Catalytic combustion of soot on metal oxides and their supported metal chlorides

Gravimetric temperature programmed oxidation was used to study the combustion of a soot mixed with various metal oxides and their supported metal chloride catalysts. It is found that the catalytic effect of metal oxide on soot combustion varies depending on property of oxides. CuO and Cr₂O₃ are better catalysts. Addition of some chloride salts (FeCl₃, NaCl and KCl) increases the catalytic activity and KCl exhibits the highest promoting effect by reducing the T_max for about 200 °C. Metal chlorides can also show a synergistic effect on soot combustion. FeCl₃–KCl/CuO can reduce the T_max of carbon oxidation from 780 to 500 °C. Investigation also demonstrates that FeCl₃–KCl/CuO is effective for NO reduction at low temperatures.     

Nanocrystalline transition metal oxides and their composites with reduced graphene oxide and carbon nanotubes for photocatalytic applications

Transition metal oxide nanoparticles (CuO, ZnO & Fe₂O₃) and mixed metal oxides CuO. ZnO.Fe₂O₃ were fabricated by facile co-precipitation approach for photocatalytic treatment of organic dyes. The structural features, phase purity, crystallite size and morphology of individual and mixed metal oxides were analysed by X-rays diffraction patterns (XRD) and scanning electron microscopic (SEM) analysis. Electrical behaviour of CuO, ZnO, Fe₂O₃ and mixed metal oxides CuO. ZnO.Fe₂O₃ was explored by current-voltage (I-V) measurements. Functional groups present in the synthesized metal oxides were investigated by Fourier transform infrared spectroscopy (FTIR) which ensures the existence of M-O functional groups in the samples. The optical bandgap analysis was carried out by UV–visible spectroscopic technique which revealed that the blend of three different transition metal oxides reduced the bandgap energy of mixed metal oxides. The reason behind this reduced bandgap energy is formation of new electronic state which arises due to the metal-oxygen interactions. Moreover, the nanocomposites of CuO.ZnO.Fe₂O₃ with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) were prepared to study the effect of the carbonaceous materials on the rate of photodegradation. These carbonaceous nanomaterials have plethora properties which can bring advancement in sector of photocatalytic treatment of wastewater. The photocatalytic experiments were performed using methylene blue (MB) as standard dye for comparative study of metal oxides and their composites with rGO and CNTs. The percentage degradation of methylene blue (MB) by nanocomposite CuO.ZnO.Fe₂O₃/rGO is 87% which is prominent among all samples. This result ascribed the photocatalytic aspects of reduced graphene oxide along with mixed metal oxides.     

Burning Characteristics and Sensitivity Characteristics of Some Guanidinium 1,5′‐bis‐1H‐Tetrazolate/Metal Oxide Mixtures as Candidate Gas Generating Agent

Burning characteristics and sensitivity characteristics of some stoichiometric ratio guanidinium 1,5′‐bis‐1H‐tetrazolate (G15B)/metal oxide mixtures were examined. The linear burning rates of the G15B/CuO mixture were higher compared to other G15B/metal oxide mixtures and 5‐amino‐1H‐tetrazole(5‐ATZ)/Sr(NO₃)₂ mixture, although the average rate of pressure rise during the closed vessel test was lower compared to 5‐ATZ/Sr(NO₃)₂ mixture. The temperature rise for both G15B/CuO and G15B/MnO₂ mixtures was considerably lower than that of 5‐ATZ/Sr(NO₃)₂ mixture. G15B/Fe₂O₃ mixture was the most insensitive among G15B/metal oxide mixtures during the drop hammer test, while G15B/CuO mixture was the second most insensitive. All G15B/metal oxide mixtures were insensitive against friction and electric spark discharge (ESD). Four seconds ignition temperature for G15B/CuO mixture was over 100 K lower than that of 5‐ATZ/Sr(NO₃)₂ mixture, but the apparent activation energy for ignition was higher. Among the G15B/metal oxide mixtures studied, G15B/CuO mixture showed the fastest burning rate, while it showed a relatively low temperature rise and low sensitivity. G15B/ZnO did not burn at all.     

Role of Additives in the Combustion of Ammonium Dinitramide

The thermal decomposition behavior and combustion characteristics of mixtures of ammonium dinitramide (ADN) with additives were studied. Micrometer‐sized particles of Al, Fe₂O₃, TiO₂, NiO, Cu(OH)NO₃, copper, CuO, and nanometer‐sized particles of aluminum (Alex) and CuO (nano‐CuO) were employed. The thermal decomposition was measured by TG‐DTA and DSC. The copper compounds and NiO lowered the onset temperature of ADN decomposition. The heat value of ADN with Alex was larger than that of pure ADN in closed conditions. The burning rates and temperature of the pure ADN and ADN/additives mixtures were measured. CuO and NiO enhance the burning rate, particularly at pressures lower than 1 MPa, because of the catalyzed decomposition in the condensed phase; the other additives lower the burning rate. This negative effect on the burning rate is explained based on the surface temperature measurements by a physicochemical mechanism, which involves a chemical reaction, a phase change of the ammonium nitrate, and the blown‐off droplets of the condensed phase.     

Total oxidation of propane over Cu-Mn mixed oxide catalysts prepared by co-precipitation method

The catalytic activity of Cu-Mn mixed oxides with varying Cu/Mn ratios prepared by co-precipitation method was examined for the total oxidation of propane. The nature and phase of the metal oxide species formed were characterized by various methods such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (TPR) as well as BET surface area measurement. The co-precipitation method provides highly interdispersed copper and manganese metallic elements forming Cu-Mn mixed oxide of spinel structure (Cu_1.5 Mn_1.5O₄). Besides the spinel-type Cu-Mn mixed oxide, CuO or Mn₂O₃ phases could be formed depending on the Cu/Mn molar ratio of their precursors. The catalytic activity of Cu-Mn mixed oxide catalyst for propane oxidation was much higher than those of single metal oxides of CuO and Mn₂O₃. The higher catalytic activity likely originates from a synergic effect of spinel-type Cu-Mn mixed oxide and CuO. The easier reducibility and BET surface area seems to be partially responsible for the high activity of Cu-Mn mixed oxide for total oxidation of propane.     

Effects of metal oxides on electrochemical hydrogen storage of nanocrystalline LaMg12-Ni composites

Nanocrystalline LaMg₁₂-Ni composites were prepared by ball-milling a LaMg₁₂ alloy and Ni powders with additions of small amounts of metal oxides (TiO₂, Fe₃O₄, La₂O₃ and CuO). The composites with additions of small amounts of metal oxides were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the effects of the addition of the metal oxides on the electrochemical hydrogen storage were investigated. It is demonstrated that the initial discharge capacities of the composites with additions of small amounts of metal oxides were significantly higher than that of the original composite. The additions of TiO₂ and Fe₃O₄ as catalysts improved the electrochemical hydrogen storage properties more effective than additions of La₂O₃ and CuO. Analysis of the electrochemical impedance spectra (EIS) showed that the function of the metal oxides was considered to reduce the electrochemical reaction resistance as catalysts and to increase the specific surface area as impurities. However, more extensive investigation is still necessary in order to improve the cyclic stability of these materials for practical application in Ni/MH batteries.     

Study of Some Low Temperature Gas‐Generating Compositions

Some low temperature gas‐generating compositions, comprised of guanidine nitrate (GN), basic cupric nitrate (BCN), and ferric oxide (Fe₂O₃), were studied herein. The thermal decomposition properties and burning characteristics of GN/BCN/Fe₂O₃ mixtures were investigated by thermogravimetry/differential scanning calorimetry (TG/DSC), burning temperature measurements, automatic calorimetry, and X‐ray diffraction (XRD). This study showed that the maximum burning temperature of GN/BCN/Fe₂O₃ mixture (613 °C) was 31 % lower than that of GN/BCN mixture and the corresponding heat of combustion (2647 J g⁻¹) decreased by 15 %. When the GN/BCN/Fe₂O₃ mixtures were burning, Fe₂O₃ did not directly react with GN but with Cu (or CuO), which was produced by reaction between GN and BCN. The combustion process of GN/BCN/Fe₂O₃ grains could be divided into four stages: pre‐heated, condensed, combustion, and cooling.     

High Efficiency of Noble Metal and Metal Oxide Catalyst Systems for the Selective Reduction of NO with Propene in Lean Exhaust Gas

An investigation was conducted of noble metal and metal oxide catalysts deposited on Al₂O₃. The noble metals Pt, Pd, Rh the metal oxides CuO, SnO₂, CoO, Ag₂O, In₂O₃, catalysts were examined. Also investigated were noble metal Pt, Pd, Rh-doped In₂O₃/Al₂O₃ catalysts prepared by single sol–gel method. Both were studied for their capability to reduce NO by propene under lean conditions. In order to improve the catalytic activity and the temperature window, the intermediate addition propene between a Pt/Al₂O₃ oxidation and metal oxide combined catalyst system was also studied. Pt/Al₂O₃ and In₂O₃/Al₂O₃ combined catalyst showed high NO reduction activity in a wider temperature window, and more than 60% NO conversion was observed in the temperature range of 300–550 °C.     

High efficiency of noble metal and metal oxide catalyst systems for the selective reduction of NO with propene in lean exhaust gas

An investigation was conducted of noble metal and metal oxide catalysts deposited on Al₂O₃. The noble metals Pt, Pd, Rh the metal oxides CuO, SnO₂, CoO, Ag₂O, In₂O₃, catalysts were examined. Also investigated were noble metal Pt, Pd, Rh-doped In₂O₃/Al₂O₃ catalysts prepared by single sol–gel method. Both were studied for their capability to reduce NO by propene under lean conditions. In order to improve the catalytic activity and the temperature window, the intermediate addition propene between a Pt/Al₂O₃ oxidation and metal oxide combined catalyst system was also studied. Pt/Al₂O₃ and In₂O₃/Al₂O₃ combined catalyst showed high NO reduction activity in a wider temperature window, and more than 60% NO conversion was observed in the temperature range of 300–550 °C.

     

Combustion Characteristics of Ammonium Nitrate and Carbon Mixtures Based on a Thermal Decomposition Mechanism

In order to obtain a better understanding of the combustion characteristics of ammonium nitrate (AN) and carbon (C) mixtures (AN/C), burning tests and differential scanning calorimetry (DSC) were performed. AN mixed with carbon that is oxidized by nitric acid (HNO₃), such as activated carbon (AC), burned at 1 MPa. However, AN mixed with carbon that is not oxidized by HNO₃, such as graphite, did not burn under 7 MPa. Compositions with more than stoichiometric amounts of activated carbon had higher burning rates. Heat characteristic examinations found a similar trend. The burning rate of AN/AC mixed with CuO as a combustion catalyst deteriorated faster than an additive‐free one. From the DSC result, AN/AC/CuO had a higher onset temperature and a lower heat of reaction than AN/AC. These results suggested that, in the combustion wave of AN/C, a thermal decomposition zone is formed on the burning surface, and combustion performance was affected by the thermal decomposition of AN/C.     

Synthesis of hybrid metal oxides with high degradation efficiency via a self-propagating process of metallic glasses

Establishing hetero-junctions are widely regarded as an efficient strategy in the area of photocatalysis. In this work, the series of hybrid CuO/ZrO₂/Y₂O₃ compounds were synthesized by self-propagating combustion of Cu₆₀Zr_40-xY_x (x = 0, 5, 10, 15) metallic glasses. The combustion process is self-sustaining and can be efficiently regulated with the ratio of Zr/Y. The synthesized products are irregularly shaped and uniformly dispersed with a particle size of approximately 100 nm–5 μm. The presence of Y₂O₃ in the hybrid oxides stabilizes the ZrO₂ phase and narrows the bandgap energy of as-synthesized powders. For the photocatalytic ability in degrading Methylene Blue (MB), it was demonstrated that the optimal addition of yttrium in the precursor is approximately 10 at% to the formation of best photocatalysts in the current work. Our findings not only provide the new approach to synthesize highly photocatalytic hybrid metal oxides, but also extend the functional applications of amorphous alloys.     

Mechanism of combustion catalysis by ferrocene derivatives. 2. Combustion of ammonium perchlorate-Based propellants with ferrocene derivatives

Combustion of mixtures of a narrow fraction of ammonium perchlorate (AP) with hydrocarbon binders and combustion catalysts diethylferrocene and 1,1′-bis(dimethyloctyloxysilyl)ferrocene, as well as nano-sized Fe₂O₃ is studied. It is shown that the efficiency of ferrocene compounds from the viewpoint of increasing the burning rate depends on the oxidizer/fuel ratio in the propellant and on the place of the leading reaction of combustion. In composites with a high oxidizer/fuel ratio whose combustion follows the gas-phase model, the catalyst efficiency is rather low. In systems with a low oxidizer/fuel ratio where the contribution of condensed-phase reactions to the burning rate of the system is rather large, the catalyst efficiency is noticeably greater, and it is directly related to the possibility of formation of a soot skeleton during combustion. The close values of the catalytic activity of ferrocenes and Fe₂O₃ in the case of their small concentrations in such compositions testify that the main contribution to the increase in the propellant burning rate is made by Fe₂O₃ formed due to rapid oxidation of ferrocene on the AP surface and accumulated on the soot skeleton. Thermocouple measurements of propellants with a low oxidizer/fuel ratio are performed, and it is shown that the temperature of their surface is determined by plasticizer evaporation. A phenomenological model of combustion of the examined propellants is proposed.     

Reaction of polyacrylic acid and metal oxides: Infrared spectroscopic kinetic study and solvent effect

In this work, we performed infrared spectroscopic studies of the reaction of poly(acrylic acid) (PAA) and metal oxides (ZnO, CaO, CuO, Cr₂O₃, and Al₂O₃). Factors such as the amount of metal oxide, reaction time, solvents, the kind of metal oxides, and temperature were also evaluated to derive the optimum condition for this reaction. The reactions of Cr₂O₃ and Al₂O₃ were far from complete. An extra solvent added to the reaction system could increase the solubility of PAA and metal oxide in the solution so as to completely react. The reactivity of the reaction was increased by using the hydrophilic solvent, particularly H₂O and CH₃OH. Moreover, the reaction rate increased when temperature decreased. The reactivity of the reaction was proportional to the pH value of the metal oxide in the aqueous solution. © 1997 John Wiley & Sons, Inc.     

Synthesis and Characterization of Hetero-metallic Oxides-Reduced Graphene Oxide Nanocomposites for Photocatalytic Applications

A new AgO.CuO.WO₃/rGO nanocomposite was designed for the investigation of the degradation ability of the hybrid material under visible light irradiation. The AgO, CuO, WO₃ NPs, and AgO.CuO.WO₃ hetero-metallic oxides were fabricated via the chemical co-precipitation method. The crystallite sizes and phase analyses were investigated by recording X-ray diffraction patterns. The crystallite sizes of three metal oxides in the AgO.CuO.WO₃ hetero metal oxide were 16.7, 15.9, and 16.9 nm, respectively. The FESEM images at various magnifications were probed to study the morphology of synthesized materials. The micrographs of hetero-metallic oxides AgO.CuO.WO₃ exposed that three metal oxides merged like small particles and gives a large bulbous appearance. EDX analyses confirmed the formation of required materials with high purity. FTIR data was in agreement with the literature which facilitated to ensure the purity of synthesized samples. The optical bandgap energy was calculated via the Tauc plot indicating that the blend of three metal oxides generated a new energy level in the electronic structure is suitable for photocatalysis in the presence of visible light. The bandgap energy of hetero metallic oxides was 1.25 eV which is less than individual metal oxides signifying the tuning of the bandgap. The incorporation of rGO in AgO.CuO.WO₃ hetero-metallic oxides gives a new photocatalyst for optimum photodegradation of methylene blue in minimum time. The percentage degradation via AgO.CuO.WO₃ was 87.20% in 70 min while the percentage degradation via AgO.CuO.WO₃/rGO recorded by photocatalytic experiment was 95% in 40 min. The photocatalysis data revealed that AgO.CuO.WO₃ hetero-metallic oxides-rGO nanocomposite ensured a strong potential to uptake organic dyes from water by promoting redox reactions during photocatalysis in the minimum time limit.     

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.     

Agglomeration of magnesium particles in magnesium-sodium nitrate combustion

Agglomeration phenomenon of magnesium particles during combustion of Mg NaNO₃ propellant has been studied. High speed photographs of combustion zones and the burning surface temperature data indicate that the metal particles form agglomerates on the burning surface in varying degree depending on the mass fraction of NaNO₃. It is found that the increase of oxidizer content increases the metal agglomeration and the agglomerate size depends on the initial particle size of the ingredients. An attempt has been made to predict the size of the agglomerates based on the consideration that the agglomerate size depends on the thickness of the molten oxidizer layer enveloping the metal particles in the condensed phase and surface heat flux providing local temperature environment to agglomerate the metal particles and to eject from the burning surface for the vapour phase combustion. The results were compared with the experimental data. The prediction describes fairly well the observed effects of the concentration and particle size.     

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.     

Effect of Nano‐Copper Oxide and Copper Chromite on the Thermal Decomposition of Ammonium Perchlorate

The catalytic effect on the thermal decomposition behavior of ammonium perchlorate (AP) of p‐type nano‐CuO and CuCr₂O₄ synthesized by an electrochemical method has been investigated using differential scanning calorimetry as a function of catalyst concentration. The nano‐copper chromite (CuCr₂O₄) showed best catalytic effects as compared to nano‐cupric oxide (CuO) in lowering the high temperature decomposition by 118 °C at 2 wt.‐%. High heat releases of 5.430 and 3.921 kJ g⁻¹ were observed in the presence of nano‐CuO and CuCr₂O₄, respectively. The kinetic parameters were evaluated using the Kissinger method. The decrease in the activation energy and the increase in the rate constant for both the oxides confirmed the enhancement in catalytic activity of AP. A mechanism based on an electron transfer process has also been proposed for AP in the presence of nano‐metal oxides.     

Thermal stability and deformation of poly(acrylic acid)–metal oxides

In this work, we investigated the thermal stability and deformation of the compound of poly(acrylic acid) (PAA) and metal oxides (ZnO, CaO, CuO, Al₂O₃, and Cr₂O₃). The kinetic parameters of the desorption of water from PAA–metal oxide were calculated. The activation energies of the water desorption of PAA–metal oxide were less than 5 kcal/mol. The order of bonding capability of oxygen (PAA–O–metal) and water was PAA–CaO > PAA–ZnO > PAA–CuO > PAA–Cr₂O ₃ > PAA–Al₂O₃. The reaction types of the composites were clarified. Incorporating metal oxide into PAA increased the thermal stability. The factors which influence the mechanical properties of the composites, e.g., the chemical compositions, curing environment, and curing time, were also studied. The various curing environments (pure water, 0.1N HCl, 0.1N NaOH, and methanol) decreased the compressive strength of PAA—metal oxide. Moreover, the thermal stability and compressive strength of PAA–ZnO and PAA–CuO reached an optimum because of their crosslinking nature. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2021–2027, 1997     

Phosphorus‐Based Nanothermites: A New Generation of Pyrotechnics Illustrated by the Example of n‐CuO/Red P Mixtures

The use of aluminium nanoparticles (e.g. Al 50P) with various metallic oxides to prepare superthermites was reported in numerous recent papers. These compositions have exceptional energetic performances, but their fabrication cannot be scaled up due to the difficulty in producing or supplying aluminium nanopowders. The use of red phosphorus as an alternative reducing agent in nanothermite compositions was found to be very promising. Surprisingly, although this substance is a component of many explosive compositions, it was never tested with metallic oxide nanoparticles. In a preliminarily study, the reactivity of different metallic oxides with red phosphorus was screened. These tests led to classify the oxides according to their combustion potential, by ascending order: NiO<Fe₂O₃ CuO PbO₂. The CuO/P mixture possesses an impressive reactivity, and its combustion residues are less hazardous than those formed with PbO₂ insofar as lead derivatives are generally more toxic than their copper counterparts. CuO‐based P‐nanothermites were prepared by physically mixing copper(II) oxide nanoparticles with micrometre‐sized red phosphorus particles. The phosphorus content was varied from 16 to 50 wt.‐% in order to investigate the effect of the mass ratio on the reactivity of CuO/P materials. The impact sensitivity of CuO/P nanothermites is moderate (27–39 J), but their friction (<5–8 J) and electrostatic discharge sensitivities (<0.12–0.21 mJ) are extremely high. The combustion of P‐nanothermites (P‐NT) gives droplets of molten copper with a typical fractal structure after cooling down.