Reaction Of NH3 Research Articles

Growth mechanism study of boron nitride atomic layer deposition by experiment and density functional theory

We investigated the fundamental mechanisms determining the limit of the atomic layer deposition (ALD) temperature window by density functional theory (DFT) simulations. Boron nitride (BN) ALD experiments were performed using BCl3 or tris-dimethylaminoborane (TDMAB) and NH3 on Si(100) substrates to check whether the ALD temperature window exists or not. With increasing the growth temperature, an increase in growth per cycle (GPC) between 700 and 900 °C was relatively small in the BCl3 and NH3 system, while the GPC exponentially increased in the TDMAB and NH3 system. Based on the experimental results, we performed DFT simulations to investigate the reaction mechanisms determining the lower ALD temperature window in the BCl3 and NH3 systems. The two initial reactions and two cyclic reactions were numerically analyzed: (a) BCl3 reactions on OH-terminated Si(100) surface, (b) NH3 reactions on Cl-terminated Si(100) surface, (c) BCl3 reactions on H-terminated BN surface, and (d) NH3 reactions on Cl-terminated BN surface. We found activation energies for reaction (c) is 30.0 kcal/mol, determining the lower limit of the ALD temperature window. The activation temperature of reaction (c) is obtained 789 °C which is just in the ALD temperature window by our experiments.

An experimental and modeling study on auto-ignition of ammonia in an RCM with N2O and H2 addition

Deep insights into the combustion kinetics of ammonia (NH3) can facilitate its application as a promising carbon-free fuel. Due to the low reactivity of NH3, experimental data of NH3 combustion can only be obtained within a limited range. In this work, nitrous oxide (N2O) and hydrogen (H2) were used as additives to investigate NH3 auto-ignition in a rapid compression machine (RCM). Ignition delay times for NH3, NH3/N2O blends, and NH3/H2 blends were measured at 30 bar, temperatures from 950 to 1437 K. The addition of N2O and H2 ranged from 0 to 50% and 0 to 25% of NH3 mole fraction, respectively. Time-resolved species profiles were recorded during the auto-ignition process using a fast sampling system combined with a gas chromatograph (GC). An NH3 combustion model was developed, in which the rate constants of key reactions were constrained by current experimental data. The addition of N2O affected the ignition of NH3 primarily through the decomposition of N2O (N2O (+M) = N2 + O (+M), R1) and direct reaction between N2O and NH2 (N2H2 + NO = NH2 + N2O, R2). The rate constant of R2 was constrained effectively by experimental data of NH3/N2O mixtures. Two-stage ignition behaviors were observed for NH3/H2 mixtures, and the corresponding first-stage ignition delay times were reported for the first time. Experimental species profiles suggested the first-stage ignition resulted from the consumption of H2. The oxidation of H2 provided extra HO2 radicals, which promoted the production of OH radicals and initiated first-stage ignition. Reactions between HO2 radicals and NH3/NH2 dominated the first-ignition delay times of NH3/H2 mixtures. Moreover, the first-stage ignition led to the fast production of NO2, which acted as a key intermediate and affected the following total ignition. Consequently, the reaction NH2 + NO2 = H2NO + NO (R3) was constrained by total ignition delay times.

Ni dopped MgAl hydrotalcite catalyzed hydrothermal liquefaction of microalgae for low N, O bio-oil production

Catalytic hydrothermal deoxygenation and denitrogenation of microalgae for bio-oil production can potentially avoid energy-intensive upgrading of bio-oil, while tandem amidation of deoxygenation products and re-esterification of NH3 with free fatty acids make simultaneous removal of N, O a dilemma to achieve. Taking advances of Ni in catalytic hydrogenation of biofuel, Ni dopped MgAl layered double hydroxides (NixMg2Al-LDHs, x = 0, 0.5, 0.7, 0.9, 1.1) with tunable acidic/basic property are synthesized to simultaneously catalyze deoxygenation and denitrogenation for low N, O biofuel production. The results indicate that Ni doping is favorable to hydrothermal liquefaction (HTL) of microalgae with maximum yield of 31.4 wt% obtained via Ni0.9Mg2Al-LDH catalyzed HTL of microalgae at temperature of 300 ℃, time of 1 h, and catalyst loading of 5 wt%. Ni doping initially reduces basicity of NixMg2Al-LDH, subsequently leading to increase of O/C ratio of bio-oil, while a continuous increase of Ni2+ provides more active species for deoxygenation with a final 13.49 % decrease of O/C ratio. Simultaneously, Ni doping of NixMg2Al-LDHs weakens denitrogenation of amino acids. However, tandem reactions of NH3 with reducing sugars, deoxygenation fatty acids radicals, and free fatty acids through Maillard reaction, amidation, and re-esterification are initially enhanced, leading to increase N/C ratio of bio-oil. Nevertheless, reducing property of NixMg2Al-LDH is continuously enhanced with increase of (Ni + Mg)/Al ratio from 0 to 2.9, finally resulting in 9.09 % decrease of N/C of biocrude. This work reports a methodology for simultaneous removal of N, O from biocrude, possibly providing a strategy for low N, O bio-oil production without further hydrogenation.

NH3[sbnd]NO interaction at low-temperatures: An experimental and modeling study

The present work provides new insight into NH3NO interaction under low-temperature conditions. The oxidation process of neat NH3 and NH3 doped with NO (450, 800 ppm) was experimentally investigated in a Jet Stirred Flow Reactor at atmospheric pressure for the temperature range 900–1350 K. Results showed NO concentration is entirely controlled by DeNOx reactions in the temperature range 1100–1250 K, while NH3NO interaction does not develop through a sensitizing NO effect, for these operating conditions.A detailed kinetic model was developed by systematically updating rate constants of controlling reactions and declaring new reactions for N2H2 isomers (cis and trans). The proposed mechanism well captures target species as NO and H2 profiles. For NH3NO mixtures, NO profiles were properly reproduced through updated DeNOx chemistry, while NH2 recombination reactions were found to be essential for predicting the formation of H2. The role of ammonia as a third-body species is implemented in the updated mechanism, with remarkable effects on species predictions. For neat NH3 mixture, the reaction H+O2(+M)=HO2(+M) was crucial to predict NO formation via the reaction NH2+HO2H2NO+OH.

A shock-tube study of NH3 and NH3/H2 oxidation using laser absorption of NH3 and H2O

Ammonia (NH3) is an attractive carbon-free fuel, yet its low reactivity presents many challenges for direct use in combustion applications. These combustion challenges could be resolved by mixing NH3 with more reactive fuels such as hydrogen (H2). To further contribute to NH3 and NH3/H2 kinetics—which arguably still requires much improvement—new experiments were conducted over a wide range of temperatures (1474–2307 K), near-atmospheric pressure, several NH3/O2 mixtures (equivalence ratios varying from 0.56 to 2.07), and near-stoichiometric NH3/H2/O2 mixtures with NH3:H2 ratios of 80:20 and 50:50. During these experiments, laser absorption diagnostics near 10.4 µm and 7.4 µm were simultaneously employed to measure NH3 and H2O time histories, respectively. Characteristic parameters, such as NH3 half-life time and H2O induction delay time, were extracted from the time-history profiles, and these parameters present stringent speciation targets for mechanism validation. After an assessment of most modern kinetics models, three, most accurate, mechanisms were compared against the experimental results. Only one model was able to partially reproduce the pure NH3 experiments, yet none of the models were capable of predicting the NH3/H2 experiments. Reaction pathway analysis showed that NH3 oxidation proceeds via forming NH2 then followed three different routes to form N2. Importantly, the models considered showed different levels of importance for each route. Sensitivity analysis showed that the NH3/H2 experiment is mostly sensitive to NH3+OH⇄NH2+H2O. Interestingly, this reaction showed no sensitivity for the NH3/O2 experiments. Overall, the models exhibited significantly slower reactivity than the NH3/H2 experiments, and the kinetics analysis showed that the start of this reactivity is governed by the levels of H-atoms in the early stages of the experiments. At these early stages of the experiments, propagation and branching reactions in the H2/O2 system are the main contributors to generating H radicals, along with the reaction NH3+H⇄NH2+H2 which proceeds in its reverse direction.

A theoretical kinetic study of the reactions of NH2 radicals with methanol and ethanol and their implications in kinetic modeling

AbstractAmino (NH2) radicals play a central role in the pyrolysis and oxidation of ammonia. Several reports in the literature highlight the importance of the reactions of NH2 radicals with fuel in NH3‐dual‐fuel combustion. Therefore, we investigated the reactions of NH2 radicals with methanol (CH3OH) and ethanol (C2H5OH) theoretically. We explored the various reaction pathways by exploiting CCSD(T)/cc‐pV(T, Q)Z//M06‐2X/aug‐cc‐pVTZ level of theory. The reaction proceeds via complex formation at the entrance and exit channels in an overall exothermic process. We used canonical transition state theory to obtain the high‐pressure limiting rate coefficients for various channels over the temperature range of 300–2000 K. We discerned the role of various channels in the potential energy surface (PES) of NH2 + CH3OH/C2H5OH reactions. For both reactions, the hydrogen abstraction pathway at the OH‐site of alcohols plays a minor role in the entire T‐range investigated. By including the title reactions into an extensive kinetic model, we demonstrated that the reaction of NH2 radicals with alcohols plays a paramount role in accurately predicting the low‐temperature oxidation kinetics of NH3‐alcohols dual fuel systems (e.g., shortening the ignition delay time). On the contrary, these reactions have negligible importance for high‐temperature oxidation kinetics of NH3‐alcohol blends (e.g., not affecting the laminar flame speed). In addition, we calculated the rate coefficients for NH2 + CH4 = CH3 + NH3 reaction that are in excellent agreement with the experimental data.

A novel resource conversion strategy of waste plastic express packaging bags using supercritical water-ammonia process: Optimization by response surface methodology

With the rapid development of e-commerce and express delivery industries, a large number of waste plastic express packaging bags (WPEPBs) are generated and urgent to be safely disposed. In this work, a novel resource conversion strategy was developed to produce high value-added chemicals from WPEPBs by supercritical water ammonia (SWA) process without any catalyst. WPEPBs could be converted into two parts by the SWA process: oil and solid residue. More than 80 % of the oil was identified as long-chain alkanes and alkenes due to the decomposition of polyethylene (PE) contained in WPEPBs. The presence of NH3 in SWA was beneficial to improve the production of long-chain alkenes. The plasticizers in WPEPBs including bisphenol A (BPA) and phthalate ester (DEHP) could be efficiently converted into aniline (≈15%) and 2-ethylhexanol (≈4 %) due to the high reactivity of NH3 in the SWA process. Compared with the degradation of WPEPBs in supercritical water, the SWA process could reduce side effects and improve the purity of target products. High-purity CaCO3 powder could be further recovered from the solid residue. The optimal parameters of the SWA process for the conversion of WPEPBs by Response Surface Methodology (RSM) were 440.5 ℃, 90 min, and CNH3 of 4.8 wt%. The conversion ratio of WPEPBs (CWPEPBs) and CaCO3 recovery ratio (RCaCO3) were 99.10 % and 98.85 %, respectively. In contrast to traditional methods for recycling of plastic waste such as mechanical recycling and incineration, the SWA process is believed to be a clean and high-efficiency resource conversion strategy for WPEPBs.

Evaluation of ammonia co-firing in the CRIEPI coal jet flame using a three mixture fraction FPV-LES

Highly resolved Large Eddy Simulations (LES) are performed to investigate co-firing of coal and ammonia in a burner experiment conducted by the Central Research Institute of Electric Power Industry (CRIEPI) in Japan. The coaxial burner with a hydrogen supported pulverized coal flame is modeled using the in-house code PsiPhi. A three mixture fraction flamelet/progress variable (FPV) approach is employed to simulate coal particle conversion due to devolatilization, hydrogen combustion, and ammonia combustion. Three cases are investigated and compared to each other: 1) a coal combustion case, injecting air and coal particles, 2) an ammonia combustion case, injecting a mixture of ammonia and air, and 3) a co-firing combustion case, injecting a mixture of coal, ammonia and air in the center tube. Two mechanisms are used to build the chemistry table and are compared against each other: a reduced CRECK mechanism with 120 reaction species and 1551 elementary reactions, originally reduced for coal combustion modeling, and a newly introduced reduced CRECK mechanism with 129 reaction species and 1644 elementary reactions, including the detailed NH3 reaction paths in addition to the coal chemistry. Species are compared for the coal case and temperature fields are compared for both the coal and co-firing case. Normalized LIF signals for OH and NH are presented for all three cases. The gas composition profiles are in good agreement with the experiment and the temperature fields are consistent with previous results for the pure coal flames. For pure ammonia and for ammonia co-firing, the new mechanism shows an improved prediction of the reaction zone.

Experimental and kinetic modeling study of the laminar burning velocity of NH3/DME/air premixed flames

Ammonia (NH3) as a carbon-free fuel and a high-density hydrogen carrier has received significant attention. Co-firing NH3 with dimethyl ether (DME) is a promising option for overcoming the low reactivity of NH3. This paper presents an experimental and kinetic modeling study of the laminar burning velocity of NH3/DME/air mixtures. Experiments were conducted for the full range of DME fraction at 0.1 MPa, 298 K, and equivalence ratios (ϕ) from 0.7 to 1.5 using a spherical constant-volume combustion chamber. The influence of pressure was examined for 20% - 80%DME at 298 K and ϕ = 0.7 - 1.4 by considering different initial pressures (0.1, 0.3, and 0.5 MPa). A small size reaction mechanism for NH3/DME/air mixtures was developed and validated against experiments. This mechanism performs well in predicting the laminar burning velocity of NH3/air, DME/air, and NH3/DME/air flames as well as the ignition delay time of NH3, DME, and NH3/DME oxidation. Detailed kinetic analyses using the mechanism helped us understand the observed effects of DME addition and initial pressure on the laminar burning velocity. The linear increase of laminar burning velocity with increasing DME fraction is mainly attributed to the enhancement of both thermal effect and chemical kinetics effect, while the negative influence of initial pressure is because of the decrease of chemical kinetics effect. In addition, it was found that the main reaction pathways based on N-atom shift with DME addition, whereas those based on C-atom vary little. Furthermore, pressure power exponent β as a function of equivalence ratio shows different behaviors for different DME fractions due to the competition between NH2 and CH3 chain-termination reactions for the rich flames. The present work provides experimental measurements of the laminar burning velocity at various conditions and insights into the chemical kinetics for NH3/DME/air mixtures.

On nanosecond plasma-assisted ammonia combustion: Effects of pulse and mixture properties

In this study, the effects of nanosecond plasma discharges on the combustion characteristics of ammonia are investigated over a wide range of mixture properties and plasma settings. The results reveal that the impacts of the plasma on ammonia combustion change non-monotonically by altering the reduced electric field value. Within the studied range of the reduced electric field, i.e., 100–700 Td, it is shown that plasma is most effective in the medium range, e.g., 250–400 Td. At lower values, the main fraction of the plasma energy is consumed to excite the diluent to higher vibrational levels. At very high reduced electric field values, a substantial portion of the plasma energy is transferred into the ionization reactions of the diluent, which compromises the effective excitations of fuel and oxidizer species. In terms of the pulse energy density, results indicate that an increase in the range of 0–20 mJ/cm3, at a given reduced electric field, decreases the ignition delay time by five orders of magnitude, and increases the laminar flame speed up to an order of magnitude, depending on the mixture composition. The results show that the plasma discharge produces more radicals, electronically excited and charged species when He is used as the diluent in the oxidizer instead of N2, since NH3 and O2 ionization reactions are strengthened in NH3/O2/He. Moreover, plasma discharge is highly effective in assisting the combustion of preheated lean mixtures. The present study also indicates that ammonia flame thickness is minimum at a critical pulse energy density in the range of 12–14 mJ/cm3. Further increases in the pulse energy density can manipulate the inner structure of the flame, altering the pre-heat zone of the flame to include some levels of chemical reactions toward the flameless mode of combustion.

Experimental study and kinetic modeling of NH3/CH4 co-oxidation in a jet-stirred reactor

This work reports an experimental and kinetic modeling study of the co-oxidation behavior of NH3/CH4 binary fuel in a jet-stirred reactor (JSR). Experimental tests are conducted by varying the reaction temperature (850–1350 K), equivalence ratio (0.5–2), and NH3 mole fraction in fuel (0–100%) individually at ambient pressure and with N2 being diluent gas. The experimental measurement shows that there exists strong competition between CH4 and NH3 oxidation in fuel-lean condition, where the addition of NH3 tends to suppress CH4 oxidation by postponing the peak CO formation to a higher reaction temperature. However, such change is not observed in stoichiometric and fuel-rich conditions. When gradually increasing the reaction temperature, a dual NO formation behavior can be noticed for both NH3/CH4 mixture and pure NH3 regardless of equivalence ratio. When gradually increasing the equivalence ratio, NO formation becomes higher with the addition of NH3 at 1100 K, while is gradually reduced with the addition of NH3 at 1300 K. Kinetic modeling of the present experimental cases is further performed with different existing reaction mechanisms for NH3/CH4 and NH3. The comparison of NO emission shows that there is still some space for the improvement of the currently existing reaction mechanisms, especially in the low-intermediate temperature range (850–1200 K) where NO is significantly under-predicted by all models for both NH3/CH4 and NH3. Further NO reaction pathway and sensitivity analysis suggest that the reactions associated with C–N interaction, H2NO, NH2, N2H2 and NNH are responsible for the under-prediction of NO in the low-intermediate temperature range, and their reaction parameters should be optimized for obtaining improved performance.

Rational design synergistic metal-free dual-atom electrocatalyst for N2 to NH3 reaction on g-CN: A first principle study

The electrocatalytic nitrogen reduction reaction (NRR) for ammonia production is promising for N2 fixation under ambient conditions. Most of the previous studies focus on transition metal-based catalysts, while the metal-free-based ones have not gotten enough attention. We designed dual-site metal-free atoms anchored on g-CN for electrocatalytic NRR based on the density functional theory (DFT) calculation. Results indicated that the B and P atoms co-doped g-CN system exhibits excellent NRR performance with a low limiting potential of −0.18 V, superior to most metal-based catalysts. In addition, a synergistic effect induced by the hybridization of B and P atoms is proposed. Eventually, the selectivity, thermodynamical stability, and conductivity are investigated. All of these modulations make the B-P@g-CN an excellent electrocatalyst. Our work provides a novel method for electrocatalytic NRR to ammonia and promotes the development of NRR.

The Gas-phase Reaction of NH2 with Formaldehyde (CH2O) is not a Source of Formamide (NH2CHO) in Interstellar Environments

The first experimental study of the low-temperature kinetics of the gas-phase reaction of NH2 with formaldehyde (CH2O) has been performed. This reaction has previously been suggested as a source of formamide (NH2CHO) in interstellar environments. A pulsed Laval nozzle equipped with laser-flash photolysis and laser-induced fluorescence spectroscopy was used to create and monitor the temporal decay of NH2 in the presence of CH2O. No loss of NH2 could be observed via reaction with CH2O, and we place an upper limit on the rate coefficient of <6 × 10−12 cm3 molecule−1 s−1 at 34 K. Ab initio calculations of the potential energy surface were combined with Rice–Rampsberger–Kassel–Marcus (RRKM) calculations to predict a rate coefficient of 6.2 × 10−14 cm3 molecule−1 s−1 at 35 K, consistent with the experimental results. The presence of a significant barrier, 18 kJ mol−1, for the formation of formamide as a product, means that only the H-abstraction channel producing NH3 + CHO, in which the transfer of an H atom can occur by quantum mechanical tunneling through a 23 kJ mol−1 barrier, is open at low temperatures. These results are in contrast with a recent theoretical study, which suggested that the reaction could proceed without a barrier and was therefore a viable route to gas-phase formamide formation. The calculated rate coefficients were used in an astrochemical model, which demonstrated that this reaction produces only negligible amounts of gas-phase formamide under interstellar and circumstellar conditions. The reaction of NH2 with CH2O is therefore not an important source of formamide at low temperatures in interstellar environments.

Nanosecond pulsed plasma assisted combustion of ammonia-air mixtures: Effects on ignition delays and [formula omitted] emission

Computational investigation of plasma assisted combustion of ammonia-air mixtures in constant volume and constant pressure reactors are conducted, to determine the impact of operating conditions on ignition delays and NOx emissions. Due to the lack of a chemical kinetic mechanism for plasma discharge of ammonia (NH3)/air mixtures, a mechanism has been assembled in this work using well-validated plasma reactions of NH3 with O2 and N2, alongside plasma kinetics of air from the literature. The impact of the reduced electric field (E/N), equivalence ratio, pressure, pulse frequency and the energy density on the ignition delays and NO/NO2 emission is discussed. At lower E/N, vibrational-to-translational (VT) relaxation of the vibrational states of NH3 and N2 is observed to play a dominant role in the gas heating process on account of the higher vibrational energy contribution. The ignition event is observed to be faster for fuel-lean mixture (ϕ = 0.5) compared to stoichiometric and fuel-rich (ϕ = 1.2) conditions owing to the lower consumption of OH radicals through the reactivity-inhibiting reaction NH3+OH→NH2+H2O between plasma pulses for leaner mixtures. Nevertheless, the fuel-lean mixture is observed to exhibit higher production of NOx than stoichiometric and fuel-rich mixtures, resulting from plasma chemistry involving oxygen radical and electronic excited states of N2. At the higher pressure of 3 atm, the pressure dependent recombination reaction H+O2+M→HO2+M is found to delay the ignition by limiting the reactive radicals compared to the corresponding 1 atm case. Higher rates of collisional quenching at higher pressures during the inter-pulse gaps resulted in lesser amount of electronically excited states of N2 and O2, which resulted in lower production of air-bound NOx during the pulses. Pulse frequency and energy density per pulse are seen to exhibit an inversely proportional effect on the ignition delay times. Most importantly, a faster ignition and lower production of NOx is observed in the case of plasma discharges compared to thermal energy deposition, owing to the enhanced production of OH radicals and the reforming of NH3 to produce N2 with plasma, respectively. Interesting roles of fuel-radicals such as NH2 and NH in both producing and reducing NO at different instants have also been discussed.

The NH[formula omitted]/NO[formula omitted]/O[formula omitted] system: Constraining key steps in ammonia ignition and N[formula omitted]O formation

Amine/NO2 interactions are important for ignition and N2O emissions in ammonia combustion. In the present work, reported results from batch reactors (580–690 K) and flow reactors (850–1350 K) for the NH3/NO2 system were re-interpreted in terms of the present understanding of the amine chemistry. Furthermore, additional flow reactor results on the impact of O2 on the NH3/NO2 reaction were presented and analyzed. Based on the experimental results and the modeling analysis, it was possible to constrain the rate constants for reactions of NH3 and NH2 with NO2 and for subsequent steps involving H2NO and HNO intermediates. The key reaction is NH2 + NO2, forming H2NO + NO (R2) and N2O + H2O (R3). The results indicate that the yield of N2O in the NH2 + NO2 reaction decreases with temperature in the 850–1350 K range, in agreement with the theoretical study by Klippenstein and coworkers. The fate of H2NO and HNO is important for the overall reactivity. In the absence of O2, formation of chain carriers is controlled by the sequence H2NO + NO2→ HNO + HONO, HNO + NO2→ NO + HONO, HONO (+M) → NO + OH (+M). At higher temperatures, in the presence of O2, the sequence H2NO + O2→ HNO + HO2, HNO + O2→ NO + HO2, NO + HO2→ NO2 + OH enhances radical formation and recycles NO2. The satisfactory agreement between experiments and modeling predictions, both without and with O2, supports the present rate constants for the reactions of H2NO and HNO with NO2 and O2, respectively.

Evolution of N2O production at lean combustion condition in NH3/H2/air premixed swirling flames

In the development of ammonia - hydrogen blends as potential substitutes for fossil fuels, the retrofitting of existing devices running at very lean condition is one of the promising solutions for decarbonisation of the power sector. However, little is known about the impact of these conditions on the production of NOX, particularly N2O that is a potent greenhouse gas. Therefore, the influence of varying thermal power and Reynolds numbers on the flame and emission characteristics, especially N2O, of ammonia-hydrogen-air swirling flames has been evaluated for the first time through the use of spatially resolved OH*, NH* and NH2* chemiluminescence, spectrometry analyses and advanced emissions characterisation at a fixed lean equivalence ratio, Φ = 0.65, representative of the Dry Low NOX (DLN) approach in traditional stationary gas turbines. NO and NO2 emissions were found to be decreasing (from ∼ 5000 ppmv to ∼ 1000 ppmv; NO and from ∼ 150 ppmv to ∼ 50 ppmv; NO2) with increasing ammonia content (from 50% to 90%) in the fuel while N2O followed reverse trends (from ∼ 50 ppmv to ∼ 200 ppmv). More than 80% ammonia content in the fuel blends exhibited high amounts of unreacted ammonia fractions (∼ 100 to ∼ 1200 ppmv), which can be potentially linked to flame instability and/or low temperatures. Furthermore, any increasing or decreasing trends in NOX with ammonia fraction were made more extreme by increasing thermal power or Reynolds number due to the differences in relevant radicals (NH, OH, NH2 etc.) formation in the flames. Experimental results suggest the unviability of these blends at the conventional lean conditions utilised at the DLN power applications due to excessive NOX emissions. Detailed sensitivity analyses of N2O concentration at the flame and post flame zone has been carried out utilising Ansys Chemkin-PRO to identify and investigate the reactions responsible for N2O formation/consumption in the experimental flames. Results have identified the reaction NH + NO ↔ N2O + H as the major source of N2O production in the flame, while the reactions N2O + H ↔ N2 + OH and N2O(+M) ↔ N2 + O(+M) are responsible for N2O consumption at the post flame zone, with higher reactivity for the latter reaction at longer residence time and relatively lower temperatures.

Green synthesis of chitooligosaccharide-PEGDA derivatives through aza-Michael reaction for biomedical applications

Chitooligosaccharide (COS) as an emerging material carbohydrate polymer with huge potential in biomedical applications was prepared using a microwave-assisted process. The obtained COS exhibited reduced molecular weight (Mw) and higher water solubility in comparison to chitosan while preserving the main saccharide structure and same degree of deacetylation (DD). The optimized COS (13 kDa) was then used to synthesize a new family of COS-poly(ethylene glycol) diacrylate (PEGDA) derivatives based on aza-Michael addition of acrylate groups of PEGDA to the amine groups of COS in the absence of any exterior agents. The modulation of the reaction time, temperature, pH and NH2:acrylate molar ratio, had a strong influence on the Michael reaction progress. At higher degrees of conversion of acrylate groups, COS-PEGDA derivative formed gel with high biocompatibility towards human bone mesenchymal stem cells (hBMSCs). These COS-PEGDA hydrogels synthesized at mild conditions through a green chemistry are, therefore, an innovative system combining adequate biological performance, ease of preparation, and an environmentally friendly concept of production.

Experimental and computational studies of the kinetics of the reaction of hydrogen peroxide with the amidogen radical.

The pulsed-laser photolysis/laser-induced fluorescence method is used to study the kinetics of the reaction of NH2 with H2O2 to yield a second-order rate constant of (2.42 ± 0.55) × 10-14cm3molecule-1s-1 at 412K in 10-22mbar of Ar bath gas. There are no prior measurements for comparison. To check this value and enable reliable extrapolation to other temperatures, we also compute thermal rate constants for this process over the temperature range 298-3000K via multi-structural canonical variational transition-state theory with small-curvature multidimensional tunneling (MS-CVT/SCT). The CVT/SCT rate constants are derived using a dual-level direct dynamics approach utilizing single-point CCSD(T)-F12b/cc-pVQZ-F12 energies-corrected for core-valence and scalar relativistic effects-and M06-2X/MG3S geometries, gradients, and Hessians-for all stationary and non-stationary points along the reaction path. The multistructural method with torsional anharmonicity, based on a coupled torsional potential, is then employed to calculate correction factors for the rate constants, accounting for the comprehensive effects of torsional anharmonicity on the kinetics of this reaction system. The final MS-CVT/SCT rate constants are found to be in good agreement with our measurements and can be expressed in modified Arrhenius form as 2.13 × 10-15 (T/298K)4.02 exp(-513 K/T) cm3molecule-1s-1 over the temperature range of 298-3000K.

Molybdenum carbide phase effects in heterogeneous catalytic ammonia synthesis

The design of an efficient catalyst utilizing non-precious metals is a top priority in ammonia synthesis, and Mo is found to be inferior in ammonia synthesis due to strong nitrogen adsorption. The carburization of Mo species might be an ideal strategy for optimizing nitrogen adsorption energy and ammonia synthesis activity. In this work, we prepare two molybdenum carbides with different crystal structures (α-MoC and β-Mo2C). The result shows that there is a larger number of Mo-C bonds and lower Mo/C ratio in α-MoC, leading to the strong adsorption of hydrogen and ammonia species on α-MoC. In contrast, the desorption energies of hydrogen and ammonia are lower for β-Mo2C, and the spillover and migration of hydrogen species are boosted. The facile desorption of hydrogen and ammonia species also limits the accumulation of H adatoms and ammonia on the surface of β-Mo2C, releasing of active sites available for the subsequent activation of hydrogen and nitrogen as well as ammonia synthesis reaction. As a result, the ammonia synthesis activity of β-Mo2C catalyst is 2.5-fold higher than that of α-MoC, and a small negative value of NH3 reaction order also would be obtained for β-Mo2C. This work not only reports the effect of molybdenum carbide phases on the adsorption–desorption properties of reactants and catalytic activities for ammonia synthesis, but also opens a perspective for the design and development of efficient metal based heterogeneous catalysts by tuning the adsorption and desorption properties of the reactant gases. Keywords: Molybdenum Carbide; Phase effect; Adsorption–desorption property; Mo catalyst; Ammonia synthesis

Kinetics Analysis of the NH3-SCR Denitration Reaction over Sintered Ore Catalysts

Utilizing sintered ore catalysts (SOC), which are used in the sintering industry for NH3-SCR denitration, is a feasible and economical way to reduce NOx emission in sintering flue gas. Therefore, in order to enhance the denitration efficiency of SOC, sintered ore modified by sulfuric acid and sulfated sintered ore catalysts (SSOC-5) were prepared. Kinetic analyses of these two catalysts for denitration were carried out in this study. On the basis of eliminating the influence of internal and external diffusion, the relationship between reactants and reaction rate was studied by a power function kinetic model. This clarified that the adsorption ability of the acid-modified catalyst for reaction gas adsorption was stronger than that of sintered ore catalysts, and the reaction rate was also accelerated. The NO, NH3 and O2 reaction orders of SOC were 1, 0.3 and 0.16 at 250~300 °C, while these values of SSOC-5 were 0.8, 0.06 and 0.09, respectively. The apparent activation energy of SOC was 83.66 kJ/mol, while the value of SSOC-5 decreased to 59.93 kJ/mol.