated, particularly in zero‐gap reactors. In this study, we detail the effect of the temperature on Cu‐catalyzed CO2RR and CORR. Our electrochemical and operando spectroscopic studies show that high temperatures increase the activity of CO2RR to CO and CORR to C2H4 by enhancing the mass transfer of CO2 and CO. As the rates of these two processes are highly influenced by reactant diffusion, elevating the operating temperature results in high local CO2 and CO availability to accelerate product formation. Consequently, the *CO coverage in both cases increases at higher temperatures. However, under CO2RR conditions, *CO desorption is more favorable than carbon‐carbon (C—C) coupling thermodynamically at high temperatures, causing the reduction in the Faradaic efficiency (FE) of C2H4. In CORR, the high‐temperature‐augmented CO diffusion overcomes the unfavorable adsorption thermodynamics, increasing the probability of C—C coupling.