Fe Loadings Research Articles

CeO2-Supported Single-Atom Cu Catalysts Modified with Fe for RWGS Reaction: Deciphering the Role of Fe in the Reaction Mechanism by In Situ/Operando Spectroscopic Techniques.

Reverse water-gas shift (RWGS) reaction has attracted much attention as a potential approach for CO2 valorization via the production of synthesis gas, especially over Fe-modified supported Cu catalysts on CeO2. However, most studies have focused solely on investigating the RWGS reaction over catalysts with high Cu and Fe loadings, thus leading to an increase in the complexity of the catalytic system and, hence, preventing the gain of any reliable information about the nature of the active sites and reaction mechanism. In this work, a CeO2-supported single-atom Cu catalyst modified with iron was synthesized and evaluated for the RWGS reaction. The catalytic results reveal a significant synergistic effect between CuCeO2 and Fe, demonstrating an activity up to three times higher than the combined catalytic activities of monometallic catalysts (Fe/CeO2 + CuCeO2) under identical conditions. Various ex situ and in situ/operando techniques are employed to unveil the concealed role of Fe in catalyst activity enhancement. The combined findings from hydrogen temperature-programmed reduction (H2-TPR) and operando electron paramagnetic resonance spectroscopy (EPR) reveal that the added Fe predominantly interacts with Cu-containing surface sites, resulting in the stabilization of higher proportions of Cu single sites. Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and operando EPR results unveil a synergistic interplay of Fe with Cu-containing sites and CeO x domains, efficiently enhancing both the reoxidation of Cu+ in Cu+-Ov-Ce3+ moieties and the reducibility of Ce4+ in CeO x domains under RWGS conditions. Detailed mechanistic studies reveal that the RWGS reaction predominantly proceeds via the redox mechanism.

Catalytic CO2 hydrogenation to hydrocarbon fuels in a potassium ion-conducting reactor

The electrochemically assisted CO2 hydrogenation directly to hydrocarbon fuels was studied, apparently for the first time, over a cheap, widespread and non-precious Fe catalyst in a potassium ion conducting (K-β-Al2O3) reactor, under atmospheric pressure, at relatively low temperatures and using representative concentrated CO2 and H2 gas mixtures and an easily scalable tubular catalyst-electrode configuration. The Fe electrocatalytic film was deposited by dip-coating on a commercial K-β-Al2O3 candle and characterized, both as prepared and after activation and testing, by TPR, TGA, XPS, XRD and SEM-EDX. The optimum operating conditions for both Fe activation (300 ºC, 75% H2, 24 hours) and electropromoted CO2 hydrogenation (300 ºC, 1.5 V, H2/CO2=3) were identified. Long-term tests on electrochemically promoted CO2 hydrogenation to hydrocarbons were performed under selected operating conditions to assess electrocatalyst stability. Both the selectivity to the target product (C5+ hydrocarbons) and the stability of the catalyst can be tuned in situ by modifying the potassium surface coverage via electrochemical pumping of potassium ions through the applied polarization. Finally, as an attempt to improve the catalyst-electrode behaviour, powdered catalysts, based on iron nanoparticles dispersed on KVO3 (a K+ and e- co-conductor) with different Fe loadings (17 and 9 wt%) were prepared and comparatively studied for CO2 hydrogenation to hydrocarbons. The catalyst with higher Fe loading was selected as the most promising, in terms of activity, selectivity and stability, for further catalyst-electrode optimisation by deposition, via dip-coating, of a Fe-KVO3 film on the K-β-Al2O3 candle.

Investigation of iron oxide supported on activated coke for catalytic reduction of sulfur dioxide by carbon monoxide

In view of the low utilization rate of by-product in limestone-gypsum wet flue gas desulfurization process, a method of catalytic reduction of SO2 to elemental sulfur was proposed. In this work, supported iron catalyst using activated coke as supporter was prepared and characterized. Moreover, the performance of SO2 reduction using CO as reducing agent at various Fe loadings, temperatures, gaseous hourly space velocities and CO/SO2 molar ratios was studied. Research shows that, compared with other metals, the highest catalytic activity is achieved over Fe-based catalyst. The iron sulfide is the main active component during the catalytic reduction reaction, hence the catalyst needs to be presulfided before use. The micropores of activated coke become more abundant after loading Fe, whereas excessive increase of Fe loading may bloke the mesopores and weaken the catalytic activity. Higher reaction temperature, lower GHSV and a stoichiometric molar ratio are conducive to the improvement of SO2 conversion and S yield. The catalytic performance at lower temperatures was further improved by loading Co. When the Co loading is 4 wt%, the SO2 conversion rate reaches 90.9% at 400 °C because loading Co enhances the redox performance of the catalyst surface. The findings are instructive for the development of cost-effective carbon-based catalysts for resource recovery of sulfur.

Cluster-Spin-Glass Magnetic Behavior and Morphology in the Coordination Polymer Alloys FeyCo1-yBTT.

We report the synthesis of a series of pseudo-1D coordination polymer (CP) materials with the formula FeyCo1-yBTT (BTT = 1,3,5-benzenetrithiolate). These materials were structurally characterized by PXRD Rietveld, EXAFS, and PDF analyses, revealing that the CP superstructure enables a continuous and isomorphous alloy between the two homometallic compounds. Lower Fe loadings exhibit emergent spin glass magnetic behavior, such as memory effects and composition-dependent spin glass response time constants ranging from 6.9 × 10-9 s to 1.8 × 10-6 s. These data are consistent with the formation of spin clusters within the lattice. The magnetic behavior in these materials was modeled via replica exchange Monte Carlo simulation, which provides a good match for the experimentally measured spin glassing and magnetic phase transitions. These findings underscore how the rigid superstructure of CP and MOF scaffolds can enable the systematic tuning of physical properties, such as the spin glass behavior described here.

On the reduction of NiFe/Al2O3 oxygen carrier in high-pressure chemical looping applications

Chemical looping represents a promising technology with various applications ranging from clean power production to alternative syngas production. In this work, two oxygen carriers with different Ni loadings (4.3% wt. and 12% wt.) and similar Fe loadings (9.9% wt. and 8.5% wt.) are synthesized through a co-precipitation/impregnation route and tested in two thermogravimetric analyzers. Firstly, the effect of temperature (700–900 °C) on the oxygen transport capacity and reduction conversion of both materials is assessed at ambient pressure (0.5 nl/min with 20% H2/N2). The influence of material loading is also studied, and it is shown that higher Ni loadings provide a significant improvement in material activity. A complete reduction conversion is achieved at 900 °C and ambient pressure. At high pressure (10–20 bar), tests are carried out in a temperature range of 700–850 °C. The effect of flow rate (2 nl/min to 6 nl/min with 50% H2/N2) is first assessed to prevent external mass transfer limitations. Higher total pressures have a negative effect on reduction kinetics, while higher Ni loadings demonstrate increased final reduction conversion also at high pressure, reaching about 75% conversion after 20 min. The long-term cyclability of the material is also investigated both at low (100 cycles) and high pressure (80 cycles) conditions and a conversion gain is observed throughout the cycles in both cases. No changes in the material microstructure are observed after 80 high-pressure cycles.

Nalidixic Acid and Fe(II)/Cu(II) Coadsorption at Goethite and Akaganéite Surfaces.

Interactions between aqueous Fe(II) and solid Fe(III) oxy(hydr)oxide surfaces play determining roles in the fate of organic contaminants in nature. In this study, the adsorption of nalidixic acid (NA), a representative redox-inactive quinolone antibiotic, on synthetic goethite (α-FeOOH) and akaganéite (β-FeOOH) was examined under varying conditions of pH and cation type and concentration, by means of adsorption experiments, attenuated total reflectance-Fourier transform infrared spectroscopy, surface complexation modeling (SCM), and powder X-ray diffraction. Batch adsorption experiments showed that Fe(II) had marginal effects on NA adsorption onto akaganéite but enhanced NA adsorption on goethite. This enhancement is attributed to the formation of goethite-Fe(II)-NA ternary complexes, without the need for heterogeneous Fe(II)-Fe(III) electron transfer at low Fe(II) loadings (2 Fe/nm2), as confirmed by SCM. However, higher Fe(II) loadings required a goethite-magnetite composite in the SCM to explain Fe(II)-driven recrystallization and its impact on NA binding. The use of a surface ternary complex by SCM was supported further in experiments involving Cu(II), a prevalent environmental metal incapable of transforming Fe(III) oxy(hydr)oxides, which was observed to enhance NA loadings on goethite. However, Cu(II)-NA aqueous complexation and potential Cu(OH)2 precipitates counteracted the formation of ternary surface complexes, leading to decreased NA loadings on akaganéite. These results have direct implications for the fate of organic contaminants, especially those at oxic-anoxic boundaries.

Elucidating the role of Fe-Mo interactions in the metal oxide precursors for Fe promoted Mo/ZSM-5 catalysts in non-oxidative methane dehydroaromatization

Literature shows that adding Fe as a separate phase to MoO3/ZSM-5 catalysts can improve benzene selectivity in methane dehydroaromatization (MDA), but only when added in small quantities, making it difficult to characterize the state of Fe in the catalyst and understand the role of Fe-Mo interactions on the catalytic properties. Here, we explore how the nature of the Mo-Fe interactions in the catalyst precursor can influence the stability and product selectivity in MDA, by employing for the first time Fe2(MoO4)3/ZSM-5 as a catalyst precursor in MDA. We have compared the activity of Fe2(MoO4)3/ZSM-5 with monometallic MoO3/ZSM-5 and mixed MoO3 + Fe2O3/ZSM-5 containing equivalent Mo and Fe loadings and found that Fe2(MoO4)3/ZSM-5 shows higher benzene selectivity than the mixed MoO3 + Fe2O3/ZSM-5 catalyst and exhibits higher stability in reaction compared to the monometallic MoO3/ZSM-5 catalyst. Structural characterization suggests that Fe2(MoO4)3 partially segregates to Fe2O3 and amorphous MoOx during thermal pretreatment. The MoOx species migrate into the zeolite channels during pretreatment, while Fe oxides remain on the external surface of the zeolite. Gas adsorption/desorption techniques and density functional theory calculations demonstrate that the preexisting Fe2O3 phases on the external surface of the zeolite in the mixed MoO3 + Fe2O3/ZSM-5 precursor trap (MoO3)3 clusters preventing them from migrating into the zeolite channels during pretreatment, whereas gradual formation of amorphous MoOx together with the segregation of the Fe2O3 phase when using the Fe2(MoO4)3 precursor diminishes trapping of (MoO3)3 and consequently enhances migration and anchoring of the MoOx species in the zeolite channels, boosting selectivity to benzene. Characterization of used catalysts suggests that the presence of Fe promotes formation of structured carbon nanofibers which reduce the rate of catalyst deactivation.

(Digital Presentation) Finding the Optimum Loading of Fe & Au in NiO/GDC, for the Reversible Operation of Solid Oxide Cells

Reversible solid oxide cells (rSOCs) are ideal candidates for renewable energy storage and usage, due to their ability to work under electrolysis mode for H2 production or fuel cell mode for power generation, both by the same unit. Operation of SOCs at high-temperatures enables high energy efficiency, increases reaction rates, and allows the use of low-cost catalysts compared to low temperature technologies. The state-of-the-art (SoA) fuel electrodes: Ni/YSZ and Ni/GDC, despite their advantages, are prone to various degradation phenomena, such as Ni coarsening, agglomeration, and depletion/migration. One way to mitigate these issues is by dispersing small amounts of transition metal additives, either non-noble or noble elements, into the Ni-based electrode [1, 2, 3].Recent studies [1] on how Fe interacts with Ni in Ni/GDC showed that the enhancing effect of Fe on the electrochemical performance under electrolysis conditions is constrained by its wt.% concentration, whereas even if the electrode exhibited high activity, it was prone to fast degradation. In our latest work, we presented a first attempt on co-depositing Fe and Au, with the primary objective being the stabilization of the enhancing effect of Fe on Ni/GDC. Thus, an electrode consisted of the, by that time, best performing loadings was synthesized, namely 0.5 wt.% Fe and 3 wt.% Au, showcasing the enhancing effect of this modification on both the activity and stability, under rSOC operation. The superiority of this electrode is primarily ascribed to the induced changes by the Fe-Au-modification on the intrinsic electrochemical characteristics, as indicated by the ohmic and polarization resistance values. These are far lower to those of Ni/GDC and of the optimum Au-Mo-modified electrode [3], particularly under SOE operation. Another remark is the rSOC stability of both electrochemical characteristics, but especially of the Rpol .The presented study focuses on how each of the Au and Fe modifiers affects the physicochemical and electrochemical characteristics of the electrode. In this respect, several electrocatalysts were synthesized, consisted of different Au and Fe loadings, and then evaluated under r-SOC operation. By reducing the Au concentration to 1 wt.%, the performance of the electrode increased, which is attributed mainly to the lower Rohm values, and less to these of Rpol that remain practically constant. On the other hand, by increasing the Fe loading to 2 wt.% and by keeping the Au loading to 3 wt.%, the electrode had the same initial performance, but after three rSOC cycles the performance slightly dropped, due to the increase of both Rohm and Rpol values. In parallel to the electrochemical measurements, physicochemical characterization is performed for further elucidation of the electrodes/powders properties.

Impact of Fe(II) on 99Tc diffusion behavior in illite

A comprehensive understanding of the geochemical behavior of 99Tc is of great importance for safe disposal of radioactive waste and remediation of contaminated environmental sites. Illite is one of the most common constituents of clay rocks, and thus used in this work as a model system for studying the retention and transport of 99Tc in clay-rich systems. In this study, a through-diffusion technique was applied to investigate the diffusion behavior of Tc in compacted illite clay under oxic and anoxic conditions. Particular focus of this investigation was on the role of Fe(II) on the redox state and mobility of Tc in clay. As the diffusion cells contained stainless steel filters for confining the clay plug, 99Tc-diffusion in the filters was assessed first, followed by 99Tc diffusion in the illite column with or without Fe-loading. Two types of Fe(II) loadings in illite were considered, surface complexed Fe(II) on illite edge sites and Fe(II) added as pyrite grains. COMSOL Multiphysics was used to analyze the diffusion data. The measured filter porosity was about 0.2 and the effective diffusion coefficient, De, for Tc (as TcO4−) in the filter was 0.59 × 10−10 m2/s. Tc diffusion in illite under ambient conditions showed a typical anion diffusion behavior with De in the range 0.38-0.44 × 10−10 m2/s and the anion accessible porosity ε of approximately 0.2. In the presence of Fe(II), De for Tc migration in illite was one order of magnitude lower, showing that Fe(II) has a significant effect on the migration of 99Tc. Analysis of the Tc distribution in the system suggests that most Tc was retarded at the filters, especially the ones connected to the high concentration reservoir. The remaining Tc quantities were immobilized at sample boundaries next to the filters with higher concentrations observed in the domains close to the reservoirs. Almost no Tc was immobilized in the middle part of the sample, where the Fe(II) was preloaded. This observation contradicts the anticipation, because Tc was expected to be immobilized in the middle of the sample preloaded with Fe(II). A possible explanation is that a delocalized redox reaction may occur, which means that electrons from the oxidation of the preloaded Fe(II) in the central part of the cell are transferred to the filter via the walls of the steel diffusion cell. Tc reacts with the electrons in the filter at a relative slow rate, which results in most of the Tc retarded in the filter, while some small amounts of it may diffuse through the clay.

Enhanced syngas production from waste lubricant oil reforming with transition metal catalysts

Waste lubricant oil (WLO) which is a spent oil from vehicles, and machinery is often incinerated or landfilled, leading to environmental pollution and heavy metal-contaminations. At the same time WLO can converted to synthesis gas using steam reforming. In this study, catalytic steam reforming of WLO was performed in a micro fixed bed reactor at atmospheric pressure. Ni and Fe metals were loaded in a ratio of 5% and 10% on dolomite and olivine catalysts through impregnation method. The effects of equivalent ratio (ER) and metal (Ni and Fe) loadings on dolomite and olivine supported catalysts were investigated. Carbon-hydrogen conversions were significantly affected by ER with the optimum data at 0.88, which resulted in low CH4, and high H2 and CO. Nonetheless, the 5%Ni/dolomite exhibited superior overall activity with the highest overall conversion and hydrogen yield. In this case, hydrogen and carbon conversions were 65.71% and 66.38%, respectively, while H2 to CO molar ratio was 1.05 and the lower heating value was 6.76 MJ/m3. Hence, this suggests that the surface-active site of Ni on dolomite has high activity for C–C cleavage and water gas shift reaction. The conversion to H2 and CO was improved through methane and hydrocarbon steam reforming on the catalyst surface. Catalytic reforming of WLO not only enhanced synthesis gas generation which can be readily used as energy, a partial source of H2 or chemical feedstock but also as an appealing, sustainable, and economical waste management alternative.

Green synthesis of Cu-Mo promoted Fe catalyst for production of the gaseous and liquid fuels through Fischer-Tropsch synthesis

Designing a novel Fe catalyst with improved selectivity to light olefins and heavier hydrocarbons attracts great attention for Fischer-Tropsch synthesis (FTS) as an alternative clean energy resource. In this work, a highly efficient Cu-Mo promoted Fe catalysts supported on activated carbon with engineered features from biomass were synthesized and tested for FTS under relevant industrial conditions (300 °C, 2 MPa, and 2000 h−1). Optimization of the Fe, Mo, and Cu loadings led to a significant increase in CO conversion (from 46.7% for unpromoted to 78.8% for Cu-Mo promoted catalysts). Light olefin selectivity for the promoted catalysts was remarkably enhanced to 33.2% and 25.0% for Cu and Mo-promoted catalysts, respectively. The improved selectivity to light olefin can be attributed to the weakened basicity of iron sites for promoted catalysts. Improved C5+ selectivity on the other hand, can be assigned to the contribution of Fe carbides with higher C:Fe ratio in the structure of the optimized catalyst. The presence of Mo carbides was confirmed by XPS, XRD, and XANES results, manifesting the contribution of Mo in the catalytic activity of the optimized catalyst. The superior selectivity to both light olefins and C5+ hydrocarbons disclosed that the prepared catalyst could be an ideal candidate for industrial iron-based FTS catalyst in future to modulate the products distribution.

Amorphous FeOOH Anchored on Boron and Nitrogen Codoped Carbon Nanotubes for Fenton-like Oxidation of Sulfamethoxazole

Amorphous iron oxide/hydroxides with structural disorder can be a potential alternative to typical crystalline structures when applied in environmental nanotechnology. In this work, novel amorphous FeOOH quantum dots (QDs) anchored on boron and nitrogen codoped graphene nanotubes (FeOOH@BNG) with different Fe loadings were synthesized and applied in the degradation of common antibiotic pollutant sulfamethoxazole (SMX). The as-fabricated catalysts were characterized by a series of physicochemical and thermal techniques, revealing the highly dispersive FeOOH QDs on the BNG surface. The as-prepared catalyst shows excellent catalytic ability toward SMX degradation via a Fenton-like approach. The excellent activity of the as-prepared FeOOH@BNG catalysts was ascribed to the enhanced textural properties and better exposure of active sites, thanks to the highly dispersive Fe sites on the BNG supports. The optimal catalyst, FeOOH-5@BNG, was further employed for the optimization of key reaction parameters such as catalyst loading, H2O2 dosage, pH, and reaction temperature. Moreover, electron paramagnetic resonance (EPR) and reactive species quenching tests were employed to reveal the responsive reactive oxygen species and the mechanism in the FeOOH@BNG/H2O2 system for SMX degradation. The current study not only opens new insights into the fabrication of amorphous but metallic nanomaterials but also leads to their potential application in environmental remediation.

Postsynthesis of β-FeOOH/SBA-15 composites via mild ozone treatment: Effective surfactant removal and perfect property preservation for enhanced arsenic adsorption

Removal of surfactant templates from freshly prepared mesoporous metal-loaded silica materials by calcination often induces structure shrinkage, loss of functional groups and metal oxide sintering. This work reported the use of ozone treatment for postsynthesis of Fe-containing SBA-15 with the surfactant almost completely removed and the other properties perfectly maintained. The ozone treatment could handle large sample quantities and treatments at 40–80 °C for 1–3 h could effectively remove the triblock copolymer P123. The hydroxyl (OH) groups of SBA-15, the high dispersion state of Fe at low loadings and the intrinsic nature of β-FeOOH at high loadings kept intact. The arsenic (As(III)) adsorption performances of the as-made, calcined and ozone-treated samples with high Fe loadings were compared. Both the adsorption rate and capacity were boosted by the ozone-treated samples. Their adsorption kinetics followed the pseudo-second-order kinetic model and their adsorption isotherms were Langmuir-type. Complete removal of As(III) and high adsorption capacity (up to 30.4 mg/g) could be reached on the ozone-treated samples. The effects of common co-existing anions on adsorption were clarified. The ozone-treated samples could be regenerated with high cyclic performance. The adsorption mechanism was associated with both electrostatic interaction and surface complexation. This study would provide guideline for surfactant removal and broaden the applicability of mesoporous metal-containing silica wherein OH groups, highly dispersed metal species or active metal hydroxides are necessities.

Photocatalytic removal of 2-chlorophenol from water by using waste eggshell-derived calcium ferrite.

A new approach to recycling low-value eggshell food waste was to produce a CaFe2O4 semiconductor with a narrow band gap (Eg = 2.81 eV) via hydrothermal treatments of powdered eggshell suspended in aqueous ferric salt (Fe3+) solutions at varying Fe loadings. It was possible to obtain a single phase of CaFe2O4 without any Ca(OH)2 and CaO impurities using an optimal Fe loading (30 wt% of Fe3+ by eggshell weight). The CaFe2O4 material was used as a photocatalyst for the breakdown of 2-chlorophenol (2-CP, a herbicide model chemical) as a pollutant in water. The CaFe2O4 with a Fe loading of 7.1 wt% exhibited a high 2-CP removal efficiency of 86.1% after 180 min of UV-visible light irradiation. Additionally, the eggshell-derived CaFe2O4 photocatalyst can be effectively reused, giving a high removal efficiency of 70.5% after the third cycle, without the requirement of regeneration processes (washing or re-calcination). Although radical trapping experiments confirmed that hydroxyl radicals were generated in the photocatalytic reactions, photogenerated holes play a significant role in the high 2-CP degradation efficiencies. The performance of the bioderived CaFe2O4 photocatalysts in the removal of pesticides from water demonstrated the benefits of resource recycling in the area of materials science and in environmental remediation and protection.

In Situ/Operando Spectroscopic Studies on the NH3–SCR Mechanism over Fe–Zeolites

Reduction/oxidation half-cycles of the selective catalytic reduction of NO with NH3 (NH3–SCR) over Fe-exchanged mordenite (MOR) zeolites at 300 °C were investigated by in situ/operando spectroscopy (infrared, UV–vis, and Fe K-edge X-ray absorption near edge structure) and density functional theory (DFT) calculation. The reduction of Fe3+ into Fe2+ and the simultaneous formation of N2 and H2O in the reduction half-cycle (under NO + NH3) were demonstrated by different spectroscopic results. In the subsequent oxidation half-cycle (under O2 or NO + O2), Fe2+ was reoxidized into Fe3+. The reduction half-cycle comprises several elementary steps. Reduction of Fe3+–OH by NO producing Fe2+ and NO+ species was observed at low temperatures (<100 °C), while N2 formation due to the reduction of NO+ was observed under subsequent NH3 exposure at 100 °C. Under transient conditions, NH3 on Brønsted acid sites (B–NH3) reacted with NO to generate N2 when the coverage of B–NH3 was low, indicating that B–NH3 is not a spectator but a reservoir of NH3. Transition state calculation theoretically suggested that the formation of nitrous acid (HONO) intermediates from [Fe3+(OH–)2]+ at a Al site and gaseous NO was a facile process (Ea = 29.2 kJ/mol). Combining the experimental observation and DFT calculation, the mechanism of the reduction half-cycle over Fe–zeolites was proposed; [Fe3+(OH–)2]+ is reduced by NO to produce a HONO intermediate, which then reacts with NH3 on Brønsted acid sites to yield H2O and N2 via NO+ species. Based on the mechanistic insights above, Fe–zeolites (MOR and β) with different Fe loadings and Si/Al ratios were tested for NH3–SCR reaction. Consequently, 2.7 wt % Fe-loaded zeolites with a relatively large number of Brønsted acid sites (Al-rich β with a Si/Al ratio of 5) showed the highest NOx conversion in a low-temperature region.

Tuning CO2 to CO Conversion on Metal-Doped Carbon Catalysts

One of the significant challenges faced during electrochemical CO2 reduction (ECO2RR) is the low selectivity of the products obtained. The best example is polycrystalline Cu, which can electrochemically produce hydrocarbons and alcohols but with poor selectivity.1, 2 To date, high selectivity has been achieved only towards CO and formate on Au and Sn surface, respectively but scalability and commercialization are limited owing to their cost and stability. Metal-nitrogen-carbon (MNC) materials are comparable to Au or Ag catalysts, albeit with their lower overpotentials, higher mass activity and high selectivity toward CO.3 , 4 During the pyrolysis of N-containing carbon molecules, different chemical functionalities such as pyridinic, pyrrolic and graphitic N atoms can be formed, each behaving as a product-specific active site. 5 It is still debatable whether pyrdinic or pyrrolic N is responsible for CO2RR activity; thus, it remains unclear how to favor CO2 reduction over hydrogen evolution.In this work, we aimed to synthesize C2N-like covalent organic frameworks, with 8-10 Å pore size, tailored to host dual atoms coordinated to nitrogen. Such sites are expected to favor C-C coupling and produce multi-carbon products during ECO2RR. A step-by-step synthetic approach was employed to optimize the CO2RR:HER ratio through: Tuning carbon:nitrogen ratio using two different synthetic approaches.Reducing nitrogen in the carbon matrix through pyrolyzing at different temperatures (700, 800 and 900 oC),Doping phosphorus and nitrogen into the carbon matrixTuning CO2RR product distribution through different metals (Fe and Ni) doping. EXAFS and STEM studies revealed the presence of a mixture of single and dual atomic sites. XPS and ICP results showed that Fe and Ni loadings <2 wt% could be obtained in the C2N materials. Higher hydrogen evolution, owing to the higher N-content, was observed at a lower pyrolysis temperature which decreased at a pyrolysis temperature of 900 oC. Both Fe-NC and Ni-NC selectively produced CO, thus suppressing FE H2 to <5%. Fe-NC also exhibited lower overpotential for CO production compared to its Ni-NC counterpart. A small percentage of ethanol and 2-propanol (FE<5%) was observed indicating the favoured C-C coupling on the dual-atomic sites. Further optimization of the metal-N coordination environment may allow for an improved selectivity for >C2 products. References K. P. Kuhl, E. R. Cave, D. N. Abram and T. F. Jaramillo, Energy Environ. Sci., 5, 7050 (2012). S. Nitopi, E. Bertheussen, S. B. Scott, X. Liu, A. K. Engstfeld, S. Horch, B. Seger, I. E. L. Stephens, K. Chan, C. Hahn, J. K. Nørskov, T. F. Jaramillo and I. Chorkendorff, Chem. Rev., 119, 7610 (2019). A. S. Varela, N. Ranjbar Sahraie, J. Steinberg, W. Ju, H.-S. Oh and P. Strasser, Angew. Chem. Int. Edit., 54, 10758 (2015). A. S. Varela, W. Ju, A. Bagger, P. Franco, J. Rossmeisl and P. Strasser, ACS Catal., 9, 7270 (2019). Y. Lum and J. W. Ager, Nat. Catal., 2, 86 (2019).

Quality or Quantity? How Structural Parameters Affect Catalytic Activity of Iron Oxides for CO Oxidation

The replacement of noble metal catalysts by abundant iron as an active compound in CO oxidation is of ecologic and economic interest. However, improvement of their catalytic performance to the same level as state-of-the-art noble metal catalysts requires an in depth understanding of their working principle on an atomic level. As a contribution to this aim, a series of iron oxide catalysts with varying Fe loadings from 1 to 20 wt% immobilized on a γ-Al2O3 support is presented here, and a multidimensional structure–activity correlation is established. The CO oxidation activity is correlated to structural details obtained by various spectroscopic, diffraction, and microscopic methods, such as PXRD, PDF analysis, DRUVS, Mössbauer spectroscopy, STEM-EDX, and XAS. Low Fe loadings lead to less agglomerated but high percentual amounts of isolated, tetrahedrally coordinated iron oxide species, while the absolute amount of isolated species reaches its maximum at high Fe loadings. Consequently, the highest CO oxidation activity in terms of turnover frequencies can be correlated to small, finely dispersed iron oxide species with a large amount of tetrahedrally oxygen coordinated iron sites, while the overall amount of isolated iron oxide species correlates with a lower light-off temperature.

Sustainable fuel production from steam reforming of waste motor oil over olivine-supported Fe catalyst

Waste Motor Oil (WMO) has great potential to be utilized as a green fuel feedstock via thermochemical process as its high carbon content is suitable as alternative source during steam reforming reactions (SR). This process not only has potential for high syngas (CO and H2) production but also elimination of undesirable components, polyaromatic hydrocarbons (PAHs) and heavy metals in WMO. Here, evaluation of optimal conditions for WMO catalytic steam reforming in fixed-bed laboratory reactor to produce quality syngas was carried out. Influences of residence time (7–20 s), reaction temperature (700–900 °C), steam to carbon (S/C) ratio (1:2, 1:1, and 2:1), and Fe loadings (5% and 10%) on olivine support on carbon and hydrogen conversions were investigated. Results showed that the highest carbon and hydrogen conversions could be obtained after 10 s due to reactions achieving equilibrium. As for temperature, carbon and hydrogen conversions increased with temperature from mainly endothermic reactions which cause more hydrocarbon cracking. S/C volume ratio of 1:1 was preferable to obtain better carbon and hydrogen conversions due to superior heat distribution. Thus, the optimal conditions of WMO reforming were 10 s and S/C ratio of 1:1 at 800 °C which resulted in 94.68% and 79.34% carbon and hydrogen conversions, respectively, while gas product LHV was 4.44 MJ/m3. As for Fe loading on olivine, the best performance was acquired at 800 °C, residence time of 15 s, and S/C ratio of 1:1 with 10% Fe/olivine. Carbon and hydrogen conversions increased by 7.60% to 69.91% and by 13.70% to 69.31%, respectively, when compared to non-catalytic cases. This is because of higher cracking of heavy hydrocarbons from greater Fe active sites. Application of this work may lead to decrease in environmental impact from WMO disposal and make available the green fuel for sustainable power generations or as chemical intermediates in many industries.

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.

Co–Fe Clusters Supported on N-Doped Graphitic Carbon as Highly Selective Catalysts for Reverse Water Gas Shift Reaction

Graphitic carbons are suitable supports of metal nanoparticles with catalytic activity. In the present study, the preparation of N-doped graphitic carbon supporting clusters of Fe–Co alloys starting from biomass waste is reported. These sub-nanometric Co–Fe clusters supported on N-doped graphitic carbon at a metal loading below 0.2 wt % exhibit high activity for the selective hydrogenation of CO2 to CO. Operating at 500 °C and 10 bar with an H2/CO2 molar ratio of 7 and a space velocity of 600 h–1, a conversion of 56% with a selectivity of over 98% to CO, and remarkable stability over 30 h operation was obtained. Interestingly, analogous catalysts based on N-doped graphitic carbon with much higher Co–Fe loadings and an average particle size range of 1–5 nm exhibit only half of this activity, with similar CO selectivity. This contrasting behavior reveals the dramatic effect of the particle size on the catalytic activity. In comparison, SiO2 as support under similar conditions affords CH4 as the main product.