Experimental study on co-firing characteristics of ammonia with pulverized coal in a staged combustion drop tube furnace

Utilizing ammonia as a co-firing fuel to replace amounts of fossil fuel seems a feasible solution to reduce carbon emissions in existing pulverized coal-fired power plants. However, there are some problems needed to be considered when treating ammonia as a fuel, such as low flame stability, low combustion efficiency, and high NO_x emission. In this study, the co-firing characteristics of ammonia with pulverized coal are studied in a drop tube furnace with staged combustion strategy. Results showed that staged combustion would play a key role in reducing NO_x emissions by reducing the production of char-NO_x and fuel(NH₃)-NO_x simultaneously. Furthermore, the effects of different ammonia co-firing methods on the flue gas properties and unburned carbon contents were compared to achieve both efficient combustion and low NO_x emission. It was found that when ammonia was injected into 300 mm downstream under the condition of 20% co-firing, lower NO_x emission and unburnt carbon content than those of pure coal combustion can be achieved. This is probably caused by a combined effect of a high local equivalence ratio of NH₃/air and the prominent denitration effect of NH₃ in the vicinity of the NH₃ downstream injection location. In addition, NO_x emissions can be kept at approximately the same level as coal combustion when the co-firing ratio is below 30%. And the influence of reaction temperature on NO_x emissions is closely associated with the denitration efficiency of the NH₃. Almost no ammonia slip has been detected for any injection methods and co-firing ratio in the studied conditions. Thus, it can be confirmed that ammonia can be used as an alternative fuel to realize CO₂ reduction without extensive retrofitting works. And the NO_x emission can be reduced by producing a locally NH₃ flame zone with a high equivalence ratio as well as ensuring adequate residence time.     

Experimental and modeling study on the auto-ignition properties of ammonia/methane mixtures at elevated pressures

Ammonia (NH₃) is considered as a promising carbon free energy carrier for energy and transportation systems. However, its low flammability and high NO_x emission potential inhibit the implementation of pure NH₃ in these systems. On the other hand, methane is a favorable low emission fuel that can be used as a co-firing fuel in ammonia combustion to promote the reactivity and control the emission levels. However, knowledge of the ignition properties of NH₃/CH₄ mixtures at intermediate temperatures and elevated pressures is still scarce. This study reports ignition delay times of NH₃/CH₄/O₂ mixtures diluted in Ar or Ar/N₂ over a temperature range of 900–1100 K, pressures of 20 and 40 bar, and equivalence ratios of 0.5, 1.0, and 2.0. The results demonstrate that a higher CH₄ mole fraction in the fuel mixture increases its reactivity, and that the reactivity decreases with increasing the fuel-oxygen equivalence ratio. The most recent mechanisms of Glarborg et al. (2018) and Li et al. (2019) were compared against the experimental data for validation purposes. Both mechanisms can predict the measurements fairly well, and key elementary reactions applied in both mechanisms were compared. A modified mechanism is provided, which can reproduce the measurements with smaller discrepancies in most cases. Detailed modeling for emissions indicated that adding CH₄ to the fuel mixture increases the emission of NO_x.     

MILD Combustion of Methanol,Ethanol and 1-Butanol binary blends with Ammonia

In the present energy transition scenario, ammonia is considered a valuable candidate as energy-dense carrier with neutral or even negative carbon balance. However, the potential high NO_x emissions and the reduced oxidation process stability, at least when conventional combustion plants are used, can burden its wide utilization on large scales. In this context, MILD Combustion, due to its inherent characteristics, may greatly improve combustion stability and keep the NO_x emissions at an acceptable level. On the other hand, the addition of low or no-carbon fuels from biomasses and wastes, more reactive than ammonia, may be beneficial in further improving its combustion performance and the global sustainability of the energy supply chain.In this respect, the present work analyzes the sustainability and combustion performance of binary mixtures of ammonia and low-molecular-weight alcohols in a cyclonic burner, where MILD conditions are attained by means of a strong internal recirculation, and compares them with those obtained with NH₃/methane blends. Results highlighted that NH₃/alcohols mixtures ensure a stable oxidation process in a wide range of operational parameters without compromising the system performance. Moreover, they showed a significant reduction of NO_x emissions for NH₃/alcohols mixtures, especially for fuel-lean conditions, when compared to NH₃/methane blends.Experimental data were also corroborated by chemical kinetic modeling results to provide some insights on the peculiar NO_x formation routes when blends of different nature are used, highlighting the interaction between carbon and nitrogen fuels kinetics.     

A DNS study on temporally evolving jet flames of pulverized coal/biomass co-firing with different blending ratios

Biomass co-firing within the existing pulverized coal boiler is thought as a practical near-term way of biomass utilization, while its detailed combustion characteristics and pollutant formation have not yet been fully understood. In the present study, we report a Carrier-phase Direct Numerical Simulation study coupled with detailed mechanism to provide a deep insight into the coal/biomass co-firing (CBCF) jet flames under different blending ratios. It is found that compared with the pure coal flame, the CBCF could (i) prompt the volatiles ignition, produce higher H₂O and similar CO₂ mass fractions at blending ratios of 20% and 40%, and obviously reduce the gas temperature and CO₂ mass fraction at the blending ratio of 50%; (ii) prompt the coal devolatilization and char burnout at blending ratios of 20% and 40%, while the char burnout is reduced when blending ratio is 50% due to the local enrichment of large particles and lack of oxygen; (iii) reduce the thermal, prompt, NNH and N₂O-intermediate routes of NO formation, but show limited effect on the NO-reburning route of NO destruction, therefore, resulting in an obvious NO reduction.     

Reduction effect of co-firing of torrefied straw and bituminous coal on PM1 emission under both air and oxyfuel atmosphere

Straw sample was torrefied at 260 °C and 300 °C in N₂, respectively, to prepare torrefied straw named as T-260 and T-300, and the reduction effect of co-firing straw or torrefied straw and steam coal on PM₁ is investigated. The combustion experiments were conducted in a high temperature drop tube furnace (DTF) at 1400 °C to collect the inorganic PM₁₀ for further analysis. Combustion atmosphere was air for all cases and 50% O₂/50% CO₂ (OXY50) for coal, T-260 and their blends of 1:1 and 4:1. The results show that all three biomass fuels show obvious emission reduction of PM with aerodynamic diameters of ≤?0.3?µm (PM_0.3) under both mix ratios. Reduction ratios of co-firing are overall higher at mix ratio of 1:1 than 4:1, and co-firing of T-260 or T-300 with coal shows higher reduction ratio than co-firing of straw. The higher ash content in torrefied straw leads to higher contents of alkali and alkaline earth metals (AAEM), which will further react with both Si and S during co-firing and coagulate into particles of larger sizes, leading to higher reduction ratios of PM_0.3 and unconspicuous reduction effects in PM_0.3–1 emitted from co-firing. During co-firing in oxyfuel atmosphere, a higher combustion temperature compared to air leads to an intensitive gasification, may resulting in effective and even higher reduction ratio in PM_0.3.     

Measurements and modelling of oxy-fuel coal combustion

Oxy-fuel combustion is one of the most promising technologies to isolate efficiently and economically CO₂ emissions in coal combustion for the ready carbon sequestration. The high proportions of both H₂O and CO₂ in the furnace have complex impacts on flame characteristics (ignition, burnout, and heat transfer), pollutant emissions (NO_x, SO_x, and particulate matter), and operational concerns (ash deposition, fouling/slagging). In contrast to the existing literature, this review focuses on fundamental studies on both diagnostics and modelling aspects of bench- or lab-scale oxy-fuel combustion and, particularly, gives attention to the correlations among combustion characteristics, pollutant formation, and operational ash concerns. First, the influences of temperature and species concentrations (e.g., O₂, H₂O) on coal ignition, volatile combustion and char burning processes, for air- and oxy-firing, are comparatively evaluated and modelled, on the basis of data from optically-accessible set-ups including flat-flame burner, drop-tube furnace, and down-fired furnace. Then, the correlations of combustion-generated particulate/NO_x emissions with changes of combustion characteristics in both air and oxy-fuel firing modes are summarized. Additionally, ash deposition propensity, as well as its relation to the formation of fine particulates (i.e. PM_0.2, PM₁ and PM₁₀), for both modes are overviewed. Finally, future research topics are discussed. Fundamental oxy-fuel combustion research may provide an ideal alternative for validating CFD simulations toward industrial applications.     

Experimental and modeling study on the ignition delay times of ammonia/methane mixtures at high dilution and high temperatures

Ammonia is a promising alternative clean fuel due to its carbon-free character and high hydrogen density. However, the low reactivity of ammonia and the potential high NO_x emissions hinder its applications. Blending methane into ammonia can effectively improve the reactivity of pure NH₃. In addition, lean combustion, as a high-efficiency and low-pollution combustion technology, is an effective measure to control the potential increase in NO_x emissions. In the present work, the ignition delay times (IDTs) of NH₃/CH₄ mixtures highly diluted in Ar (98%) with CH₄ mole fractions of 0%, 10%, and 50% were measured in a shock tube at an equivalence ratio of 0.5, pressures of 1.75 and 10 bar and a temperature range of 1421 K - 2149 K. A newly comprehensive kinetic model (named as HUST-NH₃ model) for the NH₃/CH₄ mixtures oxidation was developed based on our previous work. Four kinetic models, the HUST-NH₃ model, Glarborg model [19], Okafor model [7], and CEU model [10], were evaluated against the ignition delay times, laminar flame speeds, and species profiles of pure ammonia and ammonia/methane mixtures from the present work and literature. The simulation results indicated that the HUST-NH₃ model shows the best performance among the above four models. Kinetic analysis results indicated that the absence of NH₃ + M = NH₂ + H + M (R819) and N₂H₂ + M = H + NNH + M (R902) in the CEU model and Okafor model cause the deviations between the experimental and simulation results. The overestimation of the rate constants of NH₂ + NO = NNH + OH (R838) in the Glarborg model is the main reason for the overprediction of the NH₃ laminar flame speeds.     

Optical diagnostics on coal ignition and gas-phase combustion in co-firing ammonia with pulverized coal on a two-stage flat flame burner

Gradual substitution of coal with green ammonia is a practical approach for the coal power phasedown at a minimal cost of modification, but the ignition and gas-phase reaction during co-firing NH₃ with coal remain largely unclear. In this work, we investigate the co-combustion behaviors of NH₃ and a high-volatile coal on a two-stage flat flame burner. Remarkably, the post-flame oxygen mole fraction X_i,O2 of the inner stage can be manipulated to reproduce a proper reducing-to-oxidizing environment that coal particles experience in the practical combustor. We first reveal that, under certain values of X_i,O2 and NH₃ co-firing energy ratios E_NH3, the reaction intensity (manifested by OH-PLIF signals) in the NH₃-coal flame is stronger than burning either pure coal or NH₃. This synergetic effect originates from an NH₃-combustion-induced enhancement of volatile release. We then propose a characteristic time scale τ_OH from the OH signals for the initiation of overall reactions in the system. In the case of X_i,O2=0, τ_OH monotonically increases with E_NH3, while for X_i,O2=0.2, the trend transitions to a decreasing one. It can be interpreted by comparing τ_OH with the characteristic O₂ diffusion time, coal particle heating time, and the coal pyrolysis time under different X_i,O2. Furthermore, the coal particle ignition in coal-NH₃ flames can no longer be determined by visual images. Instead, we apply CH* chemiluminescence to identify the stages of coal particle ignition and volatile combustion in the NH₃-coal flame. While NH₃ addition has both positive (elevating temperatures & diluting coal particles) and negative (consuming O₂) effects on coal ignition, the combined influence of E_NH3 is marginal on coal ignition delay time. On the other hand, the volatile combustion time decreases linearly with E_NH3, suggesting a pure effect of reduced coal feed rate.     

Fundamental investigation of NOx formation during oxy-fuel combustion of pulverized coal

NO_x formation was measured during combustion of pulverized coals and pulverized coal char in N₂ and CO₂ environments under isothermal and nearly constant oxygen conditions (i.e. using dilute coal loading). Three different oxygen concentrations (12% O₂, 24% O₂, and 36% O₂) and two representative US coals were investigated, at a gas temperature of 1050 °C. To investigate the importance of NO reburn reactions, experiments were also performed with an elevated concentration (550 ppm) of NO in the gases into which the coal was introduced. For low levels of background NO, the fractional fuel-nitrogen conversion to NO_x increases dramatically with increasing bath gas oxygen content, for both N₂ and CO₂ environments, though the fuel conversion is generally lower in CO₂ environments. Char N conversion is lower than volatile N conversion, especially for elevated O₂ concentrations. These results highlight the importance of the volatile flame and char combustion temperatures on NO_x formation. For the high background NO_x condition, net NO_x production is only observed in the 36% O₂ environment. Under these dilute loading conditions, NO reburn is found to be between 20% and 40%, depending on the type of coal, the use of N₂ or CO₂ diluent, the bulk O₂ concentration, and whether or not one considers reburn of volatile-NO_x. This dataset provides a unique opportunity to understand and differentiate the different sources and sinks of NO_x under oxy-fuel combustion conditions.     

Properties of biomass vs. coal fly ashes deposited in electrostatic precipitator

This paper presents comparative experimental studies of the morphology and elemental composition of fly ash particles from coal- and biomass-fired boilers, deposited in each stage of 3-stage electrostatic precipitators (ESPs). It was shown that fly ash morphology, its physical properties, and the percentage of elements in the fly ash taken from each stage of ESP depend on the kind of fuel. The biomass fly ash contains many irregular large particles, which are pieces of unburned wood. Bulk density of biomass fly ash is on average lower than that of coal fly ash, and drastically decreases in the second and third stages of ESP. The resistivity, measured at electric field of 4 kV/cm, of fly ash from biomass-fired boilers is much lower than that from coal, and can be below 10² Ω m, whereas from coal, except the first stage, varies in the range from 10⁷ to 10¹⁰ Ω m. The low resistivity of coal fly ash in the first stage of ESP results from high carbon content, and of biomass is probably an effect of additional high percentage of potassium, calcium and sodium sulfates. The percentage of Si, Al, Na, Fe, and Ti in fly ash from coal-fired boilers is much higher than from biomass, and in the opposite, the percentage of Mg, K, Ca, Mn, Mo, S, Cl, and P in biomass ash exceeds that in coal fly ash. Potential detrimental effects of biomass combustion products (salts, acids, tar) leaving the boiler on the construction elements of the electrostatic precipitator, including electrodes and HV insulators have been discussed in this paper. It was concluded that the long-term effects of biomass co-firing on the electrostatic precipitator performance, including the collection efficiency, have not been sufficiently studied in the literature and these issues require further detailed investigations.     

An improved method for selective catalytic reduction of nitrogen oxides in exhaust gases

The selective catalytic reduction (SCR) of nitrogen dioxide in an air flow modeling the exhaust gas from an internal combustion engine is studied. Granulated V₂O₅ (13.5%)–MnO₂ (0.7–1.0%)/Al₂O₃ powder (AVK-10M catalyst) and ammonia injected into a SCR catalytic cell are used as a heterogeneous catalyst of NO₂ reduction and a reducing agent, respectively. If the efficiency of NO₂ removal is high enough and satisfies the requirements of the State Sanitary Standards for the maximum permissible concentrations of substances emitted into the atmosphere (\(MP{C_{N{O_2}}}\) = 0.085 mg/m³), the reducing agent (ammonia) is not completely consumed during SCR, so a considerable amount of NH₃ can be released into the atmosphere. Therefore, a strict control of both NO₂ and unreacted ammonia emissions is needed. The dependences of the concentrations of [NH₃] and [NO₂] on the [NH₃]/[NO₂] ratio for the model air flow passed through the AVK-10M granular heterogeneous catalyst are measured. It is found that the maximum degree of removal of NO₂ from the air takes place at [NH₃]/[NO₂] = 1.3. In the conventional process, the concentration of [NO₂] drop from 530.00 to 0.07 mg/m³, i.e., below the \(MP{C_{N{O_2}}}\). At the same time, the ammonia concentration increases to [NH₃] = 3.4 mg/m³, which becomes 85 times the \(MP{C_{N{O_2}}}\), 0.04 mg/m³. To remove unreacted ammonia from air flows, we developed [P–(SO₃ ^-)₂ · Me²⁺] sulfocationites, where Me are the Cu and/or Ca ions, P is a styrene–divinylbenzene copolymer. It is shown that the concentration of ammonia passed through the adsorption cell filled with a freshly sulfocationite drops below \(MP{C_{N{H_3}}}\) = 0.04 mg/m³. The dependences of the dynamic exchange capacity (DEC) before ammonia breakthrough for the [P–(SO₃ ^-)₂ · Cu²⁺] delta-sulfocationite on the air flow rate, [NH₃] concentration, and humidity are measured. The maximum value of the DEC, δ = 59.5 mg/cm³, is observed at an air flow velocity of 2.171 m/s, [NH₃] = 0.0035 mg/L, and 75% humidity. To illustrate practical applications of the proposed improved SCR method, it is shown that a 3-L replaceable [P–(SO₃ ^-)₂ · Cu²⁺] sorbent cartridge in a SCR exhaust gas purifier for a car internal combustion engine does not need replacement more frequently than every 50000 km.     

Laser probing of OH production in catalytic oxidation of NH3byNO2 and no over a polycrystalline Pt surface at high temperatures

Catalytic ammonia denox reactions over a polycrystalline Pt surface in the temperature range 800–1330 K have been investigated by laser-induced-flourescence detection of the OH radical produced on and subsequently desorbed from the surface. For the NO₂-NH₃ system, strong curvature is observed in the low temperature region of the Arrhenius plots, which could be attributed to the presence of different desorption processes. The two extracted apparent OH desorption energies increase from 30 to 49 kcal/mol and from a surprisingly low value of 2 to 27 kcal/mol as the NO₂NH₃ reactant mixture ratio is decreased from 70 to 0.037. On the other hand, for the NO-NH₃ system, no such curvature in the Arrhenius plots is observed and the OH desorption energy decreases from 38 to 26 kcal/mol as the NO/NH₃ ratio is decreased from 70 to 0.4. The different trends in the apparent OH desorption energies as a function of the NO_x/NH₃ ratio in the present two systems can be rationalized by the degree of coverage of chemisorbed O atoms relative to that in the earlier studied O₂-NH₃ system.     

Ash formation and deposition during combustion of pulverized torrefied wood and coal in a 100 kW downflow combustor

Torrefied wood originating from beetle-killed trees is an abundant biomass fuel that can be co-fired with coal for power generation. In this work, pulverized torrefied wood, a bituminous coal (Sufco coal) and their blended fuel with a mixing ratio of 50/50 wt.%, are burned in a 100-kW rated laboratory combustor under similar conditions. Ash aerosols in the flue gas and ash deposits on a temperature-controlled surface are sampled during combustion of the three fuels. Results show that ash formation and deposition for wood combustion are notably different from those for coal combustion, revealing different mechanisms. Compared to the coal, the low-ash torrefied wood produces low concentrations of fly ash in the flue gas but significantly increased yields (per input ash) of ash that has been vaporized. All the mineral elements including the semi- or non-volatile metals in the wood are found to be more readily partitioned into the PM₁₀ ash than those in the coal. The inside layer deposits sticking to the surface and the loosely bound outside deposits exposed to the gas both show a linear growth in weight during torrefied wood test. Unlike coal combustion, in which the concentration of (vaporized) ash PM₁ controls the inside deposition rate, wood combustion shows that the formation of porous bulky deposits by the condensed residual ash dominates the inside deposition process. Co-firing removes these differences between the wood and coal, making the blended fuel to have more similar fly ash characteristics and ash deposition behavior to those of the bituminous coal. In addition, results also show some beneficial effects of co-firing coal with torrefied wood, including reduction of the total deposition rate and the minimization of corrosive alkali species produced by wood.     

Stability and characteristics of NH3/CH4/air flames in a combustor fired by a double swirl stabilized burner

Compared to hydrocarbons, ammonia's low reactivity and higher NO_x emissions limit its practical application. Consequently, its implementation in combustion systems requires a different combustor geometry, by adapting existing systems or developing new ones. This study investigates the flame stability, NO emissions, and flame structure of NH₃/CH₄/air premixed flames in a novel combustor comprising a double swirl burner. A lean premixed CH₄/air mixture of equivalence ratio, Φ_out, was supplied to the outer swirl, while a NH₃/CH₄/Air mixture fed the inner swirl. The molar fraction of NH₃ in the inner fuel blend, x_NH3, was varied from 0 (pure CH₄) to 1 (pure NH₃) over far-lean to far-rich inner stream equivalence ratio, Φ_in. This new burner's stability map was established in terms of Φ_in versus x_NH3 for different Φ_out. Then, NO emissions were measured versus Φ_in for various x_NH3 and Φ_out. Finally, based on the NO emissions, eight flames were down-selected for in-flame measurements, which included temperature and OH-PLIF. The stability measurements revealed that increasing x_NH3 modifies the stability map by increasing the lean blowout limits and narrowing the flashback region. At Φ_out ≥ 0.6, a stable flame was achieved for a pure inner NH₃/air mixture. Low NO emissions were achieved in this burner configuration at x_NH3=1 by either enriching or far-leaning Φ_in. Enriching Φ_in led to a steep decrease in NO concentrations. However, to achieve low NO concentrations, precise control of Φ_out was needed. At Φ_in=1.4, 220 ppm NO at Φ_out=0.7 versus 690 at Φ_out=0.6 was measured. Moreover, substantially enriching Φ_in>1.2 led to a slight decrease in measured NO. Generally, the OH-PLIF images revealed a conical OH-layer at the burner exit. Certain flame conditions created OH-pockets inside the conical structure or formed a V-shaped OH-layer far downstream. This change in flame structure was found to impact NO emissions strongly.     

Adsorption of NH3 and NO2 molecules on C48B6N6 heterofullerene: A DFT study on electronic properties

Adsorption of NH₃ and NO₂ molecules on the external surface of C₄₈B₆N₆ heterofullerene is investigated using DFT method. Attachment of NH₃ and NO₂ on C₄₈B₆N₆ heterofullerenes are compared with the bare C₄₈B₆N₆ model optimized at the B3LYP/6-31G^? level. The high surface binding energies indicates that ammonia undergoes chemical adsorption and could be compatible with the long recovery time but C₄₈B₆N₆ should be good NO₂ sensors with quick response as well as short recovery time. Total (TDOS) and partial (PDOS) density of state calculations is also considered to elucidate the difference in the NH₃ and NO₂ gas detection mechanism of C₄₈B₆N₆. The overlap population density of state (OPDOS) indicated that the chemical adsorption is due to the overlap of atomic orbitals below the Fermi level. The calculated results suggest that the C₄₈B₆N₆ heterofullerene is a suitable sensor material for NO₂ and is an ideal material for elimination and filtering of ammonia.     

Validation of flow simulation and gas combustion sub-models for the CFD-based prediction of NOx formation in biomass grate furnaces

While reasonably accurate in simulating gas phase combustion in biomass grate furnaces, CFD tools based on simple turbulence–chemistry interaction models and global reaction mechanisms have been shown to lack in reliability regarding the prediction of NO_x formation. Coupling detailed NO_x reaction kinetics with advanced turbulence–chemistry interaction models is a promising alternative, yet computationally inefficient for engineering purposes. In the present work, a model is proposed to overcome these difficulties. The model is based on the Realizable k–? model for turbulence, Eddy Dissipation Concept for turbulence–chemistry interaction and the HK97 reaction mechanism. The assessment of the sub-models in terms of accuracy and computational effort was carried out on three laboratory-scale turbulent jet flames in comparison with the experimental data. Without taking NO_x formation into account, the accuracy of turbulence modelling and turbulence–chemistry interaction modelling was systematically examined on Sandia Flame D and Sandia CO/H₂/N₂ Flame B to support the choice of the associated models. As revealed by the Large Eddy Simulations of the former flame, the shortcomings of turbulence modelling by the Reynolds averaged Navier–Stokes (RANS) approach considerably influence the prediction of the mixing-dominated combustion process. This reduced the sensitivity of the RANS results to the variations of turbulence–chemistry interaction models and combustion kinetics. Issues related to the NO_x formation with a focus on fuel bound nitrogen sources were investigated on a NH₃-doped syngas flame. The experimentally observed trend in NO_x yield from NH₃ was correctly reproduced by HK97, whereas the replacement of its combustion subset by that of a detailed reaction scheme led to a more accurate agreement, but at increased computational costs. Moreover, based on results of simulations with HK97, the main features of the local course of the NO_x formation processes were identified by a detailed analysis of the interactions between the nitrogen chemistry and the underlying flow field.     

Fabrication of three-dimensional dendrite-like CeO2 crystallites via simple template-free solution route

Highly uniform three-dimensional dendrite-like CeO₂ crystallites were successfully prepared in large quantities with a thermal decomposition of precursor approach applied. The precursor with an average size of 10 μm was prepared in an aqueous solution containing Ce(NO₃)₃·6H₂O, CO(NH₂)₂ and ammonia at 160 °C with no additional phase. The influence of ammonia on the dendrites formation was discussed. The dendritic pattern of precursor almost remained in the as-prepared product. The optical absorption spectrum indicates that CeO₂ dendrites have a direct band gap of 3.52 eV.     

The effect of NH<Subscript>4</Subscript>NO<Subscript>3</Subscript> towards the conductivity enhancement and electrical behavior in methyl cellulose-starch blend based ionic conductors

Solid polymer electrolytes based on methyl cellulose (MC)-potato starch (PS) blend doped with ammonium nitrate (NH₄NO₃) are prepared by solution cast technique. The interaction between the electrolyte’s materials is proven by Fourier transform infrared (FTIR) analysis. The thermal stability of the electrolytes is obtained from thermogravimetric analysis (TGA). The room temperature conductivity of undoped 60 wt.% MC-40 wt.% PS blend film is identified to be (1.04 ± 0.19) × 10^?11 S cm^?1. The addition of 30 wt.% NH₄NO₃ to the polymer blend has optimized the room temperature conductivity to (4.37 ± 0.16) × 10^?5 S cm^?1. Conductivity trend is verified by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and dielectric analysis. Temperature-dependence of conductivity obeys Arrhenius rule. Conductivity is found to be influenced by the number density (n) and mobility (μ) of ions. From transference number measurements (TNM), ions are found to be the dominant charge carriers.     

Adsorption of pairs of NOx molecules on single-walled carbon nanotubes and formation of NO + NO3 from NO2

The adsorption of NO_x(x = 1, 2, 3) molecules on single-walled carbon nanotubes (SWCNTs) is investigated using first-principle calculations. Single NO, NO₂ and NO₃ molecules are found to physisorb on SWCNTs, but molecules can be chemisorbed in pairs on the top of carbon atoms at close sites of SWCNTs. The adsorption energy for pairs of NO or NO₃ molecules is larger than for pairs of NO₂ molecules. The local curvature is found to have a sizable effect on adsorption energies. The possibility of a surface reaction NO₂ + NO₂ → NO + NO₃ is examined and the relative pathway and barrier is calculated. The results are discussed with reference to available experimental results.