Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Conversion of ethanol to acetone & other produces using nano-sensor SnO2(110): Ab initio DFT  [PDF]
Leila Mahdavian
Natural Science (NS) , 2011, DOI: 10.4236/ns.2011.36065
Abstract: The material considered in this study, SnO2 (110), has a widespread use as gas sensor and oxygen vacancies are known to act as active catalytic sites for the adsorption of small mo-lecules. In the following calculations crystal line SnO2 nano-crystal have been considered. The grains lattice, which has the rutile structure of the bulk material, includes oxygen vacancies and depositing a gaseous molecule, either ethanol, above an atom on the grain surface, generates the adsorbed system. The conduc-tance has a functional relationship with the structure and the distance molecule of the na-no- crystal and its dependence on these quanti-ties parallels the one of the binding energy. The calculations have quantum mechanical detail and are based on a semi-empirical (MNDO me-thod), which is applied to the evaluation of both the electronic structure and of the conductance. We study the structural, total energy, thermo-dynamic and conductive properties of absorp-tion C2H5OH on nano-crystal, which convert to acetaldehyde and acetone.
The Structure of the Stoichiometric and Reduced SnO2 (110) Surface  [PDF]
I. Manassidis,J. Goniakowski,L. N. Kantorovich,M. J. Gillan
Physics , 1995, DOI: 10.1016/0039-6028(95)00677-X
Abstract: First-principles calculations based on density functional theory (DFT) and the pseudopotential method have been used to study the stoichiometric and reduced SnO2 (110) surface. The ionic relaxations are found to be moderate for both the stoichiometric and reduced surfaces, and are very similar to those found in recent DFT-pseudopotential work on TiO2. Removal of neutral oxygen leaves two electrons per oxygen on the surface, which are distributed in channels passing through bridging oxygen sites. The associated electron density can be attributed to reduction of tin from Sn4+ to Sn2+, but only if the charge distribution on Sn2+ is recognized to be highly asymmetric. Reduction of the surface gives rise to a broad distribution of gap states, in qualitative agreement with spectroscopic measurements.
Recognition Capability of ANN For The Analysis of PbO-Doped Sno2 Sensor For Detection of Acetone  [PDF]
Tanu Bhatnagar
International Journal of Scientific Engineering and Technology , 2013,
Abstract: In the present work thick film SnO2 sensor was fabricated on a 1 x1 alumina substrate. It consists of a gas sensitive layer (SnO2) doped with PbO, a pair of electrodes underneath the gas sensing layer serving as a contact pad for sensor. Also a heater element on the backside of the substrate was printed. The sensitivity of sensor has been studied at different temperatures (1500C-3500C) upon exposure to acetone. An approach is made to measure the sensitivity of PbO-doped SnO2 by using ANN tool. Result presented in the paper shows the potential of ANN as a design tool in the area of thick film sensor.
DFT Studies of Adsorption of Benzoic Acid on the Rutile (110) Surface: Modes and Patterns  [PDF]
Xiang Zhao,David R. Bowler
Physics , 2014,
Abstract: Adsorption of benzoic acid on the (110) surface of rutile, both unreconstructed and (1x2)- reconstructed ones, at saturation coverage of one benzoate per two adjacent five-coordinated Ti5c sites has been studied using DFT simulations, as implemented through the Vienna Ab initio Simulations Package (VASP). In order to study the effects of hydrogen bonding and Van der Waals forces in influencing the relative stabilities of different adsorbate overlayer superstructures, these studies were performed through Local Density Approximation (LDA), Generalized Gradient Approximation(GGA) and DFT-D2. Through the calculations, it was found out that although the optimized structures corresponded with the proposed models for the experimental results, the relative energetic stabilities of different overlayer structures have shown some differences with the experimental results. In the GGA calculations, the overlayer structures involving the benzene rings aligned along the (001)-direction were shown to be more stable than those aligned perpendicular to it, regardless of whether the benzoates were arranged in (1x1) or (1x2) symmetries on the (1x1)-unreconstructed surface, or on the (1x2)-reconstructed surface. These are in contrast to the experimental studies using STM, whose observations revealed that configurations with the benzene rings aligned along the (110)-direction when adsorbed on the (1x2)-reconstructed surface.
Gas-phase selective conjugate addition of methanol to acetone for methyl vinyl ketone over SnO2 nanoparticle catalysts
Fajardo, Humberto V.;Probst, Luiz F. D.;Valentini, Antoninho;Carre?o, Neftalí L. V.;Maciel, Adeilton P.;Leite, Edson R.;Longo, Elson;
Journal of the Brazilian Chemical Society , 2005, DOI: 10.1590/S0103-50532005000400018
Abstract: aldol condensation between methanol and acetone, catalyzed by undoped and rare earths (ce and y) doped tin oxide nanoparticles is presented. several methanol/acetone molar ratio conditions were evaluated aiming to produce methyl vinyl ketone as the main product. the undoped and doped ultrafine nanoparticles of tin oxide were prepared using the polymeric precursor method. the characterization was carried out by means of n2 adsorption (bet), x-ray diffraction (xrd), co2 chemisorption, x-ray photoemission spectroscopy (xps) and transmission electron microscopy (tem). the catalytic behavior observed for sno2 samples suggests that the methanol/acetone molar ratio and ce and y doping play an important role in the catalytic activity and in the product selectivity. the results from xrd and xps pointed to the de-mixing process for the doped samples, due to the heat-treatment. this segregation layer contributes to the observed change in the catalytic behavior.
甲醇在SnO2(110)表面的吸附与解离的理论研究  [PDF]
分子催化 , 2008,
Abstract: 研究气体分子在固体表面吸附过程的化学和物理性质在气体传感器研究方面有着重要的意义,尤其是一些小分子与氧化物的作用受到人们广泛的关注.SnO2具有特殊的表面性质,是适合用于催化有机物的光催化剂,同时由于SnO2在易燃易爆危险气体和有机物的检测等方面有着特殊而广阔的应用前景,成为化学工作者研究的热点[1-3].
Selective Oxidation of Ammonia on RuO2(110): a combined DFT and KMC study  [PDF]
Sampyo Hong,Altaf Karim,Talat S. Rahman,Karl Jacobi,Gerhard Ertl
Physics , 2010,
Abstract: We have used a combination of density functional theory (DFT) and kinetic Monte Carlo (KMC) simulations to calculate the reaction rates for the selective oxidation of ammonia on RuO2(110). We find that the overall energy barrier for NH3 + O -> NH + H2O is 0.56 eV, while that for N + N -> N2, and N + O -> NO to be 0.27, and 0.14 eV, respectively. Our KMC calculations enable us to examine the kinetics not only of these mainline processes but also of additional 15 reactions among several intermediate species that illuminate the reactivity and selectivity of the former. In agreement with previous studies, we find that the key role in high reactivity of RuO2(110) in ammonia decomposition is played by the way in which, by promoting easier H abstraction, H bonding between ammonia and its intermediates with the adsorbate and substrate O converts NH decomposition into a non-activated (spontaneous) process. Further, our findings confirm in detail what experiment and previous studies have suggested about NO and N2 formation rates, namely, that NO desorption is a rate-limiting process in that surface NO blocks reaction sites at lower temperatures. Our calculations concerning selectivity (93% in favor of NO over N2) are in very close agreement with experiment (95%). They also explain why NO formation is so favored over N2 formation even at low O2 pressure. The significantly reduced N diffusion caused by various intermediates present on the RuO2(110) surface severely inhibits the recombination site for N+N -> N2, but interferes with that for N + O -> NO far less owing to the nearby availability of O from dissociation of O2.
CeO2(110)负载Au纳米颗粒催化CO+NOx反应的DFT+U研究  [PDF]
催化学报 , 2014, DOI: 10.1016/S1872-2067(14)60168-6
Abstract: ?通过在位库伦校正的密度泛函理论(DFT+U)方法计算,我们研究了CO和NOx分子在Au负载CeO2(110)表面的吸附.结果表明,CO在Au纳米颗粒的顶位有很强的吸附能,大约为1.2eV,而NO在Au纳米颗粒上或者Au与CeO2载体界面处都是弱吸附.然而,当NOx在界面处形成N2O2二聚体之后,通过断裂末端的N-O键能够有效地被降解.纵观整个反应过程,第一步CO+N2O2的反应遵循了Langmuir-Hinshelwood机理,活化能只有0.4eV,通过形成ONNOCO的中间物种最终产生N2O和CO2.不同的是,第二步消除N2O反应遵循了Eley-Rideal碰撞机理,需要相当高的能垒,约为1.8eV.通过进一步分析表明,稀土Ce元素独特的电子特性能够使电子从Au上转移并且局域到载体表面的Ce阳离子上,并且有助于形成带负电的N2O2分子.而且Au纳米颗粒有很强的结构流动性,能够促进吸附的CO分子靠近界面处的N2O2并与之反应.
Re-assigning (1x2) reconstruction of rutile TiO_2(110) from DFT+U calculations  [PDF]
Hatice ünal,Ersen Mete,\cSinasi Ellialtio\uglu
Physics , 2011, DOI: 10.1103/PhysRevB.84.115407
Abstract: Physically reasonable electronic structures of reconstructed rutile TiO_2(110)-(1x2) surfaces were studied using density functional theory (DFT) supplemented with Hubbard U on-site Coulomb repulsion acting on the d electrons, so called as the DFT+U approach. Two leading reconstruction models proposed by Onishi--Iwasawa and Park et al. were compared in terms of their thermodynamic stabilities.
Selective synthesis of SnO2 hollow microspheres and nano-sheets via a hydrothermal route
Yue Li,YanQun Guo,RuiQin Tan,Ping Cui,Yong Li,WeiJie Song
Chinese Science Bulletin , 2010, DOI: 10.1007/s11434-010-0004-y
Abstract: We report a mild template-free hydrothermal route for selective synthesis of SnO2 hollow microspheres and nano-sheets using SnCl2 and NaOH as initial materials. By switching the solvent from water to ethanol, the formed SnO2 nanostructures changed from nano-sheets to hollow microspheres. The obtained nano-sheets were single crystalline in structure. On the basis of the characterization of intermediate products, the formation of SnO2 hollow microspheres was ascribed to a crystal growth process, while the formation of SnO2 nano-sheets was ascribed to the oxidation of SnO2 sheets during the hydrothermal process. Further characterization of the SnO2 hollow microspheres and nano-sheets by X-ray photoelectron spectroscopy and UV-Vis absorption spectroscopy reveals different optical absorption properties and valence band electronic structures. In addition, the SnO2 nano-sheets and hollow microspheres exhibit different sensing properties. The present work provides a facile and simple template-free method for the synthesis of nano-structured SnO2.
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.