Catalysts For CO2 Hydrogenation Research Articles

Superparamagnetic Iron Oxide Nanoparticles on ZrO2 as Catalysts for CO2 Hydrogenation to Lower Olefins

Organic synthesis presents significant opportunities for converting the abundant and hazardous carbon dioxide (CO2) in the atmosphere into a more sustainable carbon source. To reduce the carbon footprint, we explored the direct hydrogenation of CO2 to lower (C2‐4=) olefins using various catalysts composed of ZrO2‐supported alkali‐metal‐promoted superparamagnetic iron oxide nanoparticles (SPIONs; Fe3O4). These catalysts are notable for their straightforward preparation; we employed a cost‐effective dry‐mixing method to create a range of alkali metal‐doped SPIONs supported on ZrO2. Results showed that the strong interactions between Fe3O4 and the ZrO2 support enhanced CO2 hydrogenation performance compared to other forms, such as pristine Fe or Fe2O3. Under optimal conditions—using a gas hourly space velocity (GHSV) of 4500 mL/h/gcat and a feed ratio of H2:CO2 = 3:1—this catalyst achieved over 22% CO2 conversion and high selectivity for light (C2‐4=) olefins at 30 bar and 375 ºC, with 30 wt% Fe3O4 loading on ZrO2 and 2 wt% K promoter. We also investigated several variables, including alkali metal concentration, iron content, reaction conditions, and catalyst stability over 96 hours.

Ambient Sunlight Driven Photothermal Green Syngas Production at 100 m3 Scale by the Dynamic Structural Reconstruction of Iron Oxides with 38.7% Efficiency

AbstractAmbient sunlight‐driven photothermal green syngas production via reverse water‐gas shift (RWGS) reaction is important for carbon neutrality, which lacks efficient and inexpensive catalysts at low temperatures. This studydemonstrates that the scalable Fe3O4 supported with K atoms modified Ag nanoparticles (AgK/Fe3O4) exhibits a RWGS CO production rate of 1089 mmol g−1 h−1 at 300 °C and 100% CO selectivity through dynamic structural reconstruction, surpassing all reported platinum‐based catalysts. In situ characterization and theoretical simulation indicate that the AgK nanoparticles activate H2 to reduce Fe3O4 as metallic Fe. Subsequently, the metallic Fe spontaneously reacts with CO2 to form CO and Fe3O4, thereby facilitating low‐temperature RWGS. Owing to its superior low‐temperature performance, AgK/Fe3O4 equipped with a homemade photothermal device achieves one sun‐driven photothermal RWGS with a CO production rate of 1925 mmol g−1 h−1 and a 38.7% solar to enthalpy energy conversion efficiency. Furthermore, the enlarged outdoor demonstration yields 100.6 m3day−1 of green syngas with an H2/CO ratio of 3. This work paves the way for designing efficient platinum‐free CO2 hydrogenation catalysts and introduces a new approach for sunlight‐driven scalable green syngas production.

Near-Unity Photothermal CO2 Hydrogenation to Methanol based on a Molecule/Nanocarbon Hybrid Catalyst.

Solar-driven CO2-to-methanol conversion provides an intriguing route for both solar energy storage and CO2 mitigation. For scalable applications, near-unity methanol selectivity is highly desirable to reduce the energy and cost endowed by low-value byproducts and complex separation processes, but so far has not been achieved. Here we demonstrate a molecule/nanocarbon hybrid catalyst composed of carbon nanotube-supported molecularly dispersed cobalt phthalocyanine (CoPc/CNT), which synergistically integrates high photothermal conversion capability for affording an optimal reaction temperature with homogeneous and intrinsically-efficient active sites, to achieve a catalytic activity of 2.4 mmol gcat-1 h-1 and selectivity of ~99% in direct photothermal CO2 hydrogenation to methanol reaction. Both theoretical calculations and operando characterizations consistently confirm that the unique electronic structure of CoPc and appropriate reaction temperature cooperatively enable a thermodynamic favorable reaction pathway for highly selective methanol production. This work represents an important milestone towards the development of advanced photothermal catalysts for scalable and cost-effective CO2 hydrogenation.

Highly active and stable mixed-phase In2O3-supported Ni catalyst for CO2 hydrogenation to methanol

Ni/In2O3 catalysts perform well for CO2 hydrogenation to methanol. However, there is still room for improvement in terms of methanol selectivity. In this study, Ni/In2O3 catalysts with distinct crystalline phases of indium oxide, namely cubic In2O3 (c-In2O3) and a mixed phase of cubic and hexagonal In2O3 (h + c-In2O3), were synthesized. The results showed that the Ni/h + c-In2O3 catalyst demonstrated the greatest catalytic performance, with a methanol selectivity of 96.7 % and a space time yield of methanol of 15.79 mmol·g−1·h−1 at 2 MPa, 300°C, and 24.0 L·g−1·h−1. Based on the characterization results, we concluded that the improvement of the methanol synthesis performance on the Ni/h + c-In2O3 catalyst was mainly due to improved hydrogen dissociation ability and the increased surface oxygen vacancies. The energy barrier (Ea) of the rate-limiting steps for the CH3OH and CO productions was calculated. The decreased Ea(CH3OH) and increased Ea(CO) indicate the favorable improvement of catalytic activity and selectivity for CH3OH production by Ni/In2O3, especially for Ni/h-In2O3(104).

Effective synergistic interaction between InZnZrOx ternary metal oxides and SAPO-34 molecular sieve catalysts for CO2 hydrogenation to light olefins

The synergistic interaction of metal oxides with molecular sieves is essential for the catalytic hydrogenation of carbon dioxide (CO2) into light olefins (C2=–C4=) over bifunctional tandem catalysts. Herein, a series of In2O3-doped InZnZrOx (IZZ) ternary metal oxides was prepared and physically mixed with SAPO-34. The bifunctional catalyst was used in the direct conversion of CO2 to light olefins. The relationship between IZZ oxide structures prepared using different methods and the catalytic performance of bifunctional catalysts was investigated. Moreover, the migration of InOx in ternary metal oxides was revealed. Results revealed that for IZZ oxides prepared via precipitation coating and impregnation, InOx species migrated to the SAPO-34 surface during thermocatalytic reaction due to the dispersion of In2O3 on the ZnZrOx surface and its weak interaction with ZnZrOx. This led to the neutralization of acid centers on SAPO-34 by InOx, thereby destroying the synergistic interaction between the oxides and SAPO-34, resulting in a large amount of unneeded methane and poor light olefin selectivity. However, the co-precipitated IZZ-CP oxides exhibited a ternary solid solution structure and inhibited the migration of InOx. This enhanced CO2 and H2 activation, affording more formate (HCOO*) and methoxide (CH3O*) intermediates that strengthened the synergistic interaction between the oxides and molecular sieves. After optimizing the In2O3 doping amount in IZZ-CP oxide and the reaction conditions, the IZZ-CP/SAPO-34 bifunctional catalyst achieved 17.9 % CO2 conversion, 80.1 % C2=–C4= selectivity, only 7.6 % methane and 44.6 % CO selectivity. It also maintained excellent catalytic stability without significant deactivation after continuous reaction for 80 h.

Cation rearrangement at tetrahedral sites in the Cu/ZnAl2O4 spinel enhancing CO2 hydrogenation to methanol

Cu/ZnAl2O4 spinel is a promising catalyst for CO2-to-methanol due to its dual-site H2 activation. However, controlling surface properties and metal-support interactions (MSI) through the coordination environment of spinel cations remains underexplored. Herein, the occupancy of Zn2+ and Al3+ cations in Cu/ZnAl2O4 spinel is fine-tuned by manipulating the calcination atmosphere. More disordered structures (AlO4 and ZnO6) observed on the CZA-Ar catalyst benefit the creation of oxygen vacancies and surface hydroxyl groups, which facilitate the formation of highly dispersed small-sized Cu species. This enhances MSI and hydrogen spillover effects, thereby boosting CO2 conversion and the space-time yield (STY) of methanol. High-pressure in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results reveal that the crucial formate intermediates form at tetrahedral sites in ZnAl2O4 spinel, with more Al-HCOO- species observed on the CZA-Ar catalyst due to the formation of AlO4. This work advances the understanding of spinel catalysts in CO2 hydrogenation to methanol.

Constructing efficient Pd/Al2O3 catalyst for reverse water-gas shift via alkali-modification

The intrinsic nature of irreducible oxides (e.g. Al2O3) makes it hard to tune the charge state of supported late-transition metals, then difficult to adjust the selectivity of catalysts in CO2 hydrogenation. Herein, we find that modifying the Pd/Al2O3 catalyst with alkali metals (especially potassium) is efficient to boost the CO formation in CO2 hydrogenation. In comparison to Pd/Al2O3, approximately twenty-fold promotion in reverse water–gas shift (RWGS) rate was achieved on K-modified catalysts with proper K/Pd proportions. Combined structural characterizations demonstrate that the enhanced Pd-O interactions through K mediation stabilize the ca. 2 nm sized Pd particles as well as the electron-deficient state of Pd, which are robust enough during long-termed evaluation with undamped performance. In situ spectroscopy unveils a bi-dentate *HCOO associated reaction mechanism taking effect on alkali-modified catalysts, which contributes to ∼ 100 % of CO selectivity and 3318.1 mmol∙gPd-1∙h−1 of CO formation rate at 340°C.

Enhanced Selectivity to Methanol in CO2 Hydrogenation on CuO/ZrO2 Catalysts by Alkali Metal Modification

AbstractIn order to alleviate the influence of greenhouse effect on global climate change, the effective utilization of CO2 to prepare fine chemicals should be paid more attention to, however, which is greatly blocked by the catalyst with low efficiency. Here, alkali metal (Li, Na, or K) are employed as a modification aid to prepare CuO/ZrO2 catalyst for CO2 hydrogenation to methanol. The effects of alkali metal on physicochemical properties and catalytic activities of CuO/ZrO2 catalyst were studied in detail by the XRD, N2‐physisorption, ICP‐OES, SEM/EDS, H2/N2O/CO2/NH3‐chemisorption, and evaluation test. The results verified that the use of complex combustion method enabled the uniform combination of all components in precursor. High‐temperature calcination (700 °C) further enhanced the strong interaction and synergistic effect between Cu and ZrO2. Most importantly, the introduction of alkali metal effectively altered the structure and catalytic activity of CuO/ZrO2 catalysts. However, the selectivity to methanol increased while the CO2 conversion decreased regardless of different kinds of alkali metal being introduced to the CuO/ZrO2 catalysts. For example, CuO/ZrO2 catalyst modified by K exhibited excellent performance for methanol production that 98.9% selectivity of methanol based on 8.8% conversion of CO2 after 48 h online reaction.

Highly active ternary Ir/In2O3-ZrO2 catalyst for CO2 hydrogenation towards methanol: The role of zirconia

Indium oxide supported iridium catalyst has been verified to be highly active and selective for CO2 hydrogenation to methanol. In this work, zirconia is introduced into the Ir/In2O3 system as a novel Ir/In2O3-ZrO2 ternary catalyst. The solid solution generated between ZrO2 and In2O3 exhibits a strong electronic metal-support interaction with iridium, rendering the supported iridium species highly dispersed in a form of clusters. Thereout, an active interface between iridium and the solid-solution carrier is thus generated, on which electron transport is more feasible with a stronger CO2 adsorption than that of on the Ir−In2O3 interfacial site. Moreover, compared to Ir/In2O3, this ternary catalyst exhibits better catalytic activity as well as the stability. Density functional theory (DFT) simulations, combined with the in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies, further demonstrate the CO-hydrogenation pathway is the most favored for methanol synthesis, providing a rationale for the superior methanol selectivity of the Ir/In2O3-ZrO2 catalyst during CO2 hydrogenation.

Effective Screening of Metal Dopants for In2O3 Catalyst to Tune Catalytic Performance of CO2 Hydrogenation to Formic Acid

The metal doping is an effective strategy to adjust catalytic performance for indium oxide catalyst in CO2 hydrogenation. In current work, a series dopant, Co, Fe, Ni, Pd, Pt, Rh and Ru, are selected and examined in CO2 hydrogenation to formic acid by DFT based microkinetic simulation. It is found that substitutional doping is local effect which mainly promotes the reactivity of adjacent oxygen atoms. The calculations of both CO2 adsorption and hydrogen molecule dissociation certify the positive effects induced by doping, and the adsorption energy of CO2 has a linear relation with the transferred charges for all investigated catalysts which helps to explain the C‐O bond activation mechanism. Two pathways, Formate and Carboxyl, are investigated under same footing. It is noted that doping significantly reduces the hydrogenation barriers on two pathways compared with undoped surfaces. Moreover, the calculated TOF of formic acid formation is greatly increased on doped surfaces and Pt, Pd, Ru are identified as the most active dopants. In the end, it is concluded that reaction obeys Carboxyl mechanism and a valid descriptor of trans‐HCOOH* and H* formation energy is proposed for the screening of effective dopants.

Effect of Cu incorporation on Fe-based catalysts for selective CO2 hydrogenation to olefins

The process of converting CO2 into sustainable chemical feedstock and fuels through reaction with renewable hydrogen has been regarded as a promising direction in energy research. The enhancement of CO2 hydrogenation efficiency to produce valuable hydrocarbons (specifically olefins) on Fe catalysts through Cu modification has been extensively researched. However, there is ongoing vigorous debate regarding the impact of these modifications on catalytic properties and the underlying mechanism. When compared to unprompted iron-based catalysts for CO2 hydrogenation, the choice of desired products, such as C2-C4 and C5+, is relatively low. So, promoters are frequently employed to customize and enhance product distribution. This study investigates how adding Cu to Fe-based supported catalysts affects their performance in converting CO2 to hydrocarbons, with a specific emphasis on the interaction between Fe and Cu. To achieve this goal, catalysts were created using co-precipitation methods, varying the distribution of Fe and Cu within them. A set of composite catalysts underwent testing in a fixed bed setup using a reactant gas mixture at 350 °C and 30 bar pressure. Analysis techniques such as XRD, SEM, TEM, NH3-TPD, H2-TPR, and N2 adsorption-desorption isotherms revealed the presence of iron-copper interaction within the composite catalysts. This interaction between the two components synergistically enhances the catalytic activity in CO2 hydrogenation.

CoCe composite catalyst for CO2 hydrogenation: Effect of pore structure

In order to realize the dual carbon goals of “carbon peaking” and “carbon neutrality”, the design and development CO2 hydrogenation catalyst with high performances is of great significance. In this study, the CoCe composite catalysts were prepared by different methods and used to CO2 catalytic hydrogenation. The physicochemical properties of the prepared catalysts were characterized by XRD, BET, TEM/HRTEM, and H2-TPD. The characterization results indicated that the studied CoCe composite catalytsts with different pore structure can be prepared by different preparation methods. The suitable preparation method can promote Co species to be dissolved into the CeO2 lattice to form Ce-O-Co solid solution, which can promote the corresponding Co species to be reduced by H2 to form active Co0 species. The large specific surface area and developed ordered mesoporous structure of the CoCe-HT catalyst precursor, which was prepared by hard-template method, are conducive to the formation of active Co0 species and activation of H2 to produce reactive H species. The CO2 hydrogenation activity of the studied CoCe composite catalysts follows the following order: CoCe-HT > CoCe-CP > CoCe-CA > CoCe-HY. The CoCe-HT catalyst showed high CO2 hydrogenation conversion of 53.9 % and good using stability at 360 °C for 600 min. However, the CoCe-CA prepared by complex method has a poor use stability.

Active Sites for CO2 Hydrogenation to Methanol: Mechanistic Insights and Reaction Control.

Catalytic CO2 conversion to methanol is a promising way to extenuate the adverse effects of CO2 emission, global warming and energy shortage. Understanding the fundamental features of CO2 activation and hydrogenation at the molecular level is essential for carbon utilization and sustainable chemical production in the current climate crisis. This review explores the recent advances in understanding the design of catalysts with desired active sites, including single-atom, dual-atom, interface, defects/vacancies and promoters/dopants. We focused on the design of various catalytic systems to enhance their catalytic performances by stabilizing active metal in a catalyst, identifying the unique structure of active species, and engineering coordination environments of active sites. Mechanistic insights provided by advanced operando and in situ spectroscopies were also discussed. Moreover, the review highlights the key factors affecting active sites and reaction mechanisms, such as local environments, oxidation states, and metal-support interactions. By integrating recent advancements and relating knowledge gaps this review aims to endow an inclusive overview of the field and guide future research toward more efficient and selective catalysts for CO2 hydrogenation to methanol.

Optimal design of PdAu/In2O3 catalysts for CO2 hydrogenation

Efficient catalyst design has garnered significant interest in recent decades due to its potential to address both the challenges of the greenhouse effect and energy shortages by facilitating the conversion of CO2 into valuable chemicals through catalytic reactions. To investigate maximizing the synergistic effects of supported PdAu catalysts, we conducted first-principles calculations on the activation and decomposition of CO2 and H2 on the PdAu/In2O3(110) system. The results demonstrate that the incorporation of a secondary metal (Au) into the supported Pd catalyst, in conjunction with precise control over Au concentration, exerts influence on both reactant binding energy and activation. The adsorption and activation of CO2 at the interface sites of Au4/In2O3(110) and PdAu3/In2O3(110) are not observed. The transition state for the dissociation of CO2 into *CO and *O is determined based on adsorbed CO2, providing insights into the properties of activated CO2. The Bronsted–Evans–Polanyi relation, which correlates activation barriers (Ea) with reaction energies (Er), was established for the CO2 dissociation mechanism on PdAu/In2O3(110) catalysts using equation E = 0.4Ea + 0.63. It was carried out to investigate the H2-dissociated adsorption processes and mobility energy on various PdAu/In2O3(110) catalysts. Finally, a highly efficient Pd2Au2/In2O3 catalyst for the hydrogenation of CO2 into methanol has been proposed. This research provides valuable insights into the hydrogenation of CO2 to methanol using bimetal-oxide catalysts and contributes to the optimization of the design of PdAu/In2O3 catalysts for CO2 reactions.

Synergistic effect of carbon molecular sieve and alkali metal nitrate on promoting intermediate-temperature adsorption of CO2 over MgAl-layered double hydroxide

The development of intermediate-temperature adsorbents with high CO2 adsorption capacity is crucial for the tandem integration with CO2 hydrogenation catalyst, aimed at enhancing economy viability and minimizing energy consumption in Carbon capture, utilization and storage (CCUS). Although certain porous carbon materials (PCM) have been employed to enhance CO2 adsorption capability of layered double hydroxide (LDH), there remains an urgent necessity to identify more cost-effective and efficient PCM alternatives. Herein, alkali metal nitrates ((Li0.3Na0.18K0.52)NO3, hereafter referred to as LiNaK) modified layered double hydroxide (LDH)/carbon molecular sieve (CMS) composite (LiNaK-LDH/CMS) as promising adsorbents for CO2 capture was reported. The effects of CMS addition and nitrate loading, the calcination and adsorption temperature, as well as the cycling stability were investigated systematically. The results revealed that the CO2 capture capacity of the LiNaK-modified layered double oxide (LDO)/CMS composite (30 mol%LiNaK-LDO/CMS15%)-incorporating with 15 wt% CMS addition and 30 mol% nitrate loading-achieved a remarkable CO2 adsorption capacity of 1.32 mmol/g at 300 °C due to the synergetic interactions between CMS and nitrate; this represents nearly a sevenfold enhancement compared to initial LDO performance. Moreover, the 30 mol%LiNaK-LDO/CMS15% adsorbent also demonstrated commendable cyclic stability after ten adsorption cycles, retaining over 85 % of its initial adsorption capacity. Based on both obtained adsorption performance and characterization data from the adsorbents, a pre-adsorption enhancing CO2 intermediate-temperature adsorption mechanism over LiNaK-LDH/CMS composite through air calcination processes. This study significantly advances LDH-based adsorbent for future research into CO2 intermediate-temperature adsorption.

Atomically dispersed Ru on flower-like In2O3 to boost CO2 hydrogenation to methanol

Metal-based catalysts are prevalent in the CO2 hydrogenation to methanol owing to their remarkable catalytic activity. Herein, Ru/In2O3 catalysts with different morphologies obtained by doping Ru into In2O3 with irregular, rod-like, and flower-like morphologies are used for catalytic CO2 hydrogenation to methanol. Results indicate that the flower-like Ru/In2O3 (Ru/In2O3-F) exhibits higher catalytic performance than Ru/In2O3 with other morphologies, achieving a 12.9% CO2 conversion, 74.02% methanol selectivity, and 671.36 mgMeOH·h−1·gcat−1 methanol spatiotemporal yield. Furthermore, Ru/In2O3-F maintains its catalytic stability over 200 h at 5 MPa and 290 °C. The promotional effect mainly stems from the fact that electronic structure of Ru can be effectively adjusted by modulating the morphology of In2O3. The strong interaction between atomically dispersed Ru and In2O3-F enhances the structural stability of Ru, inhibiting the agglomeration of the catalyst during the reaction process. Furthermore, density-functional theory calculations reveal that highly dispersed Ru atoms not only perform efficient and rapid electronic gain and loss processes, facilitating the catalytic activation of H2 into H intermediates. It also enables the generated reactive H to rapidly overflow to the surrounding In sites to participate in CO2 reduction. These findings provide a theoretical basis for the development of high-performance catalysts for CO2 hydrogenation.

Active Sites of Cu/ZnO-Based Catalysts for CO2 Hydrogenation to Methanol: Part I

Heterogeneous Cu/ZnO-based catalysts are widely used for CO2 hydrogenation to methanol, but limitations remain for industrial applications. These include achieving high methanol selectivity and conversion and mitigating deactivation by water poisoning. Part I of this review explores the role of active sites on Cu/ZnO-based catalysts in CO2 conversion. The synergistic interaction between copper and zinc oxide is emphasised, particularly regarding interfacial effects on carbon monoxide activation and formate formation. The discussion covers theoretical and experimental perspectives on active site characteristics, including defects, vacancies, steps and strain. Additionally, the review explores the connection between Cu/ZnO-based catalysts properties and methanol synthesis activity.

Active Sites of Cu/ZnO-Based Catalysts for CO2 Hydrogenation to Methanol: Part III

Part II of this review examines how preparation methods influence catalyst performance and the impact of doping with elements like ceria, alumina and zirconia on CO2 conversion selectivity. We conclude that zinc oxide enhances copper dispersion and promotes a synergistic effect at the interface, leading to improved catalytic performance. This work presents the continuation of and conclusions from Parts I () and II ().

Active Sites of Cu/ZnO-Based Catalysts for CO2 Hydrogenation to Methanol: Part II

Part II of this review continues to explore the connection between Cu/ZnO-based catalysts properties and methanol synthesis activity. This work continues from Part I ().

Carbon-Supported Fe-Based Catalyst for Thermal-Catalytic CO2 Hydrogenation into C2+ Alcohols: The Effect of Carbon Support Porosity on Catalytic Performance

Carbon materials supported Fe-based catalysts possess great potential for the thermal-catalytic hydrogenation of CO2 into valuable chemicals, such as alkenes and oxygenates, due to the excellent active sites’ accessibility, appropriate interaction between the active site and carbon support, as well as the excellent capacities in C-O bond activation and C-C bond coupling. Even though tremendous progress has been made to boost the CO2 hydrogenation performance of carbon-supported Fe-based catalysts, e.g., additives modification, the choice of different carbon materials (graphene or carbon nanotubes), electronic property tailoring, etc., the effect of carbon support porosity on the evolution of Fe-based active sites and the corresponding catalytic performance has been rarely investigated. Herein, a series of porous carbon samples with different porosities are obtained by the K2CO3 activation of petroleum pitch under different temperatures. Fe-based active sites and the alkali promoter Na are anchored on the porous carbon to study the effect of carbon support porosity on the physicochemical properties of Fe-based active sites and CO2 hydrogenation performance. Multiple characterizations clarify that the bigger meso/macro-pores in the carbon support are beneficial for the formation of the Fe5C2 crystal phase for C-C bond coupling, therefore boosting the synthesis of C2+ chemicals, especially C2+ alcohols (C2+OH), while the limited micro-pores are unfavorable for C2+ chemicals synthesis owing to the sluggish crystal phase evolution and reactants’ inaccessibility. We wish our work could enrich the horizon for the rational design of highly efficient carbon-supported Fe-based catalysts.