New insights into reaction-diffusion kinetic coupling in the esterification of acetic acid with isopropanol over niobium pentoxide

Author(s):  
Aline C. M. Trindade ◽  
Heveline Enzweiler ◽  
Nina P. G. Salau
2018 ◽  
Vol 3 (6) ◽  
pp. 920-929 ◽  
Author(s):  
Bojana Bradić ◽  
David Bajec ◽  
Andrej Pohar ◽  
Uroš Novak ◽  
Blaž Likozar

New mechanistic insight into the modelling of the heterogeneous N-deacetylation step of α-chitin, obtained from waste crustacean shells.


2020 ◽  
Author(s):  
Ben A Johnson ◽  
Sascha Ott

<div> <p>Metal-organic frameworks (MOFs) are becoming increasingly popular as heterogenous support matrices for molecular catalysts. Given that reactants, or potentially holes/electrons, need to diffuse into the porous framework as the reaction proceeds, the reaction can possibly take place within the bulk of the particle or be confined to a thin layer at the surface due to transport limitations. Herein, a simple steady-state reaction-diffusion kinetic model is developed to diagnose these two mutually exclusive behaviors in MOF-based systems. The oxygen evolution reaction (OER) driven by a chemical oxidant is presented as an example mechanism. Quantitative metrics for assigning either bulk or surface reactivity are delineated over a wide variety of conditions, and numerical simulations are employed to verify these results. For each case, expressions for the turnover frequency (TOF) are outlined, and it is shown that surface reactivity can influence measured TOFs. Importantly, this report shows how to transition from surface to bulk reactivity and thus identifies which experimental parameters to target for optimizing the efficiency of MOF-based molecular catalyst systems.</p> </div> <br>


2018 ◽  
Vol 12 (3) ◽  
pp. 218-229 ◽  
Author(s):  
Caterine Gómez ◽  
Jorge Rodríguez-Páez

In this work, niobium pentoxide (Nb2O5) nanoparticles of varying sizes and morphology were synthesized using the controlled precipitation method. Ammonium niobate oxylate hydrate (NH4)H2[NbO(C2O4)3] ? 3H2O was used as a niobium precursor and distilled water or acetic acid was used as solvent. The obtained solids were characterized using Fourier transform infrared and Raman spectroscopies, X-ray diffraction and transmission electron microscopy. The as-synthesized solid precipitate was amorphous, but after heat treatment between 500?C and 600?C, the T-Nb2O5 phase was obtained. The size of the primary particles of the niobium pentoxide was nanometric (<100 nm), with agglomerate size of >500 nm, when water was used as a solvent for synthesis. Considering the nature of the process, a possible reaction mechanism of the precursor with the water and NH4OH was proposed, which explains the formation of the solid within an aqueous solution. Considering one potential use of Nb2O5 synthesized in this work, the photo-degradation action of the particles on the organic molecule methylene blue was tested. The sample synthesized in acetic acid at pH ~9.0 and heat treated at 600?C showed the highest photo-degradation capacity, with a degradation of ~60% of the dye for 60 minutes.


2020 ◽  
Vol 13 (05) ◽  
pp. 2051020
Author(s):  
Jing Chu ◽  
Ming Gu ◽  
Ruiheng Liu ◽  
Shengqiang Bai ◽  
Xun Shi ◽  
...  

Interfacial diffusions and/or chemical reactions are one of the key issues for the reliability of CoSb3-based skutterudite thermoelectric (TE) joint, especially for the [Formula: see text]-type joint, which limits the applications of TE devices. We investigate the interfacial evolution for [Formula: see text]-type CeyFexCo[Formula: see text]Sb[Formula: see text]/Nb joints ([Formula: see text]–1, [Formula: see text], 3, 4) and combine the previous study on [Formula: see text]-type Yb[Formula: see text]Co4Sb[Formula: see text]/Nb joint to demonstrate the effect of TE materials on the interfacial microstructure and interfacial resistivity. The reaction–diffusion kinetic analysis shows that the TE materials has little effect on chemical reactions but strongly influence the Sb diffusions. The low energy barrier of Sb diffusion leads to the absent phase decomposition of skutterudites in CeyFexCo[Formula: see text]Sb[Formula: see text]/Nb joints. The interfacial resistivity of CeyFexCo[Formula: see text]Sb[Formula: see text]/Nb joints is related with Fe content and the interfacial reaction layer (IRL) growth. In addition, since the interfacial reaction layer growth rate and interfacial resistivity of CeyFexCo[Formula: see text]Sb[Formula: see text]/Nb joints are both low, Nb is an adequate barrier layer candidate material.


2020 ◽  
Author(s):  
Ben A Johnson ◽  
Sascha Ott

<div> <p>Metal-organic frameworks (MOFs) are becoming increasingly popular as heterogenous support matrices for molecular catalysts. Given that reactants, or potentially holes/electrons, need to diffuse into the porous framework as the reaction proceeds, the reaction can possibly take place within the bulk of the particle or be confined to a thin layer at the surface due to transport limitations. Herein, a simple steady-state reaction-diffusion kinetic model is developed to diagnose these two mutually exclusive behaviors in MOF-based systems. The oxygen evolution reaction (OER) driven by a chemical oxidant is presented as an example mechanism. Quantitative metrics for assigning either bulk or surface reactivity are delineated over a wide variety of conditions, and numerical simulations are employed to verify these results. For each case, expressions for the turnover frequency (TOF) are outlined, and it is shown that surface reactivity can influence measured TOFs. Importantly, this report shows how to transition from surface to bulk reactivity and thus identifies which experimental parameters to target for optimizing the efficiency of MOF-based molecular catalyst systems.</p> </div> <br>


2008 ◽  
Vol 133-135 ◽  
pp. 106-112 ◽  
Author(s):  
Valdeilson S. Braga ◽  
Ivoneide C.L. Barros ◽  
Fillipe A.C. Garcia ◽  
Sílvia C.L. Dias ◽  
José A. Dias

Author(s):  
N.C. Lyon ◽  
W. C. Mueller

Schumacher and Halbsguth first demonstrated ectodesmata as pores or channels in the epidermal cell walls in haustoria of Cuscuta odorata L. by light microscopy in tissues fixed in a sublimate fixative (30% ethyl alcohol, 30 ml:glacial acetic acid, 10 ml: 65% nitric acid, 1 ml: 40% formaldehyde, 5 ml: oxalic acid, 2 g: mecuric chloride to saturation 2-3 g). Other workers have published electron micrographs of structures transversing the outer epidermal cell in thin sections of plant leaves that have been interpreted as ectodesmata. Such structures are evident following treatment with Hg++ or Ag+ salts and are only rarely observed by electron microscopy. If ectodesmata exist without such treatment, and are not artefacts, they would afford natural pathways of entry for applied foliar solutions and plant viruses.


Author(s):  
H.H. Rotermund

Chemical reactions at a surface will in most cases show a measurable influence on the work function of the clean surface. This change of the work function δφ can be used to image the local distributions of the investigated reaction,.if one of the reacting partners is adsorbed at the surface in form of islands of sufficient size (Δ>0.2μm). These can than be visualized via a photoemission electron microscope (PEEM). Changes of φ as low as 2 meV give already a change in the total intensity of a PEEM picture. To achieve reasonable contrast for an image several 10 meV of δφ are needed. Dynamic processes as surface diffusion of CO or O on single crystal surfaces as well as reaction / diffusion fronts have been observed in real time and space.


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