Metal Oxide Composites Research Articles

Theoretical Calculations on Metal Catalysts Toward Water-Gas Shift Reaction: a Review.

Water-gas shift (WGS) reaction offers a dominating path to hydrogen generation from fossil fuel, in which heterogeneous metal catalysts play a crucial part in this course. This review highlights and summarizes recent developments on theoretical calculations of metal catalysts developed to date, including surface structure (e. g., monometallic and polymetallic systems) and interface structure (e. g., supported catalysts and metal oxide composites), with special emphasis on the characteristics of crystal-face effect, alloying strategy, and metal-support interaction. A systematic summarization on reaction mechanism was performed, including redox mechanism, associative mechanism as well as hybrid mechanism; the development on chemical kinetics (e. g., molecular dynamics, kinetic Monte Carlo and microkinetic simulation) was then introduced. At the end, challenges associated with theoretical calculations on metal catalysts toward WGS reaction are discussed and some perspectives on the future advance of this field are provided.

Ti/Zr/O Mixed Oxides for the Catalytic Transfer Hydrogenation of Furfural to GVL in a Liquid-Phase Continuous-Flow Reactor

This work aims to develop an efficient catalyst for the cascade reaction from furfural to γ-valerolactone in a liquid-phase continuous reactor. This process requires both Lewis and Brønsted acidity; hence, a bifunctional catalyst is necessary to complete the one-pot reaction. Ti/Zr/O mixed oxide-based catalysts were chosen to this end as balancing metal oxide composition allows the acidity characteristics of the overall material to be modulated. Oxides with different compositions were then synthesized using the co-precipitation method. After characterization via porosimetry and NH3-TPD, the catalyst with equimolar quantities of the two components was demonstrated to be the best one in terms of superficial area (279 m2/g) and acid site density (0.67 mmol/g). The synthesized materials were then tested using a plug flow reactor at 180 °C, with a 10 min contact time. Ti/Zr/O (1:1) was demonstrated to be the most promising catalyst during the recycling tests as it allowed obtaining the highest selectivities in the desired products (about 45% in furfuryl isopropyl ether and 20% in γ-valerolactone) contemporaneously with 100% furfural conversion.

Enhancement in the photocatalytic and optoelectronic properties of erbium oxide by adding zinc oxide and molybdenum

Rare earth metals like erbium oxide (Er2O3) show outstanding photocatalytic properties. However, its high recombination rate and low surface area limit its performance. Therefore, various metal oxide composites with Er2O3 have been reported to improve their photocatalytic and optoelectronic properties. In this study, a composite of Er2O3 and zinc oxide (ZnO) was synthesized using the sol-gel combustion method to enhance its surface area. Moreover, molybdenum (Mo) was loaded on the matrix to suppress the charge recombination. The detailed characterizations were conducted by employing X-ray Diffraction (XRD), Raman Spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), Brunauer–Emmett–Teller (BET) analysis, Photoluminescence (PL) spectroscopy and UV–Vis spectroscopy. BET analysis revealed the enhancement in surface area by adding ZnO and Mo (from SBET = 29.07 m2/g to SBET = 45.71 m2/g). Additionally, the loading of Mo enhanced the immobilization of carriers that facilitate the photooxidation process and suppressed the electron-holes recombination (from 800 counts to 100 counts) as confirmed by the PL spectroscopy. Photocatalytic studies were comparatively analyzed by degradation of textile dye named methylene blue (MB). The efficiency of Er2O3 improved by up to 80% by adding the ZnO and Mo. The composite of Er2O3 with ZnO and loading of Mo, not only improved the photocatalytic properties but also improved the electrical properties of the Er2O3 (σ = 4.4 × 10−4 Sm−1 to σ = 5.1 × 10−4 Sm−1) as confirmed by the Hall Effect. Due to enhancement in properties, the proposed material can be rendered as one of the most suitable candidates for optoelectronic applications.

The Structural Stability Limit of Layered Lithium Transition Metal Oxides Due to Oxygen Release at High State of Charge and Its Dependence on the Nickel Content

The composition of layered transition metal oxides (LiMO2, M = Ni, Co, Mn) as cathode active materials (CAMs) is currently trending towards higher nickel contents, which can provide more capacity and energy. The origin of this performance improvement is often ascribed to the lower potential of nickel-rich CAMs, suppressing detrimental electrochemical electrolyte oxidation. In this study, it is shown that the stability limit of LiMO2-based CAMs is not determined by the stability window of typical electrolytes in terms of potential but by the CAM composition, governing the structural stability at high degrees of delithiation. The latter is investigated for five CAMs with distinct composition (LCO, NCM111, NCM622, NCM851005, and LNO) as a function of upper cutoff potential and thus state of charge (SOC). Short-term cycling experiments with an increasing upper cutoff potential as well as extended cycling to selected SOCs reveal stability limits between 66 and 86 %SOC depending on the CAM composition. On-line electrochemical mass spectrometry (OEMS) does not only allow to exclude any impact of electrochemical electrolyte oxidation on the determined stability window of the CAMs but also illuminates the concurrence of capacity fade and lattice oxygen release, with the latter being the origin of the CAM degradation.

Novel statistically optimized one pot synthesis of inherently photoluminescent and electroactive graphene oxide nanosheets as 1, 4 dioxane sensor

1, 4 dioxane predominantly found in industrial effluents and air force plants, is of great concern worldwide due to its toxic and carcinogenic nature. Currently, there are limited research on 1,4 dioxane sensors and most of these sensors are intricate metal oxide composites. This study reports the fabrication of novel inherently electroactive graphene oxide nanosheets derived from a natural polyphenolic compound, and the process parameters were statistically optimized using TOPSIS based Taguchi L9 orthogonal array. The proposed novel sensor was employed in the linear range (0.1µM to 3µM) that conforms with the WHO guideline (0.56 µM) for dioxane in water, showed good sensitivity (117 nAnM-1 cm-2 ), detection limit (20.51 nM) and quantification limit (62.16 nM) which is far superior compared to the reported literature on dioxane sensing systems.

High-Voltage Layered NaNi0.5Co0.1Ti0.3Sb0.1O2 Cathode for Sodium-Ion Batteries

Developing a high-voltage cathode material for sodium-ion batteries is a great challenge. Herein, we report an O3-type layered NaNi0.5Co0.1Ti0.3Sb0.1O2 cathode composition, which can operate at a high voltage (4.35 V). Inclusion of different valence state transition metals, like Ni, Co, and Ti, and a metalloid Sb in the sodium metal oxide composition leads to the formation of a cationic disordered structure, which enhances redox, electronic conductivity, cycling stability, and working voltage. The structural characterizations reveal that the composition is free from superstructure reflections, and electrochemical studies show that the composition suppresses multiphase transitions. As a result, NaNi0.5Co0.1Ti0.3Sb0.1O2, exhibits initial charge and discharge capacities as 129 and 112 mAh/g, respectively, at the current rate of 9.1 mA/g for 2.0–4.35 V. Thus, the high voltage, improved capacity, and retention characteristics of NaNi0.5Co0.1Ti0.3Sb0.1O2 would open up the way for bulk production of Na-ion batteries.

Hot Isostatic Pressing Control of Tungsten-Based Composites

Metal-oxide composites are commonly used in high temperature environments for their thermal stability and high melting points. Commonly employed with refractory oxides or carbides such as ZrC and HfC, these materials may be improved with the use of a low density, high melting point ceramic such as CeO2. In this work, the consolidation of W-CeO2 metal matrix composites in the high CeO2 concentration regime is explored. The CeO2 concentrations of 50, 33, and 25 wt.%, the CeO2 particle size from nanometer to micrometer, and various hot isostatic pressing temperatures are investigated. Decreasing the CeO2 concentration is observed to increase the composite density and increase the Vickers hardness. The CeO2 oxidation state is observed to be a combination of Ce3+ and Ce4+, which is hypothesized to contribute to the porosity of the composites. The hardness of the metal-oxide composite can be improved more than 2.5 times compared to pure W processed by the same route. This work offers processing guidelines for further consolation of oxide-doped W composites.

Damage of Green Synthetic Cement Slurry to Clastic Rock Reservoir

Green synthesis and metal oxide composites have attracted much attention from researchers of industry and academia. As a typical application of green synthesis and metal oxide composites, the protection of oil and gas reservoirs is related to various links such as exploration, drilling, completion, and development. It is a complex and systematic project, which directly affects whether the oil and gas fields can be discovered, evaluated, and efficiently developed in time, and it is also related to the development of oil and gas fields recovery rate. As the most critical part of oil and gas well construction, the cementing process mainly pays attention to the safe pumping of the cement slurry and the long-term effective interlayer isolation capability of the cement sheath. Less attention is paid to the reservoir protection during the cementing process. The high-pressure difference between the annulus and the formation, the high fluid loss, and the high solids content of the cementing slurry during the cementing process have also become major challenges. In order to solve this problem, this study takes a typical clastic rock block in an oilfield in western China as the research object and carries out a geological survey of fracture development, pressure deficit, and cement slurry permeability leakage in the reservoir. The reservoir physical properties, clay mineral characteristics, and formation water quality of rock reservoirs are analyzed. The influence of cement slurry filtrate and solid phase particles on reservoir clay expansion rate and permeability was tested by core porosity and permeability tester. XRD and SEM techniques were used to analyze the damage mechanism of cement slurry filtrate and solid phase particles to the reservoir. The research results show that the average porosity of the clastic rock reservoir in the study area is 15%, the permeability is high, the average pore size of the reservoir is between 37 and 56 μm, the microfractures are developed in the reservoir section, and the porosity and permeability conditions are good; high-valent cations and inorganic ions in the filtrate generate inorganic scales such as CaCO3 and Mg(OH)2 and cross-link with dissolved polymers to form flocculation substances, which cause the filtrate to damage the reservoir, and at the same time, the cement particles in the pore throats in the near wellbore zone are lost along with the leakage. Furthermore, hydration, tightly bonding the inert admixture and the clastic rock formation, forms a tight sealing layer, which reduces the permeability of the reservoir sharply; the expansive clay particles in the reservoir absorb the moisture of the cement slurry filtrate and expand. The volume of the particles increases, and the porous formation containing expansive clay minerals absorbs moisture and causes internal expansion, and the volume expansion rate can reach 9%, which eventually causes the porosity and permeability of the reservoir to decrease, resulting in reservoir damage and solid phase in the cement slurry. The damage of particles to the reservoir is mainly due to the blockage of the reservoir pore throats and the hydration and consolidation of cement particles inside the reservoir caused by the external admixtures in the cement slurry that do not participate in the hydration reaction. The solid phase particles form a filter cake on the surface of the reservoir core and cannot enter the reservoir, but under the condition of porous formation leakage, the solid phase particles with a particle size of 1–10 μm in the cement slurry will directly penetrate into the reservoir rock resulting in shallow plugging in the reservoir near the wellbore. The research results provide theoretical data support for the research on low-damage cementing slurry technology in clastic rock reservoirs. The work provides an important application guidance to green synthesis and metal oxide composites.

Recent Advances of Oxygen Carriers for Hydrogen Production via Chemical Looping Water-Splitting

Hydrogen is an important green energy source and chemical raw material for various industrial processes. At present, the major technique of hydrogen production is steam methane reforming (SMR), which suffers from high energy penalties and enormous CO2 emissions. As an alternative, chemical looping water-splitting (CLWS) technology represents an energy-efficient and environmentally friendly method for hydrogen production. The key to CLWS lies in the selection of suitable oxygen carriers (OCs) that hold outstanding sintering resistance, structural reversibility, and capability to release lattice oxygen and deoxygenate the steam for hydrogen generation. Described herein are the recent advances in designing OCs, including simple metal oxides (e.g., Fe, Zn, Ce, and Ti-based metal oxides) and composite metal oxides (e.g., perovskite, spinel, and garnets), for different CLWS processes with emphasis on the crucial parameters that determine their redox performance and future challenges.

Polygeneration of Hydrogen and Power Using Chemical Looping Water Splitting with Dual Loops of Oxygen Carrier

The demand for hydrogen as a fuel, particularly in the transportation and power sectors, has recently been increasing due to its environmental benefit of clean combustion. However, the conventional technologies for hydrogen production involve an energy penalty in purification of hydrogen and the carbon dioxide capture, which reduce the process efficiency, whereas the technique of chemical looping hydrogen production (CLH) has an inherent capacity for CO2 capture and produces pure stream of hydrogen. This paper proposes modifications in the conventional three-reactor CLH setup, leading to elimination of the energy-intensive air separation unit and imparting flexibility in terms of polygeneration (hydrogen and power). The design modification for thermally integrating the air reactor, gasifier, and splitter for an oxygen carrier has facilitated two distinct oxygen carrier loops to meet the polygeneration objectives. The performance metrics based on efficiency have been utilized to assess the performance of the proposed process and demonstrate the flexibility in polygeneration. The effect of varying operational parameters such as split fraction, composition of metal oxide, and temperature of air reactor on the performance of the proposed process has also been evaluated.

Incorporating Binary Metal Oxides in Poly(ethylene oxide)-Based Solid Electrolytes by Vapor Phase Infiltration

Vapor phase infiltration (VPI) derived from atomic layer deposition (ALD) enables inorganic materials to nucleate and grow within the free volume of polymers, which has shown promising prospects in the field of composite solid polymer electrolytes (CSPEs). However, there are only a few types of metal oxides that can be incorporated into the polymer matrix by VPI, let alone binary metal oxides, due to the limited knowledge of the VPI synthesis process. To combine the merits of different metal oxides, we investigate the VPI method to prepare ZnO-Al2O3 composites in poly(ethylene oxide) (PEO). When the introducing order is Al2O3/ZnO (AZO), due to the extremely high reactivity of trimethyl aluminum (TMA) with PEO, VPI-Al2O3 will accumulate near the surface of PEO. The surface Al2O3 layer inhibits the further diffusion of the diethyl zinc (DEZ) into the PEO matrix, leading to weak polymer-filler interactions and limited improvement of the Li+ conduction. In the incorporation order of ZnO/Al2O3 (ZAO), the moderate reactivity of DEZ renders the uniform distribution of VPI-ZnO within PEO, and the following TMA can both react with PEO and VPI-ZnO particles near the surface of PEO, which not only preserves the interactions between VPI-ZnO and PEO but also better inhibits the growth of lithium dendrites. The incorporation order plays a crucial role in the morphology and composition of binary metal oxides synthesized by VPI.

Heterobimetallic CoCeOx derived from cobalt partially-substituted Ce-UiO-66 for chlorobenzene efficient catalytic destruction

Here, a metal–organic framework (MOF)-templated strategy was applied to synthesize the CoCeOx bimetallic catalysts by calcining Co partially-substituted Ce-UiO-66. It is indicated that the substituted Co limited Ce cations in Ce-UiO-66 framework, which affects its growth and structure crystallinity to some extent. After pyrolysis treatment, the derived bimetallic oxide (CoCeOx-M) can basically keep the octahedral structure and the surface area is much higher than the bulk metal composite oxide (CoCeOx-B) prepared by traditional coprecipitation. Results reveal that CoCeOx-M performs the best chlorobenzene degradation capacity, superior stability and vapor tolerance compared with those of CeO2-M (derived from Ce-UiO-66) and CoCeOx-B. At the same time, it is favorable to inhibit the formation of CO during the oxidation reaction. The superior catalytic performance of CoCeOx-M is attributed to a good dispersion of metal cations, high surface area and active oxygen concentration, and good redox property. Moreover, the formation of organic byproducts especially chlorinated organics can be obviously prohibited over CoCeOx-M compared with that of CeO2-M. Mechanism study reveals that chlorobenzene dissociates on the surface of CoCeOx-M to form carboxylates such as acetate species, maleate and phenolate before finally oxidized into CO2, H2O, and HCl. The present work poses new insights into the fabrication of efficient catalysts for industrial CVOC purification.

A novel synthesis strategy for hybrid quaternary rGO/MnO2/NiO/CuO nanocomposite as electrode for enduring symmetric supercapacitor fabrication

Supercapacitors are one of the emerging energy devices due to the evolution in modern technologies which involve fast charging mechanisms with long-lasting stability and good retentivity. A hybrid quaternary composite of transition metal oxide consisting of MnO2, NiO, CuO nanospheres and reduced graphene oxide (rGO) was synthesized by a fusion method with enhanced supercapacitive behaviour. This nanocomposite was subjected to various structural, functional, morphological and electrochemical characterizations and further fabricated into a symmetric supercapacitor with benefiting and facile design. The electrochemical studies were carried out under electrolytes with different pH and mole concentrations both under 3-electrode and 2-electrode systems. The highest specific capacitance of 816.51 F/g was obtained with energy and power densities of 72.57 W h/kg and 0.5 kW/kg. The highest power density of 2.5 kW/kg was achieved corresponding to the current density of 5 A/g. Excellent cyclic retention of 86.46% was achieved after 5000 cycles proving long-term cyclic stability under 1 M KOH. Unfolding the nanocomposite to be a virtuous reference for supercapacitors’ future.

Novel Preoxidation-Assisted Mechanism to Preciously Form and Disperse Bi2O3 Nanodots in Carbon Nanofibers for Ultralong-Life and High-Rate Sodium Storage.

Metal oxides, as promising electrode materials for sodium-ion batteries, usually need to be formed by exposure to oxygen, which usually thermally corrodes the carbon material with which they are compounded, reducing their flexibility and electrical conductivity. Herein, we present for the first time a preoxidation-assisted mechanism to prepare bismuth oxide and carbon nanofibers (Bi2O3@C-NFs) by electrospinning, using Bi2S3 nanorods as multifunctional templates. The bismuth could be oxidized by C═O bonds formed through the cyclization reaction in the high-temperature calcination process, effectively avoiding thermal corrosion of carbon in oxygen atmosphere at high temperature. More importantly, the uniformly distributed Bi2O3 nanodots and longitudinal tunnels are formed inside the S- and N-doped carbon nanofibers with the continuous diffusion of Bi generated from the decomposition of Bi2S3 nanorods and the conversion to Bi─O bonds with C═O bonds being broken. Benefiting from the structural and composition merits arising from preoxidation, Bi2O3@C-NFs self-supporting anodes show high specific capacity (439 mAh g-1 at 0.05 A g-1), superior rate performance (243 mAh g-1 at a current density of 20 A g-1), and outstanding cycling stability (211 mAh g-1 after 2000 cycles at 5 A g-1). The effective combination of the well-established electrospinning technology and the preoxidation assisted mechanism provides a new way for the preparation of metal oxide and carbon composites.

A room-temperature gas sensor based on 2D Ni-Co-Zn ternary oxide nanoflakes for selective and sensitive ammonia detection.

While most of the reports on NH3 gas sensors are either based on metal oxide composites with other 2D materials, polymers or noble metals or involve multi-step-based synthesis routes, this work is the first report on a pristine ternary metal oxide, 2D NiCo2ZnO4 nanoflake based room-temperature (RT) NH3 gas sensor. The 2D NiCo2ZnO4 nanoflakes were prepared by a one-step hydrothermal method. FESEM and TEM images displayed micro-flower like morphologies, containing vertically aligned interwoven porous 2D nanoflakes, whereas XPS and XRD data confirmed the successful growth of this ternary metal-oxide. This sensor revealed a good response, repeatability, linearity (R2 = 0.9976), a low detection limit of 3.024 ppb, and a response time of 74.84 s with excellent selectivity towards NH3 over six other VOCs. This improved performance of the sensor is ascribed to its large specific surface area (127.647 m2 g-1) resulting from the 2D nanoflake like structure, good electronic conductivity, variable valence states and abundant surface-active oxygen of NiCo2ZnO4. Thus, this highly selective 2D NiCo2ZnO4 based RT NH3 gas sensor can be an attractive solution for the fabrication of next-generation NH3 gas sensors.

Effective adsorption of tetracycline by Fe-Mn-Ce composite metal oxides: kinetics, isotherm and mechanism

Effective adsorption of tetracycline by Fe-Mn-Ce composite metal oxides: kinetics, isotherm and mechanism

Aluminum “Core-shell” microparticles with an oxide shell - fillers of spatially strengthened composites, facilitating material digitization

The transformation of aluminum “Core-shell” microparticles formed by low-temperature oxidation with water during their heating in a controlled atmosphere has been studied. Spherical particles with an oxide shell, convenient for mathematical modeling of the structure and properties of the developed composites, are planned to be used as fillers for metal and polymer oxide composites, as well as for 3D printing.

Graphene-Based Metal Oxide Composites for Lithium-ion Batteries

Graphene-Based Metal Oxide Composites for Lithium-ion Batteries

Robust method for uniform coating of carbon nanotubes with V2O5 for next-generation transparent electrodes and Li-ion batteries.

Composites comprising vanadium-pentoxide (V2O5) and single-walled carbon nanotubes (SWCNTs) are promising components for emerging applications in optoelectronics, solar cells, chemical and electrochemical sensors, etc. We propose a novel, simple, and facile approach for SWCNT covering with V2O5 by spin coating under ambient conditions. With the hydrolysis-polycondensation of the precursor (vanadyl triisopropoxide) directly on the surface of SWCNTs, the nm-thick layer of oxide is amorphous with a work function of 4.8 eV. The material recrystallizes after thermal treatment at 600 °C, achieving the work function of 5.8 eV. The key advantages of the method are that the obtained coating is uniform with a tunable thickness and does not require vacuuming or heating during processing. We demonstrate the groundbreaking results for two V2O5/SWCNT applications: transparent electrode and cathode for Li-ion batteries. As a transparent electrode, the composite shows stable sheet resistance of 160 Ω sq-1 at a 90% transmittance (550 nm) - the best performance reported for SWCNTs doped by metal oxides. As a cathode material, the obtained specific capacity (330 mA h g-1) is the highest among all the other V2O5/SWCNT cathodes reported so far. This approach opens new horizons for the creation of the next generation of metal oxide composites for various applications, including optoelectronics and electrochemistry.

Coupling effect of reaction conditions on the catalytic activity of Cu-Mn composite oxide catalysts for toluene.

Volatile organic compounds (VOCs) are one of the major components of air pollution. Catalytic combustion is a promising technology for the treatment of VOCs and at its center is the preparation of efficient and cheap catalysts. In this study, by loading copper (Cu) and manganese (Mn) on Santa Barbara Amorphous-15 (SBA-15) molecular sieve, the Cux-Mny/SBA-15 (x = 1, 2; y = 1, 2) composite metal oxide catalyst was prepared using the equal volume impregnation method. Their performance in the toluene catalytic combustion reaction was investigated by adjusting the molar ratio (x : y), and the loading of Cu and Mn. The results of the Brunner-Emmett-Teller (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses show that the CuMnO spinel phase can be detected in the Cu-Mn composite metal oxide catalyst doped with a low concentration of Cu. The overall rod-like structure of the fibrous network structure provides a large specific surface area, and the particle crystallinity is low and the dispersion is good. Due to the synergistic effect of Cu and Mn, the greater the amount of Mn3+ and adsorbed oxygen species (Oads) that are available, and the higher the turnover frequency (TOF) value, the better and more superior catalytic performance and excellent stability is obtained, when compared with the single-component oxides used in toluene catalytic combustion. After a continuous catalytic reaction for 12 h, the toluene conversion rate remained above 95%. The coupling effect of the catalytic reaction temperature and concentration of oxygen on the catalytic combustion of toluene was also studied. At a low reaction temperature (<250 °C), the increase of the concentration of oxygen played a superior role in promoting the conversion of toluene. The kinetic analysis of the toluene catalytic combustion process showed that the catalytic combustion of toluene by Cu-Mn/SBA-15 followed both the Mars-Van Krevelen (MVK) and Langmuir-Hinshelwood (L-H) reaction mechanisms. With the increase of the Oads amount caused by the decrease of the Cu ratio, the proportion of the L-H reaction mechanism increases.