Salt-Assisted Combustion Synthesis of NdCoO_3 Nanoparticles and Their Catalytic Properties in Thermal Decomposition of Ammonium Perchlorate

Highly dispersed perovskite NdCoO3 nanoparticles were prepared by a novel salt-assisted combustion process. The effects of NaCl content and calcination temperature on the characteristics of the products were characterized by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and BET surface area measurement. The facile introduction of NaCl in the conventional combustion synthesis process was found to result in the formation of well-dispersed perovskite nanoparticles and increase specific surface areas of the resultants from 1.7 to 43.2 m2·g-1. The catalytic properties of the typical NdCoO3 samples for thermal decomposition of ammonia perchlorate (AP) and their correlation with the NdCoO3 microstructure were investigated by Differential Scanning Calorimetry (DSC). The DSC results indicate that the addition of the amorphous NdCoO3 nanoparticles to AP incorporates two small exothermic peaks of AP into a strong exothermic peak, decreases the temperature of the AP exothermic peak to 314.0 ℃ by reduction of 138.3 ℃ and increases the apparent decomposition heat from 515 J·g-1 to over 1441 J·g-1, showing the intense catalytic activity for thermal decomposition of AP. It is also clear that the catalytic activity of the resultant NdCoO3 is related to their microstructure. According to Kissinger′s method, the kinetics parameters of the thermal decomposition of AP catalyzed by the as-prepared NdCoO3 samples were calculated to account for the order of their catalytic activity.

Nanoparticles α-Al_2O_3 prepared by combustion synthesis method

Nanometer α-Al2O3 powders were synthesized by the method of low-temperature combustion synthesis （LCS） with aluminum nitrate nonahydrate and urea as raw materials. The prepared powders were studied by XRD, TG-DTA, FT-IR and TEM. It is found that the average size of particles is 6080nm. The optimal synthetic conditions are obtained, i.e., the suitable fuel is urea; the molar ratio of oxidizer to fuel is 1∶2 and the igniting temperature is 700℃. The results show that the size of particles is governed by synthesizing temperature, the fuel and the molar ratio of oxidizer to fuel. TEM image of the particles collected shows that the crystal habits of particles have a spheric structure and particles are polycrystal.

Synthesis of La_(0.9)Sr_(0.1)Ga_(0.8)Mg_(0.2)O_(3-δ) Powder for Solid Oxide Fuel Cell by a Nitrate-Citrate Combustion Route

A nitrate-citrate combustion route to synthesize La0.9Sr0.1Ga0.8Mg0.2O3-σ powder for solid oxide fuel cell application was presented. This route is based on the gelling of nitrate solutions by the addition of citric acid and ammonium hydroxide, followed by an intense combustion process due to an exothermic redox reaction between nitrate and citrate ions. The optimum technical parameters are that the pH value is 5, and the molar ratio of citric acid to the total metallic ion is 1.5:1. X-ray diffraction characterization of calcined gel shows that pure phase was synthesized after calcination at 1400℃for 10 h, and the TEM result shovvs the calcined powder with average particle size is about 150 nm. The grain resistance contributes to the total resistance of sintered peliet below 500℃. The conductivity of the sintered peliet at 800℃ was 0.07 S-1·cm-1 higher than the conductivity of YSZ (0.05 S-1·cm-1 at 800℃)

Solution combustion synthesis of Ni-Y_2O_3 nanocomposite powder

Ni-Y2O3 nanocomposite powder with uniform distribution of fine oxide particles in the metal matrix was successfully fabricated via solution combustion process followed by hydrogen reduction. The combustion behavior was investigated by DTA-TG analysis. The influence of urea to nickel nitrate（U/Ni） ratio on the combustion behavior and morphology evolution of the combusted powder was investigated. The morphological characteristics and phase transformation of the combusted powder and the reduced powder were characterized by FESEM, TEM and XRD. The HRTEM image of Ni-Y2O3 nanocomposite powder indicated that Y2O3 particles with average particle size of about 10 nm dispersed uniformly in the nickel matrix.

Preparation of ultrafine Co_3O_4 powders by continuous and controllable combustion synthesis

The continuously dynamic-controlled combustion synthesis （CDCCS） was developed based on the continuous fluidization and combustion synthesis technologies. CoC2O4·2H2O powders were transformed to Co3O4 in a gas-solid fluid bed unit designed and build independently, where the reactant of CoC2O4·2H2O powders and the reactant of air were poured and introduced from the top and the bottom of the bed at a certain rates respectively. The reagents met in the bed and ignited at a given low temperature, resulting in formation of Co3O4. The results show a significant difference in combustion wave models. In the case of CDCCS, there was an immobile combustion wave, floating in the combustion zone located in the middle of the bed, instead of propagating of the combustion wave. The temperature of the combustion wave can be controlled by adjusting the flow rate of carrier gas. The resultant Co3O4 powders （diameter size ≤0.8 μm） have a narrow particle size distribution and spherical or quasi-spherical shape. This novel technique has many advantages, such as continuation, efficiency, energy conservation and environmental friendly and has been used in mass production.

Catalytic performance enhancement by alloying Pd with Pt on ordered mesoporous manganese oxide for methane combustion

Ordered mesoporous Mn2O3 (meso‐Mn2O3) and meso‐Mn2O3‐supported Pd, Pt, and Pd‐Pt alloy x(PdyPt)/meso‐Mn2O3; x = (0.10?1.50) wt%; Pd/Pt molar ratio (y) = 4.9?5.1 nanocatalysts were prepared using KIT‐6‐templated and poly(vinyl alcohol)‐protected reduction methods, respectively.The meso‐Mn2O3 had a high surface area, i.e., 106 m2/g, and a cubic crystal structure. Noble‐metalnanoparticles (NPs) of size 2.1?2.8 nm were uniformly dispersed on the meso‐Mn2O3 surfaces. AlloyingPd with Pt enhanced the catalytic activity in methane combustion; 1.41(Pd5.1Pt)/meso‐Mn2O3gave the best performance; T10%, T50%, and T90% (the temperatures required for achieving methaneconversions of 10%, 50%, and 90%) were 265, 345, and 425 °C, respectively, at a space velocity of20000 mL/(g?h). The effects of SO2, CO2, H2O, and NO on methane combustion over1.41(Pd5.1Pt)/meso‐Mn2O3 were also examined. We conclude that the good catalytic performance of1.41(Pd5.1Pt)/meso‐Mn2O3 is associated with its high‐quality porous structure, high adsorbed oxygen species concentration, good low‐temperature reducibility, and strong interactions between Pd‐Pt alloy NPs and the meso‐Mn2O3 support.

Preparation of ultrafine Ce-based oxide nanoparticles and their catalytic performances for diesel soot combustion

The ultrafine Ce-based oxide nanoparticles with different element dopings （Zr, Y） were synthesized by the method of mi- cropores-diffused coprecipitation （MDC） using ammonia solution as the precipitation agent. The activities of the catalysts for soot oxidation were evaluated by the temperature-programmed oxidation （TPO） reaction. Ce-based oxides prepared in this study exhibited high catalytic activity for soot oxidation under tile condition of loose contact between soot particles and catalysts, and the catalytic ac- tivity ofultrafine Ce0.gZr0 iO2 nanoparticle for soot combustion was the highest, whose/＂10, Ts0 and Sco2m was 364, 442 ~C and 98.3%, respectively. All catalysts were systematically characterized by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, Brumauer-Emett-Teller （BET）, Fourier transform infrared spectroscopy （FT-IR） and UV-Vis diffuse reflectance spectroscopy （UV-Vis DRS）. It was indicated that the MDC method could prepare the ultrafine Ce-bascd oxide nanoparticles whose the crystal lattice were perfect, and the BET surface area and average crystal size of the ultrafine nanoparticles changed with the different element dopings （Zr, Y）. The H2-TPR measurements showed that the ultrafine Ce-based ox- ide nanoparticles with the doping-Zr cation could be favorable for improving the redox property of the catalysts.

Carbon combustion synthesis of lithium cobalt oxide as cathode material for lithium ion battery

Lithium cobalt oxide （LiCoO2） was synthesized by carbon combustion synthesis （CCS） using carbon as fuel. X-ray diffraction （XRD） and scanning electron microscope （SEM） measurements showed that carbon combustion led to the formation of layered structure of LiCoO2 and the particle size could be controlled by carbon content. For the LiCoO2 sample prepared at 800℃ for 2 h, at molar ratio of C/Co = 0.5, the particle-size distribution fell in the narrow range of 3-5 μm. Electrochemical tests indicated this LiCoO2 sample delivered an initial discharge capacity of 148 mAh/g with capacity retention rate higher than 97% after 10 cycles.

Combustion synthesis of high-entropy carbide nanoparticles for tetracycline degradation via persulfate activation

The development of high-entropy carbide nanoparticles merits untold scientific and technological potential,yet their synthesis remains a challenge using conventional synthetic techniques.Herein we present a facile,rapid and low-cost route for the combustion synthesis of(Ta_(0.25)Nb_(0.25)-Zr_(0.25)Ti_(0.25))C high-entropy carbide(HEC-1)nanoparticles by self-propagating reaction of metal oxides,carbon and Mg mixture precursors in NaF salt media for the first time.The combustion synthesis possibility of HEC-1 is first analyzed theoretically from thermodynamic aspects,and then the ultrafine HEC-1 nanoparticles(average particle size:~19 nm)are synthesized successfully by the combustion synthesis technique at combustion temperature of~1487 K,duration of 63 s,and heating rate of~68 K s^(-1).The as-synthesized HEC-1 nanoparticles possess high compositional uniformity and low oxygen impurity content of 2.98 wt%.To prove their utility,the as-synthesized HEC-1 nanoparticles are utilized as an effective persulfate activation catalyst for the degradation of tetracycline pollutant in groundwater or wastewater and a removal efficiency of~65.5%for tetracycline is obtained after10 h.

THERMODYNAMIC AND PARTICLE-DYNAMIC STUDY FOR COMBUSTION SYNTHESIS OF TITANIA NANOPARTICLES

Recent referential studies on combustion synthesis of titania nanoparticles were briefly reviewed. Com-putations based on the minimization of Gibbs free energy were conducted to find the equilibrium compositions, the op-timal reaction temperature, the suitable mole ratio of oxygen to titanium tetrachloride, and the best inlet positions of tita-nium tetrachloride. The mean particle diameter was obtained from particle-dynamic simulation. A combustion apparatus was setup to synthesize titania nanoparticles by the oxidation and hydrolysis of titanium tetrachloride at high tempera-tures. Experimental investigation verified some results obtained from thermodynamic and particle-dynamic computations.

Synthesis,and measurement of structural and magnetic properties,of La_(1-x)Na_xFeO_3 (0.0≤x≤0.3) perovskite oxides

Polycrystalline La1-xNaxFeO3 (0.0≤x≤0.3) solid solutions were synthesized by a solution combustion method using glycine as a fuel. The combustion synthesized compounds were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), diffused reflectance (DR) in the UV-vis, and magnetic measurements. The crystal structure examined by X-ray powder diffraction indicated that the samples were single phase and crystallized in an orthorhombic (space group, Pbnm no.62) structure. The parent and sodium-substituted compounds showed canted anti-ferromagnetic behavior associated with an increase in magnetic moment as Na content increased. The changes in magnetic properties of the materials were correlated to the changes in structural features, as shown by Rietveld structural refinement of the materials.

A review of significant factors in the synthesis of hetero-structured dumbbell-like nanoparticles

This paper reviews several important factors that influence the synthesis of dumbbell‐like nanoparticles,which can significantly enhance the catalyst activity in catalytic combustion. The dumbbell‐like nanoparticles discussed in this article refer to a hetero‐structure with two nanoparticles of different materials in contact with each other. This nanostructure can be considered as a special intermediate between individual spherical nanoparticles and a core–shell nanostructure. Therefore,the synthesis of dumbbell‐like nanoparticles is more difficult than other structures. The controllability of the synthesis process, the nanoparticle size and size distribution, and the morphology of the final products depend on many factors： the seed size and size ratio could be used to influence the controllability of epitaxial growth. The component sizes and size distribution could be varied by carefully controlling the reaction temperature and reaction time. The morphology of the dumbbell‐like nanoparticles is closely related to the solvent polarity, the precursor ratio, the lattice mismatch between the two components, and the surfactant concentration. Some related synthesis methods are also briefly introduced in each section to facilitate understanding. This summary will benefit the development of new dumbbell‐like nanoparticles with various components, which have great potential in catalytic combustion of more dysoxidizable gases.

Investigation of oxy-fuel combustion for methane and acid gas in a diffusion flame

Co-combustion of methane(CH4)and acid gas(AG)is required to sustain the temperature in Claus reaction furnace.In this study,oxy-fuel combustion of methane and acid gas has been experimentally studied in a diffusion flame.Three equivalence ratios(ER=1.0,1.5,2.0)and CH_(4)-addition ratios(CH_(4)/AG=0.3,0.5,0.7)were examined and the flame was interpreted by analyzing the distributions of the temperature and species concentration along central axial.CH_(4)-AG diffusion flame could be classified into three sections namely initial reaction,oxidation and complex reaction sections.Competitive oxidation of CH_(4)and H_(2)S was noted in the first section wherein H_(2)S was preferred and both were mainly proceeding decomposition and partial oxidation.SO_(2)was formed at oxidation section together with obvious presence of H2 and CO.However,H2 and CO were inclined to be sustained under fuel rich condition in the complex reaction section.Reducing ER and increasing CH4/AG contributed to higher temperature,H_(2)S and CH_(4)oxidation and CO_(2)reactivity.Hence a growing trend for CH_(4)and AG to convert into H_(2),CO and SO_(2)could be witnessed.And this factor enhanced the generation of CS2 and COS in the flame inner core by interactions of CH4 and CO_(2)with sulfur species.COS was formed through the interactions of CO and CO_(2)with sulfur species.The CS_(2)production directly relied on reaction of CH_(4)with sulfur species.The concentration of COS was greater than CS_(2)since CS_(2)was probably inhibited due to the presence of H_(2).COS and CS_(2)could be consumed by further oxidation or other complex reactions.

Catalytic combustion of soot over Ru-doped mixed oxides catalysts

We employed modified substrates as outer heterogeneous catalysts to reduce the soot originating from the incomplete diesel combustion. Here, we proposed that ceria（CeO2）-based catalysts could lower the temperature at which soot combustion occurred from 610 oC to values included in the operation range of diesel exhausts（270–400 oC）. Here, we used the sol-gel method to synthesize catalysts based on mixed oxides（ZnO：CeO2） deposited on cordierite substrates, and modified by ruthenium nanoparticles. The presence of ZnO in these mixed oxides produced defects associated with oxygen vacancies, improving thermal stability, redox potential, sulfur resistance, and oxygen storage. We evaluated the morphological and structural properties of the material by X-ray diffraction（XRD）, Brumauer-emmett-teller method（BET）, temperature programmed reduction（H2-TPR）, scanning electron microscopy（SEM）, and transmission electron microscopy（TEM）. We investigated how the addition of Ru（0.5 wt.%） affected the catalytic activity of ZnO：CeO2 in terms of soot combustion. Thermogravimetric analysis（TG/DTA） revealed that presence of the catalyst decreased the soot combustion temperature by 250 oC, indicating that the oxygen species arose at low temperatures, which was the main reason for the high reactivity of the oxidation reactions. Comparative analysis of soot emission by diffuse reflectance spectroscopy（DRS） showed that the catalyst containing Ru on the mixed oxide-impregnated cordierite samples efficiently oxidized soot in a diesel stationary motor： soot emission decreased 80%.

Synthesis and characterization of SrCe_(0.95)Y_(0.05)O_(3-δ) nano powders by low temperature combustion

Nanosized SrCe0.95Y0.05O3-δ powders with homogeneous composition were synthesized by the low temperature combustion process based on the Pechini method. A polymeric precursor sol was formed by using citric acid and ethylene glycol as the chelating agents of metal ions. The perovskite-type SrCe0.95Y0.05O3-δpowders with uniform shape and smaller than 25 nm in size were obtained through the combustion of the polymeric precursor sol at the existence of nitric acid and ammonium hydroxide. It was found that modulating the quantifies of nitric acid and ammonium hydroxide could control the particle size, and the quantities of residue carbonate ions were also affected by the quantifies of citric acid and ethylene glycol.

Combustion synthesis of mesoporous CoAl_(2)O_(4)for peroxymonosulfate activation to degrade organic pollutants

A mesoporous cobalt aluminate(CoAl_(2)O_(4))spinel is synthesized through a combustion method and adopted for the activation of peroxymonosulfate(PMS)to degrade organic pollutants.Multiple characterization procedures are conducted to investigate the morphology and physicochemical properties of the CoAl_(2)O_(4)spinel.Due to its mesoporous structure,large surface area,and high electrical conductivity,the obtained CoAl_(2)O_(4)exhibits remarkable catalytic activity for Rhodamine B(RhB)degradation.Its RhB degradation rate is 89.0 and 10.5 times greater than those of Co_(3)O_(4) and CoAl_(2)O_(4)spinel prepared by a precipitation method,respectively.Moreover,the mesoporous CoAl_(2)O_(4)spinel demonstrates a broad operating pH range and excellent recyclability.The influence of several parameters(catalyst amount,PMS concentration,initial p H,and coexisting inorganic anions)on the oxidation of RhB is evaluated.Through quenching tests and electron paramagnetic resonance experiments,sulfate radicals are identified as the predominant reactive species in RhB degradation.This paper provides new insights for the development of efficient,stable,and reusable cobalt-based heterogeneous catalysts and promotes the application of persulfate activation technology for the treatment of refractory organic wastewater.

Combustion synthesis and stability of nanocrystalline La_2O_3 via ethanolamine-nitrate process

Pure nanocrystalline La2O3 powders were successfully prepared by the combustion method.The effect of ethanolamine-to-nitrate ratio on phase composition and crystallite size of the combustion products was systematically investigated.Pure hexagonal La2O3 powders were almost formed in stoichiometric reaction（ψ=1.15）,while metallic La phase was obtained in fuel-rich conditions（ψ≥3.0）.The as-synthesized hexagonal La2O3 was found to be chemically unstable in ambient air since a complete transformation to hexagonal La（OH）3 was detected after 24 h exposure to air.The resulting hexagonal La（OH）3 showed an excellent ability to remove water pollutant and could nearly remove 100% of the Congo red at room temperature with a removal capacity of 143.5 mg Congo red/g.The phosphate adsorption data on hexagonal La（OH）3 agreed well with the Langmuir model with the estimated maximum adsorption capacity of 57.8 mg/g.

Risk assessment of gas control and spontaneous combustion of coal under gas drainage of an upper tunnel

The adjustment of the gas drainage rate has an immediate impact on air leakage in gob,thus resulting in the change of self-heating of coal.While regulating the gas drainage parameters,the risk of spontaneous combustion of coal should be considered.The risk assessment of gas control and spontaneous combustion of coal under gas drainage in a tunnel was investigated at different gas drainage rates.The distributions of the air volume along the working face,the gas management effects and the width of the oxidation zone were subjected to risk analysis.As the simulation results showed,with increasing gas drainage rate,although the safety of gas dilution by ventilation was assured,the intensifying air leakage caused the oxidation zone to move into the deeper gob and led to an increase in the width of the oxidation zone.A risk assessment method was proposed to determine a suitable gas drainage rate for the upper tunnel.The correctness of the risk assessment and the validity of the numerical modelling were confirmed by the field measurements.

Gas-phase oxidation of NO at high pressure relevant to sour gas compression purification process for oxy-fuel combustion flue gas

The removal of NO from oxy-fuel combustion is typically incorporated in sour gas compression purification process. This process involves the oxidation of NO to NO2 at a high pressure of 1–3 MPa, followed by absorption of NO2 by water. In this pressure range, the NO conversion rates calculated using the existing kinetic constants are often higher than those obtained experimentally. This study aimed to achieve the regression of kinetic parameters of NO oxidation based on the existing experimental results and theoretical models.Based on three existing NO oxidation mechanisms, first, the expressions for NO conversion against residence time were derived. By minimizing the mean-square errors of NO conversion ratio, the optimum kinetic rate constants were obtained. Without considering the reverse reaction for NO oxidation, similar mean-square errors for NO conversion ratio were calculated. Considering the reverse reaction for NO oxidation based on the termolecular reaction mechanism, the minimum mean-square error for NO conversion ratio was obtained. Thus, the optimum NO oxidation rate in the pressure range 0.1–3 MPa can be expressed as follows:-d[NO]/dt=d[NO2]/dt=0.0026[NO]2[O2]-0.0034[NO2]2 Detailed elementary reactions for N2/NO/NO2/O2 system were established to simulate the NO oxidation rate. A sensitivity analysis showed that the critical elementary reaction is 2 NO + O2? 2 NO2. However, the simulated NO conversions at a high pressure of 10–30 bar are still higher than the experimental values and similar to those obtained from the models without considering the reverse reaction for NO oxidation.

A New Combustion Process for Nanosized BaCe_(0.95)Y_(0.05)O_(3-δ) Powders

Nanosized BaCe_(0.95)Y_(0.05)O_(3-δ) powders with the homogeneous composition were synthesized by a new combustion process based on the Pechini method. A polymeric precursor sol was formed by use of citric acid and ethylene glycol as the chelating agents of metal ions. The perovskite-type BaCe_(0.95)Y_(0.05)O_(3-δ) powders with uniform shape and smaller than 40 nm in sized were obtained through the combustion of the polymeric precursor sol at the existence of nitric acid and ammonium hydroxide. It was found the particle size could be controlled by modulating the quantities of nitric acid and ammonium hydroxide, the quantities of the residue, carbonate ions were also affected by the quantities of the citric acid and ethylene glycol.