Enhanced CO2 Conversion Research Articles

Lithium iodide promoted CO2 hydrogenation towards ethanol via biphasic lewis-acid-base pairs synergistic catalysis

Ethanol synthesis via CO2 hydrogenation is of great importance in view of its high-value utilization. Herein, combining with heterogeneous and homogenous catalysis, we have developed an efficient biphasic Lewis-acid-base pairs synergistic catalysis strategy from CO2 hydrogenation. Apart from conventional heterogeneous ethanol synthesis route, it was surprisingly found that LiI homogenous promoter significantly enhanced CO2 conversion, ethanol selectivity, and productivity. LiI promoted CO2 dissolution in pure water and accelerated reaction intermediates consumption, favoring CO2 conversion. In detail, it can weaken C-O bond of CH3OH intermediate through Li+-I- Lewis-acid-base catalysis. The formed CH3I* with lower bond energy for C-I was more facile to dissociate into CH3*, favoring its subsequent coupling with CO* to form ethanol. In combination of Rh1/CeTiOx catalyst, LiI promoter, and methanol as solvent, a record-breaking ethanol yield was achieved (223.1 mmol·g−1·h−1). The obtained ethanol yield was about 18.7 times of that reported the best result in literatures. Especially, the established catalyst system could also be applied for synthesis of higher-carbon-number alcohols by the CO2 hydrogenation with other alcohols solvent (CnH2n+1OH, n = 2,3…).

In‐Situ Dynamic Carburization of Mo Oxide with Unprecedented High CO Formation Rate in Reverse Water‐Gas Shift Reaction

AbstractIn situ construction of active structure under reaction conditions is highly desired but still remains challenging in many important catalytic processes. Herein, we observe structural evolution of molybdenum oxide (MoOx) into highly active molybdenum carbide (MoCx) during reverse water‐gas shift (RWGS) reaction. Surface oxygen atoms in various Mo‐based catalysts are removed in H2‐containing atmospheres and then carbon atoms can accumulate on surface to form MoCx phase with the RWGS reaction going on, both of which are enhanced by the presence of intercalated H species or Pt‐dopants in MoOx. The structural evolution from MoOx to MoCx is accompanied by enhanced CO2 conversion, which is positively correlated with the surface C/Mo ratio but negatively with the surface O/Mo ratio. As a result, an unprecedented CO formation rate of 7544.6 mmol ⋅ gcatal−1 ⋅ h−1 at 600 °C has been achieved over in situ carbonized H‐intercalated MoO3 catalyst, which is even higher than those from noble metal catalysts. During 100 h stability test only a minimal deactivation rate of 2.3 % is observed.

In-Situ Dynamic Carburization of Mo Oxide with Unprecedented High CO Formation Rate in Reverse Water-Gas Shift Reaction.

In situ construction of active structure under reaction conditions is highly desired but still remains challenging in many important catalytic processes. Herein, we observe structural evolution of molybdenum oxide (MoOx) into highly active molybdenum carbide (MoCx) during reverse water-gas shift (RWGS) reaction. Surface oxygen atoms in various Mo-based catalysts are removed in H2-containing atmospheres and then carbon atoms can accumulate on surface to form MoCx phase with the RWGS reaction going on, both of which are enhanced by the presence of intercalated H species or Pt-dopants in MoOx. The structural evolution from MoOx to MoCx is accompanied by enhanced CO2 conversion, which is positively correlated with the surface C/Mo ratio but negatively with the surface O/Mo ratio. As a result, an unprecedented CO formation rate of 7544.6 mmol ⋅ gcatal -1 ⋅ h-1 at 600 °C has been achieved over in situ carbonized H-intercalated MoO3 catalyst, which is even higher than those from noble metal catalysts. During 100 h stability test only a minimal deactivation rate of 2.3 % is observed.

N-doped carbon dots-modulated interfacial charge transfer and surface structure in FeNbO4 photocatalysts for enhanced CO2 conversion selectivity to CH4

The photocatalytic carbon dioxide reduction reaction (CO2RR) is an innovative and reliable technology to address the issues of energy shortage and climate change simultaneously. However, issues such as insufficient light absorption, rapid electron-hole recombination and low surface activity during CO2RR severely limit the catalysts’ efficiency for photocatalysis. In this study, we present nanohybrid N-CDs/FeNbO4 catalysts to overcome these challenges and achieve high-efficient photocatalytic conversion of CO2 to CH4. The enhancement process starts with the introduction of modified N-CDs, which have a broad light absorption capability. These N-CDs also help to modulate the interfacial charge transfer kinetics, leading to improved charge separation and transfer. This, in turn, enhances the multielectron transfer conversion selectivity of CO2 to CH4. Meanwhile, CO2 adsorption on the photocatalysts is increased due to the creation of oxygen vacancies and lattice stresses resulting from the introduction of N-CDs. This work presents a new approach for improving the photocatalytic performance by adjusting surface structure and interfacial behaviors.

Enhanced CO2 conversion through confinement of cross-linked ionic polymer within the pores of porous carbon materials

It is crucial to employ an integrated catalyst to avoid the complications of the recovery process. This work reports the fabrication of porous carbon@ionic liquid (PC@IL) composites with readily accessible active ion sites, achieved by confining cross-linked ionic liquid (IL) within the channels of porous carbon (PC). The incorporation of porous carbon not only confines the IL within its framework, creating microsites for CO2 adsorption and conversion, but also simplifies catalyst recovery. The results indicate that PC@IL composites exhibit excellent cycloaddition activity towards CO2 in a co-catalyst- and solvent-free environment. Notably, PC@IL(C)-24 demonstrates remarkable catalytic performance across various epoxides under 1 bar of CO2, with yields above 90 % at 90 °C for 12 h, and achieving a remarkable styrene carbonate yield of up to 92.8 % under a CO2 pressure of 1 bar (at 100 °C for 12 h). Control experiments confirm that the confinement effect exerted by N,S co-doped carbon on cross-linked IL plays a pivotal role in enhancing both stability and activity of PC@IL composites, thereby providing novel insights for designing functionalized porous carbon catalysts for CO2 cycloaddition conversion.

Bimetallic NiCu catalyst derived from spent MOF adsorbent for efficient photocatalytic CO2 reduction

The metal–organic frameworks (MOFs) rich in porous structures and their derivatives have been widely developed and applied to heavy metal adsorption. However, little attention has been paid to the subsequent treatment and reutilization of spent MOFs adsorbents. A potential feasible strategy is to develop MOFs-derived bimetallic catalysts for energy conversion. Herein, a bimetallic Ni-Cu2O-Cu/C nanocomposite (Ni-Cu/C) derived from spent Cu-based MOFs (CuBTC) adsorbents was fabricated and applied to improve the performance of photocatalytic CO2 reduction. The results demonstrate that Ni doping could improve the charge transfer dynamics. The synthesized Ni-Cu/C catalyst exhibits a high CO yield (12.45 μmol g−1 h−1) in the pure water system in the absence of other photosensitizers and sacrificial agents, which is 2.05 folds higher compared to Cu/C. The CO2 conversion selectivity of the synthesized Ni-Cu/C catalyst reaches up to 99.0%. The mechanism of photocatalytic CO2 reduction reaction was further investigated by in-situ experiments and density functional theory calculation. The in-situ FT-IR characterization show that photogenerated electrons could effectively adsorb CO2 to produce CO2− and optimize *CO immediate. This work not only emphasizes the unique design of bimetallic catalyst derived from spent MOFs adsorbent, but also contributes a feasible solution to its reutilization for enhanced CO2 conversion.

The Impact of Nife-Based Metal Alloy on CO2 Conversion to CH4 and Carboxylic Acids in a Microbial Electrosynthesis Cell

The goal of this study was to evaluate the impact of NiFe-based metal alloys on the CO2 conversion to carboxylic acids and methane (CH4) in CO2-fed Microbial Electrosynthesis (MES) cells. First, the impact of transition metal alloys on CO2 conversion and product specificity was studied in a MES cell with a conductive polymer cathode with electrodeposited NiFeBi alloy. It was found that the presence of the NiFeBi alloy significantly decreased production of CH4 from 0.5 to 0.1 L (Lc d) – 1, suggesting that methanogenic activity was suppressed in the presence of NiFeBi. On the other hand, the production of carboxylic acids consisting mainly of acetate, propionate and butyrate increased. Specifically, acetate production, which represented 80% of the total carboxylic acids in the cathode liquid increased by 70% to 1.0 g(Lc d)-1. This initial study demonstrated that product selectivity can be influenced by electrodeposition of transition metal alloys such as NiFeBi. It might be preferable to achieve selective production of high value long chain carboxylic acids such as valerate and caproate instead of acetate.Accordingly, in the following experiments NiFeMn and NiFeSn alloys were electrodeposited on carbon felt cathodes and evaluated for enhanced CO2 conversion in MES cells. Both alloys enhanced CH4 production, which reached 0.8 L (Lc d)-1. However, there was no observable improvement in acetate production (0.2 – 0.5 g (Lc d)-1) or other higher chain carboxylic acids in comparison to NiFeBi – coated MES. It was suggested that by using a more biocompatible carbon-based support for alloy electrodeposition, it is possible to improve acetate, butyrate and caproate production. In addition, it is important to facilitate nutrient transport through the three-dimensional (3D) cathode. Limited transport of CO2, H2 and nutrients was identified as a potential rate-limiting factor when using carbon felt electrode. 3D-printed conductive polymer lattices were manufactured and electrodeposited with NiFeSn and NiFeMn alloys. The NiFeMn-coated lattice showed insignificant improvement in higher chain carbon production, however caproate concentration was increased five folds on NiFeSn-coated cathode. Also, electrochemical characterization demonstrated increased hydrogen evolution reaction rate over time. Nevertheless, the throughput of this product remained low at 0.1 g (Lc d)-1).These results indicate that the presence of the NiFe-based metal alloys significantly influenced the electron transfer efficiency from the cathodes to microbial electroactive biofilms leading to increased formation of carboxylic acids in the cathode liquid. Therefore, the next step is to design more efficient 3D conductive polymer lattice electrodeposited with NiFeSn metal alloy to increase CO2 conversion to longer chain carboxylic acids.

Enhanced Co3O4 Nanoflakes Reactivity via Integrated Al-Doping and Metal Vacancy Engineering for Large Capacity Li-CO2 Batteries

Rechargeable Li-CO2 batteries are well-regarded for their high-energy, environmental friendliness, and resourceful use of CO2, but suffer from poor cycle reversibility. Herein, Al-doped Co3O4 nanoflakes featuring abundant metal vacancies (V-ACO/CC) were synthesized via a facile approach employing Al ions as both a dopant and sacrificial agents, which serve as high-efficient cathode catalyst for Li-CO2 batteries. Experiment results demonstrate that the incorporation of Al doping and metal vacancies modulates the electronic structure of Co-center and optimizes the growth path of discharge product. The cation vacancies generated by the sacrificed part of the Al atoms change the local charge distribution, strengthen the affinity of CO2 and reaction intermediates and facilitate the reversible decomposition of discharge products. Concurrently, the formation of covalent Al-O bonds by the remaining Al species reinforces the stability of nanostructures. Notably, the V-ACO/CC-based LCBs exhibit enhanced CO2 conversion kinetics, as evidenced by a high specific capacity (12.06 mAh cm−2 at 0.05 mA cm−2), fast rate capability and impressive stability (over 420 cycles under 0.1 mA cm−2).

Promoting Effect of Pd Nanoparticles on SrTi0.8Mn0.2O3 in the Reverse Water‐Gas Shift Reaction via the Mars–van Krevelen Mechanism

The reverse water‐gas shift (RWGS) reaction serves as a critical pathway for converting CO2 into diverse chemicals. The Mars–van Krevelen (MvK) mechanism, which leverages lattice oxygen as the oxidant and oxygen vacancies as reductants, offers an alternative catalytic strategy for the selective RWGS reaction. While Mn‐substituted SrTiO3 (i.e., SrTi0.8Mn0.2O3) has been shown to promote the RWGS reaction selectively via the MvK mechanism, achieving a sufficient conversion of CO2 necessitates elevated temperatures. This study investigated the effect of Pd‐loaded SrTi0.8Mn0.2O3 on the activation of adsorbed H2 molecules, which generated oxygen vacancies and enhanced CO2 conversion. Notably, 1.0 wt% Pd‐loaded SrTi0.8Mn0.2O3 yielded 13.4% of CO at 673 K, whereas pristine SrTi0.8Mn0.2O3 and Pd‐loaded SrTiO3 yielded negligible or minimal amount of CO. Hydrogen temperature‐programmed reduction and X‐ray absorption spectroscopy measurements revealed that Pd promoted the formation of oxygen vacancies via both thermodynamic and kinetic mechanisms. Fourier transform infrared spectroscopy and kinetic studies revealed that the RWGS reaction over Pd‐loaded SrTi0.8Mn0.2O3 proceeded primarily via the MvK mechanism with a partial contribution from the Langmuir–Hinshelwood mechanism. This study underscores the effectiveness of combining metal and MvK‐type catalysts to enhance the efficiency of the RWGS reaction.

Efficient synthesis of CO and H2O2 via nanosecond pulsed CO2 bubble discharge

In the context of escalating global efforts to mitigate carbon emissions and explore sustainable energy resources, the transformation of CO2 into valuable chemicals and fuels via plasma technology has garnered significant attention. This study demonstrated a new pathway of CO2 conversion into CO and H2O2 via the bubble-enabled gas-liquid discharge driven by a nanosecond pulse. Results showed that the increased discharge frequency and larger pulse widths could enhance CO2 conversion rates and H2O2 yields, albeit potentially at the cost of reduced energy efficiency. Conversely, the rising time of pulse showed negligible impact on the process, whereas varying gas flow rates significantly altered CO and H2O2 yields, underscoring the nuanced influence of these parameters on the efficiency and selectivity of conversion processes. Through illuminating the dynamics of bubble discharge-assisted CO2 transformation, this study contributes to the broader understanding of gas-liquid discharge driven by nanosecond pulse, underlining its potential for addressing environmental and energy challenges.

Non-PGM hollow fibre-based after-treatment for emission control under real diesel engine exhaust gas conditions

Hollow fibre (HF)-based technologies for emission control, as an alternative to the traditional monolithic technology, offers a promising route to the uptake of non-PGM catalytic systems. In this work, a series of Cu-doped LaCoO3 perovskites were investigated as potential non-PGM Diesel Oxidation Catalysts (DOC). Two HF-based modules, comprising single-channel (i.e., 1CM) and four-channel (i.e., 4CM) HFs respectively, were impregnated with the best catalyst candidate, and their performance was tested under real exhaust gas conditions, using a single-cylinder diesel engine. Compared to the 1CM, the 4CM demonstrated enhanced CO conversion, and reduced performance towards Total Hydrocarbon (THC) conversion. Overall, these findings reveal the influence of HF morphology on catalytic performance, and in turn, will contribute towards the refinement of HF-based technology for emission control, as well as enabling the transition towards non-PGM catalytic systems.

Enhanced CO2 conversion with CH4 for greenfuel generation using coke-neutral nickel-loaded fibrous silica titania catalysts

This study reveals a groundbreaking advancement in utilizing carbon dioxide (CO2) for syngas production through methane (CH4) dry reforming using Fibrous Silica Titania (FST) as a support, loaded with different (1%, 3%, and 5%) nickel dosages. FST is distinguished by its fibrous structure, maintains a stable temperature, facilitates the confinement and dispersion of active metal, and is exceptionally effective at preventing carbon deposition. For a thorough examination of the new catalysts, characterization methods including XRD, FESEM, EDX mapping, N2 physisorption, FTIR-KBr, H2-TPR, and CO2-TPD were employed. Importantly, TEM lattice fringes verified the existence of XRD peaks and planes of Ni (111), Ni (200), and TiO2 (101). Aspects such as O-H stretching, Si-O-Si asymmetry, vibrations caused by external Si-OH groups, and Si-O-Si bending were identified using FTIR-KBr analysis. The study ingeniously identified the superior (3Ni/FST) catalyst, which exhibited moderate basicity sites on the CO2-TPD at approximately 350 °C. The catalyst converted nearly 100% CH4 at 750 °C with minimal coke production and 80% CO2 at 850 °C. Surprisingly, the 3Ni/FST catalyst demonstrated remarkable stability during a 72 h TOS stability test at 650 °C, effectively preventing coke-forming side reactions such as CO disproportionation, CO hydrogenation, CO2 and CH4 cracking with syngas ratio around unity and little coke production. The FST support exhibited exceptional attributes for low temperature carbon neutral CH4 reforming.

Modeling analysis of water-gas-shift reaction on catalyst-packed ceramic-carbonate dual-phase membrane reactor for hydrogen production

Water-gas shift (WGS) reaction for hydrogen production and CO2 removal/capture in a catalyst-packed CO2-permselective membrane reactor is studied experimentally and simulated with a computational model. The reactor utilizes a tubular dense ceramic-carbonate dual-phase membrane with a commercial high-temperature WGS catalyst. Equations governing CO2 permeation through the membrane and WGS reaction kinetics on the catalyst were obtained through independent CO2 permeation experiments and a fixed-bed reaction kinetic study. The simulation results using the validated model are presented to examine the effects of feed gas composition, steam/CO ratio, gas hourly space velocity, temperature, reactor pressure, sweep to feed molar flow rate ratio, and the membrane area to catalyst volume ratio on the performance of the membrane reactor for WGS with CO2 removal. Under optimized conditions, the catalyst-packed membrane reactor for WGS demonstrates significantly enhanced CO conversion and product H2 purity by effectively removing/capturing CO2 from the WGS reaction side.

CO2 hydrogenation to synthetic natural gas with light hydrocarbons on Mn-promoted mesoporous Co3O4-Al2O3 metal oxides

Direct CO2 conversion into synthetic natural gas (SNG, CH4) with simultaneous small production of light paraffinic C2-C4 hydrocarbons to enhance a heating value of SNG was investigated with ordered mesoporous CoMnAl mixed metal oxides (denoted as m-CoMnAl). CO2 hydrogenation activity to form hydrocarbons with small CO byproduct formed by a reverse water gas shift reaction (RWGS) was strongly affected by the MnO2 promoter content in the ordered Co3O4-Al2O3 mesoporous structures. The m-CoMnAl structures with proper amount of Mn promoter were found to be effective to enhance CO2 conversion to methane with small amount of light hydrocarbons formation, which were mainly attributed to the presence of abundant oxygen vacant sites with a stable preservation of the partially oxidized cobalt nanoparticles in the ordered mesoporous Co3O4-Al2O3 structures even under a reductive hydrogenation condition. Selective methanation of CO2 was found to be more favorable on the highly reduced metallic cobalt nanoparticles formed with smaller amount of Mn promoter (m-CoMnAl(0.05)), however, excessive Mn content such as Mn/Co ratio > 1 (m-CoMnAl(1.0)) revealed less structural stability of ordered mesoporous structures with lower CO2 conversion with relatively higher CO selectivity of 1.4 % with lower olefin selectivity through severe phase segregations of the Co-Mn-Al mixed metal oxides with selective formations of MnCO3 phases.

Enhanced CO2 conversion in dielectric barrier discharge plasma coupled with a heterojunction photocatalyst.

CsPbBr3 quantum dots were grown on ReS2 nanosheets to form CsPbBr3@ReS2 heterojunctions using an anti-solvent method. The composition, morphology, spatial distribution, and optical absorption of samples were characterized. CsPbBr3@ReS2-15 exhibits not only a higher photocatalytic performance than CsPbBr3 due to the improved optical absorption and Z-scheme charge migration, but also a higher CO2 conversion ratio (35.60%) and energy efficiency (13.10%) in the dielectric barrier discharge (DBD) plasma due to superior photocatalytic activity, increased micro-discharge time, and improved discharge uniformity. This work provides a strategy for plasma photocatalytic CO2 conversion.

Non-equilibrium plasma co-upcycling of waste plastics and CO2 for carbon-negative oleochemicals

Concept of plasma co-upcycling waste plastics and CO2. CO2 serves as an oxidant and carbon source to depolymerize polyolefins into platform chemicals, whereas plastics enhance CO2 conversion. Fatty alcohols are selectively produced by adding O2.

Up–conversion and Landau damping effect of Ni1–xNdx(OH)2/Ti3C2 to improve the selectivity of thermal coupled photocatalytic reduction of CO2

Photocatalysis is currently used to enhance CO2 conversion, while improving selectivity is challenging. Herein, Ni1–xNdx(OH)2/Ti3C2 consisting of Nd3+–doped in β–Ni(OH)2 and Ti3C2-MXene was prepared for the selective reduction of CO2 to CO by thermal coupled photocatalytic. The effect of the introduction of the up–conversion effect is (1) to increase the concentration of photogenerated electrons and (2) to increase the catalyst surface temperature. The increased concentration of photogenerated electrons leads to an enhanced Landau damping effect, thus the number of high-energy hot electrons supplementing the Ti3C2 increases. The valence band upward shift reduces the ability of Ni1–xNdx(OH)2/Ti3C2 to dissociate H2. The increased surface temperature of the catalyst and the reduced dissociation of H2 facilitate the thermal coupled photocatalytic reduction of CO2 to CO. A maximum CO yield of 532.9 μmol·gcat.−1·h−1 and CO selectivity of 82.5% was realized on the Ni0.56Nd0.01(OH)2/Ti3C2.

Rational catalyst structural design to facilitate reversible Li-CO2 batteries with boosted CO2 conversion kinetics

Lithium-CO2 batteries (LCBs) are regarded as a promising energy system for CO2 drawdown and energy storage capability which has attracted widespread interest in carbon neutrality and sustainable societal development. However, their practical application has been limited by slow kinetics in catalytic reactions and poor reversibility of Li2CO3 products which leads to the issue of a large overpotential, low energy efficiency and poor reversibility. Herein, an efficient catalyst design and synthesis strategy is proposed to overcome the abovementioned bottleneck. Through an electrical joule heating procedure, Pt with random crystal orientations is converted into a 3D porous Pt catalyst with preferred (111) crystal orientation within seconds, exhibiting enhanced CO2 conversion kinetics with superior electrochemical performance. This includes ultralow overpotential (0.45 V), fast rate charging (up to 160 µA cm−2) and high stability (over 200 cycles under 40 µA cm−2). A proof-of-concept stacked Li-CO2 pouch cell, with stable operation under practical current density is demonstrated, indicating significant potential for large-scale operations. This bottom-up design of efficient catalysts and synthesis strategy offers a rapid and cost-effective approach to maximizing catalytic sites for CO2 conversion under restricted catalyst loading, showcasing its versatility across a broad spectrum of catalyst-based energy conversion and storage systems.

Translating clean liquid fuels synthesis with low aromatics over NaFe@C/HZSM-22 directly in CO2 hydrogenation

Fuel production is an option for valorizing CO2, yet deficient catalysts meeting the standard fuel production has impeded progress of this promising technology. Herein, liquid fuel synthesis is rationalized over a catalyst consisting ‘C′, ‘Na’, and ‘Fe’, as in NaFe@C, configured with ZSM-22 and ZSM-5 in CO2 hydrogenation. While the ‘Na’ and ‘C′ functioned as structural promoters on Fe to enhance CO2 conversion and olefins synthesis, the characteristics of the zeolites facilitated oligomerization of lighter hydrocarbons. A high C5 + selectivity was obtained over the HZSM-22 composite in CO2 hydrogenation dominated by olefins and isoparaffins. Model reactions for exemplar oligomerization activity over the zeolites revealed ZSM-5 as highly active with selectivity towards isoparaffins and aromatic. The ‘Na’ cations induce Lewis’s acid sites (LAS) which suppresses hydrocracking during chain growth. This consistency, revealed between the model and CO2 hydrogenation unlocks a door to zeolite usage in CO2 hydrogenation to clean heavy hydrocarbons.

Thermodynamic analysis of ethanol synthesis by CO2 hydrogenation using Aspen Plus: effects of tail gas recycling and CO co-feeding

Synthesis of ethanol by CO2 hydrogenation presents an efficient way to convert CO2 into value-added fuels and chemicals. For practical applications, recycling unreacted tail gas as well as CO co-feeding plays a key role to enhance CO2 conversion to ethanol. Thus, it is of great significance to study the effects of recycling unreacted tail gas and CO co-feeding on the chemical equilibrium. Herein, we perform a thermodynamic study to analyze the hydrogenation of CO2 to ethanol using Aspen Plus. The effects of recycling tail gas and CO co-feeding on CO2 conversion and ethanol selectivity at different temperatures and pressures are investigated. Both the optimal recycle ratio and CO/(CO + CO2) ratio in the feed are found to enhance ethanol synthesis from CO2 hydrogenation.