Transition Metal Solutes Research Articles

Pyrolysis characteristics and hydrogen production mechanism of biomass impregnated with transition metals

The application of metal impregnation pretreatment to improve the quality of biomass pyrolysis gas production is considered as a promising upgrading technology. Transition metals have been well developed for the unique structural characteristics. After impregnation pretreatment, the product distribution of biomass pyrolysis was changed, and the transfer path of H atoms and the formation mechanism of H2 can be revealed through analysis. The effects of impregnation pretreatment with three different transition metals (iron, cobalt, and nickel) on the pyrolysis characteristics of corn straw were evaluated in this work. Three transition metal solutions with concentrations of 0.5 M, 1 M, and 2 M were used to explore the influence of impregnation concentration on the yield and composition of the pyrolysis products. The results showed that iron promoted the formation of liquid products, whose proportion increased by 37.29% upon increasing the impregnation solution concentration. The addition of cobalt and nickel led to more pyrolysis gas generation. When the impregnation solution concentration was greater than 0.5 M, the gas production rate exceeded 45 wt%. Nickel simultaneously promoted the generation of H2 and CH4 in pyrolysis gas, whose yields were increased by 63% and 20% respectively compared with raw materials. Py-GC/MS analysis showed that Co-CS had strong decarboxylation characteristics during pyrolysis. Metal impregnation decreased the content of aromatic compounds in tar, which increased the stretching vibrations of C-H bonds in char. Ring-opening rearrangements of polycyclic aromatic hydrocarbons were promoted, which formed more -H. Nickel catalyzed the removal of CH3 and H groups and the rearrangement of C-O in volatile products, which formed more H2 and CH4. These findings provide an avenue to optimize the metal impregnation conditions to produce hydrogen via biomass pyrolysis.

Production of green diesel from waste cooking oil via catalytic deoxygenation reaction using metal doped eggshell catalyst

Abstract Green diesel production via catalytic deoxygenation of waste cooking oil (WCO) over metal doped eggshell catalyst was investigated in this work. The catalyst was prepared through liquid-liquid precipitation of 5 transition metal solutions and ground eggshell (ES) as the catalyst support. The prepared catalyst, Fe-ES, Cu-ES, Co-ES, Zn-ES, and Ni-ES were characterized using BET surface area and Scanning Electron Microscopy (SEM) analysis. BET surface area data and SEM images of the catalyst shows a promising catalyst physical properties that tailor to the deoxygenation reaction. Gas Chromatography Mass Spectrometry (GCMS) was used to determine the hydrocarbon composition of the oil yield product from the reaction. The reaction also produces gas, soap and liquid acid phase while the remaining unreacted WCO becomes coke. The percentage of all products and coke were calculated using mass balance. Deoxygenation of WCO with Ni-ES catalyst produced highest oil yield at 61.6% with the hydrocarbon content of 56.11%. Ni-ES also produced 22.9% coke; the least percentage compared to other catalyst. The findings proved that Ni-ES catalyst exhibited the highest conversion of WCO into gas and liquid product with a greater yield of oil and minimal coke formation. These findings demonstrate the feasibility and practicality of using eggshell catalysts as substitutes for commercial catalysts in green diesel production.

First-principles study of the interaction of nitrogen with transition metal solutes in tungsten

The choice of tungsten (W) as the plasma-facing material requires seeding impurities into the edge plasma for radiative cooling, and gaseous nitrogen (N) is one of the most likely impurities to be used for this purpose. In this work, first-principles calculations related to the interactions between N and transition metal (TM) solutes were performed. The interactions between the TM solutes and N are predominantly attractive and very localized. Specifically, the 3d solutes exhibit a stronger attraction to N than the 4d and 5d solutes. Consequently, most TM solutes can alter the N distribution, promoting the N aggregation within their neighboring shells, and impeding the N diffusion. Moreover, this effect is more conspicuous in the 3d solutes related to the 4d and 5d solutes. In the Sol-Vac-N complexes, the vacancy assumes a predominant role. Most TM solutes diminish the capability of vacancies to capture N. The exception arises in Ti, V, Zr, Nb, Hf, and Ta, where these solutes enhance the vacancies' ability to capture N. Further investigation revealed that, for Ti, V, Zr, Hf, Ta, and Os, the capacity of Sol-N pairs to adsorb the additional N and solute atoms is significant. As a result, it can be speculated that the Sol-N pairs for these solutes might continue to adsorb additional N and solute atoms, eventually evolving into nitrides. However, for the primary transmutation product Re, the capacity of Sol-N pairs to adsorb additional Re atoms is negligible. Therefore, it is inferred that the formation of Re nitride is rather unlikely during W's service life as plasma-facing materials.

The trapping effect of transitional metals on oxygen in Mo from first-principles calculations

The trapping effect of solute on oxygen (O) can be benefit for inhibiting its segregation and embrittlement at the GBs in Mo alloys. In this work, the interaction between solutes (including 27 transition metals), interstitial O and vacancy in Mo are implemented by first-principles calculations, and their trapping effects on O are evaluated by Simonovic’s model. Single transition metal solute (TMS) has a strong attraction for O, and it is strengthened by the second solute for all 3d, oversized 4d and 5d series. Furthermore, there is a significant synergistic effect between solute, vacancy, and oxygen for oversized solutes, i.e., the binding energy between solute atom (vacancy) and oxygen atoms is enhanced by the presence of vacancy (solute). The distribution of oxygen indicates that oxygen can be captured by dilute TMS atoms, and more oxygen atoms will be trapped as the solute concentration increases in Mo. Based on our extensive calculations, Sc, Ti, Zr, Hf, and Ta can be the top priority for suppressing the segregation and embrittlement of O in Mo alloys. It is interesting that the interaction between solute and O can be accurately separated into elastic and chemical contributions though delicate calculation, and the counterintuitive strong binding effect of fifth-nearest solute-O pairs for undersized 4d and 5d elements is owning to the chemical contribution driven by Coulomb interaction.

Fabrication and characterisation of CrMnFeCoNi high entropy alloy electrocatalyst for oxygen evolution reaction

Water electrolysis is attracting increasing attention in becoming the main method for green energy production, which has long been hindered by the sluggish kinetics of oxygen evolution reaction (OER) and high cost of noble-metal (NM) containing electrodes. Template replication technique has been employed to fabricate porous CrMnFeCoNi high entropy alloy (HEA) bulk foams with > 95 % porosity. High entropy led to the formation of a single-phase solid solution of transition metals in the as-fabricated porous HEA bulk foam, and the lattice distortion brings about the outstanding OER performance that is close to that of the RuO2 reference sample. Effective electrochemically active surface area and amount of exposed active sites are increased by grinding into nanoparticles, which produced superior OER performance with a near-record low overpotential of ∼ 245 mV to drive a current density of 10 mA/cm2, a low Tafel slope of 73.6 mV/dec, a double layer capacitance of 102.3 mF, and excellent long-term stability over 24 h. This work demonstrates a cost-effective way to fabricate NM-free HEA electrocatalyst with complex structure and excellent stability in OER, which could help in advancing the research for alkaline water electrolysis.

First-principles calculations of co-segregation behavior of transition metal solutes and hydrogen along aluminum grain boundaries

In the realm of aluminum and its alloys, the susceptibility to stress corrosion during applications is often attributed to the segregation of hydrogen atoms at grain boundaries. This article is dedicated to examining the co-segregation behavior of solute atoms in conjunction with hydrogen atoms at three specific grain boundaries (Σ5 (210), Σ11 (113), Σ3 (111)). The research employs first-principles methods, using aluminum as the substrate, with a specific emphasis on choosing 3d and 4d transition metals as solute atoms. The study unveils that the co-segregation energy is intricately influenced by the distinct segregation behaviors of solute atoms and their interactions with hydrogen atoms. Notably, a stronger tendency of solute atoms to segregate, coupled with heightened solute-hydrogen attraction, amplifies the likelihood of their co-segregation. Furthermore, the interactions between different solute atoms are influenced by the combined effects of elastic interactions and charge interactions. Collectively, this research provides deep insights into the co-segregation at grain boundaries.

Construction of high-entropy oxy/hydroxides with dense nanosheet array structures on FeCoNiCrMo electrode for efficient oxygen evolution reaction

The high-entropy alloy (HEA) films prepared by magnetron sputtering on 3D substrates have excellent ability to release bubbles, good electrical conductivity, and abundant active sites, which lead to excellent performance in oxygen evolution reaction. HEA films with various elements were prepared on different substrates. In general, oxygen evolution reaction abilities of HEA film electrodes are related to morphologies of catalyst and types of active sites. Notably, nanostructures with regular array could help to increase the surface area of electrocatalysts and expose active sites. Also, chloride salt solution of transition metals can promote the formation of high-entropy oxy/hydroxides due to oxygen absorption oxidation reaction and displacement reaction on the surface of HEA film electrodes. And electrochemical oxidation at suitable high potential can also produce high-entropy oxy/hydroxides. In this work, dense nanosheet array structures of high-entropy oxy/hydroxides were constructed on the surface of FeCoNiCrMo HEA film electrodes preprocessed in NiCl2 solution and reconstructed by electrochemical oxidation in KOH solution further. The FeCoNiCrMo HEA film electrode with dense nanosheet array structures has excellent OER performance with the overpotential of 250 mV, Tafel slope of 41.5 mV dec−1, and electric double layer capacitance of 4.3 mF cm−2.

Electronic and strain-elimination effects of solute–vacancy interaction in molybdenum

The interaction between a solute and vacancy is crucial for the diffusion and precipitation of alloy elements and ultimately affects the creep resistance and safety of refractory molybdenum (Mo) alloys. In this work, the first-principles calculations of the interaction between solutes (5 light impurity atoms and 23 transition metal elements) and vacancies show that Mo is sensitive to all the light impurity elements, which indicates that these solutes are easy to combine with an Mo alloy and have relatively strong interaction. In most cases, the interaction between the 23 transition metal solutes and vacancy is attractive, but the interaction between solutes V, Ti, and the first-nearest vacancy is repulsive, and the interaction between the early elements in the 3d, 4d, and 5d series and the second-nearest vacancy is also repulsive. Then, we discuss the main factors that affect the solute–vacancy interaction, that is, the effects of electron and strain-elimination. Finally, a solute–vacancy interaction database based on the above effects is established, which would contribute to the research on heat- and radiation-resistant Mo alloys.

Affinity of phenolic compounds for transition metal ions immobilized on cation-exchange columns

Immobilized metal ion affinity chromatography (IMAC) is useful in purification of histidine-tagged or histidine-rich proteins and peptides from a variety of hosts. However, phenolic compounds including polyphenols interfere with IMAC due to their high affinities for the transition metals immobilized on the column resins, which hampers the purification of proteins from plant-based host systems. In contrast to extensive knowledge of the mechanism of the interactions between phenolic compounds and transition metal ions in solution, an understanding of the interactions on the columns, where transition metal ions are immobilized on the resins, remains elusive. This study systematically investigated the affinity of phenolic compounds for transition metal ions by varying the number and position of phenolic hydroxyl groups (OH groups) and using different transition metals—Fe(II), Cu(II) and Ni(II)—on various IMACs, in which the columns were fabricated by equilibrating the cation-exchange column with transition metal solutions. It was found that the more OH groups the aromatic compounds have, the higher the affinity for transition metal ions; in particular, methyl gallate and pyrogallol were permanently bound to the IMAC column, which reflected coordinate bond formation with the transition metal ions. Importantly, the phenolic compounds showed no obvious affinity for the Ni(II)-IMAC column, in contrast to the Fe(II)- and Cu(II)-IMAC columns, whereas imidazole and histidine-tagged proteins showed evident binding to the Ni(II)-IMAC column. Ni(II)-IMAC should thus be especially effective in isolating histidine-tagged and histidine-rich species from phenolic compound-containing systems. These results indicate that the affinity between phenolic compounds and transition metal ions on the column is consistent with the results in solution. They also provide a comprehensive view for devising strategies to improve IMAC purification of target proteins and peptides from samples containing phenolic compounds.

Selective preparation of samarium phosphates from transition metal mixed solution by two-step precipitation

ABSTRACT Samarium-cobalt alloys are used as materials for powerful magnets with relatively high Curie temperatures. Samarium is a valuable and expensive material because it is one of a group of rare earth elements. In order to utilize this rare earth resource in a sustainable society, it is necessary to recover, reuse, and recycle rare earth elements. With this in mind, a new process for recovering neodymium phosphate from neodymium-iron mixed aqueous solutions has recently been reported, avoiding the difficulties reported with conventional methods. Given that rare earth phosphates are a major component of rare earth ores, this new process was proposed to recover them as phosphates. In this method, neodymium phosphate was selectively precipitated from a neodymium-iron mixture in a two-step process with an adjusted pH value. In this study, we attempted to selectively precipitate samarium phosphate from a mixed solution of transition metals using this two-step precipitation method. The advantage of this method is that the samarium compound can be separated from other metal salts without the use of high temperatures or special equipment. Optimal conditions were determined by evaluating the precipitates by molar ratio, color hue, UV-visible reflectance spectra, X-ray diffraction, and infrared spectroscopy of the precipitates obtained. In Step 1, the pH was adjusted using sodium hydroxide to remove cobalt, iron, and copper hydroxides other than samarium. In Step 2, after adding phosphoric acid, the pH was adjusted so that a precipitate of samarium phosphate was formed.

Application of Grain Boundary Segregation Prediction Using a Nano-Polycrystalline Grain Boundary Model to Transition Metal Solute Elements: Prediction of Grain Boundary Segregation of Mn and Cr in bcc-Fe Polycrystals

A prediction method for grain boundary segregation using a nano-polycrystalline grain boundary model is applied to the grain boundary segregation of Cr and Mn in bcc-Fe polycrystals for which experimental results exist, and the validity of the prediction method is verified. In this prediction method, focusing on the fact that the atomic structure of grain boundaries is almost independent of grain size, grain boundaries of polycrystals with grain sizes of the order of micrometers are modeled as grain boundaries of nano-polycrystals, for which structural relaxation calculations by molecular dynamics calculations are possible. For this grain boundary model, the grain boundary segregation energy of each site is calculated exhaustively using the interatomic potential. In addition, the average amount of grain boundary segregation in the polycrystal is calculated from the obtained grain boundary segregation energy. With this prediction method, the average amounts of grain boundary segregation and segregation energies of Cr and Mn in bcc-Fe polycrystals can be calculated and compared with the experimental results. Calculated results for both elements reproduced the experimental results well, suggesting that this prediction method is also effective in predicting the grain boundary segregation of other solute elements.

Application of Grain Boundary Segregation Prediction Using a Nano-Polycrystalline Grain Boundary Model to Transition Metal Solute Elements: Prediction of Grain Boundary Segregation of Mn and Cr in bcc-Fe Polycrystals

A prediction method for grain boundary segregation using a nano-polycrystalline grain boundary model is applied to the grain boundary segregation of Cr and Mn in bcc-Fe polycrystals for which experimental results exist, and the validity of the prediction method is verified. In this prediction method, focusing on the fact that the atomic structure of grain boundaries is almost independent of grain size, grain boundaries of polycrystals with grain sizes of the order of micrometers are modeled as grain boundaries of nano-polycrystals, for which structural relaxation calculations by molecular dynamics calculations are possible. For this grain boundary model, the grain boundary segregation energy of each site is calculated exhaustively using the interatomic potential. In addition, the average amount of grain boundary segregation in the polycrystal is calculated from the obtained grain boundary segregation energy. With this prediction method, the average amounts of grain boundary segregation and segregation energies of Cr and Mn in bcc-Fe polycrystals can be calculated and compared with the experimental results. Calculated results for both elements reproduced the experimental results well, suggesting that this prediction method is also effective in predicting the grain boundary segregation of other solute elements.

Ni- and Cu-co-Intercalated Layered Manganese Oxide for Highly Efficient Electro-Oxidation of Ammonia Selective to Nitrogen.

We fabricated a thin film of layered MnO2 whose interlayer space was occupied by hydrated Ni2+ and Cu2+ ions. The process consisted of electrodeposition of layered MnO2 intercalated with tetrabutylammonium cations (TBA+) by anodic oxidation of aqueous Mn2+ ions in the presence of TBA+, followed by ion exchange of the initially incorporated bulkier TBA+ with the denser transition metals in solution. The resulting layered MnO2 co-intercalated with Ni2+ and Cu2+ ions (NiCu/MnO2) catalyzed the ammonia oxidation reaction (AOR) in an alkaline electrolyte with a much lower overpotential than its Ni2+- and Cu2+-intercalated single-cation counterparts. Surprisingly, the NiCu/MnO2 electrode achieved a faradic efficiency as high as nearly 100% (97.4%) for nitrogen evolution at a constant potential of +0.6 V vs Hg/HgO. This can be ascribed to the occurrence of the AOR in the potential region where water is stable and dimerization of the partially dehydrogenated ammonia species is preferred, thereby forming an N-N bond, rather than to be further oxidized into NOx species.

Transition metal solutes in Ni-based ternary model superalloys: Partitioning and effects on elastic properties from first-principles calculations

Alloying effects on the structural, elastic, as well as electronic properties of Ni-based model superalloys are systematically investigated by first-principles calculations. Twenty-seven transition-metal(TM) elements (3d:Sc-Zn, 4d:Y-Cd, 5d:Hf-Au) are taken into account in Ni-based ternary model superalloys in detail for the first time. The partitioning behaviors and site preferences of ternary alloying elements are primarily predicted based on our calculated substitutional formation energies and partitioning coefficients, with previous atom probe tomography(APT) experimental results for comparison. Temperature dependence of partitioning behaviors of TM elements in model superalloys is also presented in this work. It is found that the partitioning behaviors of Cr, Mn, Tc, Ru and Os can be reversed at a specific temperature, and these elements just lie near the boundary between the two blocks of Ni-site preferences and Al-site preferences of TM elements on the periodic table. The bulk moduli, Young’s moduli, shear moduli, ductile–brittle behavior, orientation-dependent elastic moduli and elastic anisotropy of Ni-based ternary model superalloys are systematically estimated. The calculated elastic parameters agree well with the available experimental results. The effects of TM elements on elastic properties are found to be closely associated with their d-electron number. The elements at the beginnings and ends of the TM series reduce these elastic properties, while the TM elements lying towards the center of each period can considerably increase these properties of superalloys, especially those elements with a half-filled d band, which exert greater influences on improving the elastic performance. Furthermore, different charge redistributions caused by each alloying addition can elucidate different effects thereof on the elastic properties of model superalloys to some extent. The stronger directional bonding and more covalent-like interaction between TM additions and host atoms lead to the superior elastic properties.

Magnetic behavior of transition metal solutes in [formula omitted]-iron: A classification

For several transition metals M, we have computed atomic magnetic moments for the body-centered cubic substitutional solid solution Fe1-xMx, by two comparative first-principle approaches for atomic disorder: Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA) and Density Functional Theory applied to Special Quasirandom Structures (SQS-DFT). Our results, compared with experimental and numerical literature, led to a classification of transition metal solutes in α-iron with respect to their magnetic behavior.

The influence of transition metal solutes on the dissolution and diffusion of oxygen in tungsten

First-principles calculations are applied to perform a systematic study on the interaction between transition metal (TM) solutes and oxygen in tungsten. The interactions between all considered TM solutes and oxygen are attractive, which can be understood by the combination of the elastic and electronic interactions. Based on the results of the solute-oxygen interaction, the influences of TM solutes on the oxygen dissolution and diffusion are estimated. We found that Mo, Re and Os show weak influences on oxygen while Ti, V, Cr, Zr, and Hf significantly increase oxygen solubility and reduce oxygen diffusivity. Furthermore, we explored the synergistic effect among TM solutes, vacancy and oxygen. The early TM solutes can enhance the oxygen trapping effect of the vacancy, while late TM solutes show little effects on vacancy-oxygen interaction. Meanwhile, the oxygen can increase the stability of the solute-vacancy pairs especially for the case of Ti and V. Our calculation results are in agreement with recent experimental results, and provide the necessary input parameters for subsequent multiscale studies on the atomic processes involved in oxidation.

Trends in transition metal solute diffusion in metals: The case of tungsten

The solute diffusion regulates many properties and phenomena of metal alloys. Decades of research has led to lots of knowledge of interrelationships between diffusion parameters and transition metal (TM) solutes properties in metals. But none has provided a universal relationship to elucidate the underlying physics of TM solute diffusion in metals. In this paper, we systematically study TM solutes diffusion in tungsten using the first-principles calculations coupled with harmonic transition state theory. We found the solute migration energies vary parabolically across the TM series reaching a maximum at V, Mo, and W for 3d, 4d, and 5d, respectively. The correlation factor is temperature-dependent in an Arrhenius-like way, whose fitted correlation energies and pre-factors are inversely proportional to the solute migration energies. Using the database of TM solute diffusion in tungsten developed here and other existing databases, we identify the role of the matrix metals on the law of solute diffusion. When the atomic radii of matrix metals are larger than TM solutes, the solute diffusion is dominated by metallic bonds between the solute and matrix atoms, whose solute migration energy follows a positive correlation to the melting point of the solute element. While for the reverse case, the solute diffusion is controlled by solute-induced lattice distortions and their solute migration energy shows a negative correlation with the solute radius.

Influence of the segregation of 3d transition metal solutes on the elastic modulus of a tilt grain boundary in bcc Fe: ab initio local analysis

We investigated the elastic modulus changes normal to the interface of a coincidence tilt grain boundary (GB) in bcc Fe by the substitutional segregation of 3d transition metal (TM) solutes. For the $$\Sigma $$11(332) GB, we obtained cell-averaged elastic moduli by applying small tensile and compressive strains to the GB supercell normal to the interface with and without the solute segregation, where local strains or local responses at GB atoms and segregated 3d-TM atoms were analyzed. We observed that the segregations of V to the looser site and Co to the tighter site remarkably enhance the elastic modulus normal to the GB, while the segregations of Sc and Cu remarkably reduce it. The strengthening by V and Co is originated from the strong bonding between solute and neighboring Fe atoms at the GB interface, as represented by the changes of local elastic moduli and local densities of states.

XANES and EXAFS of dilute solutions of transition metals at XFELs.

This work has demonstrated that X-ray absorption spectroscopy (XAS), both Mn XANES and EXAFS, of solutions with millimolar concentrations of metal is possible using the femtosecond X-ray pulses from XFELs. Mn XAS data were collected using two different sample delivery methods, a Rayleigh jet and a drop-on-demand setup, with varying concentrations of Mn. Here, a new method for normalization of XAS spectra based on solvent scattering that is compatible with data collection from a highly variable pulsed source is described. The measured XANES and EXAFS spectra of such dilute solution samples are in good agreement with data collected at synchrotron sources using traditional scanning protocols. The procedures described here will enable XFEL-based XAS on dilute biological samples, especially metalloproteins, with low sample consumption. Details of the experimental setup and data analysis methods used in this XANES and EXAFS study are presented. This method will also benefit XAS performed at high-repetition-rate XFELs such as the European XFEL, LCLS-II and LCLS-II-HE.

Predicting Transition Metal Solute Diffusion in Metals by Merging First-Principles Calculations and Machine Learning

The transition metal (TM) solute diffusion regulates many properties and phenomena of metal alloys. Decades of research has led to lots of knowledge of interrelationships between diffusion parameters and TM solutes properties. But none has provided a universal relationship to elucidate the underlying physics of TM solute diffusion in metals. This impedes the development of machine learning model to rapidly predict solute diffusion properties in metals. Using the database of TM solute diffusion in tungsten developed here and other existing databases, we identify the role of the atomic radii of matrix metals on the law of solute diffusion, and key properties controlling the TM solute diffusion. When the atomic radii of matrix metals are larger than most TM solutes, the solute diffusion is dominated by metallic bonds between the solute and matrix atoms, which can be measured by the melting points and unpair-d-electrons of TM solutes. While for the reverse case, the solute diffusion is controlled by solute-induced lattice distortions, and the Goldschmidt radii and bulk moduli of pure TMs are measures of the TM solute diffusion in this case. Based on these findings, we predict the solute migration energies using machine learning methods with the identified key properties as descriptors. Our predicted values show 0.09 eV fitting errors and 0.15 eV cross-validation errors compared to first-principles results, indicating a satisfactory predictive capability.