Metal Oxide Species Research Articles

A novel study of sulfur-absorption via samarium-doped cerium sorbent at high temperature

Sulfides existing in many gas mixtures of high temperature cases have a negative effect on various industrial applications. In this study, we present samarium-doped cerium (SDC) sorbent to remove H2S at high temperature. Compared with pure CeO2, the SDC sorbent shows excellent ability in sulfur removal because of the positive effect of the doping of Sm. The H2 has a negative influence on sulfidation of the SDC sorbent and significantly shortens the breakthrough time, hence breakthrough sulfur capacity (BSC). The carbon monoxide present in the feed gas has no obvious effect on the sulfur-removal performance. A suitable samarium loading in SDC leads to an optimum interaction between metal oxide species and the surface oxygen vacancies, which results in an optimal adsorbed activity of reduced gas (H2, H2S) and hence desulphurization performance. In addition, the SDC sorbents have a good regenerated ability by a simple calcination process.

Hydrogen production by catalytic decomposition of methane over Fe based bi-metallic catalysts supported on CeO2–ZrO2

Methane decomposition to produce hydrogen was studied over iron based bimetallic catalysts supported on cerium-zirconium oxide in a continuous flow fixed bed reactor at 700 °C. 15 wt% Fe/CeZrO2 was prepared by wetness impregnation and the promoted Fe catalysts (15 Fe-5 Co/CeZrO2 and 15 Fe-5 Mo/CeZrO2) were prepared by co-impregnation technique. Mo promoted Fe catalyst exhibited the maximum surface area of 24.08 m2/g. X-ray diffraction studies revealed that Fe2O3, Co3O4 and MoO3 were the phases present in freshly calcined catalysts, while the reduced catalysts consisted of phases including elemental Fe, Mo and Fe–Co alloys. Both X-ray diffraction and temperature programmed reduction studies confirmed the complete reduction of metal oxide species under H2 at 700 °C. The catalytic activity of Fe/CeZrO2 was enhanced upon addition of Co and Mo as promoters. The initial hydrogen yield on 15 Fe-5 Mo/CeZrO2 was ~90% and it decreased with increase in time on stream (TOS), and finally stabilized around ~50% after 125 min of TOS. The Co promoted catalyst exhibited similar activity while the initial hydrogen yield on 15 Fe/CeZrO2 was ~83% and dropped to ~33% after 125 min of TOS. Graphitic carbon, Fe3C and Mo2C phases were observed in the XRD patterns of spent catalysts along with elemental Fe and Fe–Co alloy. It was evident from temperature programmed oxidation results that coke formation which deactivates the catalyst was dominant in 15 Fe/CeZrO2 when compared to the promoted (Co and Mo) Fe catalysts where carbon nanostructures were dominant. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the formation of carbon nanostructures on the surface of spent catalysts. The Fe based catalysts supported both tip and base-growth mechanisms for the growth of carbon nanostructures.

Comparison of various atomic compositions of Au@Pd/C, Pd/C, and AuPd/C electrocatalysts for direct ethanol fuel cells

AbstractPd/C, Au@Pd/C (core‐shell), and AuPd/C (AR—consisting in Au microparticles) were used as electrocatalysts for ethanol oxidation in alkaline medium. A synergistic effect between Au and Pd atoms in Au@Pd/C makes the binding between ethanol and Au@Pd/C stronger. This leads to product formation in higher potentials and can be useful to select ethanol products. We also showed that the atomic composition of the electrocatalysts to be used in fuel cells and in powder form to be used in electrochemical experiments are very similar, reaching high values of correlation. The depth profiling X‐ray photoelectron spectroscopy for the anode catalysts to be used in fuel cells can provide new insights about ethanol oxidation in direct ethanol fuel cells (DEFCs), for instance, metal oxide species can act in fuel cells environment. In terms of electric generation, Au@Pd/C presented a better performance in electrochemical experiments; the current density was about 1.6 times higher than the peak current density obtained for Pd/C. In terms of electrochemical stability, Au@Pd/C presented better final current density when compared to Pd/C and AuPd/C electrocatalysts. However, in DEFC experiments, Pd/C showed better performance.

Rational design of hierarchically porous NiCo2O4 and Bi2O3 nanostructure: Anchored on 3D nitrogen doped carbonized melamine foam for flexible asymmetric supercapacitor

Recent advances in high-performance flexible energy storage devices require the development of electrode materials with optimized structure and composition. In this paper, we report the design and facile synthesis of 1D NiCo2O4 nanoneedle arrays (NiCo2O4-NNAs) and 2D Bi2O3 nanosheets arrays (Bi2O3-NSAs) on highly conductive 3D carbonized melamine foam (cMF), and explore their practical application as freestanding electrode materials for flexible asymmetrical supercapacitor. The resultant NiCo2O4-NNAs wrapped cMF (cMF@NiCo2O4-NNAs) and Bi2O3-NSAs wrapped cMF (cMF@Bi2O3-NSAs) electrodes, which in unique pine branch-like and tremella-like structure, integrate the advantages of hierarchically porous structure as well as Faraday capacitance of metal oxide species and the double layer capacitance of cMF, and therefore exhibit high structural stability, large surface area, fast electron transport and ion diffusion characteristics, which give rise to a significant improvement of the supercapacitive performance. Consequently, the flexible asymmetric all-solid-state supercapacitor assembled with cMF@NiCo2O4-NNAs as positive electrode, cMF@Bi2O3-NSAs as negative electrode and PVA/KOH as gel electrolyte demonstrates wide working voltage up to 1.5 V, a high energy density of 0.49 mWh/cm3 at the power density of 3.77 mW/cm3. In addition, the specific capacitance retention remains about 83.2% after 6000 cycles. Hence, we envision that the proposed asymmetric supercapacitor holds great promise for fulfilling the demanding applications in energy storage device.

Ionic Liquid-Based Low-Temperature Synthesis of Phase-Pure Tetradymite-Type Materials and Their Thermoelectric Properties.

Phase-pure crystalline Bi2Se3 and Bi2Te3 nanoparticles are formed in reactions of [C4C1Im]3[Bi3I12] (C4C1Im = 1-butyl-3-methylimidazolium) with [C4C1Pyr][ESiMe3] (E = Se or Te; C4C1Pyr = 1-butyl-1-methylpyrrolidinium) in the ionic liquid (IL) [C4C1Im]I. The resulting crystalline tetradymite-type nanoparticles exhibit stoichiometric Bi:E (E = Se or Te) molar ratios (2:3). Because all synthetic steps were performed under strict inert gas conditions, the surfaces of the Bi2Se3 and Bi2Te3 nanoparticles are free of metal oxide species. As proven by infrared and X-ray photoelectron spectroscopy analyses, the nanoparticle surfaces reveal only minor organic contamination from solvent residues ([C4C1Im]I). The nanomaterials show high Seebeck coefficients of -124 μV K-1 (Bi2Se3) and -155 μV K-1 (Bi2Te3) and feature high electrical conductivities (328 and 946 S cm-1, respectively) at the highest tested temperature (240 °C). The corresponding thermal conductivities (0.8 and 2.3 W m-1 K-1, respectively, at 30 °C) are comparable to those of single crystals and recently reported ab initio calculations, which is in remarkable contrast to typical findings of nanograined bulk materials obtained from compacted nanoparticles. These findings emphasize the low level of impurities, surface contamination, and, in general, defects produced by the synthetic approach reported here. The figure of merit in the in-plane direction of the compacted pellets reached peak values 0.45 for Bi2Se3 and 0.4 for Bi2Te3.

Isolated Molybdenum(VI) and Tungsten(VI) Oxide Species on Partly Dehydroxylated Silica: A Computational Perspective

Although silica-supported molybdenum and tungsten oxide systems are widely used in catalysis, the nature of the surface metal oxide species is still not fully recognized. In this work, comprehensiv...

3D-Nanosponge enabled segregation: a versatile approach for highly dispersed and high content functionalization of metal oxide species

A general 3D nanosponge enabled strategy is developed to achieve simultaneously highly dispersed and high content functionalization of metal oxide species, ebabling a liabrary of functional nanostructures with great application potential.

Enhanced Removal of Paracetamol Using Biogenic Manganese Oxides Produced by Pseudomonas putida B-14878 and Process Optimization by RSM

Over the last few decades, many classes of micropollutants have been detected in aquatic environments worldwide and paracetamol is one of the micropollutant agents detected in the aquatic environment. New treatment methods based on biologically produced metal and metal oxides have been developed for micropollutant removal. Biogenic manganese oxides are also one of the most important biogenic metal oxide species. In this study, biogenic manganese oxides produced by manganese-adapted Pseudomonas putida NRRL B-14878 were used for removing paracetamol. A complete removal of paracetamol could be achieved within 216 h at pH 7, biogenic manganese oxide amount of 5 g/L, and paracetamol concentration of 2 mg/L. Response surface methodology (RSM) was applied to determine interaction between solution pH, paracetamol concentration, and biogenic manganese oxide amount being individual variables and to optimize operating conditions. According to results of variance analysis (ANOVA), the second-order polynomial model was statistically significant and coefficient of determination value was high. The optimal conditions were obtained as the solution pH of 6.81, the paracetamol concentration of 9.82 mg/L, and the biogenic manganese oxide amount of 6.36 g/L. Transformation products including the dimers, higher-degree oligomers, 3-hydroxyacetaminophen, 4-aminophenol, 4-methoxyphenol, 1,4-dimethoxybenzene, and butenedioic acid were identified by LC-MS/MS. The results of this work indicate that biogenic manganese oxide is an effective material for removing micropollutants.

Enhanced Catalytic Activity of Nano-Fe2O3–MCM-48–SO4 as a Green Catalyst for the Esterification of Acetic Acid with Methanol

Coupling of sulphated iron oxide with MCM-48 was carried out to prepare an efficient heterogeneous catalyst for the esterification reaction of acetic acid with methanol to produce methyl acetate as desired product. The prepared catalyst has shown a remarkable acid conversion of about 90% under optimized reaction conditions, which has resulted in an approximate 71% enhancement in catalyst activity using Fe2O3–MCM-48–SO4 catalyst over bare MCM-48. The effect of various reaction parameters like calcination temperature and time, amount of metal oxide and active species, catalyst loading and reaction temperature were also studied to optimize the catalytic activity of Fe2O3–MCM-48–SO4. The prepared catalyst was characterized using SEM–EDS, FT-IR, XRD and BET techniques. In addition, a detailed kinetics of esterification reaction has been carried out and a possible reaction pathway is also proposed.

Investigation of Supported Metal Oxide Species with Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy

Raman spectroscopy is a widely employed tool for characterization of heterogeneous catalysts, although it suffers somewhat from poor sensitivity at low concentrations or under in situ conditions. I...

Cellulose Conversion to 5 Hydroxymethyl Furfural (5-HMF) Using Al-Incorporated SBA-15 as Highly Efficient Catalyst

Al-incorporated SBA-15 samples (xAl/SBA-15) were successfully prepared by “atomic implantation” method. The samples were characterized by X-ray diffraction spectroscopy (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), N2 adsorption-desorption isotherms (BET), and temperature-programmed desorption (NH3-TPD). In this catalyst, metal oxide species were highly dispersed on the SBA-15 surface and existed as isolated atoms. It was shown that the Al incorporation lead to the formation of medium and strong acid sites. The catalytic activity and selectivity were tested in a mild hydrothermal process for degradation of cotton cellulose to 5-hydroxymethyl furfural (5-HMF). A cellulose conversion of 68.5% and 5-HMF selectivity of 62.1% after 2 h of reaction at 170°C were achieved. The very high 5-HMF yield (42.57%) obtained in this paper is much higher than that was reported in the literature.

The Fe-Co-Cu supported on MWCNT as catalyst for the tri-reforming of methane – Investigating the structure changes of the catalysts

In this work we synthesized Fe-Co-Cu catalysts supported on MWCNT, using a selective mode of addition of metal on functionalized MWCNT as mono and bimetallic catalysts. The Fe was inserted in the MWCNT after functionalization and Cu impregnated selectively. Co was added in sequence. The (Fe@MWCNT/Metal, (Metal = Cu and/or Co)) catalysts were tested for methane tri-reforming at 800 °C and GSVH 60,000 h−1, for 24 h. The Fe@MWCNT/Cu catalyst was more active and very stable compared to the Fe@MWCNT/CuCo. The influence of the feed composition CH4:CO2:O2:H2O and H2/CO ratio were tested, indicating prevailing steam and reverse WGSR reactions. Both catalysts were very stable for 24 h. However, TG results of the functionalized MWCNT indicated destruction of the carbon at higher temperature in the presence of oxygen. In view of the good stability and high activity of these catalysts during the tri-reforming at 800 °C we searched the causes, analyzing the structure and morphology of these materials, using different methods, before and after reaction. In fact, the functionalized MWCNT was destroyed for this reaction condition. However, TGA, MEV-FEG, Raman and XRD results showed the presence of very small amounts of carbon and the appearance of different species and phases before and after reaction. These results evidenced that the functionalized MWCNT is like a sacrificial support, dispersing very well the active and metal oxide species, and the formation of new phases as isolated active and stable nano particles, which inhibit carbon formation.

Trimetallic NiMoW and CoMoW catalysts supported on SBA-15 modified with titania or zirconia for deep hydrodesulfurization

SBA-15, Ti-SBA-15 and Zr-SBA-15 were used to prepare trimetallic CoMoW and NiMoW catalysts in order to inquire into the effect of the support’s composition on the catalytic performance in deep hydrodesulfurization (HDS). Supports and catalysts were characterized by N2 physisorption, X-ray diffraction, temperature-programmed reduction, scanning electron microscopy (SEM-EDX) and high-resolution transmission electron microscopy. The catalytic activity was determined in the simultaneous HDS of dibenzothiophene and 4,6-dimethyldibenzothiophene. The most important characteristics of the SBA-15 material were preserved in the titania and zirconia-containing supports and the trimetallic catalysts. The deposited metal oxide species (NiO, CoO, MoO3 and WO3) were well-dispersed. NiMoW catalysts were substantially more active in deep HDS than the corresponding CoMoW ones. Titania and zirconia addition to the supports resulted in higher HDS activity of NiMoW and CoMoW catalysts, being this effect larger for the Ni-promoted samples. The NiMoW/Zr-SBA-15 catalyst was the most active for the elimination of sulfur from both dibenzothiophene and 4,6-dimethyldibenzothiophene. Its activity was twice higher than that of the NiMoW/SBA-15 analog. This was attributed to the high dispersion of the deposited metal species in the sulfided NiMoW/Zr-SBA-15 sample. Regarding the catalysts’ selectivity, it depended more strongly on the promoter used than on the support’s chemical composition.

Surface functionalization of Pt nanoparticles with metal chlorides for bifunctional CO oxidation

Incorporation of a metal oxide or hydroxide species into Pt-based electrocatalysts has been shown to lower the overpotential required to oxidatively remove carbon monoxide from the catalyst surface, a reaction that is critical to preventing catalyst poisoning and deactivation in fuel cell devices. In this work, we report a general synthetic method toward Pt-metal oxide composite nanoparticles via the adsorption of metal halide ligands onto 1–2 nm colloidal Pt nanoparticles. Pt-metal oxide composite nanoparticles spanning across the first-row transition metals and post-transition metals are synthesized and characterized with transmission electron microscopy and energy dispersive X-ray scattering. CO stripping and steady-state CO oxidation experiments reveal that Mn, Fe, Co, Ni, and In oxides are capable of participating in the catalysis as a bifunctional partner and reduce the overpotential required for CO electrooxidation by ∼200 mV relative to pure Pt.

Advances in Applications of Metal Oxide Nanomaterials as Imaging Contrast Agents

Medical diagnosis relies on imaging modalities to reveal abnormalities in organs or existence of tumorous lesion. Application of contrast agents alongside imaging techniques is essential in order to obtain high contrast images with distinguishable features. Contrast agents delivered and accumulated in target sites can enhance local signal generation and solve the inherent lack of contrast in imaging techniques. As such, various contrast agents are developed for modalities like computed tomography (CT), magnetic resonance imaging (MRI), and photoacoustic imaging (PAI). For many of these techniques, metal‐based agents possess the desired properties for signal and contrast enhancement. Metal oxide nanomaterials present a simple platform for metal‐based contrast agents with tunable structure, magnetic and optical properties, surface chemistry, and pharmacokinetics. These can be controlled through synthesis, redox reactions, and surface modification to produce desirable nanoparticles. In this review, recent advances in the development of metal oxide imaging agents are highlighted. Various metal oxide species are discussed, including iron oxides, gadolinium oxides, manganese oxides, tungsten oxides and bronzes, molybdenum oxides, and other oxides of titanium, tantalum, etc. Imaging capability and performance of these metal oxides are presented, and novel functionalization strategies are presented. Finally, recommendations for future research in this area are proposed.

Lithium adsorption from natural brine using surface-modified manganese oxide adsorbents

A series of surface-modified lithium ion adsorbents was synthesized in a pH-controlled solution using impregnation method; different oligomeric metal-hydroxide precursors were added on the surface of a spinel-type manganese oxide (Li1.33Mn1.67O4), which was then heat treated. X-ray diffractometry indicated that the crystal structure of spinel was maintained after heating. Transmission electron microscopy revealed that their surfaces were partially covered with metal-oxide layers of 10–20 nm thickness. Loaded metal-oxide contents in mass % were 7.1 of Al and 11.8 of Ni, respectively. The effect of metal-oxide species on chemical stability of the resulting materials in 0.25 mol dm−3 H2SO4 solution was investigated by inductively-coupled plasma spectrometry. Metal-oxide coated Li1.33Mn1.67O4 showed lower manganese dissolution and higher lithium extraction, compared with that of the raw Li1.33Mn1.67O4.

(Invited) Nanostructured-Metal-Oxide Functionalized-Supports for Noble Metal Catalytic Nanoparticles: Enhancement of Electrooxidation of Simple Organic Fuels

There has been growing interest in utilizing small (simple) organic molecules, as alternative fuels to hydrogen, in electrochemical energy conversion systems. In addition to ethanol (biofuel), that can be ideally oxidized to carbon dioxide thus delivering twelve electrons, recent important systems include dimethyl ether as well. But realistically the respective reaction is rather slow at ambient conditions. Obviously, there is a need to develop novel electrocatalytic materials. Platinum has been recognized as the most active catalytic metal towards oxidation of ethanol at low and moderate temperatures. But Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. To enhance activity of Pt catalysts towards methanol and ethanol oxidation, additional metals including ruthenium, tin, molybdenum, tungsten or rhodium are usually introduced as the alloying component. More recently it has been demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of metal oxo species of tungsten, titanium or zirconium. We pursue a concept of utilization of mixed metal (e.g. zirconium/tungsten or titanium/tungsten) oxide matrices for supporting and activating noble metal nanoparticles (e.g. PtRu) during electrooxidation of methanol and ethanol. Among important issues is incorporation of Rh nanostructures capable of weakening, or even breaking, the C-C bond in the ethanol molecules. On the other hand, rhodium itself is not directly electrocatalytic toward oxidation of ethanol. The oxides and noble metal nanoparticles have been deposited in a controlled manner using the layer-by-layer method. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account possibility of specific interactions of noble metals with transition metal oxide species as well as existence of active hydroxyl groups in the vicinity of catalytic noble metal sites. In addition, formation of “nanoreactors” where ethanol is partitioned (at Rh) to methanolic residues further oxidized at PtRu cannot be excluded.

Influence of the Incorporation of Basic or Amphoteric Oxides on the Performance of Cu-Based Catalysts Supported on Sepiolite in Furfural Hydrogenation

Cu-based catalysts supported on sepiolite have been tested in vapor-phase hydrogenation of furfural. The incorporation of basic or amphoteric metal oxides (magnesium oxide, zinc oxide, or cerium oxide) improves the catalytic behavior, reaching a maximum furfural conversion above 80% after 5 h of reaction at 210 °C. In all cases, the main product is furfuryl alcohol, obtaining 2-methylfuran in lower proportions. The incorporation of these metal oxide species ameliorates the dispersion of metallic Cu nanoparticles, increasing the number of available Cu0-sites, which enhances the catalytic performance. The presence of acid sites favors the hydrogenolysis of furfuryl alcohol towards 2-methylfuran, although it also causes an increase of carbon species on its surface, which is associated with the catalytic deactivation of the catalyst along the time-on-stream.

Improved Cu- and Zn-based catalysts for CO2 hydrogenation to methanol

Abstract In this study the influence of metal dispersion, spinel formation, and surface properties of binary and ternary catalysts (CuO CeO2, ZnO CeO2, CuO ZnO CeO2, and CuO ZnO Al2O3) was evaluated. The catalysts prepared by polyol method using polyethylene glycol as a solvent have been tested in the CO2 hydrogenation to methanol performed at atmospheric pressure. The catalysts prepared by polyol method presented improved properties in terms of metal oxide dispersion, morphology (i.e. sponge-like shape for the CeO2-containing catalysts), and a large variety of metal and metal oxide species on the surface. Moreover, the CuO ZnO CeO2 and CuO ZnO Al2O3 catalysts exhibited a higher activity and selectivity in the methanol synthesis by CO2 hydrogenation than those displayed by catalysts prepared by more conventional methods.

Tin oxide species as promotive additives to Ni-P/C electrocatalysts for ethanol electro-oxidation in NaOH solution

Incorporating transition metal oxide species in the chemical structure of nickel-based electrocatalysts was beneficial in improving their activity as anode materials in fuel cells. Electroless deposition technique was employed to synthesize Ni-P-SnO2/C composites containing variable wt% values of tin oxide species. Scanning electron micrographs revealed spherical nickel particles with diameter values ranging between 500 and 1100 nm. Elemental mapping images of these composites confirmed the presence of nickel, phosphorous, tin, oxygen and carbon in their structural composition. An enhanced performance of these Ni-P-SnO2/C electrocatalysts was measured during ethanol oxidation reaction in alkaline solution. The added SnO2 content in the prepared electrocatalysts was found to influence their electrocatalytic activity. The highest ethanol oxidation current density values were attained at electrocatalysts containing 2.5 or 25 wt% SnO2. Furthermore, chronoamperometry demonstrated their stable behavior over prolonged operation. The charge transfer properties of Ni-P-SnO2/C electrocatalysts were significantly affected by the chosen potential value, ethanol and NaOH concentrations.