Highly ordered crystalline mesoporous metal oxides for hydrogen peroxide decomposition

Highly ordered mesoporous metal oxides (meso-MO _x ) such as CeO₂, Co₃O₄, Cr₂O₃, Mn₂O₃, NiO, RuO₂, SnO₂ and TiO₂ were successfully synthesized using mesoporous silica KIT-6 as a hard template via the nano-replication method. The physicochemical properties of as-prepared meso-MO _x were characterized by scanning electron microscopy, X-ray diffraction, N₂ adsorption–desorption and temperature programmed techniques. Their catalytic behavior toward H₂O₂ decomposition was investigated and compared with the corresponding bulk metal oxides (bulk-MO _x ) synthesized by the conventional precipitation method. These meso-MO _x materials exhibited much higher catalytic activities than their bulk counterparts. In particular, meso-Mn₂O₃ and meso-RuO₂ showed high activities, while meso-SnO₂ resulted in no activity toward H₂O₂ decomposition. The overall conversion of H₂O₂ followed a general order: Mn₂O₃ > RuO₂ > Co₃O₄ > CeO₂ > NiO > Cr₂O₃ > TiO₂ > SnO₂.     

Co3O4 and Mn3O4 Nanoparticles Dispersed on SBA-15: Efficient Catalysts for Methane Combustion

Co₃O₄ and Mn₃O₄ nanoparticles were successfully impregnated on SBA-15 mesoporous silica. A high dispersion of these metal oxide particles was achieved while using a “two-solvents” procedure, allowing a proper control of the metal oxides loading (7 wt%) and size (10–12 nm). These Co₃O₄ and Mn₃O₄ supported oxides on SBA-15 were characterised by means of XRD, BET and TEM techniques. The influence of the nature of the silica support was investigated in terms of porosity and specific surface area. Since, an improved catalytic activity was achieved over SBA-15 mesoporous silica; it appears that its organised porous meso-structure creates a confinement medium which permits a high dispersion of metal oxide nanoparticles. Supported Co₃O₄/SBA-15 (7 wt%) showed the highest catalytic performance in the combustion of methane under lower explosive limit conditions, comparable to perovskites. These materials become therefore novel efficient combustion catalysts at low metal loading.     

Metal oxides nanoparticles on SBA-15: Efficient catalyst for methane combustion

Catalysts based on crystalline nanoparticles of Mn and Co metal oxides supported on mesoporous silica SBA-15 have been developed. These materials were characterized by XRD, BET and transmission electron microscopy (TEM) techniques. SBA-15 mesoporous silica was synthesized by a conventional sol–gel method using a tri-block copolymer as surfactant. Supported Mn₃O₄ and Co₃O₄ nanoparticles were obtained after calcination of as-impregnated SBA-15 by a metal salt precursor. The catalytic activity was evaluated in the combustion of methane at low concentration.Co₃O₄/SBA-15 (7 wt.%) exhibits the highest performance among the different oxides. Furthermore, this novel generation of catalysts appeared as active as conventional LaCoO₃ perovskite, usually taken as reference for this reaction. Thanks to its organized meso-structures, SBA-15 material creates peculiar diffusion conditions for reactants and/or products.     

Manganese and cobalt-terephthalate metal-organic frameworks as a precursor for synthesis of Mn2O3, Mn3O4 and Co3O4 nanoparticles: Active catalysts for olefin heterogeneous oxidation

The thermal decomposition of manganese and cobalt-terephthalate Metal-Organic Framework precursors was utilized as a synthetic route for fabrication of Co₃O₄, Mn₃O₄ and Mn₂O₃ nanoparticles. The prepared metal oxide nanoparticles of Co₃O₄, Mn₃O₄ and Mn₂O₃ possess average size diameter of 40, 60 and 80 nm respectively. The findings demonstrate that spinel structure nanoparticles of Co₃O₄ and Mn₃O₄ exhibit efficient catalytic activity toward heterogeneous olefin epoxidation in the presence of tert-butyl hydroperoxide. In addition, Co₃O₄ and Mn₃O₄ nanoparticles illustrated excellent catalytic stability and reusability for nine and four cycles, respectively, toward olefin oxidation.     

The Electrical Properties of Polyaniline (PANI)–Co0.5Mn0.5Fe2O4 Nanocomposite

Polyaniline (PANI)/cobalt-manganese ferrite, PANI/Co_0.5Mn_0.5Fe₂O₄, nanocomposite was synthesized by oxidative chemical polymerization of aniline in the presence of ammonium peroxydisulfate. Microwave assisted synthesis method was used for the fabrication of core Co_0.5Mn_0.5Fe₂O₄ nanoparticles. The presence of PANI on the surface of the Co_0.5Mn_0.5Fe₂O₄ NPs was confirmed by infrared spectroscopy and thermal gravimetric analysis. The crystallite size was calculated with line profile fitting method as 20 ± 9 nm. The spherical morphology of the product was presented by Scanning electron microscopy and transmission electron microscopy. The electrical characterizations showed that ac conductivity is found to be independent of frequency and increases with increase of temperatures. However, imaginary component of dielectric function obey the power law of frequency while it is almost independent of temperature. This can be attributed to the molecular interatomic interaction between Co_0.5Mn_0.5Fe₂O₄ nanoballs and PANI shells.     

TIC-09-Mesoporous Niobium-Based Mixed Metal Oxides Containing Mo, V, and Te for Propane Oxidative Dehydrogenation

The novel thermally stable mesoporous multicomponent MNbO _x (M = V, Mo, and Te) mixed metal oxides were successfully synthesized by evaporation-induced self-assembly (EISA) employing niobium oxide as a major structural component. The formation of nanocrystalline M1 phase as part of the ordered mesoporous structure was investigated. These mixed metal oxide phases displayed good thermal stability (up to 400 °C), large pore sizes (up to 14 nm), high surface areas (up to 230 m²/g) and flexible inorganic wall compositions. Thermally stable mesoporous Nb₂O₅ supported metal M/Nb (M = MoVTeNb) oxides were obtained by incipient-wetness impregnation (IWI) technique. The comparison between mesoporous bulk mixed and supported mixed metal oxides (MNbO _x and M/Nb) were addressed. The catalytic roles of the constituent metal oxides were investigated in oxidative dehydrogenation (ODH) of propane. The methods described in this paper represent promising synthetic approaches for the design of novel catalytic mixed metal oxides.     

Oxide (CeO2, NiO, Co3O4 and Mn3O4)-promoted Pd/C electrocatalysts for alcohol electrooxidation in alkaline media

This study investigated Pt/C, Pd/C and oxide (CeO₂, NiO, Co₃O₄ and Mn₃O₄)-promoted Pd/C for electrooxidation reactions of methanol, ethanol, ethylene glycol and glycerol in alkaline media. The results show that Pd/C electrocatalysts alone have low activity and very poor stability for the alcohol electrooxidation. However, addition of oxides like CeO₂, NiO, Co₃O₄ and Mn₃O₄ significantly promotes catalytic activity and stability of the Pd/C electrocatalysts for the alcohol electrooxidation. The Pd-Co₃O₄ (2:1, w:w)/C shows the highest activity for the electrooxidation of methanol, EG and glycerol while the most active catalyst for the ethanol electrooxidation is Pd-NiO (6:1, w:w)/C. On the other hand, Pd-Mn₃O₄/C shows significantly better performance stability than other oxide-promoted Pd/C for the alcohol electrooxidation. The poor stability of the Pd-Co₃O₄/C electrocatalysts is most likely related to the limited solubility of cobalt oxides in alkaline solutions.     

The Solubility of Specific Metal Oxides in Molten Borate Glass

The solubility of Co₃O₄, Cu₂O, CuO, NiO, and Mn₂O₃ in molten B₂O₃ and Na₂O–2B₂O₃ has been studied at a temperature of 900°C under static conditions. The concentration of the dissolved metal oxides was determined by X‐EDS and XPS elemental analysis. Uniformity of metal distribution has been confirmed using X‐EDS and backscatter electron image mapping. It was found that the solubility of all metal oxides increased significantly with Na₂O content in the B₂O₃ solvent. The impact of a temperature increase of 150°C and the influence of K₂O doping were evaluated and found to not cause any significant change.     

Highly Efficient Removal of Congo red from Wastewater by Nano-Cao

Nano-CaO with high surface area of 120 m² · g^?1 has been used as adsorbents for Congo red adsorption from wastewater. The maximum adsorption capability of Congo red on nano-CaO reached 357.14 mg · g^?1 in 10 min, while the maximum capability on commercial CaO was only 238.66 mg · g^?1 in 30 min. In comparison with commercial CaO, some published metal oxides for Congo red adsorption such as Fe₂O₃, NiO, MgO, and Mn₂O₃, etc., the Nano-CaO exhibited much more favorable adsorptive property. In addition, the effects of pH, salt concentration, and temperature were also investigated, and these factors played significant roles for Congo red adsorption on Nano-CaO.     

Optimal synthesis and new understanding of P2-type Na2/3Mn1/2Fe1/4Co1/4O2 as an advanced cathode material in sodium-ion batteries with improved cycle stability

A sol-gel method with ethylene diamine tetraacetic acid and citric acid as co-chelates is employed for the synthesis of P2-type Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ as cathode material for sodium-ion batteries. Among the various calcination temperatures, the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂ with a pure P2-type phase calcined at 900 °C demonstrates the best cycle capacity, with a first discharge capacity of 157 mA h g^?1 and a capacity retention of 91 mA h g^?1 after 100 cycles. For comparison, the classic P2-type Na_2/3Mn_1/2Fe_1/2O₂ cathode prepared under the same conditions shows a comparable first discharge capacity of 150 mA h g^?1 but poorer cycling stability, with a capacity retention of only 42 mA h g^?1 after 100 cycles. Based on X-ray photoelectron spectroscopy, the introduction of cobalt together with sol-gel synthesis solves the severe capacity decay problem of P2-type Na_2/3Mn_1/2Fe_1/2O₂ by reducing the content of Mn and slowing down the loss of Mn on the surface of the Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, as well as by improving the activity of Fe³⁺ and the stability of Fe⁴⁺ in the electrode. This research is the first to demonstrate the origin of the excellent cycle stability of Na_2/3Mn_1/2Fe_1/4Co_1/4O₂, which may provide a new strategy for the development of electrode materials for use in sodium-ion batteries.     

Phase diagram and supercritical deoxidation kinetics of manganese oxides in organic solvent N,N-dimethylformamide

Deoxidation of manganese oxides in supercritical N,N-dimethylformamide (SC-DMF) is revealed, contrasting to previous amounts of reports on supercritical water oxidation. Mn₃O₄ and MnO can be produced by the reaction starting from layered manganese oxides (δ-MnO₂) in a uniform supercritical process. Time effect can give rise to the transition to Mn₃O₄ under low temperature, but the prolonged time, under a temperature lower than 200 ̊C, cannot cause this transition. Phase diagram is obtained, including three regions of MnO₂, Mn₃O₄ and MnO as the main material phase. The completion of transition accompanies with an oxygen loss course. Comparison between supercritical oxidation of water and supercritical deoxidation of organic DMF demonstrates the unique mechanisms of supercritical processing. In terms of the surface contacting fluid, deoxidation kinetics has a reciprocal law of growing size for manganese oxides. The new deoxidation procedure using organic solvent is proposed for the processing of metal oxides.     

XRD Studies on the conversion from several manganese oxides to β-manganese dioxide during acid digestion in MnSO4H2SO4 system

The wet method to change crystal structure from several manganese oxides to β-manganese dioxide, iso-structural with rutile, was reported.Manganese oxides such as Mn₂O₃ and Mn₃O₄ gave the same XRD profiles as an electrolytic MnO₂ (EMD) on boiling in dilute H₂SO₄ solution at 90–100°C for several hours and finally gave the XRD pattern of β-MnO₂ for a prolonged reaction period. Interesting finding was that several MnO₂s such as δ-MnO₂, α-MnO₂, EMD and heat-treated EMD could be converted into β-MnO₂ by using the proton-assisted rearrangement reaction in a boiling dilute H₂SO₄ solution containing Mn²⁺ ion at 90–110°C for several hours to several weeks depending on starting materials. The complex situations on classifying artificial manganese dioxides especially EMDs in terms of crystal structure are discussed.     

Magnetic Properties of FeMn<Subscript>y</Subscript>Co<Subscript>y</Subscript>Fe<Subscript>2−2y</Subscript>O<Subscript>4</Subscript>@Oleylamine Nanocomposite with Cation Distribution

In this study, oleylamine (OAm) capped FeMn_yCo_yFe_2?2yO₄ (0.0?≤?y?≤?0.4) nanocomposites (NCs) were prepared via the polyol route and the impact of bimetallic Co³⁺ and Mn³⁺ ions on the structural and magnetic properties of Fe₃O₄ was investigated. The complete characterization of FeMn_yCo_yFe_2?2yO₄@OAm NCs were done by different techniques such as XRD, SEM, TGA, FT-IR, TEM, and VSM. XRD analyses proved the successful formation of mono-phase MnFe₂O₄ spinel cubic products free from any impurity. The average crystallite sizes were calculated in the range of 9.4–26.4 nm using Sherrer’s formula. Both SEM and TEM results confirmed that products are nanoparticles like structures having spherical morphology with small agglomeration. Ms continued to decrease up to Co³⁺ and Mn³⁺ content of y?=?0.4. Although Mössbauer analysis reveals that the nanocomposites consist three magnetic sextets and superparamagnetic particles are also formed for Fe₃O₄, Co_0.2Mn_0.2Fe_2.6O₄ and Co_0.4Mn_0.4Fe_2.2O₄. Cation distributions calculation was reported that Co³⁺ ions prefer to replace Fe²⁺ ions on tetrahedral side up to all the concentration while Mn³⁺ ions prefer to replace Fe³⁺ ions on the octahedral.     

Cobalt and Copper Composite Oxides as Efficient Catalysts for Preferential Oxidation of CO in H2-Rich Stream

A series of Co–Cu composite oxides with different Co/Cu atomic ratios were prepared by a co-precipitation method. XRD, N₂ sorption, TEM, XPS, H₂-TPR, CO-TPR, CO-TPD and O₂-TPD were used to characterize the structure and redox properties of the composite oxides. Only spinel structure of Co₃O₄ phase was confirmed for the Co–Cu composite oxides with Co/Cu ratios of 4/1 and 2/1, but the particle sizes of these composite oxides decreased evidently compared with Co₃O₄. These composite oxides could be reduced at lower temperatures than Co₃O₄ by either H₂ or CO. CO and O₂ adsorption amounts over the composite oxides were significantly higher than those over Co₃O₄. These results indicated a strong interaction between cobalt and copper species in the composite samples, possibly suggesting the formation of Cu _x Co_3?x O₄ solid solution. For the preferential oxidation of CO in a H₂-rich stream, the Co–Cu composite oxides (Co/Cu = 4/1–1/1) showed distinctly higher catalytic activities than both Co₃O₄ and CuO, and the formation of Cu _x Co_3?x O₄ solid solution was proposed to contribute to the high catalytic activity of the composite catalysts. The Co–Cu composite oxide was found to exhibit higher catalytic activity than several other Co₃O₄-based binary oxides including Co–Ce, Co–Ni, Co–Fe and Co–Zn oxides.     

Rates of reaction of SO2 with metal oxides

Rates of sorption of SO₂ from synthetic flue gas by 14 metal oxides were determined. These oxides had been selected for their potential applicability to processes for removing SO₂ from flue gas using thermal regeneration of sorbent. Measurements were performed using thermogravimetric analysis, and rates were fitted to semi-empirical expressions; CeO₂, Co₃O₄, Cr₂O₃, CuO, Fe₂O₃, and NiO displayed measurable rates in the range 200° to 500°C, and were converted to sulphates. Rates were immeasurably small at 25° to 800°C for Al₂O₃, Sb₂O₅, SnO₂, TiO₂, V₂O₅, WO₃, ZnO, and ZrO₂, CuO and CeO₂ showed the highest rates     

Supported Ni–W–O Mixed Oxides as Selective Catalysts for the Oxidative Dehydrogenation of Ethane

Mixed Ni–W–O catalysts (with a W/(Ni + W) atomic ratio of 0.3) supported on γ-Al₂O₃ or on mesoporous alumina have been prepared, characterized and tested in the oxidation of ethane. For comparison unsupported and supported NiO as well as bulk Ni–W–O mixed oxides catalysts have also been studied. Supported Ni–W–O materials show interesting catalytic performances in the oxidative dehydrogenation of ethane. They show similar catalytic activities than the corresponding unsupported Ni–W–O catalysts. However, the selectivity to ethylene over supported catalysts was higher than that achieved over unsupported samples (the selectivity to ethylene followed the trend: mesoporous-supported > γ-Al₂O₃-supported > unsupported Ni–W–O). In addition, it has also been observed that Ni–W–O catalysts are more efficient than the corresponding W-free NiO catalysts. The discussion of the catalytic results will be undertaken on the basis of the modification of active sites of NiO when incorporating WO₃ and/or metal oxide supports.     

Hydrocracking of vegetable oil on boron-containing catalysts: Effect of the nature and content of a hydrogenation component

Catalysts based on metals (Pt, Pd) and metal oxides (NiO, Co₃O₄, MoO₃, WO₃), supported on the surface of borate-containing aluminum oxide (B₂O₃–Al₂O₃), in the hydrocracking of sunflower oil at a temperature of 400°C, a pressure 4.0 MPa and a mass hourly space velocity MHSV 5.0 h^–1 are compared. H₂ TPR and IR spectroscopy of adsorbed CO and ESDR show that the hydrogenation catalyst components are Pt⁰ and Pd⁰, a mixture of Ni²⁺ + Ni⁰, Co²⁺ + Co⁰, or a mixture of the highest and partially reduced oxides of Mo and W. It is established that catalysts containing Pt, Pd, NiO and Co₃O₄, ensure complete oil hydrodeoxygenation. The main oxygen removal reactions in Ptand Pd-systems are decarboxylation and hydrodecarbonylation. For catalysts with NiO and Co₃O₄, characteristic reactions are reduction and methanation. The highest yield of the diesel fraction was obtained on Pt/B₂O₃-Al₂O₃ catalysts with metal contents of 0.3–1.0 wt %. Along with n-alkanes, the diesel fractions obtained on these catalysts include cycloalkanes and iso-alkanes (up to around 40 wt %) and aromatic hydrocarbons present in trace amounts. Hydrocracking on the Pt system at 400°C for 20 h with MHSV of 1.0 h^–1 produces a diesel fraction with a yield of at least 82.0 wt % and the content of iso-alkanes at least 76.1 wt %.     

Preparation and formation mechanism of Cr-free spinel-structured high entropy oxide (MnFeCoNiCu)3O4

In this work, two Cr-free high entropy oxides (HEOs), an equimolar (MnFeCoNiCu)₃O₄ and a non-equimolar (Mn_0.272Fe_0.272Co_0.272Ni_0.092Cu_0.092)₃O₄ have been synthesized by a solid-state reaction method. The reaction sequence and electrical conductivity were also studied for these two HEOs. It is demonstrated that a rock-salt phase containing a solid solution of NiO and CuO appears in the synthesizing process of (MnFeCoNiCu)₃O₄, which is ascribed to the incomplete solubilization of rock-salt phase in the spinel phase. For (Mn_0.272Fe_0.272Co_0.272Ni_0.092Cu_0.092)₃O₄, a single spinel phase (Fd-3m) is obtained at 750 °C, which is much lower than that of the (MnFeCoNiCu)₃O₄ sample. Furthermore, Mn, Fe, Co, Ni elements exist in the chemical states of +2 and + 3, and Cu exists in Cu²⁺ state. The electrical conductivity of (Mn_0.272Fe_0.272Co_0.272Ni_0.092Cu_0.092)₃O₄ is approximately 15.77 S cm^-1 at 800 °C, which is nearly three times higher than that of the (MnFeCoNiCu)₃O₄ sample.     

Catalytic Removal of Toluene over Co3O4–CeO2 Mixed Oxide Catalysts: Comparison with Pt/Al2O3

The catalytic oxidation of toluene, chosen as VOC probe molecule, was investigated over Co₃O₄, CeO₂ and over Co₃O₄–CeO₂ mixed oxides and compared with the catalytic behavior of a conventional Pt(1 wt%)/Al₂O₃ catalyst. Complete toluene oxidation to carbon dioxide and water was achieved over all the investigated systems at temperatures below 500 °C. The most efficient catalyst, Co₃O₄(30 wt%)–CeO₂(70 wt%), showed full toluene conversion at 275 °C, comparing favorably with Pt/Al₂O₃ (100% toluene conversion at 225 °C).     

Novel Y2O3 Doped MnO x Binary Metal Oxides for NO x Storage at Low Temperature in Lean Burn Condition

MnO _x -Y₂O₃ binary metal oxide catalysts are synthesized by a constant-pH co-precipitation method, their ability of NO _x storage capacity and absorbing process were investigated. The pure MnO _x and Y₂O₃ calcined at 500 °C for 4 h in static air are both of body-centre structure, while the binary metal oxides containing Mn and Y are mainly of amorphous phase. The adulteration of Y₂O₃ can remarkably improve the specific surface areas of the catalysts, which probably result of the enhancement on NO storage capacity and catalytic oxidation ability of NO at 100 °C. The XPS results indicate that both Mn and Y have 3+ chemical states in the binary oxides. FT-IR spectra could be beneficial to explain the NO storage process on the binary metal oxide: NO can be adsorbed on the MnO _x and Y₂O₃ sites as nitrates and nitrites, respectively, and then the nitrites on Y₂O₃ site are shifted to Mn₂O₃ site and then is oxidized to nitrates. As a result, the NO storage capacity is enhanced due to the adulteration of Y₂O₃, finally the NO _x are adsorbed on the Mn₂O₃ site as nitrate species.