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.

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An analytical microscopic study of metals in fluidized catalytic cracking catalyst

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100145613 ◽

1986 ◽

Vol 44 ◽

pp. 854-855

Author(s):

Clifford S. Rainey

Keyword(s):

Electron Microscopy ◽

Spatial Distribution ◽

Catalytic Cracking ◽

Catalyst Deactivation ◽

Coke Formation ◽

Acid Sites ◽

Y Zeolite ◽

Fcc Catalyst ◽

Fluidized Catalytic Cracking ◽

High Regeneration

The spatial distribution of V and Ni deposited within fluidized catalytic cracking (FCC) catalyst is studied because these metals contribute to catalyst deactivation. Y zeolite in FCC microspheres are high SiO2 aluminosilicates with molecular-sized channels that contain a mixture of lanthanoids. They must withstand high regeneration temperatures and retain acid sites needed for cracking of hydrocarbons, a process essential for efficient gasoline production. Zeolite in combination with V to form vanadates, or less diffusion in the channels due to coke formation, may deactivate catalyst. Other factors such as metal "skins", microsphere sintering, and attrition may also be involved. SEM of FCC fracture surfaces, AEM of Y zeolite, and electron microscopy of this work are developed to better understand and minimize catalyst deactivation.

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COMPUTATIONAL INVESTIGATION OF THE EFFECTS OF SPHERICAL FILLER MORPHOLOGY AND LOADING ON DIFFUSION TORTUOSITY AND RUBBER PERMEABILITY

Rubber Chemistry and Technology ◽

10.5254/rct.13.88932 ◽

2013 ◽

Vol 86 (2) ◽

pp. 175-189 ◽

Cited By ~ 1

Author(s):

T. C. Gruber ◽

S. D. Crossley ◽

A. P. Smith

Keyword(s):

Random Walk ◽

Rolling Resistance ◽

Diffusion Path ◽

Filler Loading ◽

Pressure Losses ◽

Biased Random Walk ◽

Gas Molecule ◽

Path Lengths ◽

Path Tortuosity ◽

Spherical Filler

ABSTRACT Inflation pressure loss in tires degrades performance, raises rolling resistance, and reduces fuel economy. The incorporation of solid fillers, such as carbon black, at relatively high loadings in tire innerliners helps minimize these pressure losses by reducing innerliner permeability due to increases in average gas molecule diffusion path lengths (tortuosity), as well as reductions in diffusion pathway density (capacity). The effects of filler morphology and loading on diffusion path tortuosity can be explored by modeling biased random-walk diffusion through impermeable sphere-filled matrices. Modeled diffusion rate was found to decrease with increased filler loading, reduced filler sphere sizes, increased random-walk step sizes, and the aggregation of filler spheres. Initial correlations with limited empirical permeability measurements are used to validate the model approach.

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Deconvoluting the Competing Effects of Zeolite Framework Topology and Diffusion Path Length on Methanol to Hydrocarbons Reaction

ACS Catalysis ◽

10.1021/acscatal.8b02274 ◽

2018 ◽

Vol 8 (12) ◽

pp. 11042-11053 ◽

Cited By ~ 16

Author(s):

Yufeng Shen ◽

Thuy T. Le ◽

Donglong Fu ◽

Joel E. Schmidt ◽

Matthias Filez ◽

...

Keyword(s):

Path Length ◽

Diffusion Path ◽

Zeolite Framework ◽

Methanol To Hydrocarbons ◽

Diffusion Path Length ◽

And Diffusion

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

Plant Soil and Environment ◽

10.17221/3563-pse ◽

2011 ◽

Vol 51 (No. 3) ◽

pp. 110-123 ◽

Cited By ~ 1

Author(s):

H. Merdun ◽

V.L. Quisenberry

Keyword(s):

Solute Transport ◽

Water Flow ◽

Chloride Transport ◽

Effective Diffusion ◽

Diffusion Path ◽

Silt Loam ◽

Short Term ◽

Silt Loam Soil ◽

Diffusion Path Length ◽

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.

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Synthesis of SAPO-34 Nanoplates with High Si/Al Ratio and Improved Acid Site Density

Nanomaterials ◽

10.3390/nano11123198 ◽

2021 ◽

Vol 11 (12) ◽

pp. 3198

Author(s):

Syed Fakhar Alam ◽

Min-Zy Kim ◽

Aafaq ur Rehman ◽

Devipriyanka Arepalli ◽

Pankaj Sharma ◽

...

Keyword(s):

Phosphoric Acid ◽

Molecular Sieves ◽

Active Sites ◽

High Performance ◽

Hydrothermal Process ◽

Acid Sites ◽

High Density ◽

Structure Directing Agent ◽

Transfer Resistance ◽

Low Mass

Two-dimensional SAPO-34 molecular sieves were synthesized by microwave hydrothermal process. The concentrations of structure directing agent (SDA), phosphoric acid, and silicon in the gel solution were varied and their effect on phase, shape, and composition of synthesized particles was studied. The synthesized particles were characterized by various techniques using SEM, XRD, BET, EDX, and NH3-TPD. Various morphologies of particles including isotropic, hyper rectangle, and nanoplates were obtained. It was found that the Si/Al ratio of the SAPO-34 particles was in a direct relationship with the density of acid sites. Moreover, the gel composition and preparation affected the chemistry of the synthesized particles. The slow addition of phosphoric acid improved the homogeneity of synthesis gel and resulted in SAPO-34 nanoplates with high density of acid sites, 3.482 mmol/g. The SAPO-34 nanoplates are expected to serve as a high performance catalyst due to the low mass transfer resistance and the high density of active sites.

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Mechanistic Insights into Hydrodeoxygenation of Acetone over Mo/HZSM-5 Bifunctional Catalyst for the Production of Hydrocarbons

Energies ◽

10.3390/en15010053 ◽

2021 ◽

Vol 15 (1) ◽

pp. 53

Author(s):

Kai Miao ◽

Tan Li ◽

Jing Su ◽

Cong Wang ◽

Kaige Wang

Keyword(s):

Hydrogen Pressure ◽

Catalyst Deactivation ◽

Catalyst Activity ◽

Coke Formation ◽

Bifunctional Catalyst ◽

Acid Sites ◽

Coke Deposition ◽

Enhanced Production ◽

Bio Oil ◽

Catalytic Hydropyrolysis

Catalytic hydropyrolysis via the introduction of external hydrogen into catalytic pyrolysis process using hydrodeoxygenation catalysts is one of the major approaches of bio-oil upgrading. In this study, hydrodeoxygenation of acetone over Mo/HZSM-5 and HZSM-5 were investigated with focus on the influence of hydrogen pressure and catalyst deactivation. It is found that doped MoO3 could prolong the catalyst activity due to the suppression of coke formation. The influence of hydrogen pressure on catalytic HDO of acetone was further studied. Hydrogen pressure of 30 bar effectively prolonged catalyst activity while decreased the coke deposition over catalyst. The coke formation over the HZSM-5 and Mo/HZSM-5 under 30 bar hydrogen pressure decreased 66% and 83%, respectively, compared to that under atmospheric hydrogen pressure. Compared to the test with the HZSM-5, 35% higher yield of aliphatics and 60% lower coke were obtained from the Mo/HZSM-5 under 30 bar hydrogen pressure. Characterization of the spent Mo/HZSM-5 catalyst revealed the deactivation was mainly due to the carbon deposition blocking the micropores and Bronsted acid sites. Mo/HZSM-5 was proved to be potentially enhanced production of hydrocarbons.

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Low Temperature Synthesis of Li4Ti5O12 Nanowire as Anode for Lithium Ion Batteries

Journal of Computational and Theoretical Nanoscience ◽

10.1166/jctn.2020.8783 ◽

2020 ◽

Vol 17 (2) ◽

pp. 1167-1172

Author(s):

Lukman Noerochim ◽

Widyastuti ◽

Haniffudin Nurdiansah ◽

Bambang Prihandoko

Keyword(s):

Low Temperature ◽

Lithium Ion Batteries ◽

Lithium Ion ◽

Diffusion Path ◽

Charge Transfer Resistance ◽

Holding Time ◽

Synthesis Process ◽

Low Temperature Synthesis ◽

Temperature Synthesis ◽

Transfer Resistance

Low temperature synthesis process of Li4Ti5O12 nanowire is successfully performed by hydrothermal method at temperature 100 °C with holding time for 18, 24 and 30 h. XRD results show the presence of two phases are Li4Ti5O12 and TiO2. The morphology of Li4Ti5O12 nanowire is clearly observed by SEM with the length nanowire of 1.391–5.865 μm, and diameter of 19.43–97.14 nm. The Li4Ti5O12 with holding time of 24 h has the highest specific discharge capacity of 66.287 mAh/g. While the capacity decrease of 3.22% after 30 cycle. It is attributed to the largest surface area enhancing smallest diffusion path for Li+ ion. Furthermore, the dual-phase Li4Ti5O12–Ti12 with holding time of 24 h has the most excellent conductivity due to the low of charge-transfer resistance. Therefore, the Li4Ti5O12 nanowire can be a promising material as anode for lithium-ion batteries.

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Molecular Diffusion Model of Neurotransmitter Homeostasis Around Synapses Supporting Gradients

Neural Computation ◽

10.1162/neco_a_00101 ◽

2011 ◽

Vol 23 (4) ◽

pp. 984-1014 ◽

Cited By ~ 6

Author(s):

Ashwin Mohan ◽

Sandeep Pendyam ◽

Peter W. Kalivas ◽

Satish S. Nair

Keyword(s):

Diffusion Model ◽

Path Length ◽

Molecular Diffusion ◽

Three Dimensional ◽

Release Site ◽

Diffusion Path ◽

Stochastic Diffusion ◽

Molecular Binding ◽

Chronic Cocaine ◽

Diffusion Path Length

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.

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

MRS Proceedings ◽

10.1557/proc-837-n3.5 ◽

2004 ◽

Vol 837 ◽

Cited By ~ 2

Author(s):

Yoshitsugu Kojima ◽

Yasuaki Kawai ◽

Tetsuya Haga

Keyword(s):

Composite Material ◽

Composite Materials ◽

Activation Barrier ◽

Catalyst Activity ◽

Diffusion Path ◽

Absorption Capacity ◽

Ni Catalysts ◽

Nano Composite ◽

Diffusion Path Length ◽

20 Nm

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.

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

Journal of Materials Chemistry A ◽

10.1039/c4ta06393g ◽

2015 ◽

Vol 3 (10) ◽

pp. 5368-5374 ◽

Cited By ~ 36

Author(s):

Yanyan Duan ◽

Qunwei Tang ◽

Yuran Chen ◽

Zhiyuan Zhao ◽

Yang Lv ◽

...

Keyword(s):

Solid State ◽

Dye Sensitized Solar Cells ◽

Diffusion Path ◽

Solid State Electrolyte ◽

Dye Sensitized ◽

Hole Transporting ◽

Diffusion Path Length ◽

Poly Ethylene Oxide ◽

Poly Ethylene ◽

Sensitized Solar Cells

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%.

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