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1.
Xu Lang Bhandari Saurabh Chen Jiming Glasgow Jonathan Mavrikakis Manos 《Topics in Catalysis》2020,63(7-8):762-776
Topics in Catalysis - Palladium has been shown to be an effective catalyst for chloroform hydrodechlorination, which serves as a promising treatment method for industrial chloroform waste. To... 相似文献
2.
Shampa Kandoi Jeff Greeley Marco A. Sanchez-Castillo Steven T. Evans Amit A. Gokhale James A. Dumesic Manos Mavrikakis 《Topics in Catalysis》2006,37(1):17-28
A microkinetic model for methanol decomposition on platinum is presented. The model incorporates competitive decomposition
pathways, beginning with both O–H and C–H bond scission in methanol, and uses results from density functional theory (DFT)
calculations [Greeley and Mavrikakis, J. Am. Chem. Soc. 124 (2002) 7193, Greeley and Mavrikakis, J. Am. Chem. Soc. 126 (2004)
3910]. Results from reaction kinetics experiments show that the rate of H2 production increases with increasing temperature and methanol concentration in the feed and is only nominally affected by
the presence of CO or H2 with methanol. The model, based on the values of binding energies, pre-exponential factors and activation energy barriers
derived from first principles calculations, accurately predicts experimental reaction rates and orders. The model also gives
insight into the most favorable reaction pathway, the rate-limiting step, the apparent activation energy, coverages, and the
effects of pressure. It is found that the pathway beginning with the C–H bond scission (CH3OH→H2COH→HCOH→CO) is dominant compared with the path beginning with O–H bond scission. The cleavage of the first C–H bond in methanol
is the rate-controlling step. The surface is highly poisoned by CO, whereas COH appears to be a spectator species. 相似文献
3.
Formic acid decomposition on Au catalysts: DFT,microkinetic modeling,and reaction kinetics experiments 下载免费PDF全文
Ronald Carrasquillo‐Flores Ana C. Alba‐Rubio James A. Dumesic Manos Mavrikakis 《American Institute of Chemical Engineers》2014,60(4):1303-1319
A combined theoretical and experimental approach is presented that uses a comprehensive mean‐field microkinetic model, reaction kinetics experiments, and scanning transmission electron microscopy imaging to unravel the reaction mechanism and provide insights into the nature of active sites for formic acid (HCOOH) decomposition on Au/SiC catalysts. All input parameters for the microkinetic model are derived from periodic, self‐consistent, generalized gradient approximation (GGA‐PW91) density functional theory calculations on the Au(111), Au(100), and Au(211) surfaces and are subsequently adjusted to describe the experimental HCOOH decomposition rate and selectivity data. It is shown that the HCOOH decomposition follows the formate (HCOO) mediated path, with 100% selectivity toward the dehydrogenation products (CO2 + H2) under all reaction conditions. An analysis of the kinetic parameters suggests that an Au surface in which the coordination number of surface Au atoms is ≤4 may provide a better model for the active site of HCOOH decomposition on these specific supported Au catalysts. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1303–1319, 2014 相似文献
4.
S. Kandoi A.A. Gokhale L.C. Grabow J.A. Dumesic M. Mavrikakis 《Catalysis Letters》2004,93(1-2):93-100
Self-consistent, periodic density functional theory (DFT) calculations and micro-kinetic modeling are used to compare selectivity for the preferential oxidation of CO (PROX) with respect to H2 based on studies of elementary reaction steps on the (111) facet of Au, Cu and Pt. The first step of H oxidation (OH formation) has a higher activation barrier than the second step (H2O formation) on all three metal surfaces, indicating that OH formation competes with CO oxidation for the removal of trace amounts of CO from a typical reformate gas. The activation energy barrier for CO oxidation is found to be 0.18eV on Au(111), 0.82eV on Cu(111) and 0.96eV on Pt(111), whereas the barrier for OH formation is 0.90, 1.28 and 0.83eV respectively. A micro-kinetic model based on the DFT results shows that trends in the selectivity of these metals at different temperatures is due to (i) differences in the rate constants of the competitive CO and H oxidation reactions, and (ii) differences in the CO and H surface coverages. Our results explain why Au and Cu are more selective PROX catalysts compared to Pt at low temperatures. At higher temperatures, Pt and Cu lose some of their selectivity to CO oxidation, whereas the selectivity on Au decreases substantially primarily because of the significantly weaker CO adsorption. 相似文献
5.
Daniela S Nosch Gek L Ong Ioannis Mavrikakis Judith Morris 《Contact lens & anterior eye》2007,30(4):239-248
PURPOSE: To explore the success of the application of a computerised videokeratography (CVK) software system for the fitting of rigid gas permeable (RGP) contact lenses (CLs) on irregular corneal surfaces and compare it to the standard diagnostic fitting procedure. METHODS: This was a comparative prospective study, over a 1-year period (2004-2005). It included 41 RGP CL wearers (68 eyes) with irregular corneal surfaces. Of these, 51 (75%) had keratoconus, 7 (10%) corneal scarring (infectious or traumatic), 6 (6.82%) corneal transplants, 2 (2.9%) astigmatism, and 2 (2.9%) aphakia. Each eye was being re-fitted with a new RGP CL based on a topographical measurement in conjunction with a CL fitting software programme. The performance of the CLs was evaluated regarding visual outcome, fitting characteristics, and efficiency of the fitting procedure. RESULTS: Of the 68 eyes, 53 (77.94%) chose the CL fitted using the CVK software system, 9 (13.24%) chose the CL fitted using the standard procedure, and 6 (8.82%) showed no preference for either CL. There was a statistically significant improvement regarding visual outcome [contrast sensitivity at the spatial frequencies of 0.66 (p=0.029), 3.40 (p=0.008), and 17 (p=0.032), subjective vision (p=0.009)], fitting characteristics [grading scale (p=0.00), lens comfort (p=0.00) and daily wearing time (p=0.002)], and efficiency [number of trial lenses required (p=0.00)] with the CL fitted using the CVK software system. Correlating factors for the likely preference for the CL fitted using the CVK software system were subjective vision (p=0.004), lens comfort (p=0.009), and convenience of the fitting procedure (p=0.023). CONCLUSION: The application of a CVK software system for the fitting procedure of RGP CLs on irregular corneal surfaces was a safe procedure and shown to be more successful and efficient than the standard diagnostic fitting method. 相似文献
6.
Advanced solution methods for microkinetic models of catalytic reactions: A methanol synthesis case study 下载免费PDF全文
Patricia Rubert‐Nason Manos Mavrikakis Christos T. Maravelias Lars C. Grabow Lorenz T. Biegler 《American Institute of Chemical Engineers》2014,60(4):1336-1346
Microkinetic models, combined with experimentally measured reaction rates and orders, play a key role in elucidating detailed reaction mechanisms in heterogeneous catalysis and have typically been solved as systems of ordinary differential equations. In this work, we demonstrate a new approach to fitting those models to experimental data. For the specific example treated here, by reformulating a typical microkinetic model for a continuous stirred tank reactor to a system of nonlinear equations, we achieved a 1000‐fold increase in solution speed. The reduced computational cost allows a more systematic search of the parameter space, leading to better fits to the available experimental data. We applied this approach to the problem of methanol synthesis by CO/CO2 hydrogenation over a supported‐Cu catalyst, an important catalytic reaction with a large industrial interest and potential for large‐scale CO2 chemical fixation. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1336–1346, 2014 相似文献
7.
Karthik Nayani Prabin Rai Nanqi Bao Huaizhe Yu Manos Mavrikakis Robert J. Twieg Nicholas L. Abbott 《Advanced materials (Deerfield Beach, Fla.)》2018,30(27)
The development of stimuli‐responsive materials suitable for use in wearable sensors is a key unresolved challenge. Liquid crystals (LCs) are particularly promising, as they do not require power, are light‐weight, and can be tuned to respond to a range of targeted chemical stimuli. Here, an advance is reported in the design of LCs for chemical sensors with the discovery of LCs that assume parallel orientations at free surfaces and yet retain their chemoresponsiveness. The resulting LC‐based sensors are more sensitive and exhibit faster responses than previous LC sensor designs. 相似文献
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9.
Ru-Pt core-shell nanoparticles for preferential oxidation of carbon monoxide in hydrogen 总被引:2,自引:0,他引:2
Most of the world's hydrogen supply is currently obtained by reforming hydrocarbons. 'Reformate' hydrogen contains significant quantities of CO that poison current hydrogen fuel-cell devices. Catalysts are needed to remove CO from hydrogen through selective oxidation. Here, we report first-principles-guided synthesis of a nanoparticle catalyst comprising a Ru core covered with an approximately 1-2-monolayer-thick shell of Pt atoms. The distinct catalytic properties of these well-characterized core-shell nanoparticles were demonstrated for preferential CO oxidation in hydrogen feeds and subsequent hydrogen light-off. For H2 streams containing 1,000 p.p.m. CO, H2 light-off is complete by 30 (composite function)C, which is significantly better than for traditional PtRu nano-alloys (85 (composite function)C), monometallic mixtures of nanoparticles (93 (composite function)C) and pure Pt particles (170 ( composite function)C). Density functional theory studies suggest that the enhanced catalytic activity for the core-shell nanoparticle originates from a combination of an increased availability of CO-free Pt surface sites on the Ru@Pt nanoparticles and a hydrogen-mediated low-temperature CO oxidation process that is clearly distinct from the traditional bifunctional CO oxidation mechanism. 相似文献
10.
Svenum Ingeborg-Helene Herron Jeffrey A. Mavrikakis Manos Venvik Hilde J. 《Topics in Catalysis》2020,63(7-8):750-761
Topics in Catalysis - The co-adsorption of hydrogen and carbon monoxide on Pd3Ag(111) alloy surfaces has been studied as a model system for Pd-Ag alloys in membrane and catalysis applications using... 相似文献