Development of Tandem Catalysts for CO2 Hydrogenation to Olefins

Catalysts for the Conversion of CO2 to Low Molecular Weight Olefins-A Review

There is a large worldwide demand for light olefins (C₂⁼-C₄⁼), which are needed for the production of high value-added chemicals and plastics. Light olefins can be produced by petroleum processing, direct/indirect conversion of synthesis gas (CO + H₂) and hydrogenation of CO₂. Among these methods, catalytic hydrogenation of CO₂ is the most recently studied because it could contribute to alleviating CO₂ emissions into the atmosphere. However, due to thermodynamic reasons, the design of catalysts for the selective production of light olefins from CO₂ presents different challenges. In this regard, the recent progress in the synthesis of nanomaterials with well-controlled morphologies and active phase dispersion has opened new perspectives for the production of light olefins. In this review, recent advances in catalyst design are presented, with emphasis on catalysts operating through the modified Fischer-Tropsch pathway. The advantages and disadvantages of olefin production from CO₂ via CO or methanol-mediated reaction routes were analyzed, as well as the prospects for the design of a single catalyst for direct olefin production. Conclusions were drawn on the prospect of a new catalyst design for the production of light olefins from CO₂.

Cobalt Catalysts Enable Selective Hydrogenation of CO2 toward Diverse Products: Recent Progress and Perspective

Selective hydrogenation of carbon dioxide (CO₂) into value-added chemicals has aroused great interest. The chemical inertness of CO₂ and diverse reaction pathways usually require the construction of enabled catalysts. To date, cobalt (Co) catalysts characteristic of metallic and/or divalent Co components show great potential for CO₂ hydrogenation. To better regulate the CO₂ hydrogenation, it is necessary to summarize the current progress of cobalt catalysts for selective hydrogenation of CO₂. In this Perspective, first, hydrogenation of CO₂ into methane over metallic Co sites is introduced. Second, hydrogenation of CO₂ into methanol and C₂₊ alcohols is discussed by constructing mixed-valent cobalt sites. Third, hydrogenation of CO₂ into light olefins and C₅₊ liquid fuels over cobalt-containing hybrid catalysts is introduced. Fourth, the reaction paths for selective hydrogenation of CO₂ over cobalt catalysts are illustrated. Finally, the current challenges and prospects of cobalt-based nanocatalysts for hydrogenation of CO₂ are proposed.

Visualizing Element Migration over Bifunctional Metal-Zeolite Catalysts and its Impact on Catalysis

The catalytic performance of composite catalysts is not only affected by the physicochemical properties of each component, but also the proximity and interaction between them. Herein, we employ four representative oxides (In₂ O₃ , ZnO, Cr₂ O₃ , and ZrO₂ ) to combine with H-ZSM-5 for the hydrogenation of CO₂ to hydrocarbons directed by methanol intermediate and clarify the correlation between metal migration and the catalytic performance. The migration of metals to zeolite driven by the harsh reaction conditions can be visualized by electron microscopy, meanwhile, the change of zeolite acidity is also carefully characterized. The protonic sites of H-ZSM-5 are neutralized by mobile indium and zinc species via a solid ion-exchange mechanism, resulting in a drastic decrease of C₂₊ hydrocarbon products over In₂ O₃ /H-ZSM-5 and ZnO/H-ZSM-5. While, the thermomigration ability of chromium and zirconium species is not significant, endowing Cr₂ O₃ /H-ZSM-5 and ZrO₂ /H-ZSM-5 catalysts with high selectivity of C₂₊ hydrocarbons.

A quasi-stable molybdenum sub-oxide with abundant oxygen vacancies that promotes CO2 hydrogenation to methanol

Production of methanol from anthropogenic carbon dioxide (CO₂) is a promising chemical process that can alleviate both the environmental burden and the dependence on fossil fuels. In catalytic CO₂ hydrogenation to methanol, reduction of CO₂ to intermediate species is generally considered to be a crucial step. It is of great significance to design and develop advanced heterogeneous catalysts and to engineer the surface structures to promote CO₂-to-methanol conversion. We herein report an oxygen-defective molybdenum sub-oxide coupled with Pt nanoparticles (Pt/H_xMoO_3−y) which affords high methanol yield with a methanol formation rate of 1.53 mmol g_-cat⁻¹ h⁻¹ in liquid-phase CO₂ hydrogenation under relatively mild reaction conditions (total 4.0 MPa, 200 °C), outperforming other oxide-supported Pt catalysts in terms of both the yield and selectivity for methanol. Experiments and comprehensive analyses including in situ X-ray absorption fine structure (XAFS), in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and density functional theory (DFT) calculations reveal that both abundant surface oxygen vacancies (V_O) and the redox ability of Mo species in quasi-stable H_xMoO_3−y confer the catalyst with enhanced adsorption and activation capability to subsequently transform CO₂ to methanol. Moreover, the Pt NPs act as H₂ dissociation sites to regenerate oxygen vacancies and as hydrogenation sites for the CO intermediate to finally afford methanol. Based on the experimental and computational studies, an oxygen-vacancy-mediated “reverse Mars–van Krevelen (M–vK)” mechanism is proposed. This study affords a new strategy for the design and development of an efficient heterogeneous catalyst for CO₂ conversion.

Oxygen-defective molybdenum sub-oxide coupled with Pt nanoparticles affords high methanol yield in liquid-phase CO₂ hydrogenation via reverse Mars–van Krevelen mechanism.

Rational design of tandem catalysts using a core-shell structure approach

A facile and rational approach to synthesize bimetallic heterogeneous tandem catalysts is presented. Using core-shell structures, it is possible to create spatially controlled ensembles of different nanoparticles and investigate coupled chemocatalytic reactions. The CO2 hydrogenation to methane and light olefins was tested, achieving a tandem process successfully.

Pulsed Laser in Liquids Made Nanomaterials for Catalysis

Catalysis is essential to modern life and has a huge economic impact. The development of new catalysts critically depends on synthetic methods that enable the preparation of tailored nanomaterials. Pulsed laser in liquids synthesis can produce uniform, multicomponent, nonequilibrium nanomaterials with independently and precisely controlled properties, such as size, composition, morphology, defect density, and atomistic structure within the nanoparticle and at its surface. We cover the fundamentals, unique advantages, challenges, and experimental solutions of this powerful technique and review the state-of-the-art of laser-made electrocatalysts for water oxidation, oxygen reduction, hydrogen evolution, nitrogen reduction, carbon dioxide reduction, and organic oxidations, followed by laser-made nanomaterials for light-driven catalytic processes and heterogeneous catalysis of thermochemical processes. We also highlight laser-synthesized nanomaterials for which proposed catalytic applications exist. This review provides a practical guide to how the catalysis community can capitalize on pulsed laser in liquids synthesis to advance catalyst development, by leveraging the synergies of two fields of intensive research.

Versatile Hollow ZSM-5 Nanoreactors Loaded with Tailorable Metal Catalysts for Selective Hydrogenation Reactions

Zeolites are one of the most commonly used materials in the chemical industry, acting as catalysts or catalyst supports in different applications. Recently, the synthesis and functionalization of hollow zeolites have attracted many research interests, owing to the unique advantages of their hollow morphology. In the development of more sustainable processes, the hollow zeolites are often endowed with additional stability, selectivity, and activity. Herein, we present a stepwise synthetic protocol to prepare a range of complex hollow ZSM-5 catalysts with catalytic nanoparticles. Solid ZSM-5 crystals were first synthesized from Stöber silica spheres. This solid ZSM-5 sample was then loaded with transition metals via the impregnation method. A subsequent hollowing process was carried out in hydrothermal conditions in which hollow ZSM-5 crystals with confined transition metals inside were synthesized. More specifically, after the encapsulation of transition metals inside hollow ZSM-5, two different approaches have been further devised to allow the deposition of noble metals into the interior cavities or onto the exterior surfaces of the hollow ZSM-5. The deposition of Pt on the exterior surface was carried out by mixing the hollow ZSM-5 sample with presynthesized Pt nanoparticles. Loading of Pd in the interior was achieved by the galvanic replacement reaction between the Pd ions and embedded transition metals inside the hollow ZSM-5 sample. The catalytic performance of these reactor-like nanocatalysts has been evaluated with hydrogenation reactions in both liquid and gas phases, and their compositional and structural merits have been illustrated. For the hollow ZSM-5 sample with Pd loaded inside, liquid-phase selective hydrogenation of styrene over 4-vinylbiphenyl has been achieved with the ZSM-5 shell acting as a molecular sieve. The deposition of Pt on the exterior has improved the C₂-C₄ product yield when tested for the gas-phase CO₂ hydrogenation reaction.

Recent advances in hydrogenation of CO2 into hydrocarbons via methanol intermediate over heterogeneous catalysts

This review provides recent advances in the conversion of CO₂ to methanol, methanol to hydrocarbons, and direct conversion of CO₂ to hydrocarbons via methanol intermediate over various monofunctional and bifunctional solid catalysts.

CO2 hydrogenation to methanol and hydrocarbons over bifunctional Zn-doped ZrO2/zeolite catalysts

The tandem process of carbon dioxide hydrogenation to methanol and its conversion to hydrocarbons over mixed metal/metal oxide-zeotype catalysts is a promising path to CO₂ valorization.

Highly Selective Olefin Production from CO2 Hydrogenation on Iron Catalysts: A Subtle Synergy between Manganese and Sodium Additives

Mn and Na additives have been widely studied to improve the efficiency of CO₂ hydrogenation to valuable olefins on Fe catalysts, but their effects on the catalytic properties and mechanism are still under vigorous debate. This study shows that Fe-based catalysts with moderate Mn and Na contents are highly selective for CO₂ hydrogenation to olefins, together with low selectivities for both CO and CH₄ and much improved space-time olefin yields compared to state-of-the-art catalysts. Combined kinetic assessment and quasi in situ characterizations further unveil that the sole presence of Mn suppresses the activity of Fe catalysts because of the close contact between Fe and Mn, whereas the introduction of Na mediates the Fe-Mn interaction and provides strong basic sites. This subtle synergy between Na and Mn sheds light on the importance of the interplay of multiple additives that could bring an enabling strategy to improve catalytic activity and selectivity.

Applications of Zeolites to C1 Chemistry: Recent Advances, Challenges, and Opportunities

C1 chemistry, which is the catalytic transformation of C1 molecules including CO, CO₂ , CH₄ , CH₃ OH, and HCOOH, plays an important role in providing energy and chemical supplies while meeting environmental requirements. Zeolites are highly efficient solid catalysts used in the chemical industry. The design and development of zeolite-based mono-, bi-, and multifunctional catalysts has led to a booming application of zeolite-based catalysts to C1 chemistry. Combining the advantages of zeolites and metallic catalytic species has promoted the catalytic production of various hydrocarbons (e.g., methane, light olefins, aromatics, and liquid fuels) and oxygenates (e.g., methanol, dimethyl ether, formic acid, and higher alcohols) from C1 molecules. The key zeolite descriptors that influence catalytic performance, such as framework topologies, nanoconfinement effects, Brønsted acidities, secondary-pore systems, particle sizes, extraframework cations and atoms, hydrophobicity and hydrophilicity, and proximity between acid and metallic sites are discussed to provide a deep understanding of the significance of zeolites to C1 chemistry. An outlook regarding challenges and opportunities for the conversion of C1 resources using zeolite-based catalysts to meet emerging energy and environmental demands is also presented.

High-performance light-driven heterogeneous CO2 catalysis with near-unity selectivity on metal phosphides

Akin to single-site homogeneous catalysis, a long sought-after goal is to achieve reaction site precision in heterogeneous catalysis for chemical control over patterns of activity, selectivity and stability. Herein, we report on metal phosphides as a class of material capable of realizing these attributes and unlock their potential in solar-driven CO₂ hydrogenation. Selected as an archetype, Ni₁₂P₅ affords a structure based upon highly dispersed nickel nanoclusters integrated into a phosphorus lattice that harvest light intensely across the entire solar spectral range. Motivated by its panchromatic absorption and unique linearly bonded nickel-carbonyl-dominated reaction route, Ni₁₂P₅ is found to be a photothermal catalyst for the reverse water gas shift reaction, offering a CO production rate of 960 ± 12 mmol g_cat⁻¹ h⁻¹, near 100% selectivity and long-term stability. Successful extension of this idea to Co₂P analogs implies that metal phosphide materials are poised as a universal platform for high-rate and highly selective photothermal CO₂ catalysis.

There exists an urgent need to develop new materials to convert CO₂ to useful products. Here, authors demonstrate metal phosphide nanoparticles to enable light-driven CO₂ hydrogenation with high activities and near-unity selectivity.

Turning Waste into Value: Potassium-Promoted Red Mud as an Effective Catalyst for the Hydrogenation of CO2

Since 1887, red mud has been an unavoidable waste derived from the production of alumina in the Bayer process. Because of its high alkalinity and metal loading, red mud disposal and storage constitute a significant environmental risk. With worldwide storage capacity reaching its limits and no alternatives to the Bayer Process, the development of methods for the valorization of red mud is a must. In this study, red mud is converted into an efficient catalyst for the valorization of CO₂ . By simple potassium promotion, 45 % conversion of CO₂ with a light olefin (C₂ -C₄ ) selectivity of 36 % is achieved at 375 °C, 30 bar, and 9600 mL g^-1  h^-1 , matching the performance of some of the best catalysts reported to date.

Design of a core-shell catalyst: an effective strategy for suppressing side reactions in syngas for direct selective conversion to light olefins

An elegant catalyst is designed via the encapsulation of metallic oxide Zn-Cr inside of zeolite SAPO34 as a core-shell structure (Zn-Cr@SAPO) to realize the coupling of methanol-synthesis and methanol-to-olefin reactions. It can not only break through the limitation of the Anderson-Schulz-Flory distribution but can also overcome the disadvantages of physical mixture catalysts, such as excessive CO2 formation. The confinement effect, hierarchical structure and extremely short distance between the two active components result in the Zn-Cr@SAPO capsule catalyst having better mass transfer and diffusion with a boosted synergistic effect. Due to the difference between the adsorption energies of the Zn-Cr metallic oxide/SAPO zeolite physical mixture and capsule catalysts, the produced water and light olefins are easily removed from the Zn-Cr@SAPO capsule catalyst after formation, suppressing the side reactions. The light olefin space time yield (STY) of the capsule catalyst is more than twice that of the typical physical mixture catalyst. The designed capsule catalyst has superior potential for scale-up in industrial applications while simultaneously extending the capabilities of hybrid catalysts for other tandem catalysis reactions through this strategy.

Insight into the effects of electronegativity on the H2 catalytic activation for CO2 hydrogenation: four transition metal cases from a DFT study

Electronegativity of transition metal dominates the type of H species, which has an important effect on the path choice of CO₂ hydrogenation.

Coated sulfated zirconia/SAPO-34 for the direct conversion of CO2 to light olefins

The conversion of CO₂ to light olefins via bifunctional catalysts (i.e. metal oxides/zeolites) is a promising approach to tackle CO₂ emissions and, at the same time, reduce fossil-fuel dependence by closing the carbon cycle.