Ni-Fe Bimetallic Catalysts Research Articles

The synergistic effect between Ni sites and Ni-Fe alloy sites on hydrodeoxygenation of lignin-derived phenols

The catalytic hydrodeoxygenation (HDO) of lignin-derived phenolic compounds is a critical step in the upgrading of bio-oil. Here, bimetallic Ni-Fe nanoparticles supported on mesoporous carbon spheres (MCSs) were fabricated and applied in HDO of phenol. In comparison with monometallic Ni and Fe catalysts, the bimetallic Ni-Fe catalyst exhibited better performance for phenol HDO due to the formation of Ni-Fe alloy phase identified by X-ray powder diffraction (XRD) and Mössbauer spectroscopy techniques. Among several explored ratios, the catalysts with Ni/Fe ratio of 3/1 presented the highest cyclohexane yield. The reaction occurred in two consecutive steps: the hydrogenation of phenol to cyclohexanol and the further hydrogenolysis of cyclohexanol to cyclohexane. Kinetic studies showed that the hydrogenolysis of cyclohexanol controlled the overall reaction rate of phenol HDO due to the lower reaction rate of this step. Indeed, the turnover frequency (TOF) values of cyclohexanol normalized by surface metallic Ni sites exhibited a linear correlation with Ni-Fe alloy sites. The alloying of iron in the bimetallic Ni-Fe catalysts significantly enhanced the adsorption strength of cyclohexanol, which is the reason of the high activity of the Ni-Fe alloy particles. Thus, Fe-containing sites adsorb the hydroxyl species while Ni sites perform the H2 activation, their synergistic effect plays a key role in phenol HDO process.

Low-temperature decomposition of Aroclor 1254 over AC-supported Ni-Fe bimetallic catalysts: Kinetic and thermodynamic study

Polychlorinated biphenyls (PCBs) cause serious impacts on the environment and organisms, due to their hypertoxicity, thermal stability and persistence. This study investigated the effects of temperature, reaction time and total flow rate on the low-temperature catalytic decomposition of Aroclor 1254. A modified iron-exchange method was adopted because it allows higher metal loading rates than the traditional impregnation method. We used this method to prepare three active carbon supported Fe/Ni bimetallic catalysts with different Fe/Ni molar ratios. The results indicated that the Fe/Ni bimetallic catalysts showed great potential in Aroclor 1254 decomposition. Among Fe/Ni molar ratios, Fe/Ni-1/3-C demonstrated the strongest performance with a decomposition efficiency greater than 90% even at the relatively low temperature of 200 °C. Thermodynamic analysis confirmed that the dechlorination of Aroclor 1254 over Fe/Ni-1/3-C obtained the minimum activation energy of 8.0 kJ/mol. Aroclor 1254 was decomposed rapidly over Fe/Ni-1/3-C, with a total decomposition efficiency of 83.4% at 10 min and 93.8% at 30 min. The kinetics analysis indicated a stepwise dechlorination of Aroclor 1254 over Fe/Ni-1/3-C. In addition, the total flow rate indicated a negative effect on the decomposition of Aroclor 1254 due to the decreased retention time.

Hydrogen production by methane decomposition using bimetallic Ni–Fe catalysts

The catalytic methane decomposition is the leading method for COx-free hydrogen and carbon nanomaterial production. In the present study, calcium-silicate based bimetallic Ni–Fe catalysts have been prepared and used to decompose the methane content of the ‘product gas’ obtained in the biomass gasification process for increasing total hydrogen production. Al2O3 was used as secondary support on calcium silicate based support material where Ni or Ni–Fe were doped by co-impregnation technique. The activity of catalysts was examined for diluted 6% methane-nitrogen mixture in a tubular reactor at different temperatures between 600 °C and 800 °C under atmospheric pressure, and data were collected using a quadrupole mass spectrometer. Catalysts were characterized by XRD, SEM/EDS, TEM, XPS, ICP-MS, BET, TPR, and TGA techniques. The relation between structural and textural properties of catalysts and their catalytic activity has been investigated. Even though the crystal structure of catalysts had a significant effect on the activity, a direct relation between the BET surface area and the activity was not observed. The methane conversion increased by increasing temperature up to 700 °C. The highest methane conversion has been obtained as 69% at 700 °C with F3 catalyst which has the highest Fe addition, and the addition of Fe improved the stability of catalysts. Moreover, carbon nanotubes with different diameter were formed during methane decomposition reaction, and the addition of Fe increased the formation tendency.

Effects of Cu and Fe Additives on Low-Temperature Catalytic Steam Reforming of Toluene Over Ni/AC Catalysts

Steam reforming of toluene, a model tar compound, was carried out at low temperature of 600 °C using Cu–Ni and Fe–Ni bimetallic catalysts with different molar ratios supported on activated carbon (AC). For the Cu–Ni/AC catalysts, the carbon conversion of toluene rose and then decreased with the content of Cu increasing, and the best performance was achieved at the molar ratio of 0.2. However, the Fe–Ni/AC catalyst with the optimum composition of Fe/Ni = 0.1 had a better catalytic performance for toluene steam reforming than the Cu–Ni/AC catalyst (Cu/Ni = 0.2). During the duration test of 20 h, the Fe–Ni/AC (Fe/Ni = 0.1) catalyst showed higher activity for the average carbon conversion of toluene (93.8% vs. 92.9%) and better resistance. to carbon deposition than those of Ni/AC catalyst. Moreover, the metal average sizes of the spent Ni/AC and 0.1-Fe–Ni/AC were estimated to be 30.0 nm and 19.0 nm, respectively. Based on a variety of physiochemical characterization results, it is demonstrated that the addition of iron into Ni/AC catalyst led to good dispersion of Ni, and few coke formation and limited aggregation of nickel particles during reaction.

In-situ catalytic conversion of tar from biomass gasification over carbon nanofibers- supported Fe-Ni bimetallic catalysts

Using catalytic conversion to reduce the formation of tar in biomass gasification has received great attention, and catalyst improvement is one of the key issues. In this work, Fe-Ni/carbon nanofibers composite materials were prepared and used for tar conversion during biomass gasification. Compared with non-catalyst tar conversion, the tar removal efficiency reached 85.76% and the total syngas yield doubled (0.947 L/g) with Fe-Ni/carbon nanofibers catalyst. After 13-time reuse, the tar removal efficiency and syngas yield only decreased by 7.25% and 9.07%, respectively. Due to the formation of carbon nanofibers through calcination, a high mesopore volume of catalyst was achieved which is beneficial to the adsorption and cracking of macromolecular tar components. And the Fe0.64Ni0.36 alloy detected in Fe-Ni/carbon nanofibers catalyst has a quite high catalytic ability to aromatic compounds. Furthermore, the carbon deposition of catalyst can be relieved by the interaction between Fe and Ni, which can effectively maintain the catalytic performance of catalysts. The combination of bimetallic catalyst with carbon nanofibers allows the high catalytic activity and stable cyclability of Fe-Ni/CNF for effective tar conversion.

Co-, Cu- and Fe-Doped Ni/Al2O3 Catalysts for the Catalytic Decomposition of Methane into Hydrogen and Carbon Nanofibers

The catalytic decomposition of methane (CDM) process produces hydrogen in a single stage and avoids CO2 emission thanks to the formation of high added value carbon nanofilaments as a by-product. In this work, Ni monometallic and Ni–Co, Ni–Cu, and Ni–Fe bimetallic catalysts are tested in the CDM reaction for the obtention of fishbone carbon nanofibers (CNF). Catalysts, in which Al2O3 is used as textural promoter in their formulation, are based on Ni as main active phase for the carbon formation and on Co, Cu, or Fe as dopants in order to obtain alloys with improved catalytic behaviour. Characterization of bimetallic catalysts showed the formation of particles of Ni alloys with a bimodal size distribution. For the doping content studied (5 mol. %), only Cu formed an alloy with a lattice constant high enough to be able to favor the carbon diffusion through the catalytic particle against surface diffusion, resulting in higher carbon formations, longer activity times, and activity at 750 °C; whereas Ni, Ni–Co, and Ni–Fe catalysts were inactive. On the other hand, Fe also improved the undoped catalyst performance presenting a higher carbon formation at 700 °C and the obtention of narrow carbon nanofilaments from active Ni3Fe crystallites.

The structure and performance of (Ni4Fe)mAg(PrZr4)nOx catalyst for ethanol steam reforming

Co-precipitation method is used to synthesize PrpZrqOx composite oxide support and impregnation method is adopted in preparing (Ni4Fe)mAgPrpZrqOx catalysts. X-ray power diffraction (XRD), Temperature programmed reduction (TPR) and Temperature programmed oxidation (TPO) are used to characterize the catalysts. The results indicate that not only the improvement of catalytic activity is remarkable, but also an excellent capacity of resistance to carbon deposition when Ag dropped into the Ni-Fe bimetallic catalysts. XRD spectrum of the fresh (Ni4Fe)mAg(PrZr4)nOx catalysts present characteristic diffraction peak of tetragonal crystal phase ZrO2, rhombohedral Fe2O3, hexagonal NiO and cubic Ag2O while no diffraction peak of praseodymium oxide appears because the doped praseodymium ions can enter the ZrO2 lattice. After 823K’s pretreatment by H2, the main active components are cubic Ni0 and cubic Ag0. TPR shows that the presence of Ag is of great benefit to the reduction of Fe2O3 and NiO: the peaks maximum due to the Fe2O3→Fe3O4 and NiO→Ni0 reduction of the Ag-containing sample are shifted by more than 150K to lower temperatures in comparison with Ni-Fe bimetallic metallic catalysts. (Ni4Fe)16Ag(PrZr4)64.8Ox catalyst shows its best catalytic activity in ethanol steam reforming. Under the following conditions, reaction temperature 773K, ethanol/water with molar ratio of 1:6, weight hourly space velocity (WHSV) of 11.8 h−1, the ethanol conversion rates are nearly 100% and the molar percentage of H2, CO, CH4, CO2 are 70.5%, 1.8%, 7.9%, and 19.6% respectively.

Oxidative dehydrogenation and dry reforming of n-butane with CO2 over NiFe bimetallic catalysts

The oxidative dehydrogenation of n-butane to 1,3-butadiene using CO2 as a soft oxidant is investigated over oxide-supported NiFe bimetallic catalysts. Dry reforming of n-butane with CO2 to syngas is also studied under identical conditions for comparison. The Ni1Fe3/CeO2 catalyst is identified as a promising catalyst for the oxidative dehydrogenation to 1,3-butadiene via the CH bond cleavage, while the Ni3Fe1/CeO2 catalyst mainly promotes the dry reforming pathway via the CC bond scission. The oxidation states of Ni and Fe are determined by X-ray absorption fine structure (XAFS) measurements under reaction conditions. Density functional theory (DFT) calculations are performed to further understand the different reaction pathways. Furthermore, the effect of oxide supports is studied for the Ni1Fe3 bimetallic catalysts, showing that highly reducible supports, CeO2 and CeO2-ZrO2, promote the production of 1,3-butadiene, whereas the ZrO2 support significantly suppresses the oxidative dehydrogenation.

Promotion effect of additive Fe on Al2O3 supported Ni catalyst for CO2 methanation

In this paper, the effect of additive Fe on Ni/Al2O3 catalyst for CO2 methanation was studied. A series of bimetallic Ni–Fe catalysts with different Ni/Fe ratios were prepared by impregnation method. For comparison, monometallic Fe‐based and Ni‐based catalysts were also prepared by the same method. The characterization results showed that adding Fe to Ni catalyst on the premise of a low Ni loading(≦12 wt.%) enhanced CO2 methanation performance. However, when the Ni loading reached 12 wt.%, the catalytic activity decreased with the increase of Fe content, but still higher than the corresponding Ni‐based catalyst without Fe. Among them, the 12Ni3Fe catalyst exhibited the highest CO2 conversion of 84.3 % and nearly 100% CH4 selectivity at 50000 ml g‐1 h‐1 and 420 °C. The enhancement effect of adding Fe on CO2 methanation was attributed to the dual effect of suitable electronic environment and increased reducibility generated by Fe species.

Bimetallic Ni-Fe catalysts derived from layered double hydroxides for CO methanation from syngas

Carbon deposition and sintering of active components such as nano particles are great challenges for Ni-based catalysts for CO methanation to generate synthetic natural gas from syngas. Facing the challenges, bimetallic catalysts with different Fe content derived from layered double hydroxide containing Ni, Fe, Mg, Al elements were prepared by co-precipitation method. Nanoparticles of Ni-Fe alloy were supported on mixed oxides of aluminium and magnesium after calcination and reduction. The catalysts were characterized by Brunner-Emmett-Teller (BET), X-ray diffraction, hydrogen temperature programmed reduction, inductively coupled plasma, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric techniques, and their catalytic activity for CO methanation was investigated. The results show that the Ni-Fe alloy catalysts exhibit better catalytic performance than monometallic catalysts except for the Ni4Fe-red catalyst. The Ni2Fe-red catalyst shows the highest CO conversion (100% at 260–350 °C), as well as the highest CH4 selectivity (over 95% at 280–350 °C), owing to the formation of Ni-Fe alloy. In stability test, the Ni2Fe-red catalyst exhibits great improvement in both anti-sintering and resistance to carbon formation compared with the Ni0Fe-red catalyst. The strong interaction between Ni and Fe element in alloy and surface distribution of Fe element not only inhibits the sintering of nanoparticles but restrains the formation of Ni clusters.

A comparison of furfural hydrodeoxygenation over Pt-Co and Ni-Fe catalysts at high and low H2 pressures

The hydrodeoxygenation (HDO) of furfural to 2-methylfuran (MF) was investigated in a continuous flow reactor over carbon-supported, PtCo3 nano-crystals (NCs) and NiFe bimetallic catalysts, along with their monometallic counterparts, at 1 and 33bar, respectively. At 1bar, the decarbonylation reaction to furan was a major non-selective pathway on both Pt/C and Ni/C; but this pathway was almost eliminated on the bimetallic catalysts. At 33bar, decarbonylation is not observed on any of the catalysts and the major non-selective reaction pathway on both Ni and Pt catalysts is the over-hydrogenation of MF. Catalysts based on both PtCo3 NCs and NiFe bimetallics also suppress the over-hydrogenation reactions and are able to achieve significantly better MF yields under these conditions as well. The implications of these results for understanding HDO reactions on bimetallic catalysts are discussed.

Co-production of hydrogen and carbon nanotubes from catalytic pyrolysis of waste plastics on Ni-Fe bimetallic catalyst

To explore the mechanism of the influence of Ni-Fe bimetallic catalyst for the producing high-value carbon nanotubes (CNTs) with clean hydrogen from waste plastic pyrolysis, the pyrolysis-catalysis of plastics were performed using a two stage fixed bed reaction system with Ni and Fe loading at variant molar ratios. The catalysts and produced carbon were analysed with various characterization method, including temperature-programed reduction/oxidation, X-ray diffraction, scanning electron microscopy or/and Raman spectroscopy. Both the H2 concentration and H2 yield reached maximum values of 73.93vol.% and 84.72mgg−1 plastic, respectively, as the ratio of Ni:Fe at 1:3. The amount and quality of CNTs were greatly influenced by the catalyst composition, and Ni and Fe display different roles to the overall reactivity of Ni-Fe catalyst for the pyrolysis-catalysis of waste plastics. Catalyst with more Fe loading produced more hydrogen and deposited carbon, due to higher cracking ability and the relatively lower interaction between active sites and support. The presence of Ni in Ni-Fe bimetallic catalyst enhanced the thermal stability and graphitization degree of produced carbons. The thermal quality of filamentous carbons might be associated with carbon defects.

Efficient degradation of tetrabromobisphenol A by synergistic integration of Fe/Ni bimetallic catalysis and microbial acclimation

This study provides a novel technology for the degradation of tetrabromobisphenol A (TBBPA) via an interaction of Fe redox and a shift of functional microbial community. TBBPA was degraded by integration of synthesized Fe-Ni bimetallic particles and enriched microbial consortium within an aqueous system. This cooperative integration yielded the best TBBPA-degrading capacity (100% removal after treatment for 2 h) and highest TOC-removing efficiency (94.5% removal after treatment for 96 h), as well as the lowest toxicity to Vibrio fischeri (almost 0% growth inhibition during reaction). The synergistic mechanism of integrated system was clarified based on systematical analyses of the degradation processes as well as the shifts in microbial community. Owing to the microbial metabolism and the Fenton-like process of leaked Fe2+, Fe3+ and Ni2+ from Fe-Ni bimetallic catalyst, reactive oxidative species (ROS), including superoxide (O2−), hydroxyl radicals (OH) and hydrogen peroxide (H2O2) were produced and evaluated by multiple techniques. Moreover, the quenching experiments indicated that OH was the major ROS leading to TBBPA degradation, rather than H2O2 or O2−. Based on the analysis of the 12 detected intermediates, three parallel pathways were proposed. It was clearly revealed that reductive and oxidative debromination, hydroxylation, and β-scission simultaneously occurred in the integrated system. Fe non-randomly accelerated the enrichment of TBBPA-degrading microbes (e.g. Pseudomonas sp. and Citrobacter sp., etc.). Above all, this novel technology has great promise for field-applications for remediation of TBBPA-contaminated field.

A versatile sensor for determination of seven species based on NiFe nanoparticles

A facile one-pot route was developed to synthesis NiFe bimetallic nanoparticles via a controlled co-reduction of Ni(II) acetylacetonate and Fe(II) acetylacetonate in oleylamine (OAm). Due to its unique properties originating from the synergistic effects of transition metals, NiFe exhibited excellent electrochemical catalytic activities. The electrochemical sensor based on carbon supported NiFe nanoparticles (NiFe/C) was constructed to determine various small biomolecules, and intensively showed high selectivity towards the oxidation of ascorbic acid (AA), dopamine (DA), uric acid (UA) and four DNA bases (guanine (G), adenine (A), thymine (T) and cytosine (C)), with large peak separations of 179mV (AA-DA), 123mV (DA-UA), 128mV (G-A), 274mV (A-T), 112mV (T-C) and little mutual interference. The detection limits were AA (1.0μM), DA (0.1μM), UA (0.1μM), G (0.25μM), A (0.25μM), T (10μM) and C (10μM) at S/N=3, respectively. The feasibility of the proposed sensor for real sample analysis was also investigated. These results demonstrate that NiFe bimetallic catalyst is a promising candidate of electrode material for determination of various analytes, which make it a fascinating sensor with versatile application.

Hydrogenation of biomass-derived ethyl levulinate into γ-valerolactone by activated carbon supported bimetallic Ni and Fe catalysts

Gamma-valerolactone (GVL) has been identified as a sustainable high-value platform molecular for the production of fuels and carbon-based chemicals. In this work, a series of activated carbon supported low-cost bimetallic Ni-Fe catalysts (Ni-Fe/AC) with different molar content of Fe species were prepared by using co-precipitation method for the liquid phase hydrogenation of ethyl levulinate (EL) to produce γ-valerolactone. The Ni-Fe0.5/AC exhibited the highest activity among the bimetallic or monometallic catalysts under mild reaction conditions (100°C, 4MPa H2, 6h) and achieved 99.3% conversion of EL and 99.0% yield of GVL. Under more mild conditions (60°C, 2MPa H2) and prolonging the reaction time to 24h, EL could be converted completely and the obtained GVL yield was more than 98%. The catalysts were characterized by various techniques including XRD, TEM, HRTEM, EDX, XPS, H2-TPR and NH3-TPD. Based on the structure and activity relationship study, the formation of highly dispersed Ni-Fe alloy structure and the co-presented FeOx nanoparticles could be responsible for the high catalytic hydrogenation activity.

Catalytic behavior of bimetallic Ni–Fe systems in the decomposition of 1,2-dichloroethane. Effect of iron doping and preparation route

Model bimetallic Ni–Fe catalysts were prepared by coprecipitation from aqueous solutions of nitrates and by mechanical alloying of metal powders. Pure nickel samples subjected to the similar procedures were used as references. The obtained samples were characterized by scanning electron microscopy and X-ray diffraction analysis. Catalytic chemical vapor deposition of 1,2-dichloroethane over the catalysts was studied in a quartz flow reactor equipped with a McBain balance. It was shown that in the case of coprecipitation followed by reduction, Ni–Fe solid solution is formed within the studied range of Fe loading (1–10 wt%). Activation times of 6 min and longer are required to obtain this solid solution by the mechanical alloying method. Despite the known catalytic activity of nickel and iron in hydrocarbon decomposition in accordance with carbide cycle mechanism, iron doping was found to worsen the behavior of nickel in the studied reaction where chlorinated alkane plays a role of substrate to be decomposed. The formation of thermodynamically more stable iron chloride in relation to nickel chloride leads to deactivation of the catalyst and deceleration of the overall process.

Synthesize multi-walled carbon nanotubes via catalytic chemical vapour deposition method on Fe-Ni bimetallic catalyst supported on kaolin

In this study, Fe-Ni bimetallic catalyst supported on kaolin is prepared by a wet impregnation method. The effects of mass of kaolin support, pre-calcination time, pre-calcination temperature and stirring speed on catalyst yields are examined. Then, the optimal supported Fe-Ni catalyst is utilised to produce multi-walled carbon nanotubes (MWCNTs) using catalytic chemical vapour deposition (CCVD) method. The catalysts and MWCNTs prepared using the optimal conditions are characterized using high resolution transmission electron microscope (HRTEM), high-resolution scanning electron microscope (HRSEM), electron diffraction spectrometer (EDS), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), and X-ray diffraction (XRD). The XRD/EDS patterns of the prepared catalyst confirm the formation of a purely crystalline ternary oxide (NiFe2O4). The statistical analysis of the variance demonstrates that the combined effects of the reaction temperature and acetylene flow rate predominantly influenced the MWCNT yield. The N2 adsorption (BET) and TGA analyses reveal high surface areas and thermally stable MWCNTs. The HRTEM/HRSEM micrographs confirm the formation of tangled MWCNTs with a particle size of less than 62 nm. The XRD patterns of the MWCNTs reveal the formation of a typical graphitized carbon. This study establishes the production of MWCNTs from a bi-metallic catalyst supported on kaolin.

Cooperativity and Dynamics Increase the Performance of NiFe Dry Reforming Catalysts.

The dry reforming of methane (DRM), i.e., the reaction of methane and CO2 to form a synthesis gas, converts two major greenhouse gases into a useful chemical feedstock. In this work, we probe the effect and role of Fe in bimetallic NiFe dry reforming catalysts. To this end, monometallic Ni, Fe, and bimetallic Ni-Fe catalysts supported on a MgxAlyOz matrix derived via a hydrotalcite-like precursor were synthesized. Importantly, the textural features of the catalysts, i.e., the specific surface area (172-178 m2/gcat), pore volume (0.51-0.66 cm3/gcat), and particle size (5.4-5.8 nm) were kept constant. Bimetallic, Ni4Fe1 with Ni/(Ni + Fe) = 0.8, showed the highest activity and stability, whereas rapid deactivation and a low catalytic activity were observed for monometallic Ni and Fe catalysts, respectively. XRD, Raman, TPO, and TEM analysis confirmed that the deactivation of monometallic Ni catalysts was in large due to the formation of graphitic carbon. The promoting effect of Fe in bimetallic Ni-Fe was elucidated by combining operando XRD and XAS analyses and energy-dispersive X-ray spectroscopy complemented with density functional theory calculations. Under dry reforming conditions, Fe is oxidized partially to FeO leading to a partial dealloying and formation of a Ni-richer NiFe alloy. Fe migrates leading to the formation of FeO preferentially at the surface. Experiments in an inert helium atmosphere confirm that FeO reacts via a redox mechanism with carbon deposits forming CO, whereby the reduced Fe restores the original Ni-Fe alloy. Owing to the high activity of the material and the absence of any XRD signature of FeO, it is very likely that FeO is formed as small domains of a few atom layer thickness covering a fraction of the surface of the Ni-rich particles, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites.

Low-temperature grafting of carbon nanotubes on carbon fibers using a bimetallic floating catalyst

The degradation mechanism of CFs experiencing the catalytic growth of CNTs on their surface through high-temperature CVD was revealed using microstructural analysis. Catalysts nanoparticles, if their energy was high enough to diffuse into CFs, generated micro-voids in CFs and reduced their tensile strength. Herein, we report a new low-temperature processing route to grow CNTs on CF surfaces without mechanically degrading the CFs. The use of a Ni–Fe bimetallic catalyst was key to achieving the growth of CNTs at low temperature, e.g., 500°C. Catalyst diffusion into the CFs during CVD was inhibited at this temperature, which facilitated uniform growth of CNTs on only the CF surfaces and minimized internal structural changes of the CFs.

Decomposition of methane over alumina supported Fe and Ni–Fe bimetallic catalyst: Effect of preparation procedure and calcination temperature

Catalytic decomposition of methane has been studied extensively as the production of hydrogen and formation of carbon nanotube is proven crucial from the scientific and technological point of view. In that context, variation of catalyst preparation procedure, calcination temperature and use of promoters could significantly alter the methane conversion, hydrogen yield and morphology of carbon nanotubes formed after the reaction. In this work, Ni promoted and unpromoted Fe/Al2O3 catalysts have been prepared by impregnation, sol–gel and co-precipitation method with calcination at two different temperatures. The catalysts were characterized by X-ray diffraction (XRD), N2 physisorption, temperature programmed reduction (TPR) and thermogravimetric analysis (TGA) techniques. The catalytic activity was tested for methane decomposition reaction. The catalytic activity was high when calcined at 500°C temperature irrespective of the preparation method. However while calcined at high temperature the catalyst prepared by impregnation method showed a high activity. It is found from XRD and TPR characterization that disordered iron oxides supported on alumina play an important role for dissociative chemisorptions of methane generating molecular hydrogen. The transmission electron microscope technique results of the spent catalysts showed the formation of carbon nanotube which is having length of 32–34nm. The Fe nanoparticles are present on the tip of the carbon nanotube and nanotube grows by contraction–elongation mechanism. Among three different methodologies impregnation method was more effective to generate adequate active sites in the catalyst surface. The Ni promotion enhances the reducibility of Fe/Al2O3 oxides showing a higher catalytic activity. The catalyst is stable up to six hours on stream as observed in the activity results.