Catalysts For CO2 Hydrogenation Research Articles

Exploring the sustained release catalysis of CuAl2O4 spinel for highly effective CO2 conversion to CO

Sustained Release Catalysis concept has been demonstrated over Cu-based spinel catalysts to retard Cu agglomeration via gradually releasing active copper from spinel lattice during catalytic reaction. Herein, the solid-phase synthesized stoichiometric CuAl2O4 spinel is illustrated to be an effective sustained release catalyst for CO2 hydrogenation to CO (RWGS). Characterizations point out a mechanism that active Cu can be liberated from spinel lattice under the RWGS atmosphere, forming Cu-deficiency defect spinel with abundant surface hydroxyl groups on rearranged spinel Al ions. Cu entities and surface hydroxyls can well activate H2 and CO2, producing monodentate and bidentate formate species as crucial intermediates for CO, especially, the monodentate formate located on spinel octahedral AlVI presents superior dissociation performance and contributes more to the CO formation. The successful application of the Sustained Release Catalysis concept in RWGS provides significant insight for understanding the catalytic dynamics of Cu-spinel catalysts in CO2 hydrogenation process.

A Brief Review of Recent Theoretical Advances in Fe-Based Catalysts for CO2 Hydrogenation.

Catalytic hydrogenation presents a promising approach for converting CO2 into valuable chemicals and fuels, crucial for climate change mitigation. Iron-based catalysts have emerged as key contributors, particularly in driving the reverse water-gas shift and Fischer-Tropsch synthesis reactions. Recent research has focused on enhancing the efficiency and selectivity of these catalysts by incorporating alkali metal promoters or transition metal dopants, enabling precise adjustments to their composition and properties. This review synthesizes recent theoretical advancements in CO2 hydrogenation with iron-based catalysts, employing density functional theory and microkinetic modeling. By elucidating the underlying mechanisms involving metallic iron, iron oxides, and iron carbides, we address current challenges and provide insights for future sustainable CO2 hydrogenation developments.

Mg enhanced the performance of Cu/ZnO/ZrO2 for CO2 hydrogenation to methanol and the mechanism investigation

Optimizing the microstructure of copper-based catalysts for CO2 hydrogenation to methanol is an attractive and widely reported strategy, but there are still certain barriers to improving both carbon dioxide conversion rate and methanol product selectivity. Herein, Cu/ZnO/ZrO2/MgO (CZZ1-xMx) catalysts were synthesized by co-precipitation method for CO2 hydrogenation to methanol. Furthermore, the structural features and reaction processes were systematically characterized by XRD, TEM, nitrogen adsorption/desorption, H2-TPR, CO2-TPD and in-situ DRIFT. The results showed that Mg species optimized the microstructure of the catalyst, increased the dispersion of active species and constructed appropriate basic sites. This further enhanced the capture of reactive species and improved the CO2 hydrotreating to methanol reaction performance, which was accompanied by a simultaneous increase in CO2 conversion and methanol yield. It could be convinced that the highest space time yield (STY) of methanol (305.3 gMeOH kgcat−1 h−1) was obtained at 220 °C, WHSV = 18,000 mL gcat−1 h−1 and 3 MPa (XCO2 = 7.28%, SMeOH = 71.8%) for the optimized CZZ0.8M0.2 catalyst, which exhibited twice the CO2 conversion than Cu/ZnO/ZrO2. This work elaborated a scheme for the preparation of efficient methanol catalysts. providing reference for the research of CO2 hydrogenation to methanol process.

Nanometric Cu-ZnO Particles Supported on N-Doped Graphitic Carbon as Catalysts for the Selective CO2 Hydrogenation to Methanol.

The quest for efficient catalysts based on abundant elements that can promote the selective CO2 hydrogenation to green methanol still continues. Most of the reported catalysts are based on Cu/ZnO supported in inorganic oxides, with not much progress with respect to the benchmark Cu/ZnO/Al2O3 catalyst. The use of carbon supports for Cu/ZnO particles is much less explored in spite of the favorable strong metal support interaction that these doped carbons can establish. This manuscript reports the preparation of a series of Cu-ZnO@(N)C samples consisting of Cu/ZnO particles embedded within a N-doped graphitic carbon with a wide range of Cu/Zn atomic ratio. The preparation procedure relies on the transformation of chitosan, a biomass waste, into N-doped graphitic carbon by pyrolysis, which establishes a strong interaction with Cu nanoparticles (NPs) formed simultaneously by Cu2+ salt reduction during the graphitization. Zn2+ ions are subsequently added to the Cu-graphene material by impregnation. All the Cu/ZnO@(N)C samples promote methanol formation in the CO2 hydrogenation at temperatures from 200 to 300 °C, with the temperature increasing CO2 conversion and decreasing methanol selectivity. The best performing Cu-ZnO@(N)C sample achieves at 300 °C a CO2 conversion of 23% and a methanol selectivity of 21% that is among the highest reported, particularly for a carbon-based support. DFT calculations indicate the role of pyridinic N doping atoms stabilizing the Cu/ZnO NPs and supporting the formate pathway as the most likely reaction mechanism.

Copper nanoparticles encapsulated in zeolitic imidazolate framework-8 as a stable and selective CO2 hydrogenation catalyst

Metal–organic frameworks have drawn attention as potential catalysts owing to their unique tunable surface chemistry and accessibility. However, their application in thermal catalysis has been limited because of their instability under harsh temperatures and pressures, such as the hydrogenation of CO2 to methanol. Herein, we use a controlled two-step method to synthesize finely dispersed Cu on a zeolitic imidazolate framework-8 (ZIF-8). This catalyst suffers a series of transformations during the CO2 hydrogenation to methanol, leading to ~14 nm Cu nanoparticles encapsulated on the Zn-based MOF that are highly active (2-fold higher methanol productivity than the commercial Cu–Zn–Al catalyst), very selective (>90%), and remarkably stable for over 150 h. In situ spectroscopy, density functional theory calculations, and kinetic results reveal the preferential adsorption sites, the preferential reaction pathways, and the reverse water gas shift reaction suppression over this catalyst. The developed material is robust, easy to synthesize, and active for CO2 utilization.

Effects of surface groups on Fe/ZnO catalysts for CO2 hydrogenation to olefin

Control of product distribution over CO2-FTO is challenging due to the difficulty in governing the C–C coupling of CHx species. Surface modification to iron catalysts shows potential but its role remains indistinct. Fe/ZnO was used as a model catalyst to investigate the effects of the surface groups on its catalytic performance for CO2-FTO. On hydroxyl group modified Fe/ZnO by H2O2-treatment, at 1000 h–1, 300 °C, and 1 MPa, the CO2 conversion, and the C4+ linear α-olefin selectivity rose to 50.2 % and 48.1 %, respectively. Alkyl group modified Fe/ZnO by stearic acid treatment exhibited higher activity (48.4 %) and the C2=–C3= selectivity (31.0 %). Characterizations showed that decorating the hydroxyl group boosted the formation of Fe5C2 and CHx species, promoting the chain growth for long-chain olefin, whereas the alkyl group modification retarded the activity decline through stabilizing active FeCx phases and forming graphite carbon which was conducive to suppressing secondary hydrogenation.

LDH-derived CoTiAl mixed oxide as catalyst for photo-assisted CO2 hydrogenation

A layered double hydroxide (LDH) has been used as precursor for the synthesis of a multimetallic mixed oxide with photocatalytic activity. Thus, a trimetallic CoTiAl LDH has been synthesized as spherical aggregates of nanosheets. Analysis at short synthesis times indicates that CoTiAl-LDH particles grow perpendicular to initially formed oligomeric Ti-lactate nuclei. Calcination of CoTiAl-LDH at 400 °C affords the corresponding CoTiAl mixed oxide (MO) with low crystallinity having a cobaltite structure, while also maintaining the morphology. This CoTiAl-MO exhibits at 200 °C photocatalytic activity for CO2 hydrogenation to CO, accompanied with lesser amounts of CH4, with remarkable apparent quantum yields at 365 nm of 7.0 and 4.6 for CO and CH4, respectively and very low apparent activation energy for 10 kJ/mol. The present results show a promising direction to exploit the potential that the preparation of multimetallic LDH offers for the synthesis of mixed oxides with optimal compositions for an even more enhanced photocatalytic activity.

Synthesis and evaluation of novel Cu-based adsorbent-containing catalysts for CO2 hydrogenation to methanol and value-added products

In this work, sequential incipient wetness impregnation method was used to synthesize Cu/Al2O3, Cu/Na2O/Al2O3 and Cu/CaO/Al2O3 catalysts in different compositions for CO2 conversion to value-added products. Synthesized catalysts were characterized using various analytical techniques and their performances for CO2 catalytic conversion were tested in a high-pressure packed bed reactor under reaction conditions of P = 60 bars, T = 300 °C, and H2/CO2 = 3. The obtained results revealed that the type of adsorbent had a significant impact on CO2 conversion, with CaO-containing catalyst being more efficient for methanol selectivity. Increased Cu content from 10 wt% to 30 wt% with fixed CaO content of 10 wt% resulted in a small increase in CO2 conversion where the highest CO2 conversion of 16.44% and the highest methanol selectivity (17.75%) were obtained for catalyst containing 20 wt% of copper. The best performing catalyst was further promoted using 0.5 wt% Rh promoter which improved both methanol selectivity and space time yield to 23.2% and 0.08 gMeOHgcat−1h−1, respectively. The comparative high performance of the Rh-promoted catalyst was attributed to smaller metal oxide particle size with uniform dispersion, presence of effective hydrogen spill over, moderate basic sites, surface defects and presence of induced copper species.

Alkali metal promotion on Fe-Co-Ni trimetallic catalysts for CO2 hydrogenation to light olefins

The catalyst obtained by calcination of the precursor Fe-Co-Ni trimetallic MOFs has exhibited great CO2 hydrogenation performance. To further improve the selectivity of target product light olefins and the catalyst stability, alkali metal doping is used to modify the Fe-Co-Ni trimetallic catalyst, and the effects of different types of alkali metals and different doping methods are also studied. After alkali metal doping, the increased electron concentration around Fe atoms, the enhanced alkalinity of the catalyst surface and the weakened H2 activation can improve CO2 uptake while decreasing H2 affinity, thereby inhibiting the alkane formation. Among all the catalysts doped by alkali metal, FCN-K(a) obtained by potassium citrate impregnation after calcining has the largest specific surface area, the highest microporosity and the most alkaline sites on its surface, showing the best CO2 hydrogenation performance with a CO2 conversion of 47.5 % and selectivity of light olefins 46.8 %. Meanwhile, the catalyst stability is greatly improved after alkali metal doping during ∼ 50 h test. The characterization results of spent catalysts show that FCN-K(a) has the largest amount of active phase Fe5C2 for C–C coupling. Doping with a proper amount of K can promote the carbonization of Fe and improve the stability of the active phases.

Highly active single-layer 2H-MoS2 for CO2 hydrogenation to methanol

Few-layer MoS2 were recently discovered as promising catalyst for CO2 hydrogenation to methanol, despite extreme conditions proposed for its synthesis. Herein, we developed an exceptionally facile, safe, and scalable strategy to prepare single-layer MoS2 (s-MoS2) at ambient pressure using instantaneous self-assembled micelles of didodecyldimethylammonium (DA)−MoS4 complexes as precursor. During the pyrolysis, the presence and subsequent decomposition of coordinated DA inhibited the growth and sheet-stacking of MoS2 in c-direction, resulting in discrete s-MoS2 molecular sheets which maximize the exposure of in-plane S vacancies (Sv). Remarkably, s-MoS2 displayed 77% methanol selectivity and methanol space time yield of 1.54 g·gMoS2–1·h–1, representing the top levels among reported MoS2 catalysts under similar conditions. Density functional theory (DFT) simulations attribute high activity of s-MoS2 to its ability to stabilize in-plane low-coordinated Mo atoms in the vicinity of Sv on both sides of monolayer. The superior performance of s-MoS2 creates new prospects for technological applications beyond CO2 hydrogenation.

Natural Sunlight‐Driven CO2 Hydrogenation into Light Olefins at Ambient Pressure over Bifunctional Cu‐Promoted CoFe Alloy Catalyst

AbstractThe natural sunlight‐driven conversion of CO2 into valuable C2+ products is urgently being pursued at ambient pressure, yet it poses a substantial challenge. Herein, a bifunctional Cu‐promoted CoFe alloy catalyst is designed for the natural light‐driven CO2 hydrogenation into light olefins. Under a weak solar‐irradiation intensity of 0.45 kW m−2 (0.45 sun), the optimal catalyst exhibits excellent activity and selectivity, with an impressive 73.7% selectivity for C2+ hydrocarbons and an outstanding 56.5% selectivity for C2‐4 olefins, which is the best catalyst for C2+ hydrocarbons photosynthesis from natural sunlight to date. The bifunctional design of the catalyst combines the advantages of both metallic Cu and CoFe alloy components, providing a synergistic effect that enhances the CO2 hydrogenation performance. The Cu promoter plays a crucial role in enhancing the adsorption of CO2 and hydrogen spillover, while the CoFe alloy provides a stable coupling site of the C1 intermediate for promoting the C2‐4 olefins. This study provides new insights into the design of bifunctional catalysts for CO2 hydrogenation and opens up new possibilities for sustainable production of light olefins from renewable resources.

Application of Intermetallic Compounds as Catalysts for the Selective Hydrogenation of CO2 to Methanol

AbstractDirect catalytic conversion of CO2 to methanol via renewable hydrogen has emerged as a promising technology among the various CO2 conversion techniques. However, efficient hydrogenation of CO2 using conventional Cu‐ZnO‐based catalysts, which are currently used for industrial methanol production from synthesis gas, remains a challenge due to inefficient energy conversion, poor stability and sluggish CO2 conversion kinetics. As the catalytic activity, stability and methanol selectivity of conventional Cu/ZnO catalysts are still insufficient for industrial applications, novel catalyst formulations using transition metals/metal oxides and supported noble metal nanostructures have emerged. Among them, intermetallic compounds are being explored for their unique electronic and crystalline structures, which can be tailored by controlled, precise, and seamless tuning of interatomic distances, specific arrangements and electronic structure to enhance their stability and activity for the selective hydrogenation of CO2 to methanol. In this context, intermetallic catalysts containing Pd, Cu and Ni combined with metal oxide nanoparticles (ZnO, Ga2O3, In2O3, etc.) have been shown to be more effective than the classical Cu‐ZnO‐Al2O3. This review analyses the progress made in the study of these intermetallic catalysts by analysing different aspects of their preparation, characterization, effects of promoters, support interactions, etc. Future research perspectives are discussed in the context of potential industrial applications of intermetallics for direct methanol production via CO2 hydrogenation.

Synergistic enhancement of CO2 hydrogenation to C5+ hydrocarbons using mixed Fe5C2 and Na-Fe3O4 catalysts: Effects of oxide/carbide ratio, proximity, and reduction

CO2 hydrogenation into sustainable chemical feedstocks and fuels is a pivotal focus of energy research. Fe-based catalysts have emerged as promising candidates due to their high efficiency in the CO2 hydrogenation toward C2–C4 olefins and C5+ hydrocarbons. Fe5C2 is known as the active phase of the CO2 hydrogenation. Therefore, it is imperative to discern the roles of active phases in product distribution. Accordingly, in the present study, Fe5C2 is synthesized separately and physically mixed with Na-Fe3O4. The effects of oxide/carbide ratio, the proximity of active phases, and reduction treatment are investigated. The results show that adding carbide to oxide in an appropriate ratio significantly increases CO2 conversion due to the controlled reduction of the oxide phase and enhanced CO2 adsorption. Additionally, a closer distance (mixed-powder pellets) between Na-Fe3O4 and Fe5C2 results in higher selectivity for C2-C4 olefins and C5+ hydrocarbons and less CH4. Furthermore, the graphitized layers of reduced catalyst (R-Na-Fe3O4/Fe5C2 (70/30 wt%)) enhance the selectivity to C2-C4 olefins (40 %) and C5+ hydrocarbons (35 %) at around 40 % CO2 conversion. In contrast, amorphous carbon in the non-reduced catalyst (NR-Na-Fe3O4/Fe5C2 (70/30 wt%)) favors more C2-C4 paraffins and CH4. Therefore, the interplay between the influential factors, i.e., oxide/carbide ratio, spatial distance, and reduction treatment, can result in tailoring an efficient CO2 hydrogenation catalyst toward the formation of valuable hydrocarbons.

The relationship between structure and performance of Mo-ZrO2 catalysts in CO2 hydrogenation

CO₂ hydrogenation is a structure-sensitive reaction, producing a diverse range of products based on the structure of catalysts. In this study, we present a catalyst Mo-ZrO2 for CO2 hydrogenation and observed the products vary among CO, CH4, and CH3OH as Mo changes in its loading and local environment. Kinetic studies reveal that increasing Mo loading amplifies hydrogenation ability of the catalyst while simultaneously reducing CO2 adsorption on ZrO2. Specifically, Mo loadings under 10 wt% result in Mo integration into ZrO2 support, forming a Mo-O-Zr structure. Conversely, a higher Mo loading leads to the formation of Zr(MoO4)2 clusters on ZrO2 support. The Mo5⁺-Ov-Zr structure, formed in Mo-doped ZrO2 during reduction pretreatment, emerges as an active site for methanol synthesis. In contrast, metallic Mo formed from the reduction of Zr(MoO4)2 clusters loaded on ZrO2 is responsible for methane formation. The evolution of the surface structure from Mo-O-Zr structure to Zr(MoO4)2 clusters on ZrO2 as Mo loading changes, resulting in alterations in the number of active sites for methanol synthesis and methanation, consequently leading to variations in product distribution.

Efficient Thermal Management with Selective Metamaterial Absorber for Boosting Photothermal CO2 Hydrogenation under Sunlight.

Photothermal catalytic CO2 hydrogenation is a prospective strategy to simultaneously reduce CO2 emission and generate value-added fuels. However, the demand of extremely intense light hinders its development in practical applications. Herein, this work reports the novel design of Ni-based selective metamaterial absorber and employs it as the photothermal catalyst for CO2 hydrogenation. The selective absorption property reduces the heat loss caused by radiation while possessing effectively solar absorption, thus substantially increasing local photothermal temperature. Notably, the enhancement of local electric field by plasmon resonance promotes the adsorption and activation of reactants. Moreover, benefiting from the ingenious morphology that Ni nanoparticles (NPs)are encapsulated by SiO2 matrix through co-sputtering, the greatly improved dispersion of Ni NPs enables enhancing the contact with reaction gas and preventing the agglomeration. Consequently, the catalyst exhibits an unprecedented CO2 conversion rate of 516.9mmol gcat -1 h-1 under 0.8W cm-2 irradiation, with near 90% CO selectivity and high stability. Significantly, this designed photothermal catalyst demonstrates the great potential in practical applications under sunlight. This work provides new sights for designing high-performance photothermal catalysts by thermal management.

Carrier synergistic effect of iron based catalysts for CO hydrogenation to lower olefins

Carrier synergistic effect of iron based catalysts for CO hydrogenation to lower olefins

A nonmetallic plasmonic catalyst for photothermal CO2 flow conversion with high activity, selectivity and durability

The meticulous design of active sites and light absorbers holds the key to the development of high-performance photothermal catalysts for CO2 hydrogenation. Here, we report a nonmetallic plasmonic catalyst of Mo2N/MoO2-x nanosheets by integrating a localized surface plasmon resonance effect with two distinct types of active sites for CO2 hydrogenation. Leveraging the synergism of dual active sites, H2 and CO2 molecules can be simultaneously adsorbed and activated on N atom and O vacancy, respectively. Meanwhile, the plasmonic effect of this noble-metal-free catalyst signifies its promising ability to convert photon energy into localized heat. Consequently, Mo2N/MoO2-x nanosheets exhibit remarkable photothermal catalytic performance in reverse water-gas shift reaction. Under continuous full-spectrum light irradiation (3 W·cm−2) for a duration of 168 h, the nanosheets achieve a CO yield rate of 355 mmol·gcat−1·h−1 in a flow reactor with a selectivity exceeding 99%. This work offers valuable insights into the precise design of noble-metal-free active sites and the development of plasmonic catalysts for reducing carbon footprints.

Oxygen-vacancy induced structural changes of Co species in CoAl2O4 spinels for CO2 hydrogenation

Promotional effects of oxygen vacancies of spinel catalysts in CO2 hydrogenation are reported in early works, but the mechanistic origins remain elusive. Here, CoAl2O4 spinels with varying numbers of oxygen vacancies are deliberately designed by a sol-gel method and different post-treatments. By combining catalytic testing, advanced electron microscopic and spectroscopic characterizations, and computational studies, the unusual oxygen vacancy-dependent catalytic behaviors are rationalized. Our work reveals that i) perfect spinel crystals possessing least oxygen vacancies can effectively constrain the Co2+ species at working conditions that are less active but selective to CO; and ii) vacancy-rich spinels promote both H2 and CO2 activations and COOH* formation, explaining the higher hydrogenation activity, but overwhelming vacancies cause Co2+ reduction and promote direct CO2 * dissociation to CO* and deep hydrogenation to CH4. These molecular-level understandings reinforce the idea of proper design of oxygen vacancies to achieve activity-selectivity balance.

Insight into the element migration induced tandem cooperation between CuNa-doped Fe based catalyst and Mn-treated HZSM-5 for direct CO2 hydrogenation to aromatics

Direct hydrogenation of carbon dioxide (CO2) to aromatics is a promising strategy for relieving the stress of fossil fuels. Here, a copper and sodium co-modified Fe-based catalyst (NFC-DM) was synthesized through the pyrolysis of Cu-doped MIL-101(Fe) and Na impregnation. After combining with Mn(NO3)2 solution treated HZSM-5, 46.2% CO2 conversion and 56.1% aromatics selectivity was achieved. The tandem interaction between metal oxide and HZSM-5 triggered by element migration was clarified. The Mn(NO3)2 treatment incrassated the extra-framework Al (AlEF) layer of HZSM-5, producing more surface Lewis acid sites (LAS) and decreased total Brönsted acid site (BAS) amount. Moreover, the AlEF acted as acceptor of Cu migration from NFC-DM, leading to enhanced surface LAS amount and intensity, catalyzing additional reverse water gas shift (RWGS) on zeolite surface. Formed CO could diffuse to metal oxide surface and participate in FTS, thermodynamically boosting CO2 conversion. Finally, the mechanism of CO2 activation over zeolite surface was studied and the whole reaction pattern was proposed.

Mitigating the Poisoning Effect of Formate during CO2 Hydrogenation to Methanol over Co-Containing Dual-Atom Oxide Catalysts.

During the hydrogenation of CO2 to methanol over mixed-oxide catalysts, the strong adsorption of CO2 and formate poses a barrier for H2 dissociation, limiting methanol selectivity and productivity. Here we show that by using Co-containing dual-atom oxide catalysts, the poisoning effect can be countered by separating the site for H2 dissociation and the adsorption of intermediates. We synthesized a Co- and In-doped ZrO2 catalyst (Co-In-ZrO2) containing atomically dispersed Co and In species. Catalyst characterization showed that Co and In atoms were atomically dispersed and were in proximity to each other owing to a random distribution. During the CO2 hydrogenation reaction, the Co atom was responsible for the adsorption of CO2 and formate species, while the nearby In atoms promoted the hydrogenation of adsorbed intermediates. The cooperative effect increased the methanol selectivity to 86% over the dual-atom catalyst, and methanol productivity increased 2-fold in comparison to single-atom catalysts. This cooperative effect was extended to Co-Zn and Co-Ga doped ZrO2 catalysts. This work presents a different approach to designing mixed-oxide catalysts for CO2 hydrogenation based on the preferential adsorption of substrates and intermediates instead of promoting H2 dissociation to mitigate the poisonous effects of substrates and intermediates.