Mechanism of Interaction between Ammonium Perchlorate and Aluminum.

There is an interactive effect between ammonium perchlorate (AP) and aluminum (Al) powder during the combustion process of composite solid propellants, but the mechanism of this effect is still lacking. Using quantum chemical methods, we investigated this mechanism from a molecular perspective. The interaction process between Al and AP was analyzed by comparing the chemical bond changes between the atoms during the reaction process of the Al/AP system and the AP unimolecular thermal decomposition system. The results show that Al atoms alter the reaction mechanism of AP thermal decomposition, significantly decreasing the activation energy of AP decomposition at high temperature but increasing that at low temperature. Meanwhile, the temperature-dependent rate constant of each basic reaction was calculated by transition state theory. The rate constants increase with temperature. Under high temperature and pressure, Al can increase the high-temperature decomposition rate of AP by up to 1-3 orders of magnitude.

Atmospheric-Pressure Pyrolysis Study of Chlorobenzene Using Synchrotron Radiation Photoionization Mass Spectrometry.

The pyrolysis of chlorobenzene (C6H5Cl) at 760 Torr was studied in the temperature range of 873-1223 K. The pyrolysis products including intermediates and chlorinated aromatics were detected and quantified via synchrotron radiation photoionization mass spectrometry. Furthermore, the photoionization cross sections of chlorobenzene were experimentally measured. On the basis of the experimental results, the decomposition pathways of chlorobenzene were discussed as well as the generation and consumption pathways of the main products. Benzene is the main product of chlorobenzene pyrolysis. Chlorobiphenyl (C12H9Cl), dichlorobiphenyl (C12H8Cl2), and chlorotriphenylene (C18H11Cl) predominated in trace chlorinated aromatic products. Chlorobenzene decomposed initially to form two radicals [chlorophenyl (·C6H4Cl) and phenyl (·C6H5)] and the important intermediate o-benzyne (o-C6H4). The propagation processes of chlorinated aromatics, including polychlorinated naphthalenes and polychlorinated biphenyls, were mainly triggered by chlorobenzene, chlorophenyl, and benzene via the even-numbered-carbon growth mechanism. Besides, the small-molecule products such as acetylene (C2H2), 1,3,5-hexatriyne (C6H2), and diacetylene (C4H2) were formed via the bond cleavage of o-benzyne (o-C6H4).

Understanding the roles of copper dopant and oxygen vacancy in promoting nitrogen oxides removal over iron-based catalyst surface: A collaborative experimental and first-principles study.

In this work, we proposed a novel strategy of copper (Cu) doping to enhance the nitrogen oxides (NOx) removal efficiency of iron (Fe)-based catalysts at low temperature through a simple citric acid mixing method, which is critical for its practical application. The doping of Cu significantly improves the deNOx performance of Fe-based catalysts below 200 °C, and the optimal catalyst is (Cu0.22Fe1.78)1-δO3, which deNOx efficiency can reach 100% at 160-240 °C. From the macro aspects, the main reasons for the excellent catalytic activity of the (Cu0.22Fe1.78)1-δO3 catalyst are the large number of oxygen vacancies (Ovac), appropriate Fe3+ and Cu2+ contents, stronger surface acidity and redox ability. From the micro aspects, the Ovac plays a key role in enhancing molecular adsorption, oxidation, and the deNOx reaction over the Fe-based catalyst surface, which promoting order is CuOvac > Ovac > Cu. This work provides a new insight for the mechanism study of oxygen vacancy engineering and also accelerates the development of CuFe bimetal composite catalysts at low temperature.

Calcium poisoning mechanism on the selective catalytic reduction of NOx by ammonia over the γ-Fe2O3 (001) surface.

γ-Fe2O3 has an excellent low-temperature selective catalytic reduction (SCR) deNOx performance, but its resistance to alkaline earth metal calcium (Ca) is poor. In particular, the detailed mechanism of Ca poisoning on the γ-Fe2O3 catalyst at the atomic level is not clear. Hence, the density functional theory method was used in this research to investigate the influence mechanism of Ca poisoning on the NH3-SCR over the γ-Fe2O3 catalyst surface. The findings reveal that NH3, NO, and O2 molecules can bind to the γ-Fe2O3 (001) surface to generate coordinated ammonia, monodentate nitroso, and adsorption oxygen species, respectively. The main active site is Fe1-top. For the γ-Fe2O3 with Ca poisoning, the Ca atom has a high adsorption energy on the surface of γ-Fe2O3 (001), which covers the catalyst surface and reduces the active sites. The presence of Ca atom decreases the adsorption performance of NH3, while slightly improving the NO and O2 adsorption. In particular, the Ca atom restrains the NH3 activation and NH2 formation, which is detrimental to the NH3-SCR process.

Effect of doping Cr on NH3 adsorption and NO oxidation over the FexOy/AC surface: A DFT-D study.

Activated carbon supported iron-based catalysts (FexOy/AC) show good deNOx efficiency at low temperature. The doping of chromium (Cr) greatly improves the catalyst activity. However, the detailed effect of doping Cr over FexOy/AC surface at molecular level is still a grey area. In this study, the roles of Cr dopant on gas adsorption and NO oxidation were deeply investigated by a DFT-D3 method. Results show that the synergy of Cr-Fe bimetal improves the binding capacity of Fe2O3/AC and Fe3O4/AC surfaces after doping Cr. NH3 can be adsorbed on Cr and Fe sites to form coordinated NH3. Doping Cr greatly improves the NH3 adsorption property on the Fe3O4/AC surface. NO molecule can combine with Cr, Fe, and O sites to form nitrosyl and nitrite. The doping of Cr increases the adsorption performance of NO on the Fe2O3/AC and Fe3O4/AC surfaces, especially for Fe3O4/AC surface. Furthermore, NO can be oxidized to NO2 by adsorption oxygen or active O sites of FexOy clusters. The doping of Cr restrains the formation of insoluble chelating bidentate nitrates and greatly reduces the reaction energy barrier of NO oxidation on the FexOy/AC surface, which can promote the deNOx reaction.

Heavy metal poisoning resistance of a Co-modified 3Mn10Fe/Ni low-temperature SCR deNOx catalyst.

Heavy metals have a great influence on the deNOx efficiency of catalysts. The 3Mn10Fe/Ni catalyst that used nickel foam (Ni) as the carrier, Mn and Fe as the active components, and Co as a trace auxiliary was prepared using an impregnation method. The catalysts poisoned by Pb or Zn and Co-modified catalysts with Pb or Zn poisoning were studied. The addition of Pb or Zn significantly decreases the deNOx activity of the 3Mn10Fe/Ni catalyst due to the decrease in the content of high-valence metal elements such as Fe3+ and Mn4+, lattice oxygen concentration, reduction performance, acidity, and the number of acid sites. However, after Co modification, the deNOx activity of the poisoned catalysts can be improved effectively because the strong interaction between Pb or Zn and lattice oxygen is weakened, and the contents of lattice oxygen, high valence metal elements, reduction ability, and the number of acid sites increase.

Promotional effect of Mn modification on DeNOx performance of Fe/nickel foam catalyst at low temperature.

Manganese (Mn)-modified ferric oxide/nickel foam (Fe/Ni) catalysts were prepared using Ni as a carrier, Fe and Mn as active components to study NH3-SCR of NOx at low temperature. The effects of different Fe loads and Mn-modified Fe/Ni catalysts on the DeNOx activity were investigated. Results show that when the amount of Fe is 10%, Fe/Ni catalyst has the highest NOx conversion. For the Mn-modified Fe/Ni catalysts, the NOx conversions firstly increase and then decrease with the Mn loading amount increasing. 3MnFe/Ni catalyst shows high NOx conversions, which reach 98.4-100% at 120-240 °C. The characterization analyses reveal that Mn-modified Fe/Ni catalysts increase the FeOx dispersion on Ni surface, improve significantly the valence ratio of the Fe3+/Fe2+, the content of lattice oxygen which promotes the catalyst storage and exchange oxygen capacity at low temperature, and the number of Brønsted active acid sites on the catalyst surface, and enhance the low-temperature redox capacity. These factors remarkably increase the NOx conversions at low temperature. Especially, 3Mn10Fe/Ni catalyst not only has excellent DeNOx activity but also has better water resistance. However, the anti-SO2 poisoning performance needs to be improved. To further analyze the reason why different catalysts show different DeNOx performance, the reaction kinetics was also explored.

Investigation of low-temperature selective catalytic reduction of NOx with ammonia over Cr-promoted Fe/AC catalysts.

Fe/activated coke (AC) and Cr-Fe/AC catalysts with AC as a supporter and Cr and Fe as active components were prepared by an impregnation method for low-temperature selective catalytic reduction (SCR) of NO with NH3. The effects of Cr addition and its concentrations on the deNOx performance of Fe/AC catalysts were studied at low temperature. The Cr addition promotes the low-temperature SCR activity of the 8Fe/AC catalyst and the 8Fe6Cr/AC catalyst has the best low-temperature SCR deNOx performance, which the NOx conversions are greater than 90% at 160-240 °C. The 8Fe6Cr/AC catalyst has good water resistance. However, when 100 ppm SO2 was introduced into the reaction gas, its deNOx efficiency drops to 45% at 180 °C. To clarify the specific effects of Cr addition on the NOx conversions and sulfur poisoning, the Cr-Fe/AC catalysts were characterized by X-ray diffraction, BET, H2 temperature-programmed reduction, NH3 temperature-programmed desorption, X-ray photoelectron spectroscopy, and Fourier infrared spectroscopy. The addition of Cr into Fe/AC catalysts greatly increases the BET surface area and the number of weak and medium-strong acid sites on the catalyst surface and improves the ratio of Fe3+/Fe2+. These factors enhance the NOx conversion of 8Fe/AC catalyst. The formed sulfates and hydrogen sulfates cover the active sites on the catalyst surface, which lead to the sulfur poisoning of the 8Fe6Cr/AC catalyst. Graphical abstract.

The effect of nitrate esters on the thermal decomposition mechanism of GAP.

Thermal gravimetric analysis (TG), differential thermal analysis (DTA), and in situ Fourier Transform Infra-Red spectrometer (FTIR) experiments were used to investigate the thermal decomposition mechanism of glycidyl azide polymer (GAP) crosslinked by using the curing agent isocyanate compound N-100 and the different ratios of plasticized-cured GAP/NG/BTTN, which are of potential interest for the development of high performance energetic propellants. The results of TG show the thermal decomposition temperature of GAP shifted to lower temperatures in the presence of NG/BTTN. The decomposition peak temperatures of cured GAP/NG/BTTN (1:1:1), cured GAP/NG/BTTN (1:0.5:0.5) and cured GAP/NG/BTTN (1:0.25:0.25) decrease by approximately 20 degrees C, 33 degrees C and 39 degrees C compared with cured GAP, respectively. This indicates that plasticizers NG/BTTN have good acceleration effects on the decomposition of cured GAP, especially for low content of NG/BTTN. At the same time, the results of DTA show that the decomposition heat of cured GAP/NG/BTTN is larger than that of cured GAP. In situ FTIR results show NG/BTTN not only accelerate the decomposition of -N3 groups and characteristic urethane links [Formula: see text], but also accelerate the decomposition of C-O-C groups.

[FTIR and thermal analysis studies of the effects of additives on thermal decomposition of AP/Al].

The mechanisms for AP of the main compositions of composite propellants with additives such as ammonium oxalate (AO), strontium carbonate (SC) and AO/SC were studied by FTIR and DSC. The analysis of FTIR shows that AO leads to a delay in the temperature for the disappearance of absorption peaks of AP. SC reacts with HClO4 from AP decomposition and produces more stabilized Sr(ClO4)2 in the condensed phase. FTIR proves the production of Sr(ClO4)2. The analysis of DSC shows that the temperature for high decomposition exothermic peak of AP with AO is increased, but there is no effect on the temperature for low decomposition exothermic peak of AP. Both the temperature for the low and high decomposition exothermic peaks of AP are increased by the addition of SC. Although the temperature for decomposition exothermic peak of AP is increased with the addition of AO/SC, the experimental result shows that SC and AO didn't produce synergetic effects for the high temperature decomposition of AP at low pressure. Based on the above experimental results, the mechanisms of inhibiting the decomposition of AP for AO and SC are discussed.

Natural manganese ore catalyst for low-temperature selective catalytic reduction of NO with NH3 in coke-oven flue gas.

Different types of manganese ore raw materials were prepared for use as catalysts, and the effects of different manganese ore raw materials and calcination temperature on the NO conversion were analyzed. The catalysts were characterized by XRF, XRD, BET, XPS, H2-TPR, NH3-TPD, and SEM techniques. The results showed that the NO conversion of calcined manganese ore with a Mn:Fe:Al:Si ratio of 1.51:1.26:0.34:1 at 450 °C reached 80% at 120 °C and 98% at 180~240 °C. The suitable proportions and better dispersibility of active ingredients, larger BET surface area, good reductibility, a lot of acid sites, contents of Mn4+ and Fe3+, and surface-adsorbed oxygen played important roles in improving the NO conversion.

[FTIR and thermal analysis study of GAP and GAP/B].

The thermal decomposition of GAP and GAP/B in air and nitrogen were studied by FTIR and TG-DTG. The analysis by FTIR and TG-DTG shows that the azide group elimination reactions of GAP begin at about 170 degrees C and finish around 250 degrees C, and the depolymerization of GAP delays by 40 degrees C; Boron changes the mechanism of thermal decomposition process of GAP, and the results show that GAP/B starts losing mass between 55 and 70 degrees C, which is much earlier than GAP itself does. Furthermore, the depolymerization of GAP almost takes place at the same temperature with the azide group elimination. Some kinetics parameters of the reactions were calculated based on Kissinger's processing methods. The results show that the activation energies of the thermal decomposition of GAP and GAP/B are lower and the reactions are easier to occur under air. The possible reason is that the oxygen containing thermal decomposition of GAP has happened.