Ni-Fe Catalysts Research Articles

Effect of lattice oxygen in Ni-Fe/Bio-char on filamentous coke resistance during CO2 reforming of tar

The catalyst deactivation resulted from filamentous coke deposition limits the application of CO2 reforming technology in solid waste gasification process. The bimetallic Ni-Fe catalysts have excellent encapsulating coke resistance in steam reforming of oxygenates tar, but the filamentous coke resistance of Ni-Fe/Bio-char in CO2 reforming of non-oxygenates tar remains unclear. To investigate the filamentous coke during CO2 reforming process, a non-oxygenates tar, toluene was select as filamentous coke precursor in CO2 reforming experiment. Based on the comparison between Ni/Bio-char and Ni-Fe/Bio-char, the effect of lattice oxygen in on filamentous coke resistance was explored. During CO2 reforming experiment, Ni-Fe/Bio-char showed higher hydrogen conversion (48.90–56.33%) and carbon conversion (53.57–62.94%) than Ni/Bio-char. Besides, the iron sites in the Ni-Fe oxide can be converted to iron oxide under CO2 atmosphere, providing more lattice oxygen to oxidize the filamentous coke deposition on catalysts surface. However, the lattice oxygen in Ni-Fe/Bio-char was rapidly consumed by the oxidation of massive filamentous coke, resulting in 21% of filamentous coke still accumulated on Ni-Fe/Bio-char. Overall, in addition to the oxidation capacity of filamentous coke, the inhibition ability to filamentous coke formation is critical to the filamentous coke resistance of catalyst in CO2 reforming of tar. The obtained results can provide a reference for the design of catalyst applied in CO2 reforming.

Study on Bimetallic Catalysts for Carbon Nanotube Growth on the Surface of Continuous Carbon Fibres

We investigated the influence of bimetallic catalysts with various compositions on the growth of carbon nanotubes (CNTs) on the surface of continuous carbon fibers (CFs). The samples were analyzed and characterized by scanning electron microscopy, transmission electron microscopy, and Raman spectrometry. The catalyst plays an essential role in the catalytic chemical vapor deposition of CNT. The performance of these catalysts was estimated referenced to both catalyst and CNT morphologies, while the influences of each catalytic components were summarized according to the results. This work prepared and studied six different bimetallic catalysts composed by Cu, Fe, and Ni, and pure Fe catalyst was employed as a control group. Fe and Ni have been widely studied, while the reports of catalysts containing Cu are rare. We found that pure Fe catalyst leads to banded and clustered CNT distribution, and the addition of Cu can provide uniform and slender CNTs. The efficiency of catalyst can be significantly increased by adding Ni, producing CNTs as well as superfluous amorphous carbon. We determined that bimetallic catalyst can utilize multiple catalytic abilities of various metals by adjusting its composition, which can contribute to obtaining high-quality CNTs on CF surface.

Multi-functional, high-performing fuel electrode for dry methane oxidation and CO2 electrolysis in reversible solid oxide cells

Intermittency of renewable energy sources can be profitably faced using efficient energy storage systems. Reversible solid oxide cells (RSOCs) able to operate with carbon-containing species are likely among the most appealing choices. Energy can be obtained by natural gas and/or biogas (SOFC mode), with useful recovery of CO2 in the exhausts. Besides, if the electrode is also active towards CO2 electrolysis (SOEC mode), CO2 is reduced to CO and O2. In this work a composite material with in-situ formed Ni-Fe alloy catalyst consisting of La1.2Sr0.8Fe0.6Mn0.4O4 Ruddlesden-Popper perovskite and Ni-Ce0.85Sm0.15O2-δ fluorite was developed as a multi-functional fuel-electrode for RSOCs. The composite electrode was tested in SOFC mode as anode for hydrogen, dry methane and carbon monoxide oxidation and showed power density outputs of 657, 668 and 527 mW/cm2 at 850 °C, respectively, together with redox stability and coking tolerance for over 120 h. In SOEC mode, it was tested as cathode and delivered 2.66 A/cm2 at 2 V in a 95:5 CO2:CO mixture, retaining a current density of 1 A/cm2 for more than 40 h.

Enhanced hydrogen-storage properties of MgH2 by Fe–Ni catalyst modified three-dimensional graphene

High dehydrogenation temperature and slow dehydrogenation kinetics impede the practical application of magnesium hydride (MgH2) serving as a potential hydrogen storage medium. In this paper, Fe–Ni catalyst modified three-dimensional graphene was added to MgH2 by ball milling to optimize the hydrogen storage performance, the impacts and mechanisms of which are systematically investigated based on the thermodynamic and kinetic analysis. The MgH2+10 wt%Fe–Ni@3DG composite system can absorb 6.35 wt% within 100 s (300 °C, 50 atm H2 pressure) and release 5.13 wt% within 500 s (300 °C, 0.5 atm H2 pressure). In addition, it can absorb 6.5 wt% and release 5.7 wt% within 10 min during 7 cycles, exhibiting excellent cycle stability without degradation. The absorption-desorption mechanism of MgH2 can be changed by the synergistic effects of the two catalyst materials, which significantly promotes the improvement of kinetic performance of dehydrogenation process and reduces the hydrogen desorption temperature.

FeNi co-doped electrocatalyst synthesized via binary ligand strategy as a bifunctional catalyst for Zn-air flow battery

Developing low-cost and excellent performance bifunctional catalysts for Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) in rechargeable Zn-air batteries is of great significance. Recently, metal organic frameworks (MOFs)-derived electrocatalysts have been widely studied in ORR and OER due to their large specific surface area and tunable pore structure. However, it is still a challenge to prepare hierarchical porous structure catalysts via facile approach, which is desired in the device manner. Herein, we synthesized a MOF-derived FeNi co-doped catalyst (termed as B-FeNi-N/C-1000) using the binary ligand strategy with a large specific area and suitable hierarchical pore structures which efficiently improves mass transfer to boost the high device performance. As a result, the B-FeNi-N/C-1000 exhibits an outstanding ORR performance with a half potential of 0.9 V vs. RHE and a low potential of 1.62 V vs. RHE at 10 mA cm−2 in alkaline media, which exceeds FeNi catalyst (i.e., FeNi-N/C-1000) via single ligand method and commercial Pt/C + IrO2. Additionally, the B-FeNi-N/C-1000 presents a higher power density of 102 mW cm−2 and a long-term stability that only losses 2% after 95 h in the self-assembly Zn-air battery. Accordingly, this work can provide a facile method to synthesize efficient bifunctional catalyst for, but not limit to Zn-air flow batteries.

Hydrodeoxygenation of guaiacol over BEA supported bimetallic Ni-Fe catalysts with varied impregnation sequence

BEA supported Ni-Fe catalysts, prepared by various impregnation techniques, were characterised and examined for their activity for the hydrodeoxygenation (HDO) of guaiacol and hydrogenation of toluene. The aim of the study was to explore the factors affecting the formation of Ni-Fe active species and explore the relationship between the concentration of surface Ni, Ni-Fe species and HDO activity. Catalysts prepared initially with Fe, or co-currently with Fe and Ni exhibited a higher level of HDO rate compared to catalyst that was prepared with Ni initially. When a catalyst was impregnated initially with Fe, metal-supported interaction was relatively weak, thus the formation of Ni-Fe species was promoted. In contrast, a reduced number of Ni sites was involved in the formation of Ni-Fe species when the catalyst was initially impregnated with Ni, resulting in a low HDO rate. The rate of cyclohexane formation is proportional to the concentration of surface Ni-Fe over the catalysts with similar Ni and Fe loadings but prepared by different impregnation sequences. The enhanced HDO rate is attributed to the hydrogenolysis activity of Ni-Fe species. The effect of Ni/Fe ratio on HDO activity was also investigated under differential conditions and the catalyst with a Ni/Fe mass ratio of 3.3 exhibited the highest rate of cyclohexane formation.

Effect of Ni/Fe ratio in Ni–Fe catalysts prepared under external magnetic field on CO2 methanation

BackgroundThe power-to-gas (PtG) method has significant potential as a strategy for storing excess renewable energy in the form of synthetic natural gas. PtG involves the hydrogenation of CO2 to CH4 from H2 obtained from renewable energy. MethodsIn this study, Ni–Fe catalysts with different Ni/Fe ratios were prepared for high-efficiency CO2 methanation using chemical reduction with an external magnetic field. The Ni–Fe catalysts were characterized by XRD, inductively coupled plasma, and SEM-EDS measurements, and their performance and chemical properties were measured by H2 temperature programmed reduction experiments. Significant findingsThe catalyst with the best performance for CO2 methanation had a ratio of Ni to Fe of 8/2 (Ni8Fe2). The Ni8Fe2 catalyst could convert over 80% of CO2 to methane at 150 °C. In addition, the CH4 selectivity of CO2 methanation was 95% when the reaction conditions were controlled at H2/CO2 = 4 and GHSV ∼1000 h−1. The low cost and simple preparation of these Ni–Fe catalysts have high potential for future commercialization.

Polyol-pretreated SBA-16 supported Ni-Fe bimetallic catalyst applied in CO methanation at low temperature

• Polyols were used to pretreat the mesoporous silica molecular sieve SBA-16 to adjust the surface groups. • Bimetallic Ni-Fe catalysts with polyol-pretreated support were obtained. • The mechanism of how the polyols influence the surface SiOH groups and thus the metal particles distribution was figured out. • Catalysts with polyol-pretreated support lowered the minimum temperature for CO complete conversion to 230 °C from 290 °C. Polyols were used to pretreat the mesoporous silica molecular sieve SBA-16 and thus supported bimetallic Ni-Fe catalyst was prepared in order to address the low activity of CO methanation at lower temperature. The characterization of the pretreated support and catalysts indicated that the residual polyols release heat during combustion, which could provide energy for the decomposition of metal precursors, lowering the decomposition temperature and reducing the metal particle size. More importantly, the pretreatment of support with polyols could increase the isolated silicon hydroxyl, and strengthen the metal-support interaction, thus obtaining smaller metal particles. The smaller metal particles promoted the dissociation of reactant gas, as a result, Ni-Fe bimetallic catalyst with polyol-pretreated support could lower the minimum temperature for CO complete conversion from 290 °C to 230 °C while keeping CH 4 selectivity above 90%. Catalysts with polyol-pretreated support provide a new possibility for low-temperature CO methanation technology.

Selective aqueous phase hydrogenation of xylose to xylitol over SiO2-supported Ni and Ni-Fe catalysts: Benefits of promotion by Fe

A monometallic Ni and a bimetallic Ni-Fe catalyst were used in the aqueous phase hydrogenation of xylose in batch conditions (T = 50–150 °C, PH2 = 10–30 bar, xylose mass fraction in water = 3.7–11.0 wt.%) to evidence the benefits of promoting Ni by Fe. The activity of the catalysts increased with temperature, but a temperature of 80 °C allowed minimizing nickel leaching at full conversion. The presence of reduced Fe at the surface of the bimetallic nanoparticles increased both the first-order apparent rate constant and the adsorption constant of xylose. The catalytic activity of Ni/SiO2 strongly declined and no deactivation was found for the Ni-Fe catalyst. A restructuring of the bimetallic nanoparticles took place, as the size of the metal particles and the Fe proportion in the surface layers increased, suggesting a flattening and coalescing of the particles over the silica surface.

Activated char supported Fe-Ni catalyst for syngas production from catalytic gasification of pine wood

Char-based catalyst has a promising application for biomass thermal conversion technology. In this work, Fe-Ni/Activated Char (AC) catalyst was prepared by impregnation method and used for the catalytic gasification of pine wood to obtain syngas. Further, the catalytic performance of Fe-Ni/AC was established by doing a comparative study of catalytic gasification of different biomass feedstocks. The results showed that under the catalysis of Fe-Ni/AC, the increase of gasification temperature was beneficial to increase gas yield, but not conducive to regulate the H2/CO ratio of syngas. The steam flow rate was directly related to the catalytic effect of Fe-Ni. The H2/CO ratio of syngas could reach 1.97 under the optimal conditions. Fe-Ni/AC had different catalytic effects on different biomass feedstocks, with the best for pine wood and the worst for cotton stalk, indicating that gasification intermediates of pine wood were difficult to decompose and depended more on catalyst.

Bed packing configuration and hot-spot utilization for low-temperature CO2 methanation on monolithic reactor

The revival of CO2 methanation (Sabatier reaction) as part of the large-scale Power-to-Gas technology has stimulated the development of novel reactor concepts for better heat management due to its exothermic nature. The generation of hot-spots in fixed bed reactors could reduce methane yield, accelerate catalyst deactivation, and potentially cause thermal runaway. However, hot-spots could be utilized to achieve outstanding CO2 methanation performance at low temperatures and high gas flow rate in monolithic reactors, whereas strategic bed packing configurations could boost the performance of low-activity catalytic beds. We prepared NiFe catalysts derived from in-situ grown layered double hydroxides via urea hydrolysis on washcoated cordierite honeycomb substrate with varying activities. Temperature profiles by both experimental and computational fluid dynamic (CFD) studies revealed hot-spot formation along catalytic beds. Hot-spots increased the catalytic beds’ temperature due to high thermal conductivity of cordierite monolith, thus accelerated the reaction. The monolithic reactor with a single-monolith bed exhibited a methane yield of 16.5% at 250 °C, which was significantly increased to 80.4% on the reactor with three-monolith bed of the same catalyst at similar reaction condition with a constant ratio of catalyst mass to gas flow rate. A combined low-high activity monolithic bed was proposed which demonstrated high methane yield and excellent stability. Interestingly, the methane yields were higher at a gas flow rate of 1500 mL/min than that at 500 mL/min, again ascribed to the beneficial effect of hot-spot formation on monolithic reactors. Therefore, strategic bed packing configuration plays an important role in the optimization of monolithic methanation reactors, and hot-spot formation could be exploited to achieve excellent CO2 methanation performance at low temperatures.

Clean and stable conversion of oxygen-bearing low-concentration coal mine gas by solid oxide fuel cells with an additional reforming layer

Direct power generation using low-concentration coal mine gas (LC-CMG, < 30% CH4) by solid oxide fuel cells (SOFCs) is an attractive approach for the clean and efficient utilization of abundant LC-CMG resources. In this study, Ni–Fe alloy catalyst from in situ decomposition of NiFe2O4 oxide is used to promote the electrochemical performance, efficiency and robustness of SOFCs using simulated LC-CMG as fuel. The modified SOFC is fed with humidified H2 and CH4–N2 in sequence and exhibits high electrochemical performance. There is only a slight performance drop from 783 to 660 mW cm−2 when adding O2 in humidified CH4–N2 fuel. The operation of all cells with different concentrations of LC-CMG is quite stable during over 100-h tests and no coking is found on the entire anode and Ni–Fe alloy catalyst, suggesting the cell with superior resistance to coking. Besides, a heterogeneous reaction model is established to reveal the anti-carbon effect of the Ni–Fe catalyst. Our findings indicate the great application potential of direct power generation from LC-CMG by SOFCs with an additional reforming layer.

Surface structure regulation and evaluation of FeNi-based nanoparticles for oxygen evolution reaction

FeNi-based catalyst is very promising for oxygen evolution reaction (OER) in practical water electrolysis for hydrogen generation. Herein, we found the catalytic performance of FeNi nanoparticles, as proof of concept, for OER can be optimized via surface structure regulation by rational thermal oxidation and/or reduction approaches. Surface structure of FeNi pre-catalyst in a fully oxidized or metallic state is not active while proper synergism of these states is favorable as supported by some spectroscopic techniques and electrochemical measurements. The as-optimized FeNi catalyst requires only 230 mV overpotentials to offer 10 mA cm−2, with faster catalytic kinetics, good stability and high active site efficiency. The efficient high valence state of Fe/Ni species synergism generated from the optimized FeNi pre-catalyst is revealed by the post and in-situ Raman spectrum analysis. The results could answer the varied performance of FeNi reported for OER and are also instructive for their performance optimization.

Are Ni/ and Ni5Fe1/biochar catalysts suitable for synthetic natural gas production? A comparison with γ-Al2O3 supported catalysts

Among challenges implicit in the transition to the post–fossil fuel energetic model, the finite amount of resources available for the technological implementation of CO2 revalorizing processes arises as a central issue. The development of fully renewable catalytic systems with easier metal recovery strategies would promote the viability and sustainability of synthetic natural gas production circular routes. Taking Ni and NiFe catalysts supported over γ-Al2O3 oxide as reference materials, this work evaluates the potentiality of Ni and NiFe supported biochar catalysts for CO2 methanation. The development of competitive biochar catalysts was found dependent on the creation of basic sites on the catalyst surface. Displaying lower Turn Over Frequencies than Ni/Al catalyst, the absence of basic sites achieved over Ni/C catalyst was related to the depleted catalyst performances. For NiFe catalysts, analogous Ni5Fe1 alloys were constituted over both alumina and biochar supports. The highest specific activity of the catalyst series, exhibited by the NiFe/C catalyst, was related to the development of surface basic sites along with weaker NiFe–C interactions, which resulted in increased Ni0:NiO surface populations under reaction conditions. In summary, the present work establishes biochar supports as a competitive material to consider within the future low-carbon energetic panorama.

Synthesis of modified char-supported Ni–Fe catalyst with hierarchical structure for catalytic cracking of biomass tar

The ubiquitous challenge of tar problem has limited the further development of biomass pyrolysis/gasification. In view of this, the directional construction of modified char-supported Ni–Fe catalyst by hydrothermal carbonization followed by heat treatment to strengthen tar cracking was reported in this study. At the optimized temperature of 700 °C for catalytic cracking, the corresponding tar conversion efficiency of catalyst appeared to be 95.46% with the superior catalytic performance of tar. With the presence of such catalyst, the relative content of polycyclic aromatic hydrocarbon (PAH) compounds in residue tar was drastically reduced due to the high activity of Ni–Fe alloy active phases for the cleavage of tar macromolecules. The hierarchical pore structure derived from the dense carbon nanofiber shell layer and porous carbon core reduced the resistance of tar macromolecules diffusion and promoted the contact with metallic active sites. The Fe atoms enriched on the surface of Ni–Fe alloy with a high oxygen affinity promoted the catalytic cracking reaction of tar. The coated metallic active sites with multi-layer graphitic carbon prevented the catalyst from deactivation and sintering. The results are expected to establish the theory foundation and construction method of char-supported Ni–Fe catalyst for tar catalytic cracking in the industry.

Isolating the Electrocatalytic Activity of a Confined NiFe Motif within Zirconium Phosphate

AbstractUnique classes of active‐site motifs are needed for improved electrocatalysis. Herein, the activity of a new catalyst motif is engineered and isolated for the oxygen evolution reaction (OER) created by nickel–iron transition metal electrocatalysts confined within a layered zirconium phosphate matrix. It is found that with optimal intercalation, confined NiFe catalysts have an order of magnitude improved mass activity compared to more conventional surface‐adsorbed systems in 0.1 m KOH. Interestingly, the confined environments within the layered structure also stabilize Fe‐rich compositions (90%) with exceptional mass activity compared to known Fe‐rich OER catalysts. Through controls and by grafting inert molecules to the outer surface, it is evidenced that the intercalated Ni/Fe species stay within the interlayer during catalysis and serve as the active site. After determining a possible structure (wycherproofite), density functional theory is shown to correlate with the observed experimental compositional trends. It is further demonstrated that the improved activity of this motif is correlated to the Fe and water content/composition within the confined space. This work highlights the catalytic enhancement possibilities available through zirconium phosphate and isolates the activity from the intercalated species versus surface/edge ones, thus opening new avenues to develop and understand catalysts within unique nanoscale chemical environments.

Sodium-Mediated Bimetallic Fe–Ni Catalyst Boosts Stable and Selective Production of Light Aromatics over HZSM-5 Zeolite

Conversion of syngas into aromatics via the Fischer–Tropsch (FT) route provides a promising way to supply the value-added chemicals. However, it is still a great challenge to achieve controllable a...

N-Doped Graphene-Supported Diatomic Ni–Fe Catalyst for Synergistic Oxidation of CO

Polynary single-atom structures can provide synergistic functions based on multiple active sites and reactants, which significantly improve their catalytic performance. However, the structure–activ...

Synergistic effects altering reaction pathways: The case of glucose hydrogenation over Fe-Ni catalysts

Carbon black (CB) supported Ni, Fe, or Fe-Ni alloy catalysts were synthesized by sol-gel to elucidate the reaction pathways over each catalyst, as well as synergistic effects in glucose to sorbitol hydrogenation. The bimetallic materials presented small and alloyed nanoparticles that were richer in reduced metallic sites at the surface than their monometallic counterparts. Glucose isomerization to fructose was favoured over Fe/CB, while glucose hydrogenation to sorbitol is the dominating pathway over Ni/CB catalyst. By contrast, sorbitol production was promoted and undesired isomerization was suppressed when Fe and Ni formed a nanoalloy. In addition, the alloy catalyst presented better stability than the corresponding monometallic catalyst. A comparison with a mechanical mixture of Fe/CB and Ni/CB monometallic catalysts demonstrated the synergy at the nanoscale in the alloy. By comparing different Fe:Ni ratios, the 1:1 formulation was identified as the best compromise to achieve a high activity while maintaining high sorbitol selectivity.

Catalytic waste Kraft lignin hydrodeoxygenation to liquid fuels over a hollow Ni-Fe catalyst

Conversion of Kraft lignin (KL) into liquid fuels is critically attractive but hampered by the inherent recalcitrant structure of KL. The phenolic intermediates formed during depolymerization of KL are prone to rapid repolymerization generating undesired repolymerization products (heavy oil and/or coke). In this work, KL depolymerization coupled with demethoxylation was achieved via a novel hollow Ni-Fe (H-NiFe2O4) catalyst under mild conditions. The liquid product yield reached 90 wt% with minimum coke yield of 3.4 wt% at 320 °C for 24 h. The petroleum ether soluble product has a yield of 70 wt%, molecular weight of 222 g/mol and a HHV of 35.3 MJ/kg. The H-NiFe2O4 catalyst exhibited excellent activity in promoting lignin depolymerization while depressing condensation. The meticulous characterization and control experiments indicated the catalytic performance of H-NiFe2O4 benefits from the synergy of Ni and Fe. Additionally, plausible reaction pathways of KL depolymerization over H-NiFe2O4 are discussed.