Selective Hydrogenation Of CO2 Research Articles

Selective Gas‐Phase Hydrogenation of CO2 to Methanol Catalysed by Metal‐Organic Frameworks

AbstractLarge scale production of green CH3OH obtained from CO2 and green H2 is a highly wanted process due to the role of CH3OH as H2/energy carrier and for producing chemicals. Starting with a short summary of the advantages of metal–organic frameworks (MOFs) as catalysts in liquid‐phase reactions, the present article highlights the opportunities that MOFs may offer also for some gas‐phase reactions, particularly for the selective CO2 hydrogenation to CH3OH. It is commented that there is a temperature compatibility window that combines the thermal stability of some MOFs with the temperature required in the CO2 hydrogenation to CH3OH that frequently ranges from 250 to 300 °C. The existing literature in this area is briefly organized according to the role of MOF as providing the active sites or as support of active metal nanoparticles (NPs). Emphasis is made to show how the flexibility in design and synthesis of MOFs can be used to enhance the catalytic activity by adjusting the composition of the nodes and the structure of the linkers. The influence of structural defects and material crystallinity, as well as the role that should play theoretical calculations in models have also been highlighted.

Tuning CO2 hydrogenation selectivity via support interface types on Cu-based catalysts

Growing interest has been shown in controlling the selectivity of CO2 hydrogenation to produce specific compounds and fuels with additional value. However, it is challenging to selectively generate target products due to the complexity and diversity of the products in CO2 hydrogenation reaction. Herein, we reported a finding in the CO2 hydrogenation reaction: selectivity could be totally reversed by just altering support interface types on Cu-based catalysts. Cu/ZnO-MgO catalysts showed high CH3OH selectivity, while Cu/ZnO-CoO catalysts exhibited good selectivity of CH4. According to in-depth characterization, varied basicity sites most likely as results of the different support interface types. Density functional theory (DFT) calculations pointed that support interface types altered the adsorption position of H2COO* on catalysts and affect the adsorption and activation of intermediates, and thus resulted in noticeably varied product selectivity. This study demonstrated the value of regulating CO2 hydrogenation selectivity via support interface types on Cu-based catalysts, which can aid in the rational design of catalysts for not only CO2 hydrogenation but also other significant reactions.

Interface mediated CO2 hydrogenation on inverse supported ZrO2/Ni(1 1 1) nanocluster catalyst

To tune the activity and selectivity of CO2 hydrogenation, inverse supported Zr9O18/Ni(111) catalysts are designed based on ab initio molecular dynamics simulation and density functional theory calculation under the consideration of the number of interfacial O and Zr atoms as well as the interaction between O and Zr atoms. For the most stable catalyst with coordinatively unsaturated interface Zr sites, charge transfer from surface to oxide has been found. The Ni(111) surface is pre-covered by H atoms and the interface Zr sites can activate CO2 to a large extent, and their interaction results in the spontaneous formation of surface formate. Further hydrogenation of surface formate leads to the selective formation of methanol with an apparent Gibbs free energy barrier of 0.62 eV, lower than that of methane formation (1.09 eV). On the contrary to metallic nickel and supported nickel catalysts, the most favoured methanol formation route [HCOO → CHO → CH2O → CH3O → CH3OH] does not involve CO as intermediate, revealing the mediated interface effect.

Ni12P5 Confined in Mesoporous SiO2 with Near-Unity CO Selectivity and Enhanced Catalytic Activity for CO2 Hydrogenation.

CO2 hydrogenation via the reverse water gas shift (RWGS) reaction is a promising strategy for CO2 utilization while constructing Ni-based catalysts with high catalytic activity and perfect CO selectivity remains a great challenging. Here, we demonstrate that the product selectivity for CO2 hydrogenation can be significantly tuned from CH4 to CO by phosphating of SiO2-supported Ni catalysts due to the geometric effect. Interestingly, nickel phosphide catalysts with different crystalline phases (Ni12P5 and Ni2P) differ sharply in CO2 conversion, and Ni12P5 is remarkably more active. Furthermore, we developed a facile strategy to confine small Ni12P5 nanoparticles in mesoporous SiO2 channels (Ni12P5@SBA-15). Enhanced activity is exhibited on Ni12P5@SBA-15, ascribed to the highly effective confinement effect. The in situ diffuse reflectance infrared Fourier transform spectroscopy and density functional theory calculations unveil that catalytic CO2 hydrogenation follows a direct CO2 dissociation route with adsorbed CO as the key intermediate. Notably, strong multibonded CO (threefold and bridge-bonded CO) is feasibly formed on the Ni catalyst accounting for CH4 as the dominant product whereas only weak linearly bonded CO exists on nickel phosphide catalysts resulting in almost 100% CO selectivity. The present results indicate that Ni12P5@SBA-15 combining the geometric effect and the confinement effect can achieve near-unity CO selectivity and enhanced activity for CO2 hydrogenation.

Defect-Driven Efficient Selective CO2 Hydrogenation with Mo-Based Clusters.

Synthetic fuels produced from CO2 show promise in combating climate change. The reverse water gas shift (RWGS) reaction is the key to opening the CO2 molecule, and CO serves as a versatile intermediate for creating various hydrocarbons. Mo-based catalysts are of great interest for RWGS reactions featured for their stability and strong metal-oxygen interactions. Our study identified Mo defects as the intrinsic origin of the high activity of cluster Mo2C for CO2-selective hydrogenation. Specifically, we found that defected Mo2C clusters supported on nitrogen-doped graphene exhibited exceptional catalytic performance, attaining a reaction rate of 6.3 gCO/gcat/h at 400 °C with over 99% CO selectivity and good stability. Such a catalyst outperformed other Mo-based catalysts and noble metal-based catalysts in terms of facile dissociation of CO2, highly selective hydrogenation, and nonbarrier liberation of CO. Our study revealed that as a potential descriptor, the atomic magnetism linearly correlates to the liberation capacity of CO, and Mo defects facilitated product desorption by reducing the magnetization of the adsorption site. On the other hand, the defects were effective in neutralizing the negative charges of surface hydrogen, which is crucial for selective hydrogenation. Finally, we have successfully demonstrated that the combination of a carbon support and the carbonization process synergistically serves as a feasible strategy for creating rich Mo defects, and biochar can be a low-cost alternative option for large-scale applications.

Effect of Different In2O3(111) Surface Terminations on CO2 Adsorption.

In2O3-based catalysts have shown high activity and selectivity for CO2 hydrogenation to methanol; however, the origin of the high performance of In2O3 is still unclear. To elucidate the initial steps of CO2 hydrogenation over In2O3, we have combined X-ray photoelectron spectroscopy and density functional theory calculations to study the adsorption of CO2 on the In2O3(111) crystalline surface with different terminations, namely, the stoichiometric, reduced, and hydroxylated surface. The combined approach confirms that the reduction of the surface results in the formation of In adatoms and that water dissociates on the surface at room temperature. A comparison of the experimental spectra and the computed core-level shifts (using methanol and formic acid as benchmark molecules) suggests that CO2 adsorbs as a carbonate on all three surface terminations. We find that the adsorption of CO2 is hindered by hydroxyl groups on the hydroxylated surface.

ZrO2 promoted Ru/In2O3 catalyst for selective hydrogenation of CO2 to methanol

With the strong metal-support interaction, In2O3 supported Ru catalyst has been confirmed to be active for selective hydrogenation of CO2 to methanol. Herein, we report that the addition of ZrO2 into Ru/In2O3 further improves the catalytic activity for CO2 hydrogenation to methanol. The catalyst characterization shows a formation of In2O3-ZrO2 solid solution, which is an excellent support for the highly dispersed Ru catalyst. Compared to Ru/In2O3, a significantly higher methanol selectivity is achieved over the Ru/In2O3-ZrO2 catalyst with 1 wt% Ru loading. The methanol space–time yield (STY) reaches 0.685 gMeOH h−1 gcat−1 at 300 ℃, 5 MPa, and 21000 cm3 gcat−1h−1. It has more than 20% increase compared to Ru/In2O3. The addition of ZrO2 optimizes the oxygen vacancies of In2O3, improves the CO2 adsorption and enables a more stable catalyst architecture, while the hydrogen spillover by the highly dispersed ruthenium improves the hydrogen activation ability of the catalyst. All these results in a high level of methanol yield.

Insight into the impacts of MnO2 crystal phases on CO2 selective hydrogenation to CH4 on Ni/MnOx catalysts

Ni-based catalysts using ε-, α- and β-MnO2 crystal phases supports were prepared and applied to CO2 hydrogenation. The samples were characterized by XRD, H2-TPR, BET, SEM, (HR)TEM, CO2-TPD, Raman, quasi in situ XPS, and in situ DRIFTS. Ni/MnOx-NS (ε-MnO2) was found to exhibit stable activity (with 69.0% CO2 conversion) and selectivity to CH4 (99.0%) at 350 ℃, much higher than Ni/MnOx-R (α-MnO2) and Ni/MnOx-B (β-MnO2). Partially reduced Mn3+ and enriched defects facilitated CO2 and intermediates adsorption/activation, enabling unpaired electrons trapped in defect oxide surface to accelerate the cleavage of C-O to form CH4 assisted by active H, whereas CO production via reverse water-gas reaction was strongly suppressed. This work highlights the key role of synergistic interaction between Ni and MnOx-NS and CO2 activation abilities by various MnO2, which directed the selective CO2 hydrogenation performance.

Bifunctionality of Re Supported on TiO2 in Driving Methanol Formation in Low-Temperature CO2 Hydrogenation.

Low temperature and high pressure are thermodynamically more favorable conditions to achieve high conversion and high methanol selectivity in CO2 hydrogenation. However, low-temperature activity is generally very poor due to the sluggish kinetics, and thus, designing highly selective catalysts active below 200 °C is a great challenge in CO2-to-methanol conversion. Recently, Re/TiO2 has been reported as a promising catalyst. We show that Re/TiO2 is indeed more active in continuous and high-pressure (56 and 331 bar) operations at 125-200 °C compared to an industrial Cu/ZnO/Al2O3 catalyst, which suffers from the formation of methyl formate and its decomposition to carbon monoxide. At lower temperatures, precise understanding and control over the active surface intermediates are crucial to boosting conversion kinetics. This work aims at elucidating the nature of active sites and active species by means of in situ/operando X-ray absorption spectroscopy, Raman spectroscopy, ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Transient operando DRIFTS studies uncover the activation of CO2 to form active formate intermediates leading to methanol formation and also active rhenium carbonyl intermediates leading to methane over cationic Re single atoms characterized by rhenium tricarbonyl complexes. The transient techniques enable us to differentiate the active species from the spectator one on TiO2 support, such as less reactive formate originating from spillover and methoxy from methanol adsorption. The AP-XPS supports the fact that metallic Re species act as H2 activators, leading to H-spillover and importantly to hydrogenation of the active formate intermediate present over cationic Re species. The origin of the unique reactivity of Re/TiO2 was suggested as the coexistence of cationic highly dispersed Re including single atoms, driving the formation of monodentate formate, and metallic Re clusters in the vicinity, activating the hydrogenation of the formate to methanol.

Reaction-Induced Metal-Metal Oxide Interactions in Pd-In2 O3 /ZrO2 Catalysts Drive Selective and Stable CO2 Hydrogenation to Methanol.

Ternary Pd-In2 O3 /ZrO2 catalysts exhibit technological potential for CO2 -based methanol synthesis, but developing scalable systems and comprehending complex dynamic behaviors of the active phase, promoter, and carrier are key for achieving high productivity. Here, we show that the structure of Pd-In2 O3 /ZrO2 systems prepared by wet impregnation evolves under CO2 hydrogenation conditions into a selective and stable architecture, independent of the order of addition of Pd and In phases on the zirconia carrier. Detailed operando characterization and simulations reveal a rapid restructuring driven by the metal-metal oxide interaction energetics. The proximity of InPdx alloy particles decorated by InOx layers in the resulting architecture prevents performance losses associated with Pd sintering. The findings highlight the crucial role of reaction-induced restructuring in complex CO2 hydrogenation catalysts and offer insights into the optimal integration of acid-base and redox functions for practical implementation.

Reaktionsinduzierte Metall‐Metalloxid‐Wechselwirkungen in Pd‐In2O3/ZrO2 Katalysatoren fördern die selektive und stabile CO2‐Hydrierung zu Methanol

AbstractTernäre Pd‐In2O3/ZrO2 Katalysatoren beweisen technologisches Potenzial für die CO2‐basierte Methanolsynthese, wobei die Entwicklung skalierbarer Systeme und das Verständnis komplexer dynamischer Wechselwirkungen zwischen der aktiven Phase, des Promotors und des Trägers der Schlüssel zur Erreichung einer hohen Produktivität sind. Hier zeigen wir, dass durch einfache Imprägnierung hergestellte Pd‐In2O3/ZrO2 Katalysatoren unter CO2‐Hydrierbedingungen eine stabile und selektive Nanoarchitektur bilden, unabhängig von der Reihenfolge der Zugabe von Pd‐ und In‐Komponenten auf den Zirkonoxidträger. Detaillierte operando Charakterisierung und Simulationen deuten auf eine schnelle Umstrukturierung, dessen Treiber die Energie der Metall‐Metalloxid‐Wechselwirkung ist. Die Nähe von InOx‐Schichten auf den entstehenden InPdx‐Partikeln verhindern Leistungsverluste durch Pd‐Sinterung. Weiterhin unterstreichen die Ergebnisse die entscheidende Rolle der reaktionsinduzierten Umstrukturierung in komplexem CO2‐Hydrierkatalysatoren und bieten Einblicke in die optimale Integration von Säure‐Base‐ und Redoxfunktionen für die technische Umsetzung.

Rationally designing NaFeMn/core–shell HZSM-5@Si bifunctional catalyst for selective synthesis of para-Xylene from CO2 hydrogenation

Selective production of aromatics from CO2 hydrogenation has attracted wide attention, but still remains big challenges, especially tuning the selectivity towards value-added p-xylene. Here, an effective NaFeMn/HZSM-5 catalyst was synthesized for selective CO2 hydrogenation to aromatics, over which a high aromatics selectivity of 72 % was realized at 45 % CO2 conversion. It was observed that the co-existence of Na and Mn can generate a beneficial interaction, promoting catalyst reduction and CO2 adsorption. In addition, the selectivity towards benzene-toluene-xylene (BTX) was significantly enhanced from 30 % to 46 % in the presence of organosilicon, by which the structural and acidic properties of the zeolite were improved. Furthermore, when NaFeMn catalyst was combined with core–shell HZSM-5@Si-vap zeolite, synthesized by vapor-crystallization, selectivity of p-xylene in xylene was increased from 28 % to 50 %. Compared with traditional hydrothermal treatment, vapor-crystallization endows intact silicalite encapsulation and surface acidity passivation.

Boosting the selectivity of Pt catalysts for cinnamaldehyde hydrogenation to cinnamylalcohol by surface oxidation of SiC support

The selective hydrogenation of cinnamaldehyde (CAL) is very important, but still remains challenging due to the coexistence of easily hydrogenated CC and CO bonds in CAL molecule. In this work, we report that employing partially oxidized SiC (SiC–O) as the support of Pt can evidently enhance the catalytic selectivity for the selective hydrogenation of CO in CAL. Further investigations show that the partially oxidized SiC surface can change the adsorption mode of CAL and facilitate the selective adsorption of CO in CAL. During the catalytic process, H2 was dissociated on Pt particles while CAL was mainly adsorbed and activated on the surface of support. The active H species generated on the Pt surface then spilled over to the support surface and reacted with the CO bond activated by the support surface to selectively form cinnamylalcohol. The present work revealed an important cooperative catalysis of metal and SiC, which would be helpful to design and application of more SiC-based catalysts.

Cu/ZnAl2O4 catalysts prepared by ammonia evaporation method: Improving methanol selectivity in CO2 hydrogenation via regulation of metal-support interaction

Numerous studies have demonstrated that improving the metal-support interaction is beneficial for reaction activity and stability in methanol synthesis from CO2. In this research, we deposit Cu onto ZnAl2O4 spinel by the ammonia evaporation method and obtain excellent catalytic performance with methanol selectivity close to 100% at 220 ℃ (STY of methanol: 317 gMeOH·kgcat-1·h−1) at low Cu loading (4 wt%). As opposed to the wet impregnation method, more well-dispersed Cu species are dispersed on the surface of ZnAl2O4 with a higher copper surface area, forming a strong interaction between Cu and ZnAl2O4. And meanwhile the distribution of basic sites is also improved. Thus, the adsorption and activation of CO2 are significantly enhanced. In addition, more Cu+ is readily generated upon reduction due to the fine interaction, which accelerates the stabilization and transformation of methoxy species, promoting the production of methanol.

Reactive ball-milling synthesis of Co-Fe bimetallic catalyst for efficient hydrogenation of carbon dioxide to value-added hydrocarbons

Catalytic hydrogenation of CO2 using renewable hydrogen not only reduces greenhouse gas emissions, but also provides industrial chemicals. Herein, a Co-Fe bimetallic catalyst was developed by a facile reactive ball-milling method for highly active and selective hydrogenation of CO2 to value-added hydrocarbons. When reacted at 320 °C, 1.0 MPa and 9600 mL h−1 gcat−1, the selectivity to light olefin (C2=–C4=) and C5 + species achieves 57.3% and 22.3%, respectively, at a CO2 conversion of 31.4%, which is superior to previous Fe-based catalysts. The CO2 activation can be promoted by the CoFe phase formed by reactive ball milling of the Fe-Co3O4 mixture, and the in-situ Co2C and Fe5C2 formed during hydrogenation are beneficial for the C–C coupling reaction. The initial C–C coupling is related to the combination of CO species with the surface carbon of Fe/Co carbides, and the sustained C–C coupling is maintained by self-recovery of defective carbides. This new strategy contributes to the development of efficient catalysts for the hydrogenation of CO2 to value-added hydrocarbons.

Kinetic Investigation on Selective CO2 Hydrogenation to Formic Acid over Rhodium Hydrotalcite (Rh-HT) Catalyst

Kinetic Investigation on Selective CO2 Hydrogenation to Formic Acid over Rhodium Hydrotalcite (Rh-HT) Catalyst

Selective Hydrogenation of CO2 to Aromatics over Composite Catalyst Comprising NaZnFe and Polyethylene Glycol-Modified HZSM-5 with Intra- and Intercrystalline Mesoporous Structure

CO2 hydrogenation to aromatics can significantly reduce emissions of the CO2 and provide a complementary route for the production of aromatics. Herein, we report a composite catalyst comprising Na- and Zn-promoted Fe catalyst (NaZnFe) and highly stable hierarchical nanocrystalline HZSM-5 modified by PEG for CO2 hydrogenation to aromatics. The subtle synergy between Na and Zn in NaZnFe promoted the formation and exposure of active iron species and the conversion of CO2 and intermediates. In addition, the PEG modification of HZSM-5 cannot only fabricate intracrystalline mesopores to improve mesoporosity but also provide appropriate acidity, endowing high aromatic selectivity and catalytic stability. Significantly, the high-efficiency diffusion on hierarchical HZSM-5 intensifies the synergistic effect in the catalytic system. The composite catalyst could suppress the total selectivity of CO and CH4 to less than 15% with an aromatic selectivity of up to 63.68% among all hydrocarbons and BTX selectivity in aromatics of up to 56.35% at a CO2 conversion of 42.08%.

Ni Single Atoms Confined in Nitrogen-Doped Carbon Nanotubes for Active and Selective Hydrogenation of CO2 to CO

Developing efficient non-precious-metal catalysts capable of selectively converting CO2 into fuels and chemicals is desirable yet remains a challenge. Ni-based catalysts usually exhibit high activity in methanation reactions but low selectivity and stability in the reverse water-gas shift (RWGS) reaction. Herein, we report a Ni single-atom catalyst with Ni–Nx motifs confined in N-doped carbon nanotubes as an active, selective, and stable catalyst for the RWGS reaction, achieving almost 100% CO selectivity with a STY of 1.88 molCO gNi–1 h–1 at 500 °C and atmospheric pressure. In addition to weak CO adsorption, strong CO2 adsorption and weak H2 adsorption at the Ni–Nx active site were found to be responsible for the high catalytic activity and CO selectivity.

CO2 Activation on Ni(111) and Ni(110) Surfaces in the Presence of Hydrogen

The structure sensitivity of CO2 activation in the presence of H2 has been identified by ambient-pressure X-ray photoelectron spectroscopy (APXPS) on Ni(111) and Ni(110) surfaces under identical reaction conditions. Based on the APXPS results and computer simulations, we propose that, around room temperature, the hydrogen-assisted activation of CO2 is the major reaction path on Ni(111), while the redox pathway of CO2 prevails on Ni(110). With increasing temperature, the two activation pathways are activated in parallel. While the Ni(111) surface is fully reduced to the metallic state at elevated temperatures, two stable Ni oxide species can be observed on Ni(110). Turnover frequency measurements indicate that the low-coordinated sites on Ni(110) promote the activity and selectivity of CO2 hydrogenation to methane. Our findings provide insights into the role of low-coordinated Ni sites in nanoparticle catalysts for CO2 methanation.

Boosting the Production of Light Olefins from CO2 Hydrogenation over Fe–Co Bimetallic Catalysts Derived from Layered Double Hydroxide

CO2 hydrogenation to light olefins (C2–C4═) is especially attractive for the chemical utilization of CO2, and currently, effective catalysts are still under development. Herein, we report a succession of Fe–Co bimetallic catalysts derived from Fe–Co–Mg layered double hydroxides (LDHs) with different Fe/Co ratios [(c(Fe3+) + c(Co2+))/c(Mg2+) = 1] for converting CO2 to light olefins, which were also compared to MgO-supported Fe–Co prepared by the impregnation method. The best catalyst FeCo-9:1-LDH presented a high selectivity of C2–C4═ over 36% at a CO2 conversion higher than 40%. With ex/in situ characterization including X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Mössbauer spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), we found that the Fe–Co–Mg LDH-derived catalyst (FeCo-9:1-LDH) is easily carburized to Co-modified iron carbide (Fe5C2), which is superior to the FeCo-9:1-I catalyst synthesized by impregnating Co and Fe onto MgO support. The former shows a higher CO2 conversion and higher C2–C4═ selectivity, while the latter produces more CH4. This work provides a series of catalysts for selective hydrogenation of CO2 to light olefins, as well as insights into the reaction pathway, favoring the rational design of CO2 hydrogenation catalysts.