Dual-engine-driven realizing high-yield synthesis of Para-Xylene directly from CO2-containing syngas

The direct synthesis of light aromatics, especially para-xylene (p-X), from syngas/CO2 is drawing strong interest, but improving the space-time yield (STY) of p-X is a significant challenge. Here, a dynamic "dual-engine-driven" (DED) catalytic system is designed by combining two partners of ZnCr and FeMn (named "dual-engine") with Z5@SiO2 capsule zeolite. The DED catalyst of 1.0%FeMn&[ZnCr&Z5@SiO2] shows an extremely higher p-X STY of 36.1 gp-x·kgcat-1·h-1, about eight times higher than that of [ZnCr&Z5]. DED manipulates ZnCr engine for methanol formation and drives FeMn engine for light olefins generation together, and then the formed methanol and light olefins are coordinately converted in situ into p-X-rich aromatics over Z5@SiO2. The DED model boosts the driving force for syngas/CO2 conversion, simultaneously concerting the cooperation of "dual-engine" for p-X generation, resulting in extremely high STY of p-X. This study achieves non-petroleum p-X production at industrial-relevant level and advances knowledge in designing innovative heterogeneous catalysts.

Application of metal-organic frameworks and their derivates for thermal-catalytic C1 molecules conversion

One-carbon (C1) catalysis refers to the conversion of compounds with a single carbon atom, especially carbon monoxide (CO), carbon dioxide (CO2), and methane (CH4), into clean fuels and valuable chemicals via catalytic strategy is crucial for sustainable and green development. Among various catalytic strategies, thermal-driven process seems to be one of the most promising pathways for C1 catalysis due to the high efficiency and practical application prospect. Notably, the rational design of thermal-driven C1 catalysts plays a vital role in boosting the targeted products synthesis of C1 catalysis, which relies heavily on the choice of ideal active site support, catalyst fabrication precursor, and catalytic reaction field. As a novel crystalline porous material, metal-organic frameworks (MOFs) has made significant progress in the design and synthesis of various functional nanomaterials. However, the application of MOFs in C1 catalysis faces numerous challenges, such as thermal stability, mechanical strength, yield of MOFs, and so on. To overcome these limitations and harness the advantages of MOFs in thermal-driven C1 catalysis, researchers have developed various catalyst/carrier preparation strategies. In this review, we provide a concise overview of the recent advancements in the conversion of CO, CO2, and CH4 into clean fuels and valuable chemicals via thermal-catalytic strategy using MOFs-based catalysts. Furthermore, we discuss the main challenges and opportunities associated with MOFs-based catalysts for thermal-driven C1 catalysis in the future.

Highly Efficient Iron-Based Catalyst for Light-Driven Selective Hydrogenation of Nitroarenes

Light-driven hydrogenation of nitro compounds to functionalized amines is of great importance yet a challenge for practical applications, which calls for the development of high-performance, nonprecious photocatalysts and efficient catalytic systems. Herein, we report a high-efficiency Fe3O4@TiO2 photocatalyst via a sol-gel and subsequent pyrolysis strategy, which exhibits desirable photothermal hydrogenation performance of nitro compounds to functionalized amines with the excellent selectivity of >90% exceeding those of the state-of-the-art heterogeneous photocatalysts. Our experimental results and theoretical calculations for the first time reveal that Fe3O4 is the major active phase, and the strong metal-support interaction between Fe3O4 and reducible TiO2 further leads to performance improvement, taking advantage of the enhanced photothermal effect and the improved adsorption for the reactant and hydrazine hydrate. Notably, a variety of halonitrobenzenes and pharmaceutical intermediates can be completely converted to functionalized amines with high selectivities, even in gram-scale reactions. This work provides a new insight into the rational design of nonprecious photo/thermo-catalysts for other catalytic reactions.

Precise solid-phase synthesis of CoFe@FeOx nanoparticles for efficient polysulfide regulation in lithium/sodium-sulfur batteries

Complex metal nanoparticles distributed uniformly on supports demonstrate distinctive physicochemical properties and thus attract a wide attention for applications. The commonly used wet chemistry methods display limitations to achieve the nanoparticle structure design and uniform dispersion simultaneously. Solid-phase synthesis serves as an interesting strategy which can achieve the fabrication of complex metal nanoparticles on supports. Herein, the solid-phase synthesis strategy is developed to precisely synthesize uniformly distributed CoFe@FeOx core@shell nanoparticles. Fe atoms are preferentially exsolved from CoFe alloy bulk to the surface and then be carburized into a FexC shell under thermal syngas atmosphere, subsequently the formed FexC shell is passivated by air, obtaining CoFe@FeOx with a CoFe alloy core and a FeOx shell. This strategy is universal for the synthesis of MFe@FeOx (M = Co, Ni, Mn). The CoFe@FeOx exhibits bifunctional effect on regulating polysulfides as the separator coating layer for Li-S and Na-S batteries. This method could be developed into solid-phase synthetic systems to construct well distributed complex metal nanoparticles.

Atomic Structure of the Fe3O4/Fe2O3 Interface During Phase Transition from Hematite to Magnetite

Phase transition between iron oxides practically defines their functionalities in both physical and chemical applications. Direct observation of the atomic rearrangement and a quantitative description of the dynamic behavior of the phase transition, however, are rare. Here, we monitored the structure evolution from a rod-shaped hematite nanoparticle to magnetite during H₂ reduction at elevated temperatures. Environmental transmission electron microscopy observations, along with selected area electron diffraction experiments, identified that the reduction preferentially commenced with Fe₃O₄ nucleation on the surface defective sites, followed by laterally growing into a Fe₃O₄ film until fully covering the particle surface. The Fe₃O₄ phase then propagated toward the bulk particle via a Fe₃O₄/α-Fe₂O₃ interface with the relationship α-Fe₂O₃(0001)//Fe₃O₄(111) in an aligned orientation of [112]_Fe3O4||[112̅0]_α-Fe2O3. Upon this Fe₃O₄/α-Fe₂O₃ interface, the Fe-O octahedra in Fe₃O₄(111) (as layer A) matches that of α-Fe₂O₃(0001) at a rotation angle of 30°, and the reduction proceeds in such a pattern that two-thirds of the Fe_Oh in the adjacent layer (layer B) is transformed into Fe_Te.

Light olefin synthesis from a diversity of renewable and fossil feedstocks: state-of the-art and outlook

Light olefins are important feedstocks and platform molecules for the chemical industry. Their synthesis has been a research priority in both academia and industry. There are many different approaches to the synthesis of these compounds, which differ by the choice of raw materials, catalysts and reaction conditions. The goals of this review are to highlight the most recent trends in light olefin synthesis and to perform a comparative analysis of different synthetic routes using several quantitative characteristics: selectivity, productivity, severity of operating conditions, stability, technological maturity and sustainability. Traditionally, on an industrial scale, the cracking of oil fractions has been used to produce light olefins. Methanol-to-olefins, alkane direct or oxidative dehydrogenation technologies have great potential in the short term and have already reached scientific and technological maturities. Major progress should be made in the field of methanol-mediated CO and CO₂ direct hydrogenation to light olefins. The electrocatalytic reduction of CO₂ to light olefins is a very attractive process in the long run due to the low reaction temperature and possible use of sustainable electricity. The application of modern concepts such as electricity-driven process intensification, looping, CO₂ management and nanoscale catalyst design should lead in the near future to more environmentally friendly, energy efficient and selective large-scale technologies for light olefin synthesis.

Effect of Different Iron Phases of Fe/SiO2 Catalyst in CO2 Hydrogenation under Mild Conditions

The effect of different active phases of Fe/SiO2 catalyst on the physio-chemical properties and the catalytic performance in CO2 hydrogenation under mild conditions (at 220 °C under an ambient pressure) was comprehensively studied in this work. The Fe/SiO2 catalyst was prepared by an incipient wetness impregnation method. Hematite (Fe2O3) in the calcined Fe/SiO2 catalyst was activated by hydrogen, carbon monoxide, and hydrogen followed by carbon monoxide, to form a metallic iron (Fe/SiO2-h), an iron carbide (Fe/SiO2-c), and a combination of a metallic iron and an iron carbide (Fe/SiO2-hc), respectively. All activated catalysts were characterized by XRD, Raman spectroscopy, N2 adsorption–desorption, H2-TPR, CO-TPR, H2-TPD, CO2-TPD, CO-TPD, NH3-TPD, and tested in a CO2 hydrogenation reaction. The different phases of the Fe/SiO2 catalyst are formed by different activation procedures and different reducing agents (H2 and CO). Among three different activated catalysts, the Fe/SiO2-c provides the highest CO2 hydrogenation performance in terms of maximum CO2 conversion, as well as the greatest selectivity toward long-chain hydrocarbon products, with the highest chain growth probability of 0.7. This is owing to a better CO2 and CO adsorption ability and a greater acidity on the carbide form of the Fe/SiO2-c surface, which are essential properties of catalysts for polymerization in FTs.

Enhanced stability of a fused iron catalyst under realistic Fischer–Tropsch synthesis conditions: insights into the role of iron phases (χ-Fe5C2, θ-Fe3C and α-Fe)

The performance and stability of fused-Fe catalyst in FTS reaction are enhanced through the control synthesis of iron phases (χ-Fe5C2, θ-Fe3C and α-Fe).

Microwave modification of iron supported on beta silicon carbide catalysts for Fischer–Tropsch synthesis

Beta silicon carbide is a good microwave absorber support. Microwave irradiation can improve the surface properties of Fe/β-SiC catalysts. Microwave irradiation can be used to improve the catalytic performance of Fe/β-SiC catalysts.

Theoretical Study of CO Adsorption and Activation on Orthorhombic Fe7C3(001) Surfaces for Fischer–Tropsch Synthesis Using Density Functional Theory Calculations

Fischer–Tropsch synthesis (FTS), which converts CO and H2 into useful hydrocarbon products, has attracted considerable attention as an efficient method to replace crude oil resources. Fe-based catalysts are mainly used in industrial FTS, and Fe7C3 is a common carbide phase in the FTS reaction. However, the intrinsic catalytic properties of Fe7C3 are theoretically unknown. Therefore, as a first attempt to understand the FTS reaction on Fe7C3, direct CO* dissociation on orthorhombic Fe7C3(001) (o-Fe7C3(001)) surfaces was studied using density functional theory (DFT) calculations. The surface energies of 14 terminations of o-Fe7C3(001) were first compared, and the results showed that (001)0.20 was the most thermodynamically stable termination. Furthermore, to understand the effect of the surface C atom coverage on CO* activation, C–O bond dissociation was performed on the o-Fe7C3(001)0.85, (001)0.13, (001)0.20, (001)0.09, and (001)0.99 surfaces, where the surface C atom coverages were 0.00, 0.17, 0.33, 0.33, and 0.60, respectively. The results showed that the CO* activation linearly decreased as the surface C atom coverage increased. Therefore, it can be concluded that the thermodynamic and kinetic selectivity toward direct CO* dissociation increased when the o-Fe7C3(001) surface had more C* vacancies.

Stabilization of ε-iron carbide as high-temperature catalyst under realistic Fischer-Tropsch synthesis conditions

The development of efficient catalysts for Fischer–Tropsch (FT) synthesis, a core reaction in the utilization of non-petroleum carbon resources to supply energy and chemicals, has attracted much recent attention. ε-Iron carbide (ε-Fe₂C) was proposed as the most active iron phase for FT synthesis, but this phase is generally unstable under realistic FT reaction conditions (> 523 K). Here, we succeed in stabilizing pure-phase ε-Fe₂C nanocrystals by confining them into graphene layers and obtain an iron-time yield of 1258 μmol_CO g_Fe⁻¹s⁻¹ under realistic FT synthesis conditions, one order of magnitude higher than that of the conventional carbon-supported Fe catalyst. The ε-Fe₂C@graphene catalyst is stable at least for 400 h under high-temperature conditions. Density functional theory (DFT) calculations reveal the feasible formation of ε-Fe₂C by carburization of α-Fe precursor through interfacial interactions of ε-Fe₂C@graphene. This work provides a promising strategy to design highly active and stable Fe-based FT catalysts.

ε-Fe₂C has been identified as the highly active phase for Fischer-Tropsch synthesis (FTS), but is stable only at low-temperature. Here, the authors show that ε-Fe₂C phase can be stabilized even at ~ 573 K by being encapsulated inside graphene layers, and retains high activity in FTS.

Catalytic Properties and Recycling of NiFe2O4 Catalyst for Hydrogen Production by Supercritical Water Gasification of Eucalyptus Wood Chips

Nickel iron oxide (NiFe2O4) catalyst was prepared by the combustion reaction method and characterized by XRD, N2 adsorption/desorption, thermogravimetric analysis (TG), and temperature programmed reduction (TPR). The catalyst presented a mixture of oxides, including the NiFe2O4 spinel and specific surface area of 32.4 m2 g−1. The effect of NiFe2O4 catalyst on the supercritical water gasification (SCWG) of eucalyptus wood chips was studied in a batch reactor at 450 and 500 °C without catalyst and with 1.0 g and 2.0 g of catalyst and 2.0 g of biomass for 60 min. In addition, the recyclability of the catalyst under the operating conditions was also tested using recovered and recalcined catalysts over three reaction cycles. The highest amount of H2 was 25 mol% obtained at 450 °C, using 2 g of NiFe2O4 catalyst. The H2 mol% was enhanced by 45% when compared to the non-catalytic test, showing the catalytic activity of NiFe2O4 catalyst in the WGS and the steam reforming reactions. After the third reaction cycle, the results of XRD demonstrated formation of coke which caused the deactivation of the NiFe2O4 and consequently, a 13.6% reduction in H2 mol% and a 5.6% reduction in biomass conversion.

MOF-Templated Preparation of Highly Dispersed Co/Al2O3 Composite as the Photothermal Catalyst with High Solar-to-Fuel Efficiency for CO2 Methanation

CH₄ production from CO₂ hydrogenation provides a clean approach to convert greenhouse gas CO₂ into chemical energy, but high energy consumption in this reaction still restrains its further application. Herein, we use a light-driven CO₂ methanation process instead of traditional thermocatalysis by an electrical heating mode, with the aim of greatly decreasing the energy consumption. Under UV-vis-IR light irradiation, the photothermal CO₂ methanation over highly dispersed Co nanoparticles supported on Al₂O₃ (Co/Al₂O₃) achieves impressive CH₄ production rates (as high as 6036 μmol g^-1 h^-1), good CH₄ selectivity (97.7%), and catalytic durability. The high light-harvesting property of the catalyst across the entire solar spectrum coupled with its strong adsorption capacity toward H₂, CO₂, CO, and abundant active sites are proposed to be responsible for the better photothermocatalytic performance of Co/Al₂O₃. Furthermore, a novel light-promotion effect is also revealed in CO₂ methanation, where UV-vis light irradiation induces oxygen vacancies and improves the proclivity toward adsorption of H₂, CO₂, and CO, finally resulting in a significant enhancement of the photothermocatalytic activity for CH₄ production. By concentrating the low-intensity light (120 mW/cm²) via a Fresnel lens, a photothermal CO₂ conversion efficiency of more than 50% with a good CH₄ selectivity (76%) is achieved on the optimal catalyst under a dynamic reaction system, which indicates the bright prospect of photothermal CO₂ methanation.

A novel stabilized carbon-coated nZVI as heterogeneous persulfate catalyst for enhanced degradation of 4-chlorophenol

Nano zero-valent iron (nZVI) and its composite materials have been extensively studied in the field of environmental remediation. However, the oxidation and agglomeration of nZVI limits the large-scale application of nZVI in environmental remediation. This study developed a two-step method to prepare stable carbon-coated nZVI (Fe⁰@C) which combined hydrothermal carbonization and carbothermal reduction methods and used glucose and iron oxide (Fe₃O₄) as precursors. When the carbothermal reduction temperature was 700 °C and the elemental molar ratio of carbon to iron was 22:1, stable Fe⁰@C can be generated. The nZVI particles are encapsulated by mesoporous carbon and embedded in the carbon spheres. The unique structure of carbon coating not only inhibits the agglomeration of nZVI, but also makes nZVI stable in air for more than 120 days. Not only that, the as-synthesized Fe⁰@C exhibited high catalytic activity toward the degradation of 4-chlorophenol (4-CP) by activating persulfate. Different from conventional nZVI catalysts in generation of sulfate radicals, Fe⁰@C selectively induced hydroxyl radicals for 4-CP degradation. Moreover, Fe⁰@C has been shown to efficiently degrade 4-CP by using the dissolved oxygen in water to form hydroxyl radicals. This study not only provides a simple, green method for the preparation of stabilized nZVI, but also provides the possibility of large-scale application of nZVI in the field of environmental remediation.

Structural evolution of carbon in an Fe@C catalyst during the Fischer–Tropsch synthesis reaction

A pseudo-in situ research method was applied to provide insight into the structural evolution of carbon in an Fe@C catalyst at different stages of the Fischer–Tropsch reaction.

Suppression by Pt of CO adsorption and dissociation and methane formation on Fe5C2(100) surfaces

To understand the chemical origin of platinum promotion effects on iron based Fischer–Tropsch synthesis catalysts, the effects of Pt on CO adsorption and dissociation as well as surface carbon hydrogenation on the Fe₅C₂(100) facet with different surface C* contents have been studied using the spin-polarized density functional theory method.

Ethanol synthesis from syngas over Cu(Pd)-doped Fe(100): a systematic theoretical investigation

The selectivity of ethanol formation are in the order of Fe₃Cu₆/Fe(100) > Fe₃Pd₆/Fe(100) > Fe₉/Fe(100) > Cu₉/Fe(100).

Use of stability diagrams to predict catalyst speciation during Fischer Tropsch reduction stage: a mini-review

An alternative way of predicting phase evolution of iron-based Fischer Tropsch synthesis catalysts during activation.

Influence of copper and potassium on the structure and carbidisation of supported iron catalysts for Fischer–Tropsch synthesis

In silica supported iron Fischer–Tropsch catalysts, promotion with copper strongly enhances both hematite reduction and magnetite carbidisation, while potassium promotion hinders reduction of hematite to magnetite but enhances magnetite carbidisation in carbon monoxide.

Two-dimensional graphene-directed formation of cylindrical iron carbide nanocapsules for Fischer–Tropsch synthesis

Cylindrical Hägg carbide nanocapsules with a single (510) crystal facet were formed during the FTS reaction with the assistance of GO, which show excellent activity and selectivity for olefins.

Fe-based heterogeneous catalysts for the Fischer-Tropsch reaction: Sonochemical synthesis and bench-scale experimental tests

The sonochemical synthesis of nanostructured materials owes its origins to the extreme conditions created during acoustic cavitation, i.e., the formation of localized hot spots in the core of collapsing bubbles in a liquid irradiated with high intensity ultrasound (US). In particular, in the present work a sonochemical synthesis has been investigated for the production of three different iron-based samples supported on SiO₂ and loaded with different metals and promoters (10 %wt of Fe; 30 %wt of Fe; 30 %wt of Fe, 2 %wt of K and 3.75 %wt of Cu) active in the Fischer-Tropsch (FT) process. Sonochemically synthesized heterogeneous catalysts were characterized by BET, XRPD, TPR, ICP, CHN, TEM, SEM and then tested in a fixed bed FT-bench-scale rig fed with a mixture of H₂ and CO at a H₂/CO molar ratio equal to 2, at activation temperatures of 350-400°C and reaction temperatures of 250-260°C. The experimental results showed that the ultrasonic samples are effective catalysts for the FT process. Notably, increasing the activation temperature increased CO conversion, while product selectivity did not diminish. All the sonochemically prepared samples presented in this work provided better catalytic results compared to the corresponding traditional FT impregnated catalysts.