High Selectivity To Light Olefins Research Articles

Using brewing waste diatomite activated by ball milling to simple and sustainable synthesis of nano-H-ZSM-5 aggregates

Brewing waste diatomite (BSDT) from the beer industry is a highly productive silica-aluminate solid waste and realizing the resource utilization of BSDT is the key to achieving the circular economy. Synthesis of zeolites from BSDT is a high value-added utilization method, but using BSDT to synthesize zeolites via “silica-alumina homologation” is difficult because of its high SiO2/Al2O3 ratio and low chemical activity. Further, using BSDT to synthesize high-quality nano-zeolites on a large scale through a simple and green method is a huge challenge. In this study, we propose a facile and scalable strategy to utilize BSDT as the only Si-Al source to prepare high-quality nano-H-ZSM-5 aggregates with hierarchical structures in a single templating agent system by solid-like transformations. The activation of BSDT was achieved by mechanical ball milling. Crystallite size and hierarchical structures are controlled by decoupling the crystal nucleation and growth processes. Due to the “silica-alumina homologation” system, aluminum species enter the zeolite framework along with the dynamic crystallization process and provide uniform acidic sites. In the methanol conversion reaction, the obtained catalysts showed longer lifetime (172.5 h) and higher light olefin selectivity (62.5%) compared to commercial catalysts. This strategy is simple, economical, and scalable, and can be extended to the synthesis of other framework-type zeolites with high SiO2/Al2O3 ratios.

Exploring the effect of polyacrylamide/graphene oxide composite hydrogel on the synthesis and application of ZSM-5 molecular sieves

Herein, we demonstrate the synthesis of coffin-shaped ZSM-5 molecular sieves in polyacrylamide (PAM)/graphene oxide (GO) composite hydrogel using the hydrothermal method. The as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS), and Thermogravimetry analyses (TGA). The effect of PAM and GO addition on the morphology and structure of ZSM-5 was investigated. The results indicated that the introduction of PAM and GO promoted the growth of the ZSM-5 (101) plane. Moreover, samples synthesized in the PAM/GO hydrogel exhibited a longer c-axis and a more pronounced coffin-shaped morphology compared to samples synthesized solely in PAM hydrogel. The Si/Al ratio decreased with the addition of GO, possibly due to interface effects leading to the formation of ZSM-5 precursors with a higher Al content. TG, FT-IR, and XPS characterization revealed hydrogen bonding interactions between PAM and GO, and the addition of GO likely restricted the movement of polymers, improving cross-linking between monomers and forming a more uniform network structure. The sample G-15 (P-5) exhibited higher mesopore volume and average pore diameter, contributing to enhanced catalytic performance. However, with increasing GO content, the average pore diameter decreased, potentially due to functional groups on the surfaces of graphene oxide and polyacrylamide forming a more uniform and structurally stable three-dimensional network structure. This allowed for controlled modulation of the molecular sieve morphology and pore size. The introduction of PAM/GO hydrogel resulted in a moderate amount of weak acid and an increased amount of strong acid, both shifting to lower temperatures. The ZSM-5 molecular sieves synthesized in the PAM/GO composite hydrogel demonstrated outstanding MTO catalytic performance, exhibiting high selectivity for light olefins and an extended catalytic lifespan. This work is expected to provide new ideas and methods for developing efficient ZSM-5 catalysts.

Synthesis of a phosphomolybdic acid-modified AlPO4-5/SAPO-34 composite catalyst and its catalytic performance in the MTO reaction

SAPO-34 catalysts with high selectivity for light olefins were first synthesized via the introduction of phosphomolybdic acid (HPMo) and AlPO4-5 zeolite into the initial gel. The physical and chemical characteristics of the synthesized catalysts were determined by a series of techniques and the catalytic performance of the modified composite zeolites for the methanol-to-olefin (MTO) reaction was investigated. The results indicated that HPMo-modified SAPO-34 was featured with more Brønsted acid sites, more mesopores, and a smaller crystal size, thereby demonstrating superior catalytic performance. The further combination with AlPO4-5 (16.7 wt%) prolonged the lifetime of the HPMo-modified SAPO-34, which is thought in this paper related to its 12-ring straight channel (0.7–0.8 nm) and the absence of any Brønsted acid sites. The MTO tests showed that the light olefins selectivity for the modified composite zeolites reached 95.1 %, while the catalyst lifetime remained at 445 min

Boosting CO2 hydrogenation of Fe-based monolithic catalysts via 3D printing technology-induced heat/mass-transfer enhancements

The direct transformation of CO2 into valuable chemicals with the aid of sustainable energy-generated H2 has attracted enormous interest owing to the integrated functions of carbon elimination and non-fossil fuel-derived products supply. As one of the most promising catalysts for CO2 hydrogenation, the chemical properties of Fe-based catalysts, such as electronic structure and coordination environment, have been widely studied. However, the mass/heat transfer effects in Fe-based catalysts are also crucial to the targeted product selectivity and catalytic stability, but have been rarely investigated due to the lack of facile fabrication protocols. Herein, we precisely fabricate and tailor the architecture of the Fe-based monolithic catalysts by a direct ink writing (DIW)-type three-dimensional (3D) printing technology under the guidance of the computationally controlled printing procedure. The Fe-based monolithic catalyst with spiral-type architecture delivers extremely high light olefins selectivity (52.6%) and space time yield (STY, 451.8 gCH2 kgcat−1 h−1) from CO2 hydrogenation. Based on the mass-transfer simulation, the spiral-structured channels in the Fe-based monolithic catalyst lower the coverage of intermediates and products on the catalytic interface due to the optimal mass-transfer effect, thus maximizing the utilization of active sites and timely terminating the carbon-chain growth. More in-depth, the density functional theoretical (DFT) simulations verify that the relatively electron-rich catalytic interface with low intermediate coverage could facilitate the desorption of olefins and decelerate the C-C coupling step, which synergistically guarantee the enhanced light olefins synthesis performance. Furthermore, the enhanced heat-transfer effect endowed by the 3D architecture prolongs the life-time of catalyst by avoiding undesirable active site aggregation and carbon deposition. The powerful strategy for catalyst fabrication not only provides a new concept of regulating the CO2 hydrogenation performance of Fe-based catalysts but also holds a great promise to spread into other catalytic systems for targeted synthesis.

Unraveling the role of GaZrOx structure and oxygen vacancy in bifunctional catalyst for highly active and selective conversion of syngas into light olefins

The direct conversion of syngas to light olefins (STO) over metal oxide-zeolite (OX-ZEO) bifunctional catalyst has aroused wide interest. However, due to unmatched reaction temperature for CO conversion to oxygenated hydrocarbons over metal oxide (200–300 °C) and C−C coupling reaction over zeolite (350–450 °C), it is still a great challenge to achieve both high light olefins selectivity and high CO conversion; moreover, the reaction mechanism needs to be further studied. Herein, the Ga-Zr oxide is taken as a probe oxide to mix with SAPO-34 zeolite for STO. A high light olefins selectivity of 88.6% is achieved at an extremely high CO conversion of 51.6% with a stable activity for 200 h. The incorporation of Ga into ZrO2 generates the GaZrOx solid solution structure with abundant concentration of oxygen vacancy and hydroxy group, the strong synergetic effect between Ga and Zr in GaZrOx benefits the CO activation and CH3O* formation at high temperatures (280–430 °C), providing a compatible temperature match for C−C coupling over SAPO-34. The GaZrOx is a promising and potential catalyst for industrial application in direct conversion of syngas to olefins, aromatics, and liquid fuels.

Designing ABC-6 family small pore zeolites by epitaxial growth approach

Aluminosilicate small pore zeolites belonging to ABC-6 family play crucially important roles in the high methanol conversion with the high selectivity of light olefins, gas separation and storage, and selective catalytic reduction of NOx. In this work, we report a general method, called the epitaxial growth approach, for designing ABC-6 family small pore zeolites. It is mainly realized through the epitaxial growth on the nonporous SOD-type zeolite in the presence of inorganic cations (Na+ and K+) combined with a variety of organic structure directing agents (OSDAs). In this case, a series of ABC-6 family small pore zeolites such as ERI-, SWY-, LEV-, AFX-, and PTT-type zeolites have been successfully synthesized within a few hours. More importantly, the advanced focused ion beam (FIB) and the low-dose high-resolution transmission electron microscopy (HRTEM) imaging technique have been utilized for unraveling the zeolite heterojunction at the atomic level during the epitaxial growth process. It turns out (222) crystallographic planes of the SOD-type zeolite substrate provide unique pre-building units, which facilitate the growth of targeted ABC-6 family small pore zeolites along its c-axis. Moreover, the morphologies of ERI-type zeolite can also be tuned through the epitaxial growth approach, achieving a longer lifetime in the methanol conversion.

Effect of MgFe-LDH with Reduction Pretreatment on the Catalytic Performance in Syngas to Light Olefins

MgFe-layered double hydroxides (LDH) were widely used as catalysts for Fischer–Tropsch synthesis to produce light olefins, in which the state of Fe-species may affect the resulting catalytic active sites. Herein, the typical MgFe-LDH was hydrothermally synthesized and the obtained MgFe-LDH was pretreated with H2 at different temperatures to reveal the effects of the state of Fe-species on the catalytic performance in Fischer–Tropsch synthesis. MgFe-LDH materials were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). It was found that a MgO-FeO solid solution would be formed with the increase of the reduction temperature, which made the electrons transfer from Mg atoms to Fe atoms and strengthened the adsorption of CO. The pre-reduced treatment toward Mg-Fe-LDH enabled the FeCx active sites to be easily formed in situ during the reaction process, leading to the high conversion of CO. CO2 temperature-programmed desorption (CO2-TPD) and H2 temperature-programmed desorption (H2-TPD) analysis confirmed that the surface basicity of the catalysts was increased and the hydrogenation capacity was weakened, the secondary hydrogenation of the olefins was inhibited, and therefore as were the enhancement of O/P in the product and the high selectivity of light olefins (42.7%).

A highly efficient SAPO-34 catalyst for improving light olefins in methanol conversion: Insight into the role of hierarchical porosities and tailoring acid properties based on in situ NH3-poisoning

Hierarchical SAPO-34 zeolites with tunable porosity were hydrothermally synthesized by modulating the Si/Al molar ratios of the gel precursors, and the morphologies of SAPO-34 crystals gradually evolve from well-dispersed ultra-small nanocrystals to compactly polycrystalline aggregates, and to analogous polycrystallinites but adhered with minute amorphous debris by increasing the Si/Al ratio ranging from 0.20 to 0.67. The catalytic tests during methanol-to-olefins (MTO) reaction indicate that the Hier-SAPO-34-0.20 (Si/Al = 0.20) catalyst constructed by loosely nano-sized crystals centered at 50 nm presents prominent catalytic performances with about 2.5 times prolonged catalytic longevity and around 10 % improvement for the selectivity toward light olefins (ethylene and propylene) as compared to a reference catalyst. More interestingly, when Hier-SAPO-34-0.20 catalyst was in situ pretreated with NH3 flowing, the selectivity of light olefins can be greatly increased by 18.1 % at the initial stage and the corresponding even selectivity with time-on-stream can be elevated by 6.9 %. It founds that in situ NH3-poisoned catalysts with improved light olefins selectivity are also suitable for ZSM-5 zeolite. These results reveal that the weakened strong acid sites modified by NH3-poisoning play a pivotal role in suppressing the undesired hydrogen transfer reactions and thus giving a high selectivity for light olefins. This work highlights the importance of acidity fine-tailoring by in-situ NH3-poisoning strategy on hierarchical zeolites for the improvement of light olefin selectivity, which would be valuable guidance for industrial applications.

Catalytic performance of Zn-containing MFI zeolites in acetone-to-aromatics reactions

MFI metallosilicates AlMFI and FeMFI were prepared by hydrothermal synthesis, and Zn species were introduced into these MFI-type zeolites by ion exchange. Acetone-to-aromatics (ATA) reactions were carried out using the MFI-type zeolites before and after Zn ion exchange treatment. We examined the effects of zeolite Brønsted acid strength, Zn species, and Zn dose on (1) selective production of benzene-toluene-xylene (BTX) from acetone, and (2) catalyst lifetime. AlMFI selectively produced BTX due to its strong Brønsted acidity, and the introduction of Zn further enhanced its BTX selectivity. In contrast, FeMFI showed high selectivity for light olefins even after Zn ion exchange treatment. Increasing the Zn dose added to AlMFI did not improve its BTX selectivity but did suppress the catalytic deactivation rate. Together, the effects of Zn addition and AlMFI's strong Brønsted acidity resulted in highly selective BTX production and long catalyst lifetimes in the ATA reaction.

Effect of Rb promoter on Fe3O4 microsphere catalyst for CO2 hydrogenation to light olefins

Alkali metals have been widely studied to improve the efficiency of CO2 hydrogenation to light olefins on iron-based catalysts. Herein, a series of Rb-promoted Fe3O4 microsphere catalysts were developed to understand the effects of Rb promoter on the catalytic performance. The 3wt%Rb/Fe3O4 catalyst showed high selectivity of light olefins (C2–C4, 47.4%) with a high olefin/paraffin ratio (10.7). XRD, H2-TPR, CO2-TPD, XPS analyses show that the proper Rb loading rate may adjust carbonaceous species content and ferric oxide content on the surface of the catalyst which is help for the synergistic effect to produce light olefins.

High-efficient hierarchical [B]-ZSM-5 catalyst by simultaneously using of CTAB surfactant and boron promoter for methanol to olefins reaction

In this work, a one-pot hydrothermal route was applied to prepare the hierarchical high-silica ZSM-5 catalyst (Si/Al = 200), including boron promoter in the structure and CTAB surfactant. XRD, FE-SEM, BET, NH3-TPD, and FT-IR techniques were applied to evaluate the physical and chemical properties. The effect of different amounts of secondary template (CTAB) and different operating conditions was studied on the ZSM-5 catalyst preparation and performance in methanol to olefins reaction. The results showed the high surface area (391.8 m2g−1), mesoporous structure, high crystallinity, and well-adjusted acidity for the modified catalyst. The prepared catalyst with CTAB/TPABr molar ratio of 1 led to the highest propylene selectivity (48.56%), the highest P/E ratio of 6.3, and the highest light olefin selectivity (71%). This improved performance can be assigned to the high surface area, short diffusion path length by mesopore structure, and optimum acidity. It was found that the optimum temperature and weight hourly space velocity were 480 °C and 7.2 h−1, respectively.

Directed transforming of coke to active intermediates in methanol-to-olefins catalyst to boost light olefins selectivity

Methanol-to-olefins (MTO), the most important catalytic process producing ethylene and propylene from non-oil feedstocks (coal, natural gas, biomass, CO2, etc.), is hindered by rapid catalyst deactivation due to coke deposition. Common practice to recover catalyst activity, i.e. removing coke via air combustion or steam gasification, unavoidably eliminates the active hydrocarbon pool species (HCPs) favoring light olefins formation. Density functional theory calculations and structured illumination microscopy reveal that naphthalenic cations, active HCPs enhancing ethylene production, are highly stable within SAPO-34 zeolites at high temperature. Here, we demonstrate a strategy of directly transforming coke to naphthalenic species in SAPO-34 zeolites via steam cracking. Fluidized bed reactor-regenerator pilot experiments show that an unexpectedly high light olefins selectivity of 85% is achieved in MTO reaction with 88% valuable CO and H2 and negligible CO2 as byproducts from regeneration under industrial-alike continuous operations. This strategy significantly boosts the economics and sustainability of MTO process.

Catalytic activity of SAPO-34 molecular sieves prepared by using palygorskite in the synthesis of light olefins via CO2 hydrogenation

Palygorskite was used as a silicon and partial aluminum source to prepare SAPO-34 molecular sieves using diethylamine, triethylamine, morpholine and tetraethylammonium hydroxide as templates. The synthesized SAPO-34 molecular sieves were characterized by using the methods of XRD, SEM, EDS, BET, FT-IR, NH3-TPD, H2-TPR and TG. Composite catalysts of CuO-ZnO-Al2O3/SAPO-34 were prepared by mechanically mixing SAPO-34 molecular sieves with CuO-ZnO-Al2O3 and were used in the direct synthesis of light olefins via CO2 hydrogenation. The results showed that SAPO-34 molecular sieves prepared by acid-treated palygorskite using tetraethylammonium hydroxide as a template had a higher specific surface area, a greater CO2 conversion rate and higher light olefin selectivity. The CO2 conversion rate reached 53.5%, the light olefin selectivity reached 62.1%, and the yield reached 33.2% when the reaction conditions were as follows: reaction temperature 673 K, reaction pressure 3.0 MPa, volume ratio of CO2/H2 1:3 and 0.5 g composite catalyst.

Graphitic carbon nitride catalyzes selective oxidative dehydrogenation of propane

Exothermic oxidative dehydrogenation of propane (ODHP) to olefins is a promising alternative to industrialized direct dehydrogenation. However, it encounters a great challenge to control the olefin selectivity as the over-oxidation to produce carbon oxides (COx) is thermodynamically more favorable. In this work, graphitic carbon nitride was reported to be a new kind of metal-free catalyst for ODHP, obtaining high selectivity for propylene (74.7%) and ethylene (14.9%) at a given propane conversion of 12.8%. Based on the spectroscopic insights and in situ experiments, the carbonyl groups modified on the graphitic carbon nitride were affirmed as active sites. A feasible ODHP reaction pathway was hypothesized by density functional theory (DFT) in which two adjacent carbonyl groups on the edge of carbon nitride can activate two C–H bonds of propane simultaneously, thus avoiding the generation of free C3H7* radicals and leading to the high selectivity of light olefins.

Dimethyl Ether Conversion to Light Olefins on Zeolite Catalysts: Effect of MFI-Type Zeolite Nature and SiO2/Al2O3 Molar Ratio on Catalyst Efficiency

The physicochemical and catalytic properties of magnesium-containing zeolite catalysts based on MFI-type zeolites (ZSM-5 and CBV) were compared. The presence of larger mesopores volume in MgCBV was found to decrease selectivity towards light olefins. In order to improve the catalytic properties of MgCBV, the effect of SiO2/Al2O3 molar ratio of CBV (SiO2/Al2O3 = 30, 55, 80 and 300) on its physicochemical and catalytic properties in the reaction of the dimethyl ether (DME) into light olefins was studied. Increasing SiO2/Al2O3 molar ratio from 30 to 80, was shown not change practically the DME conversion and olefin selectivity, but under a SiO2/Al2O3 molar ratio of 300, DME conversion significantly reduces, olefin selectivity increases, while the ethylene/propylene ratio decreases twice. By changing residence time, DME conversion increases under high total light olefins selectivity, while the ethylene/propylene ratio raises with increasing residence time.

Effects of initial crystal structure of Fe2O3 and Mn promoter on effective active phase for syngas to light olefins

Although it is generally acknowledged that iron carbides are the active phase in Fischer-Tropsch synthesis (FTS), adjusting the formation of active phase and catalytic performance via the initial crystal structure of iron oxides has never been studied. Herein, we take one-dimensional pure phase α-Fe2O3 and γ-Fe2O3 nonporous nanorods to explore the effects of initial crystal phase of Fe2O3 on both formation of active phase and corresponding catalytic performance, in which the influence of diffusion limitation on selectivity can be ignored. In situ characterizations uncovered that the formation of iron carbides with high selectivity of light olefins strongly depends on the initial crystal phase of iron oxide and its induced metal-promoter interaction. Responding to the morphology effect and crystallographic phase effect, Mn located on surface of γ-Fe2O3 nanorods exhibit a low oxidation state due to a strong Fe-Mn interaction. This interaction was beneficial to the formation of C-poor iron carbide species at the metal-promoter interface during carburization. Hence, outstanding selectivity for light olefins (61.2%) was achieved on 0.5 Mn/γ-Fe2O3 nanorods catalyst at a CO conversion of 55.1% under industrially relevant conditions (320 °C, 1 MPa, H2/CO ratio of 1, and W/F = 5 gcat h mol−1). This finding enriches the fundamental understanding of active phase evolution and promoter effect in STO process and may guide the design of a catalyst with high selectivity.

Li-decorated Fe-Mn nanocatalyst for high-temperature Fischer–Tropsch synthesis of light olefins

Fe-Mn-Li nanocomposite particles were prepared using the combined urea hydrolysis and incipient wetness impregnation method. No surfactant or capping agents were involved in the preparation process, which ensured that this was low-cost and environmentally friendly method. In this study, the effects of urea hydrolysis temperature and Li amount on the catalyst structure, morphology, and particle size were analyzed combining various characterization techniques, including N2 adsorption–desorption, X-ray diffraction (XRD), H2 temperature-programmed reduction, CO2 temperature programmed desorption, CO temperature programmed desorption, X-ray photoelectron spectroscopy, scanning electron microscopy, and Mössbauer spectroscopy. The nanocatalyst synthesized at 140 °C (Fe-Mn-140) presented the largest specific surface area and highest selectivity for light olefins and the lowest selectivity for CO2 and CH4 of all Fe-Mn-x samples in this study. These findings were consistent with the results of the Mössbauer spectroscopy and XRD testing, where Fe-Mn-140 was determined to contain the maximum amount of χ-Fe5C2 and minimum amount of Fe3O4 after reaction of all Fe-Mn-x samples in this study. It was also determined that Li slightly restrained the reduction of iron oxides. In addition, Li increased the surface basicity of the catalysts, which reduced their selectivity for CH4 and light alkanes while increases those for light olefins and heavier hydrocarbons. Therefore, this study could lead to developing a facile and environmentally-friendly method for synthesizing iron-based nanocatalysts that present high activity and selectivity for light olefins for high-temperature Fischer–Tropsch synthesis processes.

Direct CO2 hydrogenation to light olefins by suppressing CO by-product formation

We evaluate the direct CO2 conversion to light olefins reaction via a hybrid catalyst of In2O3/ZrO2 metallic oxide and zeolite SAPO34 components. On this catalyst, it can realize producing high light olefins selectivity of 77.59% via a direct tandem catalysis process, that is, the formed methanol on the oxygen vacancies surface of In2O3/ZrO2 in the first step will continue passing through the SAPO34 zeolite channel, where it is changed into light olefins simultaneously. Even there are many studies focused on this tandem catalysis reaction via bi-functional catalyst in recent years, however, to reduce the poisonous byproduct CO is still in a big challenge. In this reaction, large amounts of poisonous CO will be easily formed from reverse water gas shift reaction. Therefore, in our research, by optimizing the reaction, the catalyst can suppress the undesirable CO formation obviously. It shows good potential leading to scale-up cause of the outstanding reaction performance and its friendly-environment properties.

Cobalt-isomorphous substituted SAPO-34 via milling and recrystallization for enhanced catalytic lifetime toward methanol-to-olefin reaction

Silicoaluminophsophate (SAPO)-34 is considered as a promising catalyst for methanol-to-olefin (MTO) reaction, because its cylinder-like cages with small 8-ring pore openings restrict the diffusion of large hydrocarbons and exceptionally give high selectivity for light olefins. However, its main drawback is rapid catalytic deactivation by heavy hydrocarbons confined inside the cages. Here, we report a facile synthetic strategy for submicro-sized cobalt (Co)-isomorphous substituted SAPO-34 with controlled Co content through milling and Co-incorporated recrystallization. Co-isomorphous substitution on the CHA framework of SAPO-34 was thoroughly proven by XRD patterns, HADDF scanning TEM images, EDS mapping images, H2-TPR profiles, and diffuse reflectance UV-Vis spectra. Regarding the modified particle size, pore structure and acidity of the as-synthesized Co-isomorphous substituted SAPO-34, evaluation of MTO reaction revealed the correlation between the catalytic lifetime and the content of Co-isomorphous substitution. As an efficient platform to overcome the intrinsically low catalytic lifetime toward MTO reaction, this work provides a versatile strategy to generate various transition metal-isomorphous substituted SAPO-34 materials on the submicro scale.

Overcoating the Surface of Fe-Based Catalyst with ZnO and Nitrogen-Doped Carbon toward High Selectivity of Light Olefins in CO2 Hydrogenation

ZnO and nitrogen-doped carbon (NC) overcoated Fe-based catalysts (Fe@NC) were synthesized and evaluated in CO2 hydrogenation reaction. The Fe@NC exhibited enhanced catalytic activity, stability, and high selectivity toward light olefins and C5+ hydrocarbons. The olefins over paraffins ratio in the range of C2–C4 increased 24 times from 0.07 to 1.68 compared with the benchmark Fe3O4 catalyst. The evolution of iron species was observed during the hydrogenation reaction. The inactive θ-Fe3C phase disappeared, and the active phases for CO2 hydrogenation, Fe3O4 and Fe5C2, formed during the hydrogenation reaction. Overcoating the surface of Fe-based catalysts can be used as a useful strategy to modulate the product selectivity toward sustainable production of value-added hydrocarbons from CO2.