Time-resolved X-ray Absorption Spectroscopy Research Articles

Engineering Band Gap and Photoconduction in Semiconducting Metal Organic Frameworks: Metal Node Effect.

We report a systematic study on the correlation of the metal nodes in M-THQ conducting MOFs (M = Fe, Ni, Cu, and Zn; THQ = tetra-hydroxybenzoquinone) with their structure, photophysical property, and photoconductivity. We found that the structural preference in these MOFs is controlled by metal node identity where Cu prefers a square planar coordination which leads to a 2D Kagome-type structure. Fe, Ni, and Zn prefer an octahedral sphere which leads to a 3D structure. Fe-THQ has the smallest band gap and highest photoconduction as well as a long-lived ligand-to-metal charge transfer state due to the mixed valence state revealed by time-resolved optical and X-ray absorption and terahertz spectroscopy. These results demonstrate the importance of the metal node in tuning the photophysical and photocatalytic properties of MOFs.

Development of Hydrogen Oxidation Reaction Catalysts to Overcome CO Poisoning and Elucidation of Reaction Mechanism

Passive autocatalytic recombiner (PAR) represents a potential technology for ensuring process safety in the hydrogen society. PARs function through the catalytic oxidation of generated or leaked hydrogen, facilitating its conversion into water and effectively mitigating the risk of hydrogen explosions. CO is recognized as a catalyst poison that hampers surface catalytic reactions. To investigate the negative effects of CO on the local structure of platinum metal nanoparticle catalysts during water formation, in situ and time-resolved X-ray absorption spectroscopy analyses were conducted. The results revealed that the Pt–Fe/CZY catalyst exhibited notable hydrogen oxidation activity even in the presence of CO. The enhanced performance can be attributed to the combined effects of Pt–Fe alloy composition and CZY support materials.

Lewis Acidic Support Boosts C-C Coupling in the Pulsed Electrochemical CO2 Reaction.

Copper-oxide electrocatalysts have been demonstrated to effectively perform the electrochemical CO2 reduction reaction (CO2RR) toward C2+ products, yet preserving the reactive high-valent CuOx has remained elusive. Herein, we demonstrate a model system of Lewis acidic supported Cu electrocatalyst with a pulsed electroreduction method to achieve enhanced performance for C2+ products, in which an optimized electrocatalyst could reach ∼76% Faradaic efficiency for C2+ products (FEC2+) at ∼-0.99 V versus reversible hydrogen electrode, and the corresponding mass activity can be enhanced by ∼2 times as compared to that of conventional CuOx. In situ time-resolved X-ray absorption spectroscopy investigating the dynamic chemical/physical nature of Cu during CO2RR discloses that an activation process induced by the KOH electrolyte during pulsed electroreduction greatly enriched the Cuδ+O/Znδ+O interfaces, which further reveals that the presence of Znδ+O species under the cathodic potential could effectively serve as a Lewis acidic support for preserving the Cuδ+O species to facilitate the formation of C2+ products, and the catalyst structure-property relationship of Cuδ+O/Znδ+O interfaces can be evidently realized. More importantly, we find a universality of stabilizing Cuδ+O species for various metal oxide supports and to provide a general concept of appropriate electrocatalyst-Lewis acidic support interaction for promoting C2+ products.

Operando time-resolved soft x-ray absorption spectroscopy for photoexcitation processes of metal complexes in solutions.

Operando time-resolved soft x-ray absorption spectroscopy (TR-SXAS) is an effective method to reveal the photochemical processes of metal complexes in solutions. In this study, we have developed the TR-SXAS measurement system for observing various photochemical reactions in solutions by the combination of laser pump pulses with soft x-ray probe pulses from the synchrotron radiation. For the evaluation of the developed TR-SXAS system, we have measured nitrogen K-edge x-ray absorption spectroscopy (XAS) spectra of aqueous iron phenanthroline solutions during a photoinduced spin transition process. The decay process of the high spin state to the low spin state in the iron complex has been obtained from the ligand side by N K-edge XAS, and the time constant is close to that obtained from the central metal side by time-resolved Fe K-edge XAS in the previous studies.

Synthesis of tunable near infrared absorbance of gold nanorods (AuNRs) and their gold oxidation states during nanorod formation following by synchrotron based X-ray absorption spectroscopy (XANES)

A study of growth mechanism on AuNRs synthesized using seed-mediated method has been conducted via time resolved synchrotron based XAS. The synthesized AuNRs were characterized by TEM and UV–vis spectroscopy. It was found that the volume change of AgNO3 solution influenced their surface plasmon resonances (SPR) of AuNRs. An increase of silver ions concentration resulted in an increase of the aspect ratio (AR). For the growth mechanism investigation, time-resolved XANES in fluorescent mode and UV–vis measurement were employed. The potential growth mechanism was proposed according to the XANES spectrums. The reduction of Au(3+) oxidation state to Au(0) occurs after the reducing agent were added. The change in oxidation state of the AuNRs corresponded to the XANES spectrum of AuCl illustrating the oxidation states were reduced from Au(3+) to Au(+) then Au(0), respectively. Moreover, the rate of change in oxidation state depended on the AR. The formation of AuNRs was completed for the shorter rods (AR∼2.0) while the longer rods (AR∼4.2) still exhibit higher feature of oxidation state compared at the same reaction time. In addition, the change in absorbance from UV–vis spectrums revealed that AuNRs with AR∼2.0 took 50 min to complete rod formation which is faster than that of the AuNRs with AR∼4.2 (60 min). These UV–vis results were in a good agreement with the XANES spectrums. This finding leaded to conclude that the rod formation of AuNRs with lower AR could occurred faster than the formation of AuNRs with higher AR.

Determining the proton diffusion coefficient in highly hydrated iridium oxide films by energy dispersive X-ray absorption spectroscopy

Charge transfer reactions in electrodeposited iridium oxide films (EIROF) are investigated by means of operando energy dispersive X-ray absorption spectroscopy (EDXAS), where oxidation and reduction conditions are selected to drive the Ir(III)/Ir(IV) and Ir(IV)/Ir(V) reactions in acidic solutions. The Ir(III)/Ir(IV) couple is related to a well-known electrochromic phenomenon, while the Ir(IV)/Ir(V) couple might play an important role in the catalysis of the oxygen evolution reactions (OER). In the experiments, current intensity and time-resolved X-ray absorption spectroscopy (XAS) are simultaneously recorded upon application of appropriate potential steps, leading to the independent determination of both the relevant reaction rates and the rate-determining steps. This is allowed by the fast acquisition time (∼10−2 s) at the ESRF Energy Dispersive XAS (EDXAS) ID24 beam-line, in combination with the highly hydrated amorphous iridium oxide electrode material, which in turn allows to maximize the fraction of Ir sites participating in the electrochemical processes. If the experimental conditions exclude the possibility of having either oxygen evolution (or reduction), the Degree of Reaction (DoR), determined by both electrochemistry and XAS, exhibits exponential time dependence, clearly pointing to diffusion-controlled processes. Vice versa, under concomitant OER + oxidation of iridium centers or ORR + iridium reduction, the electrochemical and XAS DoRs highlight different phenomena, providing fully complementary information of the ongoing electrode reactions. In all cases, data elaboration allows to determine the diffusion coefficient of H+ ions within the catalyst layer, that is compared and confirmed by data obtained by electrochemical impedance spectroscopy (EIS). The high values of D obtained for EIROF is compared to values obtained on other IrO2 materials can help in explaining the relevant high electrocatalytic activity.

Application of Time-Resolved Synchrotron X-ray Absorption Spectroscopy in an Energy Conversion Reaction

The rational design of high-efficiency catalysts is hindered by the knowledge of active sites, which always experience dynamic transformations within different time scales. In this regard, tracking these time-dependent processes is essential to building the correlation between the active site and catalytic performance. Achieving this goal requires powerful characterization techniques to overcome the obstacle induced by the time mismatch. By virtue of the local structure sensitivity, synchrotron X-ray absorption spectroscopy (XAS) comprising step-scanning XAS, quick-scanning XAS, and energy-dispersive XAS has been widely applied to record structural evolution events. In this Perspective, we highlight the substantial accomplishments achieved by these time-resolved XAS techniques. Their principles, advantages, and limitations involved in monitoring energy-involving electrocatalysis were also introduced. Meanwhile, the key challenges that we are encountering and the further directions of time-resolved XAS are also provided. We sincerely hope that these insights could offer a reliable guideline for other researchers to design more efficient in situ experiments.

Simultaneous quick-scanning X-ray absorption spectroscopy and X-ray diffraction

The existing setup for time-resolved quick-scanning X-ray absorption spectroscopy (QEXAFS) at beamline P64 at the PETRA III storage ring is complemented by new infrastructure suited for the collection of X-ray diffraction data simultaneously to the QEXAFS experiment. In particular, the sinusoidal periodic movements of the quick-EXAFS mono-chromator are modified in such a way, that an energy plateau with approximately constant energy over a certain time is created in the pre-edge region of the absorption edge of interest. By employing a properly defined trigger signal in this time, the exposure of a two-dimensional X-ray detector placed behind the sample is actuated, thus allowing to collect an X-ray diffraction pattern over a certain angular range as defined by the actual X-ray energy and the position of the 2D-detector. Details of the new setup as well as exemplary results obtained during the solvothermal synthesis of ZnO nanoparticles and the bcc-fcc phase transition of iron at elevated temperatures are presented.

In Situ Observation of ZnO Nanoparticle Formation by a Combination of Time-Resolved X-ray Absorption Spectroscopy and X-ray Diffraction.

The formation of ZnO nanomaterials from different Zn acetylacetonate precursor solutions was studied in situ by employing simultaneous, time-resolved X-ray diffraction (XRD) and X-ray absorption spectroscopy (EXAFS) at the Zn K-edge. The precursor solutions were heated from room temperature to the desired reaction temperatures in a hermetically sealed cell dedicated to X-ray experiments. In general, the first indications for the formation of hexagonal ZnO were found for elevated temperatures of about 80 °C both by XRD and EXAFS, and the contributions increase with temperature and time. However, no reaction intermediates could be proved in addition to the Zn precursors and the formed hexagonal ZnO materials. Furthermore, the results show that the efficiency of the reaction, i.e., the conversion of the precursor material to the ZnO product, strongly depends on the solvent used and the reaction temperature. ZnO formation is accelerated by an increased temperature of 165 °C and the use of 1-octanol, with a conversion to ZnO of more than 80% after only a ca. 35 min reaction time according to a detailed analysis of the EXAFS data. For comparison, an identical concentration of Zn acetylacetonate in water or dilute alkaline NaOH solutions and a reaction temperature of around 90 °C leads to a smaller conversion of approximately 50% only, even after several hours of reaction. The particle size determined from XRD for different orientations shows a preferred orientation along the c-direction of the hexagonal crystal system, as well in accordance with scanning electron microscopy. The LaMer model explained this highly non-uniform growth of needle-like ZnO crystallites.

Characterizing coherences in chemical dynamics with attosecond time-resolved x-ray absorption spectroscopy.

Coherence can drive wave-like motion of electrons and nuclei in photoexcited systems, which can yield fast and efficient ways to exert materials' functionalities beyond the thermodynamic limit. The search for coherent phenomena has been a central topic in chemical physics although their direct characterization is often elusive. Here, we highlight recent advances in time-resolved x-ray absorption spectroscopy (tr-XAS) to investigate coherent phenomena, especially those that utilize the eminent light source of isolated attosecond pulses. The unparalleled time and state sensitivities of tr-XAS in tandem with the unique element specificity render the method suitable to study valence electronic dynamics in a wide variety of materials. The latest studies have demonstrated the capabilities of tr-XAS to characterize coupled electronic-structural coherence in small molecules and coherent light-matter interactions of core-excited excitons in solids. We address current opportunities and challenges in the exploration of coherent phenomena, with potential applications for energy- and bio-related systems, potential crossings, strongly driven solids, and quantum materials. With the ongoing developments in both theory and light sources, tr-XAS holds great promise for revealing the role of coherences in chemical dynamics.

Symmetry-resolved CO desorption and oxidation dynamics on O/Ru(0001) probed at the C K-edge by ultrafast x-ray spectroscopy.

We report on carbon monoxide desorption and oxidation induced by 400nm femtosecond laser excitation on the O/Ru(0001) surface probed by time-resolved x-ray absorption spectroscopy (TR-XAS) at the carbon K-edge. The experiments were performed under constant background pressures of CO (6 × 10-8 Torr) and O2 (3 × 10-8 Torr). Under these conditions, we detect two transient CO species with narrow 2π* peaks, suggesting little 2π* interaction with the surface. Based on polarization measurements, we find that these two species have opposing orientations: (1) CO favoring a more perpendicular orientation and (2) CO favoring a more parallel orientation with respect to the surface. We also directly detect gas-phase CO2 using a mass spectrometer and observe weak signatures of bent adsorbed CO2 at slightly higher x-ray energies than the 2π* region. These results are compared to previously reported TR-XAS results at the O K-edge, where the CO background pressure was three times lower (2 × 10-8 Torr) while maintaining the same O2 pressure. At the lower CO pressure, in the CO 2π* region, we observed adsorbed CO and a distribution of OC-O bond lengths close to the CO oxidation transition state, with little indication of gas-like CO. The shift toward "gas-like" CO species may be explained by the higher CO exposure, which blocks O adsorption, decreasing O coverage and increasing CO coverage. These effects decrease the CO desorption barrier through dipole-dipole interaction while simultaneously increasing the CO oxidation barrier.

Enhanced Property Tunability of Doubly Doped Semiconductor Nanomaterials Using the Cluster Seed Method

Semiconductor Quantum Dots (QDs) have great potential in applications for renewable energy generation due to their size-tunable redox potentials. They may be prepared with different morphologies and coated to create complex heterostructures. Doping of semiconductor nanomaterials is another mechanism to realize property tunability, and doped QDs are playing an increasing role in green energy generation applications. In 2013 our group reported a method to create a batch of doped quantum dots where each particle was embedded with the same number of guest ions, thus circumventing Poisson statistics. This was accomplished by nucleating the QD around an organometallic seed cluster that contains guest ions. As a result, each QD has the same number of dopants, which eliminates problems due to inhomogeneity of the guest ion stoichiometry. These materials were studied using time-resolved X-ray absorption spectroscopy, which allows us to characterize the electronic and coordination structure in both the ground and excited states.Current research reveals the potential to doubly dope semiconductors using cluster seeding, and that the originating organometallic structure may be represented in the final material product. To this end, ZnCdSe nanowires were prepared in the presence of (MnTe)4 cluster seeds. The results reveal that Mn(2+) has been successfully incorporated into the host matrix, while temperature dependent optical measurements suggest significantly enhanced semiconductor exciton-magnetic dopant interactions in materials prepared by cluster seeding compared to doped control samples. This could be due to ferromagnetic Mn-Mn interactions in the host resulting from enhanced exchange coupling mediated by highly spin-orbit coupled tellurium bridging. Consequently, cluster seeding may be used to "dope the dopants", affording a heretofore unrealized method for developing designer materials with enhanced electronic and optical properties. Figure 1

(Invited) Excited States and Reaction Mechanisms of Catalysts with Redox Active Ligands Investigated with X-Ray Spectroscopy

Metal dithiolenes and related molecular catalysts known for their redox-active ligands and their efficient and robust electro- and photo-catalysis of the hydrogen evolution reaction are investigated. To understand how the redox-active ligands of these catalysts influence their electronic excited states and participate in their chemical reactions, we need element-specific probes of charge and bonding at both metal and ligand atomic sites. X-ray absorption spectroscopy (XAS) affords us this opportunity and is used to study the electro- and photo-catalytic reaction mechanisms of these complexes, with a specific focus on the role of metal versus ligand atomic sites. Steady-state and time-resolved XAS studies at the Ni and S K-edges will be presented to identify the redox activity of metal vs. ligand sites on timescales spanning from the ultrafast excited state relaxation and photochemical activation processes to the steady-state creation of important intermediates in the multi-step hydrogen evolution reaction.

Deciphering Photochemical Reaction Pathways of Aqueous Tetrachloroauric Acid by X-ray Transient Absorption Spectroscopy.

Photolysis reaction pathways of [Au(III)Cl4]- in aqueous solution have been investigated by time-resolved X-ray absorption spectroscopy. Ultraviolet excitation directly breaks the Au-Cl bond in [Au(III)Cl4]- to form [Au(II)Cl3]- that becomes highly reactive within 79 ps. Disproportionation of [Au(II)Cl3]- generates [Au(I)Cl2]-, which is stable for ≤10 μs. In contrast, intense near-infrared lasers photolyze water to generate hydrated electrons, which then reduce [Au(III)Cl4]- to [Au(II)Cl3]- at 5 ns. Hydrated electrons further induce a chain reaction from [Au(II)Cl3]- to [Au(0)Cl]- by successively removing one Cl-. The zero-valency Au anions quickly polymerize and condense to form Au nanoparticles, which become the dominating product after 400 s. Our results reveal that the condensation of zero-valency Au starts with dimerization of gold clusters coordinated with chloride ions rather than direct condensation of pristine Au atoms.

(Digital Presentation) Time-Resolved Operando XAS of FexNi100-XOy Electrocatalysts for the Oxygen Evolution Reaction Reveals Temporal Shift in Ni K-Edge during Ni2+/3+ Redox Reaction

FexNi100-xOy electrocatalysts have become a focus for alkaline water electrolysis and the oxidative half reaction of oxygen evolution. Under alkaline conditions, the oxygen evolution reaction (OER) can be promoted by non-precious metal oxide and hydroxide electrocatalysts. In particular, electrocatalyst compositions from first row late transition metals such as iron, nickel, manganese, and cobalt have emerged as some of the most active catalysts for the OER, and the role of iron has been identified as key within multi-metallic compositions. In our research, we have focused specifically on the iron-nickel bimetallic composition and have developed synthesis methods to be able to control the bimetallic composition, surface chemistry, and three-dimensional morphology of a suite of FexNi100-xOy nanoparticle electrocatalysts. With this subset of highly-active FexNi100-xOy nanoparticle electrocatalysts, we have recently been focused on operando x-ray absorption spectroscopy (XAS) studies to understand how the chemistry of the iron and nickel species within these nanocatalysts changes as a result of exposure to the electrochemical environment. This talk will focus on a set of operando data obtained with a quick scan detector at beamline 9-3 at SSRL, where we were able to capture temporal, dynamic changes to the nickel chemistry as a function of applied voltage in the Faradaic region of the OER. Specifically, we have captured the change in the Ni K-edge that occurs as a result of the voltage stepping through the Ni redox reaction, where the Ni species in our electrocatalyst oxidizes from a 2+ to a 3+/4+ oxidation state. This redox reaction is associated with a phase transition from Ni(OH)2 to NiOOH. Our measurements were able to obtain 90 s scans during a 15 min time period of measurement, where we find that the Ni redox reaction and phase transition occurs during the first 10 minutes of measurement. Modeling of the extended x-ray absorption fine structure (EXAFS) region suggests that both Ni – O and Ni – M (M = metal) scattering path atomic pairs undergo a compression in distance. Further, the time scale of the phase transition suggests that the Ni redox reaction is mass transport limited. In this talk, I will discuss these results and present our analysis of the time-resolved x-ray absorption spectroscopy data.

Green reduction route via ethanol dehydrogenation and decomposition for Pd-promoted Co3O4/SBA-15 catalysts in reverse water gas shift reaction: An operando time-resolved X-ray absorption spectroscopy investigation

An alternative reduction route of Pd-promoted Co3O4 supported on SBA-15 under ethanol dehydrogenation and decomposition (ED) was studied by an operando time-resolved X-ray absorption spectroscopy (TR-XAS) to understand the insight nature of materials. The catalysts, xPd-10Co/SBA-15, were prepared by co-impregnation method where the Pd content, x = 0.2, 0.5 or 1.0 wt% and Co content = 10.0 wt%. The precursors were transformed to PdO and Co3O4 after calcination and to metallic form after reduction. The reducibility of Co3O4 to metallic Co in 1Pd-10Co/SBA-15 was 98.0%, whereas the metallic form was not produced in the absence of Pd. This catalyst also provided the highest H2 yield of 80% from ED at 500 °C. The ED-reduced 1Pd-10Co/SBA-15 was tested in reverse water gas shift reaction (RWGS) and characterized by the operando TR-XAS. The CO selectivity from CO2 was 97.8%, slightly higher than conventional H2-reduced 1Pd-10Co/SBA-15.

Direct observation of ultrafast exciton localization in an organic semiconductor with soft X-ray transient absorption spectroscopy

The localization dynamics of excitons in organic semiconductors influence the efficiency of charge transfer and separation in these materials. Here we apply time-resolved X-ray absorption spectroscopy to track photoinduced dynamics of a paradigmatic crystalline conjugated polymer: poly(3-hexylthiophene) (P3HT) commonly used in solar cell devices. The π→π* transition, the first step of solar energy conversion, is pumped with a 15 fs optical pulse and the dynamics are probed by an attosecond soft X-ray pulse at the carbon K-edge. We observe X-ray spectroscopic signatures of the initially hot excitonic state, indicating that it is delocalized over multiple polymer chains. This undergoes a rapid evolution on a sub 50 fs timescale which can be directly associated with cooling and localization to form either a localized exciton or polaron pair.

Electrochemical properties of ACNF/Li2FeSiO4 composite nanostructures for supercapacitors

This work reports the synthesis and electrochemical properties of activated carbon nanofibers (ACNF) composited with Li2FeSiO4 for supercapacitors. The prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller analyzer (BET), transmission electron microscopy (TEM), and thermal gravimetric analyzer (TGA). The electrochemical properties were tested using a variety of techniques, such as cyclic voltammetry (CV), galvanostatic charge-discharge (GDC), and electrochemical impedance spectroscopy (EIS). The structural transformation during charging and discharging processes was studied by in-situ time resolved X-ray absorption spectroscopy (in-situ TRXAS). The ACNF/Li2FeSiO4 presented monoclinic structure with space group of P21/n, although there was a small impurity of FeO. The structural transformations of iron upon cycling in the + 2 to + 3 state were responsible for high capacity of ACNF/Li2FeSiO4 materials. The maximum specific capacitance of 158 Fg−1 at 2 mVs−1 and 201 Fg−1 at 0.25 Ag−1 with the corresponding specific energy of 17.8 Whkg−1 and specific power of 99.7 Wkg−1 were observed. Moreover, this composite material exhibited an excellent cycle performance through maintaining over 85% of its initial capacitance after 1000 cycles. The interesting electrochemical properties of ACNF/Li2FeSiO4 composite nanostructure make it a potential candidate for supercapacitors.

Insight into the Nature of the ZnO x Promoter during Methanol Synthesis.

Despite the great commercial relevance of zinc-promoted copper catalysts for methanol synthesis, the nature of the Cu–ZnOx synergy and the nature of the active Zn-based promoter species under industrially relevant conditions are still a topic of vivid debate. Detailed characterization of the chemical speciation of any promoter under high-pressure working conditions is challenging but specifically hampered by the large fraction of Zn spectator species bound to the oxidic catalyst support. We present the use of weakly interacting graphitic carbon supports as a tool to study the active speciation of the Zn promoter phase that is in close contact with the Cu nanoparticles using time-resolved X-ray absorption spectroscopy under working conditions. Without an oxidic support, much fewer Zn species need to be added for maximum catalyst activity. A 5–15 min exposure to 1 bar H2 at 543 K only slightly reduces the Zn(II), but exposure for several hours to 20 bar H2/CO and/or H2/CO/CO2 leads to an average Zn oxidation number of +(0.5–0.6), only slightly increasing to +0.8 in a 20 bar H2/CO2 feed. This means that most of the added Zn is in a zerovalent oxidation state during methanol synthesis conditions. The Zn average coordination number is 8, showing that this phase is not at the surface but surrounded by other metal atoms (whether Zn or Cu), and indicating that the Zn diffuses into the Cu nanoparticles under reaction conditions. The time scale of this process corresponds to that of the generally observed activation period for these catalysts. These results reveal the speciation of the relevant Zn promoter species under methanol synthesis conditions and, more generally, present the use of weakly interacting graphitic supports as an important strategy to avoid excessive spectator species, thereby allowing us to study the nature of relevant promoter species.

How magnetic field affects catalytic CO2 hydrogenation over Fe-Cu/MCM-41: In situ active metal phase—reactivity observation during activation and reaction

In this work, a systematic investigation of external magnetic field affecting metal phase transformation of Fe-Cu/MCM-41 catalysts both during activation and reaction, and their performances by means of CO2 conversion and C2 + C3 hydrocarbons selectivity were for the first time examined in-situ using time-resolved X-ray absorption spectroscopy (TRXAS) and an online quadrupole mass spectrometer. The in-situ XANES result confirmed that FeO and Fe3O4 are major active forms of the catalyst. With magnetic flux intensities of 28.91–58.59 mT, iron oxide phases, specifically Fe3O4 and FeO, within the catalysts were stabilized and maintained. The CO2 conversion was increased for 1.03 – 1.09 times, while the concentrations of C2 + C3 hydrocarbons were considerably improved by 24.03 – 35.37 times compared to those without magnetic field. The reaction steps of CO2 hydrogenation were theoretically confirmed on the isolated catalysts using M06-L with the 6-31G(d,p) + LANL2DZ mixed basis set based on the results from LCF analysis. Fe4, Fe4O4, and Fe2Cu2 clusters were used to represent the active species of pristine Fe and iron oxide (FeO) and bimetallic Fe-Cu catalyst, respectively. It was found that CO2 hydrogenation could take place via the bimolecular route in which adsorbed CO2 on the Fe center was hydrogenated by dissociative adsorption of H2 on the Cu center—promoting chain growth probability of CO2 to form C2 + C3 hydrocarbons due to the active iron oxides (Fe3O4 and FeO) were maintained by magnetic field during the reaction.