CO Conversion Rate Research Articles

Modulating CO2 methanation activity on Ni/CeO2 catalysts by tuning ceria facet-induced metal-support interaction

Comprehending the metal-support interactions (MSI) as well as interface structures plays a crucial role in creating efficient interface sites. However, the interfacial nature is influenced by multiple structural factors, making it challenging to establish a direct correlation between interfacial sites and CO2 methanation activity. Herein, the CeO2 with uniform facets were used as supports to study the influence of facet-induced MSI on methanation performance. CeO2 cubes with (1 0 0) facet and octahedrons with (1 1 1) facet was fabricated over Ni/CeO2 by altering hydrothermal parameters. (HR)TEM, XPS and Raman characterizations etc. revealed that the presence of embedded MSI structures in Ni/CeO2-Cub resulted in the well-dispersed Ni0. The embedded Ni–CeO2 interaction owned a maximized interface with more surface oxygen vacancies. The FT-IR spectrum indicated that the synergistic effect of H2 dissociation on Ni NPs surfaces and CO2 activation in adjacent surface oxygen vacancies occurred in Ni–CeO2 interfaces, improving CO2 methanation activity with a large number of formates. CO2 conversion rate for Ni/CeO2-Cub was 18.4 times as high as that for Ni/SiO2 without MSI at 548 K. This study elucidated how the facet-induced interfaces impacted the methanation activity, providing new ideas for the development of efficient CO2 hydrogenation catalysts.

Effect of Yttrium on Ce/Ni-Metakaolin Catalysts for CO2 Methanation.

In recent years, major economies have implemented carbon reduction and carbon neutrality policies. Furthermore, with advancements in science and technology, carbon dioxide (CO2) is now considered a valuable raw material for producing carbon-based fuels through hydrogenation. Various concentrations of yttrium (referred to as Y hereafter) were introduced to assess their influence on the catalytic performance of CO2 methanation. At a temperature of 300 °C, the catalyst exhibited an impressive CO2 conversion rate of 78.4% and maintained remarkable stability throughout a rigorous 100 h stability assessment. The findings suggest that the inclusion of yttrium (Y) promotes the formation of oxygen vacancies and alkaline sites on the catalyst. This, in turn, enhances the reducibility of nickel species, improves the dispersion of nickel particles, and plays a pivotal role in enhancing thermal stability. Furthermore, it offers an innovative design approach for creating highly efficient composite CO2 methanation catalysts by controlling particle size and harnessing synergistic catalytic effects at the metal/support interface.

Influence of humidity on the plasma‐assisted CO2 conversion

AbstractThe current research focuses on carbon dioxide (CO2) conversion at ambient conditions using streamer plasma. In this study, treatment time and humidity have been found to influence CO2 conversion. Our findings reveal a maximum CO2 conversion rate of 35.2%, achieved with a remarkably high energy efficiency of CO2 conversion at 135% and a low energy cost of 2.17 eV/molecule. We employed optical emission and fourier‐transform infrared spectroscopy spectroscopy to analyze the different dissociation products of CO2 and determine the percentage of CO2 conversion. Furthermore, we utilized a two‐dimensional (2D) fluid dynamics model and a zero‐dimensional (0D) chemistry model to gain insights into the reactor mechanism.

Ultrastable bifunctional multi-stage active metal catalysts for low concentration CO2 capture and in-situ conversion

Integrating CO2 capture and in-situ conversion is a promising means of processing low concentration CO2 in flue gas. The development of a low cost, highly stable catalyst to reduce the running cost is key to the development of this technology. The ultrastable bifunctional multi-stage active metal catalysts (Ca12Al14O33-y (Ca2Fe2O5)-CoxCaO) were synthesized by the solid phase synthesis method with low cost industrial powder raw materials. The catalyst was stabilized with calcium aluminate (Ca12Al14O33) and calcium ferrite (Ca2Fe2O5) as a substrate structural framework for CaO and enhanced the dispersion of CaO. It not only solved the problem of CaO deactivation due to sintering, pore collapse, and agglomeration in the continuous high-temperature reaction, but also showed excellent catalytic performance for reverse-water–gas-shift (RWGS) reaction. On the basis of calcium-looping and RWGS reaction, the high temperature CO2 capture and in-situ conversion process is realized in the same fixed-bed reactor for processing simulated flue gas with 16.7 vol% CO2. The results showed that at the optimum operating temperature of 610 °C, the catalyst still maintains a stable CO2 capture capacity, over 98% CO2 conversion rate and close to 100% CO selectivity after 100 cycles. The multi-stage active metal structure catalysts provided a unique construction idea for designing ultrastable catalysts for low concentration CO2 capture and in-situ conversion with great potential for industrial application.

Metagenomic insights into the improvement of CO2/H2 biomethanation or biogas upgrading using zirconium metal organic frameworks

The inefficient conversion of carbon dioxide (CO2) to methane often restricts the advancement of CO2 biomethanation technologies. This study explored the degrading performance, microbial community compositions, and functional gene abundance to examine the impact of zirconium metal-organic frameworks (Zr-MOFs) on the CO2 biomethanation process. The results showed that the maximum utilization rates of CO2 and H2 increased by 2.77 times and 2.36 times after the addition of Zr-MOFs, respectively, and the corresponding conversion rate of CO2 to methane also increased by 57.53%. Additionally, Zr-MOFs enhanced the COD removal efficiency and hydrolysis of tryptophan-like proteins and humic acid-like substances, resulting in more volatile organic compounds, such as tetradecane, 2-pentanone, and hexadecanoic acid. The analysis of microbial community structure revealed that the relative abundance of Methanothrix and Metanobacterium increased by 24.40% and 36.02% after the addition of Zr-MOFs, respectively. The methane metabolism revealed that Metanobacterium was a member of the same aceticlastic methanogenic pathway as Metanothrix, which encodes acetyl-CoA synthetase to catalyze the synthesis of acetyl-CoA from acetate, and Zr-MOFs also increased the relative abundance of genes that encode the enzyme responsible for converting intermediates to methane. Finally, Zr-MOFs improved the biogenesis and utilization of acetate and hydrogen (H2) by enhancing the activity of enzymes, thereby providing more nutrients for methanogenesis. This study provided thorough explanations for the application and improvement of Zr-MOFs in CO2 biomethanation technology.

Boosted photothermal synergistic CO2 methanation over Ru doped Ni/ZrO2 catalyst: From experimental to DFT studies

The hydrogenation of CO2 to CH4 presents a captivating and challenging avenue for CO2 reutilization. In this study, we explored the potential of photo-thermal catalytic (PTC) reactions for CO2 conversion to CH4. Herein, we employed a novel catalyst, NiRu/ZrO2, for photothermal CO2 methanation. Remarkably, the Ru-doped Ni/ZrO2 catalyst demonstrated significantly higher catalytic activity compared to the Ni monometallic catalyst. The optimized Ru doping conditions led to decreased temperature requirements and promoted CO2 conversion rates, achieving an impressive 100% CH4 selectivity. Detailed characterizations of the catalyst revealed several advantageous properties of NiRu/ZrO2, including superior optical absorption performance, a higher temperature of CO2 resolved peak, and an increased binding energy of the Ni2+ peak. Furthermore, density functional theory (DFT) calculations demonstrated that the addition of Ru positively influenced CO2 adsorption, thereby lowering the energy barrier for CO2 decomposition and C species hydrogenation. This research sheds light on the potential of the Ru-doped Ni/ZrO2 catalyst for efficient CO2 conversion to CH4 through photothermal catalysis. These findings offer valuable insights for the development of advanced catalysts in CO2 reutilization strategies.

Highly productive and robust core@shell HeatPath SiC-Al2O3 @Co/Re/Al2O3 catalyst for Fischer–Tropsch synthesis

Co-based catalysts are highly active for synthesizing long-chain paraffins through Fischer–Tropsch synthesis. However, their exothermic reactions can cause overheating and catalyst deactivation. To address this, thermally conductive SiC-Al2O3 pellets (HeatPath™) were coated with a Co/Re/Al2O3 shell, significantly boosting the CO conversion rate and the yield of C2–4 and C5+ hydrocarbons over a wide range of temperatures by dissipating the reaction heat. The core@shell HeatPath@Co/Re/Al2O3 catalyst demonstrated high productivity (up to 19.7 gCOgcat−1 h−1), exceptional long-term stability over 660 h time-on-stream, with high-temperature operation up to 260 °C, a low CH4 selectivity (7.1 %) and a chain growth probability (α) > 0.8. In contrast, the irreversible deactivation of a powder Co/Re/Al2O3 catalyst started at 195 °C, resulting in >60 % CH4 selectivity and ∼100 % CO conversion due to excessive local heat. The CO conversion rate on the core@shell catalyst could be further improved by increasing the H2/CO ratio and temperature, with commercially viable CH4 selectivity.

Photo- and Thermocatalytic CO2 Methanation: A Comparison of Ni/Al2O3 and Ni-Ce Hydrotalcite-Derived Materials under UV and Visible Light.

Catalysts derived from Ni/Al/Mg/Ce hydrotalcite were prepared via a co-precipitation method, varying the Ce/Al atomic ratio. All of the catalytic systems thus prepared were tested for CO2 methanation under dark and photocatalytic conditions (visible and ultraviolet) under continuous flow with the light intensity set to 2.4 W cm-2. The substitution of Al by Ce formed a solid solution, generating oxygen vacancies and Ce3+/Ce4+ ions that helped shift the dissociation of CO2 towards the production of CH4, thus enhancing the activity of methanation, especially at lower temperatures (<523 K) and with visible light at temperatures where other catalysts were inactive. Additionally, for comparison purposes, Ni/Al2O3-based catalysts prepared via wetness impregnation were synthesized with different Ni loadings. Analytical techniques were used for the characterization of the systems. The best results in terms of activity were as follows: Hydrotalcite with Ce promoter > Hydrotalcite without Ce promoter > 25Ni/Al2O3 > 13Ni/Al2O3. Hydrotalcite, with a Ce/Al atomic ratio of 0.22 and a Ni content of 23 wt%, produced 7.74 mmol CH4 min-1·gcat at 473 K under visible light. Moreover, this catalyst exhibited stable photocatalytic activity during a 24 h reaction time with a CO2 conversion rate of 65% and CH4 selectivity of >98% at 523 K. This photocatalytic Sabatier enhancement achieved activity at lower temperatures than those reported in previous publications.

Computational Modeling of Photo-Electrochemical Reduction of CO2 Utilizing Concentrated Light

Solar energy conversion of water and CO2 into H2/CO by an integrated photo-electrochemical (IPEC) cell and utilizing concentrated solar light allows for high power density and, if carefully designed, delivers high solar-to-fuel efficiency [1], [2]. In such devices, light absorption, charge generation/separation/transport, electrochemical reactions, and mass and ionic transport are required to occur simultaneously. Managing the coupled photon, charge, mass, and heat transport is central to a functioning and stable device. If not carefully designed, challenging operating conditions (high irradiation fluxes, critical thermal management) can induce irreversible damage to the IPEC cell and impact its performance. Thus, the optimal design of a high-performance device is conditioned by the development of a multi-dimensional and multi-physics computational model capable of estimating experimentally inaccessible quantities in complex porous geometries [3]. While such models have already been developed for water splitting, computational modeling of CO2 reduction under concentrated light is still missing.We present an IPEC cell computational model operating under highly concentrated radiation that accounts for both water splitting and CO2 reduction in a zero-gap gas diffusion electrode configuration. The continuum modeling is based on the solution of the coupled conservation and transport equations: species conservation and transport with electrochemical reactions, mass and momentum conservation, conservation and transport of electron and holes in the semiconductors, and Maxwell’s equations for the light propagation and absorption. We quantify spatially resolved non-uniform fields (local temperature, partial current densities, molar species fractions, etc.), inhomogeneities (e.g., local hotspots that could damage sealing), and CO2 conversion rates to demonstrate how such simulations can help to address engineering and operating conditions challenges. Finally, we show that the data obtained in experiments of an IPEC device operating under concentrated light are in agreement with our computational findings.Our simulations reveal that critical thermal management is required to improve IPEC cell efficiency. We provide evidence that challenging operating conditions (high solar irradiation concentration, low mass flow rate) can affect the CO partial current density, favor the competing hydrogen evolution reaction, lead to quartz window failure and decrease the photo-absorber efficiency.Overall, this work provides a validated multi-physics computational model of an IPEC cell operating with concentrated radiation that can be used to conduct feasibility studies and provide design guidelines for such thermally integrated IPEC devices for CO2 reduction at large solar irradiation concentrations. Keywords : Solar fuel, simulation, concentrated light, high power[1] S. Tembhurne, F. Nandjou, S. Haussener, A thermally synergistic photo-electrochemical hydrogen generator operating under concentrated solar irradiation, Nat. Energy. 4 (2019) 399–407. https://doi.org/10.1038/s41560-019-0373-7.[2] E. Boutin, M. Patel, E. Kecsenovity, S. Suter, C. Janáky, S. Haussener, Photo-Electrochemical Conversion of CO2 Under Concentrated Sunlight Enables Combination of High Reaction Rate and Efficiency, Adv. Energy Mater. 12 (2022). https://doi.org/10.1002/aenm.202200585.[3] S. Tembhurne, S. Haussener, Integrated Photo-Electrochemical Solar Fuel Generators under Concentrated Irradiation, J. Electrochem. Soc. 163 (2016) H999–H1007. https://doi.org/10.1149/2.0321610jes.

Direct solar-driven thermochemical CO2-to-fuel conversion with efficiency over 39 % employing hierarchical triply periodic minimal surfaces biomimetic foam reactors

Solar-driven CO2 reforming of CH4 is considered a promising approach for achieving CO2 emission reduction and clean energy utilization simultaneously. However, reactors suffer from uneven temperature distribution and severe carbon deposition, leading to low solar-to-fuel efficiency. This study introduces a novel strategy for highly efficient solar-driven thermochemical CO2-to-fuel conversion based on hierarchical triply periodic minimal surfaces (TPMS) biomimetic foam reactors. The biomimetic hierarchical foam reactor exhibits a remarkably high light-to-fuel efficiency of 39.14 %, with CH4 and CO2 conversion rates reaching 72.6 % and 83.9 %, respectively, along with no obvious attenuation over 50 h. A 73.7 % reduction in temperature non-uniformity and a 96.9 % decrease in the carbon deposition rate are also demonstrated. The underlying mechanism is attributed to unique highly interconnected and smooth hierarchical pores, for which large pores promote the penetration of sunlight while small pores enhance fluid-solid energy transfer. Effects of solar irradiation conditions and foam thermal conductivity are investigated numerically, providing guides for further reactor optimization under different operating scenarios. This work presents a new approach for designing and manufacturing efficient direct solar-driven thermochemical CO2-to-fuel conversion reactors using hierarchical TPMS biomimetic foams.

A strategy for CO2 capture and utilization towards methanol production at industrial scale: An integrated highly efficient process based on multi-criteria assessment

CO2 capture and utilization are an effective solution to the problem of CO2 emissions, and a combination of ammonia-based CO2 capture and its use for methanol production is a highly feasible strategy. However, the uses of conventional technologies have resulted in a high demand for energy, with limited use of hydrogen. To address these problems, an innovative strategy is proposed and demonstrated in this study that enhances the conventional design, i.e., to use ammonia-based CO2 capture with double tower absorption and solvent split, along with wet hydrogen for methanol production at industrial scale. The process is further improved through a multi-criteria assessment that considered the CO2 capture rate, NH3 loss rate, CO2 conversion rate, and energy saving factors, in which the latter is based on two components, namely the reboiler duty and the condenser duty. Moreover, an exergy analysis method is used to optimize the improved process, and a highly efficient integrated process is finally established. It has been found that the use of a double-tower absorption process ensures high rates of CO2 capture and low rates of NH3 loss. Additionally, adjusting the molar ratio of H2 to CO2 leads to an impressive 8% increase in the CO2 conversion rate, reaching 25%. In terms of energy savings, the average reboiler duty was reduced from 13.39 to 11.85 MJ/kgCO2, i.e., by 11.50%; while the condenser duty was reduced by 11.36%; both contributed to the overall energy savings. In the I-ACCMP process, the total exergy loss is 437.24 kW, of which the exergy loss of the heat exchangers accounts for 16%, and the desorption tower (DES) accounts for 48%. After optimization, the exergy loss of the heat exchangers decreases from 70.02 kW to 40.45 kW, the exergy loss of the DES decreases from 209.29 kW to 180.91 kW, and the reboiler duty is reduced from 10.60 MJ/kgCO2 to 7.71 MJ/kgCO2. The total exergy loss decreases from 437.24 kW to 372.68 kW, which is a reduction by 14.8%.

Plasma dynamic synthesis of dispersed metal oxide materials in CO2 medium

The steadily high interest in metal oxides, including in the form of fine powders, has led to a rapid increase in their production, the search for new synthetic methods and the expansion of possible applications. CO2 has proven itself as a cheap and abundant source of mild oxidant, which can potentially be used for oxidation reactions. However, the key problem of CO2 application is the necessity to break the bonds of the CO2 molecule that requires a large amount of energy. This work presents a fundamentally new approach for metal oxide synthesis, when applying CO2 as a gaseous precursor and oxidant, based on application of a pulsed arc discharge plasma of the electroerosion type. The implementation of the proposed method called plasma dynamic synthesis results in obtaining dispersed metal oxides that is demonstrated by the examples of Cu–O, Fe–O, Ti–O and Al–O systems. The influence of the metal-containing plasma type and operation modes on the formation of metal-oxide dispersed materials is studied. The multi-pulse operation mode in the considered system with titanium and aluminum electrodes provides obtaining almost completely oxidized products that is found to depend on the electronegativity of the initial metals. When applying aluminum electrodes, the process not only provides a high productivity of obtaining dispersed materials (up to 15 g per cycle), but also allows the CO2 conversion rate of up to 14.5%. Moreover, the electroerosion plasma demonstrates the energy efficiency of CO2 decomposition exceeding other plasma-based methods due to ongoing exothermic reactions of metal oxide formation. The as-synthesized products can be used to obtain bulk ceramic materials that is shown by the example of aluminum oxide powders. The hardness of the obtained ceramic specimens produced by SPS method is found to be ∼22 GPa and correlates with the best samples for aluminum oxides.

Unraveling the morphology and crystal plane dependence of bifunctional MnO2 catalyst for simultaneous removal of NO and CO at low temperature

It is indeed a challenging problem to simultaneously remove NO and CO from the steel sintering flue gas, in which a bifunctional catalyst has proven to be an efficient solution for removing both pollutants at low temperature. In this study, four different crystalline phases of MnO2 (α-, β-, γ-, and δ-) catalysts were synthesized via a facile hydrothermal method, and the effects of their crystal structure, morphology, and physicochemical properties on the catalytic performance for NO reduction and CO oxidation were elucidated. The results indicated that γ-MnO2 catalyst exhibited the best catalytic activity, achieving 90% NO removal efficiency and 82% CO conversion rate at 175 °C. Reaction kinetics confirmed that γ-MnO2 catalyst exhibited a lower Ea for both NO reduction and CO oxidation compared to α-MnO2, β-MnO2 and δ-MnO2 catalysts. Meanwhile, the interaction of between NH3-SCR and CO catalytic oxidation reactions over the catalysts was also studied. Intriguingly, it was found that the presence of CO enhanced the catalytic activity of γ-MnO2 catalyst in the NH3-SCR reaction. The results of NO + O2-TPD and in situ DRIFTS experiments revealed that CO contributed to the adsorption and oxidation of NO, thus promoting the L-H pathway over γ-MnO2 catalyst. Finally, a possible mechanism model for simultaneous removal of NO and CO over γ-MnO2 catalyst was proposed.

A simulation model for ruthenium-catalyzed dry reforming of methane (DRM) at different temperatures and gas compositions

Dry reforming of methane (DRM) is an environmentally friendly technology for producing syngas while consuming CO2. However, the short lifespan of catalysts due to metal sintering, coke deposition, and sulfur poisoning hinders its widespread adoption. To address such issues, perovskite catalysts, which have shown superior performance and resistance to coke formation and poisoning, were developed. In this study, a comprehensive simulation model of a DRM reactor that employs Sr0·92Y0·08Ti0·95Ru0·05O3-d (SYTRu5) using COMSOL Multiphysics software was developed. The objective of this study is to contribute to the understanding of the intricate dynamics of DRM process via utilizing simulation models. The simulation model considered five main reactions and calculated the properties of the gas mixture considering temperatures and compositions. Using the simulation model, the distribution of gas mole fractions and temperatures were obtained. According to the results, the H2 yield and CO2 conversion rate increased with increasing operating temperature. The temperature of the catalyst bed decreased rapidly owing to the endothermicity of the reaction. Additionally, the CH4 conversion rate increased with increasing proportion of CO2, whereas the reaction converged to an equilibrium state and the temperature difference in the catalyst bed decreased with decreasing gas flow rate.

Promotional effects of Ru and Fe on Ni/ZrO2 catalyst during CO2 methanation: A comparative evaluation of the mechanism

Ni-based catalysts are widely investigated non-noble metal-based systems for CO2 methanation. However, their industrial application is still limited due to lower activity at low-temperature and catalyst deactivation. Incorporating a second metal such as Ru and Fe is considered as a successful strategy to overcome these challenges through alloy formation or the synergies provided by the interplay of two adjacent metallic sites. Nonetheless, their promotional effect on the CO2 methanation mechanism under similar conditions has not been reported yet. In this work, Fe and Ru-promoted Ni/ZrO2 catalysts were investigated to evaluate their promotional effect on the mechanism. The Ni/Fe ratio was first optimized and a CO2 conversion rate of 37.7 mmolCO2/(molNi+Fe s) and 96.3% CH4 selectivity was obtained over the Ni0.8Fe0.2/ZrO2 catalyst. In comparison with Ni0.8Fe0.2/ZrO2, Ni0.8Ru0.2/ZrO2 prepared with the same composition showed higher activity and stability in CO2 methanation. Characterization results indicate alloys formation and H spillover for Ni0.8Ru0.2/ZrO2 to be responsible for promotion. Besides, in situ DRIFTS studies evidenced the occurrence of both CO2 dissociative and associative pathways over Ni0.8Ru0.2/ZrO2 catalyst, while solely the CO2 associative pathway occurred for Ni0.8Fe0.2/ZrO2.

The Effect of Alkali Metals (Li, Na, and K) on Ni/CaO Dual-Functional Materials for Integrated CO2 Capture and Hydrogenation.

Ni/CaO, a low-cost dual-functional material (DFM), has been widely studied for integrated CO2 capture and hydrogenation. The core of this dual-functional material should possess both good CO2 capture-conversion performance and structural stability. Here, we synthesized Ni/CaO DFMs modified with alkali metals (Na, K, and Li) through a combination of precipitation and combustion methods. It was found that Na-modified Ni/CaO (Na-Ni/CaO) DFM offered stable CO2 capture-conversion activity over 20 cycles, with a high CO2 capture capacity of 10.8 mmol/g and a high CO2 conversion rate of 60.5% at the same temperature of 650 °C. The enhanced CO2 capture capacity was attributed to the improved surface basicity of Na-Ni/CaO. In addition, the incorporation of Na into DFMs had a favorable effect on the formation of double salts, which shorten the CO2 capture and release process and promoted DFM stability by hindering their aggregation and the sintering of DFMs.

Delaminated and Pit-rich Nano-kaolinites obtained via an Intercalation-etching Method and their Application to Fischer–Tropsch Synthesis

AbstractModified kaolinites possess excellent adsorption properties and, therefore, are regarded widely as potential catalytic components. The use of modified kaolinites as a catalytic component for Fischer–Tropsch synthesis (FTS) has remained unexplored, however. In the current study, delaminated and pit-rich nano-kaolinite was prepared via acid treatment of N-methylformamide (NMF)-intercalated kaolinite (intercalation-etching strategy), and was used as a support to prepare a cobalt-based FTS catalyst (denoted as 15%-Co-HNKln). Compared with other FTS catalysts, the supports for which were raw kaolinite or directly acid-treated kaolinite, the 15%-Co-HNKln showed several advantages such as large specific surface area, dispersed Co particles with small particle size, more new active sites, and significant surface acidity. Given the aforementioned advantages, the 15%-Co-HNKln catalyst demonstrated very good FTS performance. Compared with that of the raw kaolinite-supported FTS catalyst, the CO conversion rate and C5–C12 hydrocarbon selectivity of 15%-Co-HNKln increased by 20% and 15%, respectively.

THE EFFECT OF Mn, Al DOPING ON THE CO2 HYDROGENATION PERFORMANCE OF CaCO3-SUPPORYED Fe-BASED CATALYSTS.

With increasingly serious environmental problems caused by the greenhouse effect, it has also become essential to reduce the concentration of CO2 in the atmosphere. In this paper, CaCO3-supported Fe-based catalysts doped with Mn, Al, and K are prepared by a straightforward method and used for CO2 hydrogenation. The fresh and spent catalysts were characterized by SEM-EDS, BET, TG, CO2-TPD, XRD, and XPS. The experimental results show that the highest CO2 conversion rate of Fe10Mn2Al10Ca is 35.99%, the maximum FTY value is 293.98 μmolCO2·g-1 Fe·s-1, the maximum O/P value is 6.61, and the lowest CO selectivity is 32.21%. At the same time, according to the characterization results, the doping of Mn and Al increased the Fe3O4/FeCx ratio. As the Fe3O4/FeCx ratio increases, the proportion of short-chain hydrocarbons (CH4, C2-4) in the products increases, and the proportion of long-chain hydrocarbons (C5+) decrease. Therefore, the co-doping of Mn and Al promotes the conversion of CO and reduces its selectivity, and promotes the formation of light olefins. Finally, it is hoped that this study can provide a reference for further research on CaCO3-supported Fe catalysts.

Pt clusters in carbon network to enhance photocatalytic CO2 and benzene conversion of WOx/g-C3N4 nanosheets

Noble metals in carbon networks dramatically improve the carrier separation and transfer efficiencies of layered graphic carbon nitride (g-C3N4) based heterostructures for efficient CO2 and benzene photocatalytic conversion. Here, Pt clusters are homogeneously incorporated into ultrathin g-C3N4 nanosheets via multi-step treatment method using the combinations of mechano-chemical pre-reaction and two-step thermal condensation processes. Small Pt nanoparticles with diameters of less than 5 nm are observed and WOx nanobelts with increased oxygen vacancies (as the active sites) are horizontally grown on the thin Pt-g-C3N4 nanosheets. The photocatalytic activities of the constructed composite materials are evaluated under full solar spectrum irradiation condition including water splitting, CO2 photoreduction, and benzene to phenol conversion. The WOx/Pt-g-C3N4 nanosheet heterostructures with optimized preparation condition and without adding any co-catalyst reveals enhanced H2 generation (5267 μmolg−1h−1) and CO2 photoreduction (5.89 and 3.12 μmolg−1h−1 for CO and CH4 conversion rate, respectively), as well as improved benzene to phenol conversion (89.0%) and selectivity (98.2%). The presence of Pt clusters in the heterostructures improves charge transport in-between g-C3N4 and WOx, thus enhances the charge separation efficiency of the composite material. Detailed photocatalytic mechanisms are discussed on the alteration from S-scheme WOx/g-C3N4 heterostructure to Z-scheme WOx/Pt-g-C3N4 heterostructure.

Preparation of Ce-MnOx Composite Oxides via Coprecipitation and Their Catalytic Performance for CO Oxidation.

Ce-MnOx composite oxide catalysts with different proportions were prepared using the coprecipitation method, and the CO-removal ability of the catalysts with the tested temperature range of 60-140 °C was investigated systematically. The effect of Ce and Mn ratios on the catalytic oxidation performance of CO was investigated using X-ray diffraction (XRD), X-ray energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), H2 temperature programmed reduction (H2-TPR), CO-temperature programmed desorption (CO-TPD), and in situ infrared spectra. The experimental results reveal that under the same test conditions, the CO conversion rate of pure Mn3O4 reaches 95.4% at 170 °C. Additionally, at 140 °C, the Ce-MnOx series composite oxide catalyst converts CO at a rate of over 96%, outperforming single-phase Mn3O4 in terms of catalytic performance. With the decrement in Ce content, the performance of Ce-MnOx series composite oxide catalysts first increase and then decrease. The Ce MnOx catalyst behaves best when Ce:Mn = 1:1, with a CO conversion rate of 99.96% at 140 °C and 91.98% at 100 °C.