Alumina-supported Iron Catalysts Research Articles

Non-thermal plasma-catalytic ammonia synthesis over alumina-supported iron catalyst: Insights into the effect of alumina calcination temperature

Non-thermal plasma-catalytic ammonia synthesis (NTPCAS) has been regarded as a promising route to store hydrogen by utilizing renewable electricity. Alumina is a suitable support of the catalysts in NTPCAS and its properties can influence the performance of catalysts remarkably. In this study, the influence of the alumina calcination temperatures (Tc) on the catalytic performance of Fe-Al-x (x represents the value of Tc) was analyzed in a dielectric barrier discharge (DBD) reactor for NTPCAS. The results suggested that an increase in Tc transforms the alumina crystalline from γ phase to α phase. The best performance with a synthesized ammonia concentration of 11833 ppm was achieved over Fe-Al-900 with coexisting γ and θ phases of alumina under N2: H2 = 1:1 and SEI = 37.05 kJ/L conditions, which was 37 % higher than that of Fe-Al-800 with only γ phase. In addition, the larger Tc (i.e. 1100 and 1200 °C) decreased the specific surface area, increased the mean catalyst particle size, and led to the non-uniform dispersion of Fe species. The NH3-TPD and XPS studies suggested that an increase in Tc could influence the surface acidity and oxygen vacancy concentration of Fe catalysts, which were crucial to adjusting the catalytic activity for NTPCAS. This study clarifies the value of a suitable design of support of catalysts for improving NTPCAS.

Investigation of effects of sulfur on dry reforming of biogas over nickel–iron based catalysts

The aim of this study is to maintain and increase the activity of the catalyst in the presence of H2S with the addition of iron to the Ni catalyst. Alumina-supported monometallic iron and bimetallic nickel-iron catalysts with different weight percentages (8% Fe, 3% Ni – 3% Fe and 8% Ni – 8% Fe) were synthesized using the wet impregnation method in this study. Alumina was prepared by the sol-gel method. The activities of these synthesized catalysts in the methane dry reforming reaction were investigated at different H2S concentrations (0 ppm, 2 ppm, and 50 ppm) with a total flow rate of 60 mL/min containing an equimolar ratio of CH4, CO2, and Ar at 750 °C and atmospheric pressure. To investigate the effect of sulfur compounds on the catalytic activity, the catalysts were also exposed to different gas compositions such as the mixture of H2S + He, H2S + CO2 + He, and H2S + CO2 + CH4 + He. In this case, FT-IR with a gas cell was used to determine the components in the gas stream at the reactor outlet. To explain catalytic performance, characterization studies were carried out using XRD, N2 adsorption/desorption, DRIFT, SEM, TGA, and XPS analysis. All-synthesized materials showed Type-IV isotherm with a hysteresis loop corresponding to an ordered mesoporous structure. The DRIFT analysis showed a decrease in the Lewis acid sites after the addition of iron into the Ni-catalysts. In the activity test carried out in the presence of 50 ppm H2S, it was observed that the iron-containing 8Ni–8Fe@SGA catalyst increased the sulfur resistance slightly, compared to the monometallic 8Ni@SGA catalyst. TGA analysis showed that Fe addition reduced coke deposition, as the Ni–Fe catalyst had a lower nickel crystal size than the Ni-based catalyst. FTIR analysis with a gas cell showed that sulfur in H2S transformed to other sulfur compounds such as COS and/or SO2 during dry reforming of biogas over alumina-supported Ni–Fe catalysts.

Alumina-supported iron catalyst - long-term study of the light product distribution in Fischer-Tropsch synthesis

Several models have been proposed to describe the carbon number product distribution and mechanism in Fischer-Tropsch synthesis (FTS). However, these models have not fully explained the product distribution and mechanism owing to the wide range and complexity of hydrocarbons in FTS. This study was conducted based on the Yao and Anderson-Schulz-Flory (ASF) carbon number product distribution models for light (C1–C6) hydrocarbon products of a Fe/Al2O3 catalyst. The product distribution based on the molar ratio of olefin to paraffin (O/P) and the neighboring olefins was also studied in order to better understand the mechanism in FTS and C2 olefin deviation during FTS.Two sets of experiments (A and B) with different reaction conditions were conducted in microtubular fixed-bed reactors on the Fe/Al2O3 catalyst for 2249 h and 360 h, respectively. We found that the α values from the Yao and ASF carbon number product distribution models are relatively similar. The α values from the Yao carbon number product distribution plots are relatively constant, irrespective of the reaction conditions.Interestingly, it was also found that the secondary reactions of the C2 olefin by re-adsorption to produce paraffins and long-chain olefins are dependent on the CO conversion and the reaction temperature during the FTS. Also, the product distribution of the neighboring olefins during the reduction condition gave a similar trend to what was observed for other reaction conditions. This result confirmed what was observed in the Yao and ASF carbon number product distribution of the olefins.

SiO2-promoted growth of single-walled carbon nanotubes on an alumina supported catalyst

Developing supported catalyst and elucidating the catalyst activation mechanism are of significant importance for large scale synthesis of single-walled carbon nanotubes (SWNTs). In the work, we designed an alumina-supported iron (Fe–Al2O3) catalyst for catalytic growth of carbon nanotubes by CO chemical vapor deposition (CVD). In the temperature range of 800–1000 °C, the prepared powder catalyst only affords the growth of carbon fibers or multi-walled carbon nanotubes. In contrast, when placing the powder catalyst on flat SiO2 substrates, such as SiO2/Si and quartz, SWNTs were observed to grow at the catalyst-substrate interface, highlighting the contributions of the SiO2 substrate in SWNT synthesis. Systematic characterizations on both the catalysts and carbon nanotubes revealed that the SiO2 substrate promotes the reduction of iron oxide in the adjacent Fe–Al2O3 catalyst, facilitating the generation of small Fe particles at the catalyst-substrate interface, which act as the active phase for the subsequent growth of SWNTs. This work opens a new avenue for growing SWNTs from supported catalyst and sheds light on enhancing SWNT growth efficiency by tuning catalyst reduction behaviors.

Effect of temperature on deactivation models of alumina supported iron catalyst during Fischer-Tropsch synthesis

Determination of catalyst deactivation model plays prominent role in process controlling. The aim of this study is to investigate deactivation models of Fe/Al2O3 catalyst at different temperature during the Fischer-Tropsch synthesis. Data analysis determined the suitability of second-order GPLE model to describe deactivation behavior of the catalyst. Comparing model parameters at different conditions demonstrated that the catalyst deactivation rate increased by temperature elevation. Analysis of the models also revealed that the catalyst deactivation involves two stages, the first stage occurs at high temperatures while the next step happens at low temperatures, and the deactivation energy of both stages was calculated.

Steam reforming of toluene as model biomass tar to H2-rich syngas in a DBD plasma-catalytic system

Biomass tar is one of the most troublesome issues limiting the further development of biomass pyrolysis and gasification. In this study, a plasma enhanced catalytic steam reforming technology was applied for biomass tar removal. Toluene was selected as biomass tar surrogate. The nano-sized alumina-supported nickel and iron catalysts with different molar ratios of M/Al (M: Ni or Fe, 0:1, 1:3, 1:1, 3:1, 1:0) were prepared for catalytic steam reforming of toluene in a non-thermal plasma reactor featuring dielectric barrier discharge (DBD). The results showed that syngas was the dominant gas product of toluene decomposition. The conversion efficiency of toluene and energy efficiency using Ni-Al and Fe-Al catalysts both followed a sequence: M1Al3 > M1Al1 > M3Al1, which is in line with the BET surface area and pore volume. However, the selectivity of H2 and CO catalysed by Ni-Al and Fe-Al catalysts follows the order of M1Al3 < M1Al1 < M3Al1. Presumably, toluene dissociation is a process composed of adsorption-reaction-desorption. The formation of syngas is supposed to proceed as a series of ionic and free radical reactions occurring preferably in the gas phase. Ni1Al3 catalyst shows the largest potential in converting biomass tar into H2-rich syngas, with a maximum toluene conversion of 96% and a largest H2 yield of 2.18 mol/mol-toluene. Besides, the results showed that this hybrid plasma-catalysis system was potential in anti-carbon deposition.

CO2 hydrogenation to hydrocarbons over alumina-supported iron catalyst: Effect of support pore size

The effect of support pore size of FeK/Al2O3 catalysts on the catalytic performance in CO2 hydrogenation reaction was investigated. A total of 8 iron-based catalysts supported on alumina with different pore size were prepared by incipient wetness impregnation where the amount of Fe and K were fixed at 15 and 10wt%, respectively. N2 adsorption/desorption, XRD, TPR and PZC were used to characterize the supports and catalysts. The results show that the support pore size impacts the size of Fe2O3 particles formed in the catalyst; increasing pore size of Al2O3 supports led to increased size of Fe2O3 particles formed in the pores. Catalyst pore sizes of 7–10nm and the corresponding Fe2O3 particle sizes of 5–8nm were the most active for CO2 hydrogenation to hydrocarbons. Outside this range, larger pore size further decrease the iron dispersion and reduce the number of active sites; smaller pore size is not favorable on account of the too small Fe2O3 particle sizes and lower reducibility of the small particle.

Hydrogen production via catalytic methane decomposition over alumina supported iron catalyst

In this paper, iron-based catalysts, calcined at different temperatures (300–800°C), supported over alumina, were investigated for hydrogen production via catalytic methane decomposition. The catalysts were prepared by using different methods such as impregnation and co-precipitation. The fresh and spent catalysts were characterized using different techniques such as Brunauer, Emmett and Teller (BET), temperature-programmed reduction by hydrogen (H2-TPR), X-ray powder diffraction (XRD), thermogravimetry analysis (TGA), Field Emission Scanning Electron Microscope (FESEM) and transmission electron microscopy (TEM). Results revealed that for both impregnated and co-precipitated catalysts, calcination temperature of 500°C is optimal. Type of precursor iron oxide on the alumina support has a strong influence on its performance for methane decomposition.

Catalytic conversion of glycerol to polymers in the presence of ammonia

In this contribution, the development of a process for the synthesis of potentially highly valuable polymeric products from the reaction of waste glycerol with ammonia is reported for the first time. The polymers were the result of a single step, continuous gas phase process, catalysed by an alumina-supported iron catalyst, operating under relatively mild reaction conditions. The solid product was characterised using 1D and 2D NMR spectroscopy, FTIR spectroscopy, qualitative chemical tests and elemental analysis. Characterisation revealed building blocks with unsaturated, amido and ester functionalities shaping a mixture of polymers. Nitrogen atoms were present in the main chain of the resultant polymers. NMR analyses of the polymer denotes the formation of structural defects such as unsaturation and branching; whilst the partial solubility of the polymer in solvents such as CDCl3 and THF is indicative of the formation of cross-linked structures. Insights into the mechanism of formation of these functional groups were based on the liquid and gas phase product distribution. Polymers with chain structures similar to those synthesised in this work are currently manufactured from fossil fuels and are widely used in biomedical applications not only because of their architecture but also due to their response to changes in pH and temperature.

English

English

Influence of structural and textural parameters of carbon nanofibers on their capacitive behavior

Herringbone, platelet, and tubular carbon nanofibers (CNFs) were synthesized by catalytic chemical vapor deposition using methane, propane, and ethylene as carbon precursors. Alumina-supported nickel and iron catalysts were used for the syntheses. The resultant CNFs were characterized by scanning electron microscopy, transmission electron microscopy, and nitrogen sorption at 77 K. The performance of a CNF-based supercapacitor working in 6 mol L−1 KOH was analyzed using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy techniques. The Brunauer–Emmett–Teller (BET) surface area of the CNFs ranged between 150 and 296 m2 g−1. An increase in the CNF diameter was accompanied by a decrease in the BET surface area. A comparison of the porous textures and the structure types of the CNFs demonstrated that the performance of the CNF-based supercapacitor is enhanced primarily by the exposed edges of the graphitic layers on the CNF surface, followed by the specific surface area. Among the studied CNFs, the highest capacitance value, 26 F g−1 at 0.2 A g−1, was obtained for the platelet-type CNFs. Tubular CNFs exhibited the lowest capacitance value, which increased from 4 to 33 F g−1 at 0.2 A g−1 upon air treatment at 450 °C. The presence of exposed graphitic edges on the air-treated CNT surface and an increase in the specific surface area are considered to be responsible for the enhancement of the capacitor performance.

Electromagnetic interference shielding of Nitrogen-doped and Undoped carbon nanotube/polyvinylidene fluoride nanocomposites: A comparative study

Abstract Nitrogen-doped and Undoped carbon nanotubes (CNTs) were synthesized by selective transmission of source and carrier gases (ethane, ammonia, hydrogen, and argon) over an alumina-supported iron catalyst in a quartz tubular reactor at 650 °C. Conductive nanocomposites were prepared by mixing CNTs and a polyvinylidene fluoride (PVDF) matrix using a small scale melt mixer (APAM mixer) at 240 °C and 235 rpm. Various characterization techniques, such as X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman spectroscopy revealed that nitrogen doping altered the structure of CNTs, reduced the aspect ratio, deteriorated the crystalline structure, and changed the electronic properties of CNTs. It was also observed that the Undoped CNT/PVDF nanocomposites presented better state of dispersion, higher electrical conductivity, lower percolation threshold, and significantly higher electromagnetic interference shielding than their Nitrogen-doped counterparts. For instance, at 3.5wt% the Undoped CNT/PVDF nanocomposites shielded the incident electromagnetic wave 16 times more than the Nitrogen-doped ones. The enhanced electrical properties of the Undoped CNT/PVDF nanocomposites were attributed to enhanced dispersion, superior crystalline structure, and higher aspect ratio of Undoped CNTs.

Effects of Nitrogen Doping on X-band Dielectric Properties of Carbon Nanotube/Polymer Nanocomposites.

Nitrogen-doped and undoped carbon nanotubes (CNTs) were synthesized by selective passing of source and carrier gases (ethane, ammonia, hydrogen, and argon) over an alumina-supported iron catalyst in a quartz tubular reactor at 650 °C. Synthesized CNTs were mixed with polyvinylidene fluoride with an Alberta polymer asymmetric minimixer (APAM) mixer at 240 °C and 235 rpm, and the resulting nanocomposites were compression molded. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and thermogravimetric analysis (TGA) techniques revealed that introducing nitrogen into the crystalline structure of CNTs resulted in higher crystalline defects. Dielectric measurements showed that nitrogen doping significantly increased dielectric permittivity for a known dielectric loss. This was ascribed to the role of the crystalline defects and nitrogen atoms, which acted as polarizing centers, blocked the nomadic charges, polarized them, and prevented them from moving along CNTs. The obtained results introduce nitrogen doping as a regulative tool to control the dielectric properties of CNT/polymer nanocomposites.

Methane decomposition over iron catalyst for hydrogen production

Methane is the most stable hydrocarbon and the highest component of natural gas. The occurrence of vast resources of natural gas promotes the catalytic decomposition of methane to produce hydrogen and valuable carbon. Hydrogen is an excellent energy carrier and can play a very significant role in energy systems. The present study explored the decomposition of methane by iron catalyst to produce hydrogen and carbon. The catalysts were calcined at 700 °C and reduced with pure H2 at 650 °C. The reaction was carried out at 700 °C. The study involved the use of different iron loadings (15–100%) supported on alumina catalysts obtained by co-precipitation technique. The yield of hydrogen production was investigated. Spent and fresh catalysts were characterized by BET, XRD, H2-TPR, TGA, EDS and HRTEM. The catalyst characterization revealed the formation of multi-walled nanotubes from alumina supported iron catalysts. Alternatively, time on stream tests of the supported catalyst for about 4 h at 700 °C showed the relative profiles of hydrogen production and hydrogen yield increased as the % loading of Fe was increased. The maximum H2 yield of 77.2% was obtained using 60% Fe/Al2O3 catalyst. Higher Fe loadings decreased the surface area of the catalyst.

Kinetics modeling of ethylbenzene dehydrogenation to styrene over a mesoporous alumina supported iron catalyst

The kinetics of ethylbenzene (EB) dehydrogenation over a FeOx-meso-Al2O3 catalyst is studied. The models were developed based on physicochemical characterization and a CREC fluidized Riser Simulator data. N2 adsorption shows that the synthesized FeOx-meso-Al2O3 catalyst is mesoporous with pore size between 9 and 35nm. TPR profile indicates that iron on meso-Al2O3 forms easily reducible nanostructured crystals which is confirmed by TEM image. NH3- and CO-TPD analysis, respectively reveals the availability of both acidic and basic sites. The dehydrogenation of ethylbenzene on FeOx-meso-Al2O3 catalyst mainly gives styrene (∼99%) while a small amount of benzene, toluene and coke are also detected. Based on the experimental observations two Langmuir–Hinshelwood type kinetics models are formulated. The possible catalyst deactivation is expressed as function of EB conversion. Parameters are estimated by fitting of the experimental data implemented in MATLAB. Results show that one type site Langmuir–Hinshelwood model appropriately describes the experimental data, with adequate statistical fitting indicators and also satisfied the physical constraints. The activation energy for the formation of styrene (80kJ/mol) found to be significantly lower than that of the undesired products benzene (144kJ/mol) and toluene (164kJ/mol). The estimated heat of adsorptions of EB and ST are found to be 55kJ/mol and 19kJ/mol, respectively.

Catalytic chemical vapour deposition of carbon nanotubes using Fe-doped alumina catalysts

The catalytic chemical vapour deposition (CCVD) of carbon nanotubes onto Fe-doped alumina catalysts, with varying iron concentrations and reaction times is described. Methane was used as a carbon source, and nanostructural growth was afforded at 1000 °C. Characterization of alumina-supported iron catalysts was done using N 2 adsorption–desorption measurement and X-ray diffraction. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Raman spectroscopy were used for characterization of resultant carbon nanotubes (CNTs). The SEM images indicate that diameter and length of as-produced CNTs depends on both iron content of the catalyst and reaction time; with lower iron concentrations, longer and thinner nanotubes were obtained. The yield of products was investigated by TGA, and showed that increasing the catalyst iron content and reaction time directly affect the amount of formed product.

An original growth mode of MWCNTs on alumina supported iron catalysts

Multi-walled carbon nanotubes (MWCNTs) have been produced from ethylene by fluidized bed-catalytic chemical vapor deposition (FB-CCVD) on alumina supported iron catalyst powders. Both catalysts and MWCNTs-catalyst composites have been characterized by XRD, SEM-EDX, TEM, Mössbauer spectroscopy, TGA and nitrogen adsorption measurements at different stages of the process. The fresh catalyst is an alumina/iron oxide powder composed of amorphous iron(III) oxide nanoparticles located inside the porosity of the alumina support and of a micrometric crystalline α-iron(III) oxide surface film. The beginning of the CVD process provokes a brutal reconstruction and simultaneous carburization of the surface film that allows MWCNT nucleation and growth. These MWCNTs grow aligned between the support and the surface catalytic film, leading to a uniform consumption and uprising of the film. When the catalytic film has been consumed, the catalytic particles located inside the alumina porosity are slowly reduced and activated leading to a secondary MWCNT growth regime, which produces a generalized grain fragmentation and entangled MWCNT growth. Based on experimental observations and characterizations, this original two-stage growth mode is discussed and a general growth mechanism is proposed.

On the Development of Fluidized Bed Chemical Vapour Deposition for Large-Scale Carbon Nanotube Synthesis: Influence of Synthesis Temperature

The absence of large-scale carbon nanotube synthesis technology (which we define as being of the order of 10 000 tonnes per plant per year) is limiting research and development activities across the sector. We contend that fluidized bed chemical vapour deposition (FBCVD) is the most promising technology for large-scale, low-cost, carbon nanotube synthesis. In this work, multi-walled carbon nanotubes were synthesized on alumina-supported iron, cobalt, or nickel catalysts by catalytic chemical vapour deposition in a 0.5 kg h–1 FBCVD reactor, using ethylene as a carbon source. The carbon nanotube yield was shown to increase with an increase in synthesis temperature from 3.3% at 550°C to 87.6% at 900°C. At higher synthesis temperatures the quality of the nanotubes appeared to improve, although further experiments are required to quantify this within statistically significant limits.

Morphology of Carbon Nanotubes Prepared on Alumina Supported Iron Catalyst by Mechanochemical Treatment

Morphology of Carbon Nanotubes Prepared on Alumina Supported Iron Catalyst by Mechanochemical Treatment

Behaviour of a cyanide-derived Fe/Al 2O 3 catalyst during Fischer-Tropsch synthesis

The interaction of carbon monoxide and hydrogen with an alumina-supported iron catalyst has been studied at temperatures ranging from 300 to 523 K and at a pressure of 103 kPa. The species produced and adsorbed on the catalyst surface have been examined by infrared spectroscopy, while the chemical state of the iron within the catalyst was investigated by magnetization measurements and Mössbauer spectroscopy. At 300 K the main type of adsorbed species on the iron particle surface appeared to be molecular carbon monoxide and formate groups. The amount of the latter species increases considerably at elevated reaction temperatures up to 473 K. Changes in the infrared absorption bands of CO, and in the magnetization and Mössbauer data indicate that under the applied conditions the surface properties of the iron particles are affected by the synthesis gas, but that the bulk remains metallic. The increased Fischer-Tropsch activity at more elevated temperatures, viz. 473 and 523 K, is accompanied by significant changes in the in situ recorded infrared spectra. The formation of hydrocarbons is evident from the well developed absorption bands in the 3000-2800 cm −1 range, due to (a)symmetric stretching vibrations of CH 2 and CH 3 groups. Assignment of the various absorption bands in the 1700-1200 cm −1 wavenumber range is speculative due to (partial) coincidence of the bands and the gradual change in chemical composition of the catalyst particles. At higher temperatures the bulk of the iron particles reacts rapidly to a mixture of carbides. Initially the unstable ε-Fe 2C is formed which reacts to ε′-Fe 2.2C upon prolonged periods of time of reaction and/or increased reaction temperatures. These carbides appeared to be thermally unstable: upon heating in helium they are converted into a mixture of χ-Fe 5C 2 and metallic Fe. Interaction of the reduced iron catalysts with ethylene or methane at 523 K gives rise to absorption bands at 1555, 1345 and 1050 cm −1, which are assigned to CH x adsorbed species. Upon reaction with ethylene also a band at 2160 cm −1 was observed, which was assigned to an ethylidyne species.