A better understanding of catalyst deactivation is needed to improve catalyst design and performance in microwave-enhanced methane dehydroaromatization (MDA). This study investigates the deactivation of a molybdenum supported H-ZSM-5 zeolite (Mo/H-ZSM-5) catalyst in MDA under microwave-heated conditions, comparing its performance to that of the same catalyst under conventional heating. While the microwave-assisted (MW) process achieved higher benzene yields, the catalyst experienced faster deactivation due to the selective and rapid deposition of coke within the pores of the zeolite, as confirmed through Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), ammonia-temperature programmed desorption (NH3-TPD), thermal gravimetric analysis (TGA), temperature programmed oxidation (TPO), and X-ray photoelectron spectroscopy (XPS) analyses. The quantification of total coke content via TGA/TPO and surface carbon (XPS) revealed that nearly twice as much coke was deposited on the catalyst under MW conditions compared to that on the conventionally heated material, and the coke exhibited a more conductive and graphitic nature. The accelerated deactivation rates were attributed to the formation of hot spots in the MW system, leading to enhanced coupling with coke formed in situ during the reaction and resulting in increased Mo reduction. Observations indicated that the CO activation used to carburize the catalyst prior to the reaction is not advantageous in the MW heating environment. The presence of large amounts of Mo oxides at elevated temperatures (through hot spots) exposed to methane leads to instability under the reaction conditions. Optimizing the activation environment and improvement of the Mo dispersion within the pores are potential strategies to improve catalyst stability.

Microwave-assisted methane dehydroaromatization has the potential to address challenges of traditional dehydroaromatization reactions. However, catalysts for microwave-enhanced reaction systems require effective coupling of fields with the catalyst to produce heat and reach reaction temperatures. This work presents an in-depth understanding of the effect of the addition of silicon carbide as a microwave absorber on catalyst performance among other variables, the viability of the microwave reactor configuration, and insights into designing an effective and reliable microwave-based methane dehydroaromatization process. The effect of other parameters including temperature, weight hourly space velocity, role of microwave absorber, and methane concentration during microwave-assisted methane dehydroaromatization reaction are studied. Mo/ZSM-5 was found to suffer from low permittivity and nonuniform heating under microwave conditions. Mixing silicon carbide powder as a microwave absorber with the catalyst was found to provide more uniform heating. When assessing the catalytic performance of the mixture, it was found that higher methane partial pressures at 2000 cc/gcat.h and a temperature range of 500-600°C produced the highest amount of benzene. The formation of graphitic carbon on the spent catalyst increased with temperature, gas-solid contact period, and methane concentration, which resulted in higher methane conversion and benzene selectivity. The study indicates that under microwave heating the presence of localized carbon enhanced catalyst life by coupling with microwave energy, leading to localized heating, and improving benzene selectivity.

Pyrotechnics are a unique set of materials because they can be formulated to control combustion behavior to elicit desired effects such as light emission, smoke formation, and noise. The ability to enhance and control light emission is particularly desirable for entertainment purposes, as well as military applications. Designing such materials for high color purity at a specific wavelength requires an understanding of the different factors that affect their performance. This review will cover the various aspects of color production, including light emission mechanisms, components of a color composition, and key parameters that determine the optical wavelength band for these compositions. Additionally, because conventional pyrotechnic formulations are known to produce toxic emissions, less hazardous and sustainably formulated pyrotechnics for color production will also be reviewed. Finally, a short perspective is presented on the possible extension of pyrotechnic applications beyond conventional, civilian, and military purposes. image

Efficiency in the control operation of the boilers for coal and coal with biomass can be further improved if the flue gas temperature distribution can be better characterized. This is very difficult in these harsh environmental systems, where spatially resolved measurements are nearly impossible with solid-state sensors. In this work, we evaluate the development of pyrotechnic compounds that would serve as the basis for a novel optical mapping of the temperature inside coal boilers. For this purpose, various green-colour-emitting pyrotechnics using BaCl2 & BULL; 2H(2)O and Ba(NO3)(2) as the green light source were prepared, as this colour offers a distinct signal from the combustion-based background in the boiler. These pyrotechnics were characterized using thermogravimetric analysis (TGA) and X-ray diffraction (XRD) and tested using a flat-flame burner. Furthermore, the composition was varied to evaluate the effect of different metal fuels such as Sn, Co, and Mg, as well as various binders such as ethylcellulose, shellac, parlon, and PVC on green light emission. The emission intensity and the apparent ignition temperature were strongly dependent on the metal type, with Mg showing higher intensities. On the other hand, the effect of the binder showed that the ignition behaviour, emission intensity, and spectral purity were influenced by the nature and exothermicity of the binder. The addition of other potential green light-producing materials, such as boric acid, increased the intensity of emission by 17% for a BaCl2 & BULL; 2H(2)O-based composition. This study identified prospective compositions with intense and bright green-colour emissions that have high spectral purities.

Hydrogen isotope separation can be achieved using a palladium (Pd) membrane because protium (H) and deuterium (D) exhibit different solubility, diffusivity and, hence, mixed-gas permeability in Pd. The permeability of H (k(H2)) and D (k(D2)) were evaluated using a 4 vol% D-2 - 96 vol% H-2 feed mixture at temperatures of 293 K-473 K and pressures of 239 kPa-446 kPa in a continuous Pd membrane separation unit. The Pd foil membrane (0.1 mm thick) is shown to be selective toward H-2 over the entire temperature range, with both k(H2) and k(D2) increasing with temperature. As temperature increases, the mixed-gas selectivity (k(H2)/k(D2)) rises from 4.0 at 300 K to a maximum value of 9.6 in the 363 K-373 K temperature range (which represents the operating temper-atures that would render the highest concentration of H-2 in the permeate and the greatest concentration of D-2 in the retentate), then decreases to 6.2 at 480 K. Competitive transport during co-permeation is a likely cause for the maximum separation factor k(H2)/k(D2) observed in this temperature range, being larger than the values predicted using pure gases ( root 2 for diffusion dominant separation). The membrane selectivity presumably decreases from the observed maximum because the reverse solubility isotope effect decreases as the temperature increases. Additionally, isotope diffusion begins to increasingly affect the selectivity at higher temperatures.

AbstractPyrotechnics are a unique set of materials because they can be formulated to control combustion behavior to elicit desired effects such as light emission, smoke formation, and noise. The ability to enhance and control light emission is particularly desirable for entertainment purposes, as well as military applications. Designing such materials for high color purity at a specific wavelength requires an understanding of the different factors that affect their performance. This review will cover the various aspects of color production, including light emission mechanisms, components of a color composition, and key parameters that determine the optical wavelength band for these compositions. Additionally, because conventional pyrotechnic formulations are known to produce toxic emissions, less hazardous and sustainably formulated pyrotechnics for color production will also be reviewed. Finally, a short perspective is presented on the possible extension of pyrotechnic applications beyond conventional, civilian, and military purposes.