Understanding the Deactivation Phenomena of Small-Pore Mo/H-SSZ-13 during Methane Dehydroaromatisation

Small pore zeolites have shown great potential in a number of catalytic reactions. While Mo-containing medium pore zeolites have been widely studied for methane dehydroaromatisation (MDA), the use of small pore supports has drawn limited attention due to the fast deactivation of the catalyst. This work investigates the structure of the small pore Mo/H-SSZ-13 during catalyst preparation and reaction by operando X-ray absorption spectroscopy (XAS), in situ synchrotron powder diffraction (SPD), and electron microscopy; then, the results are compared with the medium pore Mo/H-ZSM-5. While SPD suggests that during catalyst preparation, part of the MoOx anchors inside the pores, Mo dispersion and subsequent ion exchange was less effective in the small pore catalyst, resulting in the formation of mesopores and Al2(MOO4)3 particles. Unlike Mo/H-ZSM-5, part of the Mo species in Mo/H-SSZ-13 undergoes full reduction to Mo0 during MDA, whereas characterisation of the spent catalyst indicates that differences also exist in the nature of the formed carbon deposits. Hence, the different Mo speciation and the low performance on small pore zeolites can be attributed to mesopores formation during calcination and the ineffective ion exchange into well dispersed Mo-oxo sites. The results open the scope for the optimisation of synthetic routes to explore the potential of small pore topologies

Determination of Debye Temperatures and Lamb-Mössbauer Factors for LnFeO3 Orthoferrite Perovskites (Ln = La, Nd, Sm, Eu, Gd)

Lanthanide orthoferrites have wide-ranging industrial uses including solar, catalytic and electronic applications. Here a series of lanthanide orthoferrite perovskites, LnFeO3 (Ln = La; Nd; Sm; Eu; Gd), prepared through a standard stoichiometric wet ball milling route using oxide precursors, has been studied. Characterisation through X-ray diffraction and X-ray fluorescence confirmed the synthesis of phase-pure or near-pure LnFeO3 compounds. 57Fe Mössbauer spectroscopy was performed over a temperature range of 10 K to 293 K to observe hyperfine structure and to enable calculation of the recoil-free fraction and Debye temperature (θD) of each orthoferrite. Debye temperatures (Ln = La 474 K; Nd 459 K; Sm 457 K; Eu 452 K; Gd 473 K) and recoil-free fractions (Ln = La 0.827; Nd 0.817; Sm 0.816; Eu 0.812; Gd 0.826) were approximated through minimising the difference in the temperature dependent experimental Centre Shift (CS) and theoretical Isomer Shift (IS), by allowing the Debye temperature and Isomer Shift values to vary. This method of minimising the difference between theoretical and actual values yields Debye temperatures consistent with results from other studies determined through thermal analysis methods. This displays the ability of variable-temperature Mössbauer spectroscopy to approximate Debye temperatures and recoil-free fractions, whilst observing temperature induced transitions over the temperature range observed. X-ray diffraction and Rietveld refinement show an inverse relationship between FeO6 octahedral volume and approximated Debye temperatures. Raman spectroscopy show an increase in the band positions attributed to soft modes of Ag symmetry, Ag(3) and Ag(5) from La to GdFeO3 corresponding to octahedral rotations and tilts in the [010] and [101] planes respectively

Influence of the Direct Coulomb Interactions on the Resistivity in NdPb3\text{}_{3}

In order to investigate the influence of the 4f electrons on the scattering processes we measured resistivity of the NdPb$\text{}_{3}$ in the temperature range 7-300 K. As a result, we could compare the experimentally determined magnetic contribution to the resistivity with the theoretically calculated ones for the exchange and quadrupolar scattering. The results may confirm that the direct Coulomb interactions between 4f and conduction electrons predominate

Numerical study of energy-absorbing mats as an element increasing the safety of the military vehicle crew

W pracy zostały przedstawione wyniki modelowania oraz symulacji numerycznych paneli energochłonnych absorbujących energię pochodzącą od wybuchu. Przedstawiono syntetyczny sposób analizy zagadnienia od opracowania geometrii po przygotowanie modelu numerycznego. Wyniki w postaci sił obciążających charakterystyczne punkty pomiarowe manekina Hybryd III 50th w wersji Fast oraz pozostałe charakterystyki przedstawiono w formie wykresów.This study presents the results of numerical simulations of an energy absorbing panels as an element increasing the safety of the military vehicle crew. The simulations are made by a finite element method in LS-Dyna. A numerical Hybrid III 50th dummy is used to simulate the tibia axial compressive forces and accelerations. Simulations results are compared with literature data to validate the Hybrid III dummy. Forces and accelerations results are presented in the form of a charts

Investigation of human body exposed to blast wave derived from improvised explosive devices

The analysis of contemporary military conflicts shows, that the most dangerous threat for soldiers are Improvised Explosive Devices (IEDs). Blast resistance of military vehicles and structures is broadly discussed in many articles. However, information about human body response to impact loading is hard to find and very general. Both experi-mental trials with dummies and numerical analyses are needed. To design and develop better protection system it is necessary to identify and measure the effects of blast wave impact on crew of military vehicle. This paper presents numerical simulation results of special armoured vehicle subjected to mine threat of 8 and 10 kg of TNT. Possible effects of mine explosion on human body are described. Review of modern-mine and IED countermeasure solutions is presented. The analysis is conducted using LS-DYNA explicit code. Only vehicle’s hull is considered with suspension and turret is modelled using mass. Gravity is taken into account. Numerical model of Hybrid-III dummy is used. Accelerations and forces in tibia, neck and spine were calculated. HIC-36 criterion was also evaluated Different types of possible seat configuration are examined. Results show convergence between explosive size and injury risk

Modelling and numerical analysis of explosion underneath the vehicle

The article presents a method for numerical modelling of interaction of a shock wave on a simplified model of a light armoured vehicle. Detonation of the explosive material occurs centrally underneath the vehicle. The mass of an explosive charge was from 0.5 to 10 kg off TNT. Acceleration, displacement and kinetic energy of the floor plate/panel were verified during the tests. The model and numerical calculations were carried out using the following programs: CATIA, HyperMesh, LS-PrePost, LS-Dyna. CONWEP approach was applied to describe interaction of a pressure wave on the structure. For each case, the explosive charge was located at the same place under 700 mm from the top surface of the range stand. The results of the calculations present the effects of detonation under the vehicle without a protective system and with the protective system. The proposed protection system is made of low-density materials such as aluminum foam and cork. Thanks to such an approach, the effectiveness of the protective system will be checked to reduce the adverse physical quantities that threaten the health of the soldiers. Thanks to very simple solutions, it is possible to increase passive safety of passers and use of low-density materials will slightly increase the vehicle's mass leaving manoeuvrability at a similar level

Influence of internal space frame in body shell on change of its response as a result of impulse forcing

In order to increase the stiffness anybody chassis in Wheeled Armoured Vehicle on impact of the shock wave, the space frame part in body shell was conducted. The aim of this action is to reduce deformation and damage as a result of the detonation of the mine or an Improvised Explosive Device (IED) under the vehicle. To verify the conducted modernization, numerical calculations of the system response to a blast wave effect were carried out. The mass of the detonated explosive was increased from 6 to 20 kg of TNT. An explosive material was detonated centrally under the vehicle front part according to NATO requirements [1, 2]. The results of the calculations allowed for a deformation assessment of the floor plate and its displacement before and after modernization. A model and numerical calculations were performed using the following software: CATIA, HyperMesh, LS-PrePost, LS-Dyna. CONWEP approach was used to describe an influence of a pressure wave on the structure

Experimental and numerical investigation of connector with elastomer joint

This article presents works associated with the design, numerical analyses and experimental tests of an energyabsorbing mat designed for increasing the safety of the soldiers inside military vehicles, especially their legs. One of the most important branches of engineering interests is high technologies accompanying the safety of soldiers. Energy absorbing mats are one of an additional equipment of a military vehicle, which is directly targeted to increase leg safety during explosion of IED (Improvised Explosive Device) under vehicle. The presented invention allows protection legs of the crew’s feet resting on the floor of the vehicle during explosion of a mine or IED. In most solutions, crewmembers’ foot rests directly on the floor, causing serious injuries. The value of the load on the metatarsus and tibia is closely related to the overall vehicle structure, which generally has limitations in the use of available external and internal protection solutions. Energy absorbing mats are a universal solution because they are adaptable to any type of vehicle. Their role is particularly important in flat-bottomed armoured vehicles. The article will show the results of the analysis showing how the mat works. Experimental results will be compared with the results of numerical analysis. The analysis is conducted using the LS-DYNA explicit code