Fe Al Catalysts Research Articles

Role of the hydrocarbon molecular structure in CNT growth on Fe-Al catalysts.

Upgrading plastic wastes into high-value products via the thermochemical process is one of the most attractive topics. Although carbon nanotubes (CNTs) have been successfully synthesized from plastic pyrolysis gas over Fe-, Co-, or Ni-based catalysts, a deep discussion about the reaction mechanism was seldom mentioned in the literature. Herein, this work was intended to study the growth mechanism of CNTs from hydrocarbons on Fe-Al2O3 catalysts. C5-C7 hydrocarbons were used to synthesize CNTs in a high-temperature fixed-bed reactor, and the carbon products and cracked gas were analyzed in detail. The CNT yield was in the order of cyclohexane, cyclohexene > n-hexane > n-heptane > n-pentane, 1-hexene. It was proposed that CNT growth on Fe-Al2O3 catalysts was mainly determined by the yield and structure of six-membered cyclic species, which was tailored by the carbon chain length, C-C/CC bonds, and linear/cyclic structures of C5-C7 hydrocarbons. Compared with n-hexane, the six-membered rings of cyclohexane and cyclohexene promoted six-membered cyclic species formation, increasing CNT and benzene yields; the seven-membered carbon chain of n-heptane promoted methyl-six-membered cyclic species formation, decreasing CNT and benzene yields while increasing the toluene yield; the five-membered carbon chain of n-pentane and the CC bond of 1-hexene inhibited six-membered cyclic species formation, decreasing CNT and benzene yields. This work revealed the structure-activity relationship between C5-C7 hydrocarbons and CNT growth, which may direct the process design and optimization of CNT synthesis from plastic pyrolysis gas.

Synthesis of Fe-Al catalysts to boost CNTs formation from polymer wastes via the improved two-stage system

Carbon nanotubes (CNTs) has been considering as a high-value product from polymer wastes via the coupled thermal-catalytic technology, and how to improve the yield and quality of CNTs is the key to the further industrialization. Herein, a series of Fe-Al catalysts with different Fe-loading and calcination temperature were prepared and expected to boost CNTs formation from low-density polyethylene (LDPE) in the improved two-stage reaction system. The fresh and spent Fe-Al catalysts were characterized in detail by SEM-EDX, XRD, N2 physisorption, NH3-TPD, H2-TPR, TG-DSC, Raman, and TEM to explore the effects of Fe-loading (5–20%) and calcination temperature (450–650 °C) on the physicochemical properties of Fe-Al catalysts as well as the quantity and quality of CNTs. An increase of Fe-loading generated more active sites for CNTs growth while intensified the competition for the carbon source, promoting the yield while reducing the length of CNTs. A decrease of calcination temperature reduced the interaction between Fe sites and Al2O3 support, promoting both the yield and the length of CNTs. This work provided a promising strategy for optimizing Fe-Al catalysts to boost CNTs production from polymer wastes.

Fe–Al core-shell structure as an efficient catalyst for dual hydrogen production and storage by thermochemical water splitting: A reactive molecular dynamic simulation

Catalysts with dual functions in hydrogen production and storage are desired for the low-cost technology. In the preceding view, we used reactive force molecular dynamics to demonstrate how effective the Fe–Al core-shell structure is at breaking up water molecules and storing hydrogen free radicals via thermochemical water splitting. The results show that at T ∼600 K, water molecules begin to dissociate in the presence of a Fe–Al catalyst, releasing OH and H free radicals. It is worth noting that the produced OH free radicals are bonded to the Al-shell, whereas the H free radicals move to the Fe-core and stores via chemical bond. Interestingly, at T < 1200 K, there is no Fe–O bond. This could be due to Al having a higher oxidation potential than Fe, causing OH free radicals to preferentially associate with the Al-shell. Furthermore, at 2000K < T > 3000 K, the number of Fe–H bonds decreases while the number of H–H bonds increases, indicating that the stored H atom desorbs and forms an H2 molecule. Temperature can thus be used to monitor the ability of Fe–Al catalysts to dissociate water, store hydrogen, and produce hydrogen. This research shows that developing core-shell type catalysts can provide an effective solution for hydrogen generation, storage, and transportation.

Dry Reforming of Methane over Ni–Fe–Al Catalysts Prepared by Solution Combustion Synthesis

Dry Reforming of Methane over Ni–Fe–Al Catalysts Prepared by Solution Combustion Synthesis

Promotion effect of cobalt doping on microwave-initiated plastic deconstruction for hydrogen production over iron catalysts

Microwave-initiated deconstruction of plastic into hydrogen and high-value carbons is an attractive upcycling technology. However, the interplay between microwave field and catalyst material and the reaction mechanism were not fully understood. In this study, Co doping Fe-Al catalysts were synthesized for hydrogen production from LDPE using microwave and conventional heating. The Fe1Co1Al2 catalyst yielded hydrogen at 61.39 mmol/gplastic under microwave, which was almost two times higher than conventional heating. Characterization indicated Co doped spinel iron catalyst under microwave rapidly transformed into the highly active FeCo alloy for plastic dehydrogenation. The microwave field was responsible for the rapid formation of FeCo, as it enhanced the charge transfer from H to Fe. The Co doping also inhibited the formation of Fe3C during plastic deconstruction, which changed the carbon diffusion pathway and promoted the formation of nanotubes and hydrogen production.

Enhanced microwave absorption capacity of iron-based catalysts by introducing Co and Ni for microwave pyrolysis of waste COVID-19 Masks

Inexpensive iron-based catalysts are the most promising catalysts for microwave-assisted deconstruction of waste plastics. However, the microwave heating efficiency of most of the synthesized iron-based catalysts is very low, in particular, the FeAl catalyst was prepared by microwave combustion method, and its mixture with disposable medical masks (DMMs) was only heated to about 150℃ within 10 min. Here, we introduce the second-phase metals (Co or Ni) into the FeAl catalyst, resulting in the rearrangement of the catalyst structure and electrons to give the catalyst good microwave absorption ability. The mixture of the catalyst and DMMs can be quickly heated to above 900℃ in 10 min, especially after reaching the melting point of plastic, the instantaneous heating rate reaches 350 ℃·min−1. under the unique microwave hot-spot pyrolysis mechanism, DMMs can be rapidly pyrolyzed into carbon nanotubes (19.65 wt%) and gas (77.65 wt%) within 14 min due to the efficient dehydrogenation efficiency and activity of Co. The corresponding H2 yield is up to 38.66 mmolH2·g−1DMMs, and the percentage of CO and H2 in the gas is as high as 90 wt%. This work improves the microwave conversion efficiency of iron-based catalysts by introducing second phase metals, and waste DMMs were efficiently converted into CO, H2 and CNTs, which can also be extended to other polymer or biomass chemical cycles.

The quantitative conversion of polyethylene terephthalate (PET) and Coca-Cola bottles to p-xylene over Co-based catalysts with tailored activities for deoxygenation and hydrogenation

The highly selective conversion of polyethylene terephthalate and Coca-Cola bottles to p-xylene with a yield of &gt;99.0% was achieved over the Co–Fe–Al catalyst with a CoFe alloy.

Regulating iron species compositions by Fe-Al interaction in CO2 hydrogenation

Different iron species exhibit distinct activity and selectivity in CO2 hydrogenation reaction. Herein, by controlling calcination temperature, Fe-Al interaction in Na promoted Fe-Al catalysts has been regulated, which further leads to various compositions of iron oxide (FeOx) and iron carbides (Fe7C3 and Fe5C2) after CO activation and CO2 hydrogenation reaction. The phase compositions and structures of Fe-Al catalysts are carefully distinguished by multiple characterizations, including XRD, XPS, MES and TEM, and the reactivity of different phases is studied with the combination of experiments (kinetics, TP and in situ DRIFTS) and Density Functional Theory (DFT) calculations. Our FeAl350 with the highest FeCx content shows the highest CO2 conversion of 48.2% and the lowest CO selectivity of 10.1%, and FeAl900 with the highest Fe5C2 / FeCx ratio presents the highest C5+ selectivity of 44.6%. Finally, a correlation between different compositions of iron species with the activity and selectivity of Fe-based for CO2 hydrogenation to olefins was established.

Alloying cobalt in Co–Fe–Al catalyst for achieving the selective conversion of furfural to cyclopentanone

Production of cyclopentanone (CPO) from biomass-derived furfural is attractive but challenging, as deep hydrogenation or ring-opening of furan ring in furfural over Co-based catalysts hinders the formation of the targeting products. In this study, alloying Co with Fe species in Co–Fe–Al catalysts is proposed for selective conversion of furfural to CPO in water. The formation of CoFe alloy in Co–Fe–Al catalyst weakened the interaction between Co species and the alumina carrier, lowered the adsorption/activation of H2, suppressed the formation of especially Brønsted acidic sites, facilitated the electron transfer from Co0 to Fe species, increased the activation energy for hydrogenation of furfural (from 17.2 kJ mol−1 over Co–Al to 33.4 kJ mol−1 over 1.5Co-1.5Fe-1.0Al), and weakened the adsorption of CC and C–O–C functionalities in furan ring of furfuryl alcohol (FA) on metallic sites. These factors together suppressed deep hydrogenation of furan ring in FA or ring-opening of FA to diols, producing CPO and CPL with total yield of 91.5%, which was attributed to the synergy between hydrogenation and Brønsted acidic sites. In addition, the presence of Fe in Co–Fe–Al catalysts also enhanced the structural stability of Co species, preventing the phase transformation and aggregation of Co species, and rendering the catalyst with superior reusability.

Upgrading waste plastic derived pyrolysis gas via chemical looping cracking–gasification using Ni–Fe–Al redox catalysts

A novel chemical looping cracking–gasification process was investigated to produce separate H2 and syngas from plastic-derived pyrolysis gas over synthetic Ni–Fe–Al redox catalysts. The non-condensable pyrolysis gas was catalytically cracked at 800 °C, followed by catalyst regeneration with steam. The highest activity was obtained over NiFeAl (molar Ni:Fe:Al = 1:1:1), producing concentrated H2 (83.1 vol%, 0.46 mol g(Ni+Fe)−1) and coke intermediate (232.1 wt%) from cracking. During the steam gasification stage, coke removal efficiency of 96% was obtained with a high syngas yield of 0.89 mol g(Ni+Fe)−1. With equimolar Ni/Fe, increasing Al/(Ni+Fe) ratio led to decreased catalyst activity due to enhanced metal–support interaction. Plausible reaction mechanisms were proposed to interpret the catalytic effects on tuning the morphologies, chemical structure and activity of the coke deposits. This work demonstrates the important role of Ni–Fe–Al catalysts on the production of H2 and syngas via chemical looping cracking–gasification process.

Ternary Fe–Zn–Al Spinel Catalyst for CO2 Hydrogenation to Linear α-Olefins: Synergy Effects between Al and Zn

Direct conversion of CO2 into linear α-olefins with Fe-based catalysts is promising both technically and economically. Al as a widely employed structural additive to Fe-based CO/CO2 hydrogenation catalysts is known to exhibit a side effect of shifting the selectivity from olefins to undesirable methane. Here, we report that by doping Zn into a binary Fe–Al spinel, a ternary Fe–Zn–Al spinel catalyst could be obtained with a high space–time yield with respect to linear α-olefins of 150.8 mmolC·gFe–1·h–1 in CO2 hydrogenation reactions. Multiple in situ/ex situ characterizations combined with DFT calculations illustrate that active Fe5C2 nanoparticles are wrapped with Fe–Al spinel overlayers with the introduction of Al alone, which is responsible for facilitating hydrogenation and inhibiting C–C coupling over the Fe–Al catalysts. Extra doping of Zn allows redistribution of Al to alleviate undesirable strong interactions between Fe5C2 and spinel phases, rendering a high selectivity to higher olefins. The revelation of a subtle synergy effect between Al and Zn underscores the pivotal role of precise tuning of multiple catalyst additives in optimizing the overall catalytic performance.

Investigation of Co–Fe–Al Catalysts for High-Calorific Synthetic Natural Gas Production: Pilot-Scale Synthesis of Catalysts

Co–Fe–Al catalysts prepared using coprecipitation at laboratory scale were investigated and extended to pilot scale for high-calorific synthetic natural gas. The Co–Fe–Al catalysts with different metal loadings were analyzed using BET, XRD, H2-TPR, and FT-IR. An increase in the metal loading of the Co–Fe–Al catalysts showed low spinel phase ratio, leading to an improvement in reducibility. Among the catalysts, 40CFAl catalyst prepared at laboratory scale afforded the highest C2–C4 hydrocarbon time yield, and this catalyst was successfully reproduced at the pilot scale. The pelletized catalyst prepared at pilot scale showed high CO conversion (87.6%), high light hydrocarbon selectivity (CH4 59.3% and C2–C4 18.8%), and low byproduct amounts (C5+: 4.1% and CO2: 17.8%) under optimum conditions (space velocity: 4000 mL/g/h, 350 °C, and 20 bar).

Influence of sugars in preparing improved FeAl catalyst for carbon dioxide hydrogenation

The influences of sugars (sucrose, fructose and glucose) on the performance of FeAl catalysts were investigated for CO2 hydrogenation. FeAl catalysts were prepared with two steps. At first, the catalyst precursors were obtained by co-precipitation. During this step, three methods were used to add sucrose into the precursors. Then, promoter K and Cu were impregnated into the precursors. The improved CO2 conversion and C5+ hydrocarbon selectivity by sucrose addition were attributed to the formation of γ-Fe2O3 phase in the catalyst precursor, which was different from the popular opinion that sucrose acted as a chelating agent. With the inspiration from sucrose hydrolysis effect, FeAl oxide, mainly in γ-Fe2O3 phase was prepared by adding fructose and glucose (the products of sucrose hydrolysis) into the newly centrifuged precipitate. The formation of γ-Fe2O3 phase was explained based on the results of XRD and XPS. The best catalyst possessed CO2 conversion of 30.3% and C5 + selectivity of 52.2% under the reaction conditions of H2:CO2 = 3:1, 6.0 L/(h·g-cat), 1.6 MPa and 235 °C.

Effect of Calcination Temperature on Activity of Fe2O3–Al2O3 Nanocomposite Catalysts in CO Oxidation

Nanocomposite Fe–Al oxide catalysts were prepared by the melting of iron and aluminum nitrates with the subsequent calcination in air at different temperatures. It was found that the catalysts calcined at 450 °C are more active in the oxidation of CO than the catalysts calcined at 700 °C. X-ray diffraction and X-ray photoelectron spectroscopy showed that all the catalysts consist of hematite, α-Fe2O3 nanoparticles, and Al2O3 in an amorphous state. Iron oxide is the active component, which provides the oxidation of CO, while alumina is a texture promoter. The increase in the calcination temperature leads to a minor increase in the average size of hematite nanoparticles and an insignificant decrease in the specific surface area. Kinetic measurements showed that the oxidation of CO over the Fe–Al catalysts calcined at 450 and 700 °C proceeds with the activation energy of 61–69 and 91 kJ/mol, respectively. This means that the low-temperature and high-temperature catalysts contain different active species. Temperature-programmed reduction with CO indicated that the decrease in the calcination temperature improves the reducibility of the Fe-Al nanocomposites. According to 57Fe Mossbauer spectroscopy, the low-temperature catalysts contain hydrated iron oxides (acagenite and ferrihydrite) and a significant amount of highly defective hematite, which is absent in the high-temperature catalyst. These species can provide the enhanced activity of the low-temperature catalysts in the oxidation of CO.

Production of Phenolic-Rich Bio-Oil from Catalytic Fast Pyrolysis of Biomass Over Tailored Fe-Based Catalysts

The objective of this study is to catalytically upgrade fast pyrolysis vapors of sawdust using various Fe-based catalysts for producing phenolic-rich bio-oil by analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) technique. A variety of parameters, including support characteristic, calcination temperature, pyrolysis temperature, as well as the catalyst-to-biomass ratio during the pyrolysis process were evaluated for their effects on product distribution of bio-oil. GC-MS analysis showed that compared to Fe–Mg and Fe–Al catalysts, the developed Fe–Ca catalyst significantly promoted the formation of phenols and its derivatives. The phenolic concentration declined with increasing calcination temperature and pyrolysis temperature, while increased monotonically along with increasing catalyst-to-biomass ratio. The phenolics concentration was high upto 81% (peak area) under optimum conditions of calcination temperature of 500 °C, pyrolysis temperature of 600 °C and catalyst-to-biomass ratio of 10. At higher catalyst-to-biomass ratio of 20, phenolics (88.03% in peak area) and hydrocarbons (including 7.86% of aromatics and 4.1% aliphatics) were the only two components that can be detected, with all the acids, aldehydes and ketones completely eliminated. This indicated the excellent capability of developed Fe–Ca catalyst in promoting the decomposition of lignin in biomass to generate phenolic compounds and meanwhile inhibiting the devolatilization of holocellulose.

The Influence of Cu and Al Additives on Reduction of Iron(III) Oxide: In Situ XRD and XANES Study.

The reduction of Fe-based nanocomposite catalysts doped with Al and Cu has been studied using in situ X-ray diffraction (XRD), in situ X-ray absorption near-edge structure (XANES), and temperature-programmed reduction (TPR) techniques. The catalysts have been synthesized by melting of iron, aluminum, and copper salts. According to XRD, the catalysts consist mainly of Fe2O3 and Al2O3 phases. Alumina is in an amorphous state, whereas iron oxide forms nanoparticles with the protohematite structure. The Al3+ cations are partially dissolved in the Fe2O3 lattice. Due to strong alumina-iron oxide interaction, the specific surface area of the catalysts increases significantly. TPR and XANES data indicate that copper forms highly dispersed surface CuO nanoparticles and partially dissolves in iron oxide. It has been shown that the reduction of iron(III) oxide by CO proceeds via two routes: a direct two-stage reduction of iron(III) oxide to metal (Fe2O3 → Fe3O4 → Fe) or an indirect three-stage reduction with the formation of FeO intermediate phases (Fe2O3 → Fe3O4 → FeO → Fe). The introduction of Al into Fe2O3 leads to a decrease in the rate for all reduction steps. In addition, the introduction of Al stabilizes small Fe3O4 particles and prevents further sintering of the iron oxide. The mechanism of stabilization is associated with the formation of Fe3- xAl xO4 solid solution. The addition of copper to the Fe-Al catalyst leads to the formation of highly dispersed CuO particles on the catalyst surface and a mixed oxide with a spinel-type crystalline structure similar to that of CuFe2O4. The low-temperature reduction of Cu2+ to Cu0 accelerates the Fe2O3 → Fe3O4 and FeO → Fe transformations but does not affect the Fe3O4 → FeO/Fe stages. These changes in the reduction properties significantly affect the catalytic performance of the Fe-based nanocomposite catalysts in the low-temperature oxidation of CO.

CuFeAl-composite catalysts of oxidation of gasification products of solid fuels: In situ XAS and XRD study

The reduction of high-active FeAl and CuFeAl composite catalysts was investigated in situ by XRD and XAS in the temperature range between 100 and 600 °C. It was found that the fresh catalysts consist of Fe2O3 and Al2O3 phases only. The Al3+ cations partially dissolute in the Fe2O3 lattice. The addition of copper to the Fe-Al catalyst leads to formation of highly dispersed CuO nanoparticles and mixed oxide with a spinel-type crystalline structure similar to that of CuFe2O4. The low-temperature reduction of Cu2+ to Cu0 accelerates the Fe2O3 → Fe3O4 and FeO → Fe0 transformations. In the presence of oxygen we did not observe the reduction of Cu and Fe to the metallic state. This means that the oxidation of CO over FeAl and CuFeAl composite catalysts proceeds via a redox mechanism.

Pyrolysis of sawdust with various Fe-based catalysts: Influence of support characteristics on hydrogen-rich gas production

In the present study, we studied the hydrogen-rich gas production from catalytic pyrolysis of sawdust using various Fe-based catalysts derived from layered double hydroxide (LDH) precursor in a two-stage fixed-bed reactor. Specifically, we investigated the effect of support characteristics (Fe–Mg, Fe–Ca and Fe–Al) on the physicochemical properties and catalytic performances in relation to hydrogen production and coke formation. Various characterization techniques, such as XRD, SEM, BET, H2-TPR and TG-DTG temperature-programmed oxidation (TPO), were employed to thoroughly characterize the fresh and reacted Fe-based catalysts. It revealed that the support characteristics played an important role in determining the iron species form, textural properties and catalytic abilities of the resulting catalysts. The Al-supported Fe-based catalyst was found to be the most effective catalyst for hydrogen-rich gas production with the highest gaseous efficiency of 61.4 wt.%, gas yield of 598 mL/g biomass, H2 yield of 217 mL/g biomass, and H2/CO molar ratio of 2.5 at 700 °C. Based on the results of structural characteristics, this might be attributed to its fine particle, enhanced reducibility, high surface area and generation of surface acidity by introduction of Al form, which could provide efficient active sites for pyrolysis volatiles to crack and reform through a series of catalytic reactions. According to GC–MS experiment results, the Fe–Al catalyst was capable of selectively producing aromatic compounds, with the maximum yield as high as almost 100%. Therefore, the Fe–Al catalyst developed in this work could provide a promising route for hydrogen-rich gas production from catalytic pyrolysis of biomass.

Structure and Chemistry of Cu–Fe–Al Nanocomposite Catalysts for CO Oxidation

High-active Fe–Al and Cu–Fe–Al nanocomposite catalysts were synthesized by fusion of aluminium, iron, and copper salts and then tested in the oxidation of CO. It was found that the activity of Fe–Al catalysts depends on the Fe concentration and the maximum is achieved when the Fe2O3 content is approximately 82 wt%. The addition of Cu leads to a significant increase in activity. Using adsorption techniques, X-ray diffraction, X-ray absorption spectroscopy, and Fourier-transform infrared spectroscopy, morphology, structure, and chemistry of the catalysts were studied. It was shown that the Fe–Al catalysts consist of Fe2O3 and Al2O3 phases mainly. Alumina is in an amorphous state whereas iron oxide forms nanoparticles with the protohematite structure. The Al3+ cations partially dissolute in the Fe2O3 lattice. X-ray absorption spectroscopy indicated that the Cu–Fe–Al catalysts in addition contain CuO and CuFe2O4 oxides in an amorphous state.

Copper promoter effect on acid–base and redox sites of Fe/Al2O3 catalysts and their role in ethanol–acetone mixture conversion

The redox site properties favours the hydride transfer.