Transformation of Dilute Ethylene at High Temperature on Micro- and Nano-Sized H-ZSM-5 Zeolites

Ethylene dehydroaromatisation (EDA) was investigated at 700 °C under 1 bar of ethylene (5 mol% in N2) over a micro-(M) and a nano-sized (N) H-ZSM-5. On the M zeolite an induction period followed by deactivation was observed, which could be related to the presence of long diffusion path lengths in this sample, leading to mass transfer resistance. During the induction step, the aromatics yield increases, despite a significant loss of the acid site concentration as a result of coking. This induction period corresponds to the formation of an active hydrocarbon pool (HCP) composed of units of 2 to 5 aromatic rings with a molecular weight ranging from 130 to 220 g mol−1 (light coke). A kinetic study revealed that the developing HCP species is two times more active than Brønsted acid sites in the fresh zeolite. Diffusion limitations yet impact the product desorption by promoting coke growth and, therefore the deactivation of the HCP and hence of the catalyst. From MA-LDI/LDI-TOF MS (Matrix Assisted Laser Desorption Ionization—Time of Flight Mass Spectroscopy) characterisation was deduced that even after complete catalyst deactivation, the as-deposited coke continues growing at the external surface of the zeolite by condensation reactions, thus leading to heavy coke composed of more than 100 carbon atoms and a molar mass exceeding 1300 g mol−1. Unlike the micro-sized zeolite, the nano-scaled zeolite features a short diffusion path length and promotes fast formation of the active HCP. As a result, higher activity and selectivity into benzene were observed, whilst catalyst deactivation was significantly mitigated.

NiCo2S4 nanosheet-decorated 3D, porous Ni film@Ni wire electrode materials for all solid-state asymmetric supercapacitor applications

The NiCo2S4 ultra-nanosheet-decorated 3D porous electrode displayed an excellent electrochemical performance due to its porous nature, shorter diffusion path length, good adhesive properties and lower interface contact resistance.

Solid-state dye-sensitized solar cells from poly(ethylene oxide)/polyaniline electrolytes with catalytic and hole-transporting characteristics

Iodide/triiodide-incorporated PEO/PANi solid-state electrolyte is realized for dye-sensitized solar cell with the aim of expanding the catalytic event of the triiodide species and shortening the charge diffusion path length, yielding an impressive efficiency of 6.1%.

Evaluation of MACRO model by short-term water and solute transport simulation in Maury silt loam soil

Modeling preferential flow has been a concern of many academic fields in the past 30 years all over the world and helps to prevent groundwater contamination. A dual-porosity model, MACRO, was evaluated for short-term (less than 2 days) simulation of water flow and non-reactive solute (chloride) transport through the profile of six plots in well-structured Maury silt loam soil. Water flow in micropores is calculated by the Richards’ equation while simple gravity flow is assumed in the macropores. Solute transport in the micropores is calculated by the convection-dispersion equation (CDE) while the dispersion and diffusion in the CDE is neglected for the solute transport in the macropores. The applied water and chloride reached the bottom of the profile during the 2 and 1-hour(s) application periods in studies 2 and 3, respectively. There is a strong indication of macropore flow in this soil. Based on the statistical criteria, the model accurately simulated water flow and solute transport with depth and time in all plots. The mean values of three statistical parameters (coefficient of residual mass, model efficiency, and correlation coefficient) for water and chloride transport were –0.0014, 0.791, 0.903 and 0.0333, 0.923, 0.956, respectively. Preliminary studies showed that the model could not simulate flow and transport well enough with the one-domain flow concept. In the two-domain flow, effective diffusion path-length, boundary hydraulic conductivity, and boundary soil water pressure were the three most important parameters that control flow and transport between the two domains. The effective diffusion path-length represented the structural development with depth in the Maury silt loam soil.

Molecular Diffusion Model of Neurotransmitter Homeostasis Around Synapses Supporting Gradients

Neurotransmitter homeostasis in and around a synapse involves complex random processes such as diffusion, molecular binding, and uptake by glial transporters. A three-dimensional stochastic diffusion model of a synapse was developed to provide molecular-level details of neurotransmitter homeostasis not predicted by alternative models based on continuum approaches. The development was illustrated through an example case cortico-accumbens synapse that successfully integrated neuroadaptations observed after chronic cocaine. By incorporating cystine-glutamate exchanger as a nonsynaptic release site for glutamate, the stochastic model was used to quantify the relative contributions of synaptic and nonsynaptic sources to extracellular concentration and to estimate molecular influx rates into the perisynapse. A perturbation analysis showed that among the parameters considered, variation in surface density of glial transporters had the largest effect on glutamate concentrations. The stochastic diffusion model of the example synapse was further generalized to characterize glial morphology by studying the role of diffusion path length in supporting neurotransmitter gradients and isolating the synapse. For the same set of parameters, diffusion path length was found to be proportional to the gradient supported.

Stochastic Model of Glutamatergic PFC-NAc Synapse Predicts Cocaine-Induced Changes in Receptor Occupancy

Neurotransmitter homeostasis in and around synapses involves random processes such as diffusion, molecular binding and unbinding. A three-dimensional stochastic diffusion model of a synapse was developed to provide molecular level details of neurotransmitter homeostasis not predicted by alternative models based on continuum approaches. This framework was used to estimate effective diffusion and provide a more accurate prediction of geometric tortuosity in the perisynaptic region. The stochastic model was used to predict the relative contributions of non-synaptic sources to extracellular concentration in control, natural reward seeking, and chronic cocaine cases; and estimation of molecular influx rates required to maintain tone on presynaptic autoreceptors. Also, this was the first stochastic model to confirm the prediction of down-regulation of glutamate transporters by 40% after chronic cocaine. The model can be further generalized to study the role of diffusion path length in supporting neurotransmitter gradients and isolating the synapse.

Hydrogen Absorption and Desorption by Magnesium-Based Nano-Composite Materials

ABSTRACTMgH2 was mechanically milled with nano-Ni (nano-Ni/Al2O3/C) and Ni catalysts (Ni), yielding Mg-based nano-composite materials. X-ray and TEM measurements revealed that nano-Ni particles, which are 6–20 nm size, were dispersed in the MgH2 matrix. The nano-composite material with nano-Ni/Al2O3/C showed excellent properties as compared to that with Ni, a ball-milled MgH2 and the mixture of MgH2 and nano-Ni/Al2O3/C in terms of the H2 desorption and absorption. The nano-composite material with nano-Ni/Al2O3/C desorbed H2 of 4.9–5.8 wt% at 423–473 K, while the mixture could not desorb H2 at the temperature. The H2 absorption capacity at 9 MPa and room temperature in 6 hr. increased from below 0.1 wt% for the mixture to 5.0 wt % for the nano-composite material, approaching a maximum of 6.5 wt% in 70 hr. The catalyst activity was improved with decreasing Ni size. The improved kinetics is indicated by the small activation barrier, the short diffusion path length and the high driving force.