First-Principles Investigation of Graphene and Fe2O3 Catalytic Activity for Decomposition of Ammonium Perchlorate

Thermal Decomposition Mechanism of Ammonium Nitrate on the Main Crystal Surface of Ferric Oxide: Experimental and Theoretical Studies

Understanding the decomposition process of ammonium nitrate (AN) on catalyst surfaces is crucial for the development of practical and efficient catalysts in AN-based propellants. In this study, two types of nano-Fe2O3 catalysts were synthesized: spherical particles with high-exposure (104) facets and flaky particles with high-exposure (110) facets. Through thermal analysis and particle size analysis, it was found that the nanosheet-Fe2O3 catalyst achieved more complete AN decomposition despite having a larger average particle size compared to nanosphere-Fe2O3. Subsequently, the effects of AN pyrolysis on the (110) and (104) facets were investigated by theoretical simulations. Through studying the interaction between AN and crystal facets, it was determined that the electron transfer efficiency on the (110) facet is stronger compared to that on the (104) facet. Additionally, the free-energy step diagrams for the reaction of the AN molecule on the two facets were calculated with the DFT + U method. Comparative analysis led us to conclude that the (110) facet of α-Fe2O3 is more favorable for AN pyrolysis compared to the (104) facet. Our study seeks to deepen the understanding of the mechanism underlying AN pyrolysis and present new ideas for the development of effective catalysts in AN pyrolysis.

Construction of Hydrophobic Ammonium Perchlorate with Synergistic Catalytic Effect Based on Supramolecular Self-Assembly for Synchronously Catalyzing the Thermal Decomposition of Ammonium Perchlorate and the Combustion of Aluminum

Ammonium perchlorate (AP), as an important additive component of composite propellants, is critical to the combustion performance of propellants. Herein, AP@1H,1H,2H,2H-perfluorodecyltrichlorosilane (AP@PF) was prepared by establishing a tannic acid-iron ion (TA-Fe) supramolecular self-assembly layer on the AP surface and connecting the 1H,1H,2H,2H-perfluorodecyltrichlorosilane interfacial layer. Results demonstrate that TA-Fe and 1H,1H,2H,2H-perfluorodecyltrichlorosilane are uniformly bound to the surface layer of AP. AP@PF has a lower high-temperature thermal decomposition peak compared to AP. Meanwhile, the exothermic values of low-temperature thermal decomposition (338 J/g) and high-temperature thermal decomposition (597 J/g) of AP@PF are significantly higher than those of AP. In addition, AP@PF exhibits different surface interfacial properties, such as floating on the water surface and exhibiting a static contact angle of 105° on water. AP@PF shows almost no moisture absorption after aging in humid air for 30 days. The exothermic value of the mixture of AP@PF and aluminum powder (156 J/g) is significantly higher than that of the mixture of AP and aluminum (54 J/g), and the mixture of AP@PF and aluminum powder exhibits a higher calorific value and a stronger emission spectrum. Finally, the synergistic catalytic mechanism of AP@PF on the thermal decomposition of AP and the combustion of aluminum powder is also discussed.

Different Doping of VSe2 Monolayers as Adsorbent and Gas Sensing Material for Scavenging and Detecting SF6 Decomposed Species

The application of intrinsic and transition metals (TM)-doped VSe₂ monolayers for the detection of faulty gases in SF₆ electrical insulated equipment is investigated based on first-principles calculations. The electron density difference, density of state, and adsorption energy are analyzed to further clarify the reaction mechanism. The results show that the intrinsic VSe₂ monolayer has weak adsorption performance for SO₂ and SOF₂ molecules, but the adsorption properties of the system are significantly improved after doping TM atoms. Among them, the TM-doped VSe₂ monolayer has better sensing performance for SO₂ than for SOF₂ molecules. Furthermore, the modulating effect of biaxial strain on the gas-sensitive properties of TM-doped VSe₂ system is also analyzed. Finally, the recovery time of the gas molecules on the solid adsorbent is evaluated. The results confirm that the TM-doped VSe₂ monolayer can be used as a novel sensing material or scavenger to ensure the normal operation of SF₆ electrical insulated equipment. This will provide a prospective insight for experimenters to implement VSe₂-based sensing materials or scavengers.

Preparation of a Chitosan-Lead Composite Carbon Aerogel and Its Catalytic Thermal Decomposition Performance on Ammonium Perchlorate

Chitosan-lead (CS-Pb) carbon aerogels were prepared by ionic cross-linking and high-temperature carbonization using chitosan (CS) as the carbon precursor. The obtained carbon aerogels were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), and X-ray photoelectron spectroscopy (XPS). The obtained aerogels have a 3D structure and a large surface area, which can effectively prevent the agglomeration phenomenon of metals. Differential thermal analysis (DTA) was used to analyze the catalytic performance of a carbon aerogel for ammonium perchlorate (AP). The results showed that the CS-Pb carbon aerogel reduced the peak temperature of AP pyrolysis from 703.9 to 627.7 K. According to the Kissinger method calculations, the E_a of AP decomposition decreased about 27.2 kJ/mol. The TG data at different warming rates were analyzed by the Flynne-Walle-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) methods, which are two of the isoconversion methods, and the activation energies of AP and AP+CS-Pb-3.5 were calculated. Between the conversion degrees (α) of 0.1 and 0.9, the E_a values obtained by the two isoconversion methods are similar and have a certain match. Also, the two isoconversion methods confirm Kissinger's calculation. Finally, thermogravimetry-mass spectrometry (TG-MS) was used to monitor the gases generated during the thermal decomposition of the AP+CS-Pb-3.5 system in real time.

Enhancement of the Catalytic Activity of Double Metal Cyanides for the Oxidation of Styrene by the Presence of Included Alcohols

In recent years, people have focused on the development of simple and efficient heterogeneous catalysts for the styrene epoxidation reaction. In this work, a FeCo double metal cyanide (DMC) was modified with C1 to C6 linear alcohols, and the prepared materials were used to catalyze the reaction of styrene epoxidation in various solvents. It is noteworthy that the styrene conversion is mainly affected by modification with alcohols, while the selectivity in styrene oxide (SO) is obviously influenced by the solvent. FeCo DMC along with MeOH exhibits the best catalytic performance, with a conversion rate of 96% and a SO selectivity of 86%, in N,N-dimethylformamide (DMF) solvent. Various physical and chemical methods were used to analyze the structures and compositions of the materials. To clarify the mechanism of the improvement, we set up an original approach to investigate the kinetics of the adsorption process between the oxidant and the catalyst, using isothermal titration calorimetry (ITC). The obtained results illustrate that the adsorption process of the oxidant on the surface of FeCo DMC can be dramatically promoted by the presence of MeOH. Such a difference in adsorption thus explains the significant improvement of its catalytic activity by modification with MeOH. This study thus provides a new fundamental understanding of DMC catalysts for the styrene epoxidation reaction.