| 1. |
- Zhdanov, Vladimir, 1952
(författare)
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Kinetics and percolation: coke in heterogeneous catalysts
- 2022
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Ingår i: Journal of Physics A: Mathematical and Theoretical. - : IOP Publishing. - 1751-8121 .- 1751-8113. ; 55:17
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Tidskriftsartikel (refereegranskat)abstract
- In the conventional lattice percolation models, bonds or sites are open at random, whereas in reality there is often interplay of percolation and the kinetics under consideration. An interesting and practically important example is hydrocarbon conversion occurring in a reactor containing similar to 1 mm-sized porous pellets with catalytic nanoparticles deposited at walls of the nanopores. Such catalytic heterogeneous reactions are often accompanied by coke formation deactivating catalytic nanoparticles and blocking pores for reactant diffusion, so that one needs to remove coke from time to time e.g. via reaction with oxygen. Herein, I first present generic coarse-grained Monte Carlo simulations of coke formation in a single pellet with the emphasis on the reaction regime influenced by reactant diffusion in pores. Then, the obtained coke distributions are used for similar simulations of coke removal. This combination of the models has allowed me to illustrate qualitatively new spatio-temporal regimes of the processes under consideration. For example, the removal of coke can be slow in the beginning, due to blocking of oxygen diffusion near the external pellet-gas interface and preventing its penetration to the central part of a pellet, and then fast when the pathways for diffusion to the center become to be open.
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| 2. |
- Zhdanov, Vladimir, 1952
(författare)
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Kinetic aspects of virus targeting by nanoparticles in vivo
- 2021
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Ingår i: Journal of Biological Physics. - : Springer Science and Business Media LLC. - 0092-0606 .- 1573-0689. ; 47:2, s. 95-101
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Tidskriftsartikel (refereegranskat)abstract
- One of the suggested ways of the use of nanoparticles in virology implies their association with and subsequent deactivation of virions. The conditions determining the efficiency of this approach in vivo are now not clear. Herein, I propose the first kinetic model describing the corresponding processes and clarifying these conditions. My analysis indicates that nanoparticles can decrease concentration of infected cells by a factor of one order of magnitude, but this decrease itself (without feedback of the immune system) is insufficient for full eradication of infection. It can, however, induce delay in the progress of infection, and this delay can help to form sufficient feedback of the immune system.
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| 3. |
- Zhdanov, Vladimir, 1952, et al.
(författare)
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Virions and respiratory droplets in air: Diffusion, drift, and contact with the epithelium
- 2020
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Ingår i: BioSystems. - : Elsevier BV. - 1872-8324 .- 0303-2647. ; 198
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Forskningsöversikt (refereegranskat)abstract
- Some infections, including e.g. influenza and currently active COVID 19, may be transmitted via air during sneezing, coughing, and talking. This pathway occurs via diffusion and gravity-induced drift of single virions and respiratory droplets consisting primarily of water, including small fraction of nonvolatile matter, and containing virions. These processes are accompanied by water evaporation resulting in reduction of the droplet size. The manifold of information concerning these steps is presented in textbooks and articles not related to virology and the focus is there frequently on biologically irrelevant conditions and/or droplet sizes. In this brief review, we systematically describe the behavior of virions and virion-carrying droplets in air with emphasis on various regimes of diffusion, drift, and evaporation, and estimate the rates of all these steps under virologically relevant conditions. In addition, we discuss the kinetic aspects of the first steps of infection after attachment of virions or virion-carrying droplets to the epithelium, i.e., virion diffusion in the mucus and periciliary layers, penetration into the cells, and the early stage of replication. The presentation is oriented to virologists who are interested in the corresponding physics and to physicists who are interested in application of the physics to virology.
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| 4. |
- Carlsson, Per-Anders, 1972, et al.
(författare)
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Self-sustained kinetic oscillations in CO oxidation over silica-supported Pt
- 2006
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 8:23, s. 2703-2706
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Tidskriftsartikel (refereegranskat)abstract
- Isothermal self-sustained kinetic oscillations in CO oxidation over silica-supported Pt at near-atmospheric pressure were studied by combined in situ Fourier transform infrared spectroscopy and mass spectrometry. The use of a specially designed reactor and careful choice of the physical properties of the catalyst and reaction conditions made it possible to eliminate diffusion limitations, to determine the maximum CO oxidation rate per Pt site in the purely kinetic regime and to clarify the mechanism of the oscillations. Specifically, our results indicate that during the high reactive periods the reaction mainly occurs on the oxide surface.
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| 5. |
- Larsson, Elin Maria Kristina, 1979, et al.
(författare)
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Real time indirect nanoplasmonic in situ spectroscopy of catalyst nanoparticle sintering
- 2012
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 2:2, s. 238-245
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Tidskriftsartikel (refereegranskat)abstract
- Catalyst deactivation by sintering significantly reduces productivity and energy efficiency of the chemical industry and the effectiveness of environmental cleanup processes. It also hampers the introduction of novel energy conversion devices such as fuel cells. The use of experimental techniques that allow the scrutiny of sintering in situ at high temperatures and pressures in reactive environments is a key to alleviate this situation. Today, such techniques are, however, lacking. Here, we demonstrate by monitoring the sintering kinetics of a Pt/SiO2 model catalyst under such conditions in real time that indirect nanoplasmonic sensing (INPS) has the potential to fill this gap. Specifically, we show an unambiguous correlation between the optical response of the INPS sensor and catalyst sintering. The obtained data are analyzed by means of a kinetic model accounting for the particle-size-dependent activation energy of the Pt detachment. Ostwald ripening is identified as the main sintering mechanism.
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| 6. |
- Zhdanov, Vladimir, 1952
(författare)
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Kinetics of Reaction on a Single Catalytic Particle in a Fluidic Nanochannel
- 2020
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Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 150:6, s. 1749-1756
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Tidskriftsartikel (refereegranskat)abstract
- One of the frontiers in heterogeneous catalysis is focused on reactions occurring on single catalytic nanoparticles. In this context, a reaction taking place on a single nanoparticle in a fluidic nanochannel is herein described by using the equation similar to that employed for a plug-flow reactor with dispersion. In the literature, one can find various boundary conditions for this equation. In the practically interesting case of a relatively long channel, the Dirichlet boundary conditions are shown to be valid. The corresponding analytical and numerical results illustrate the specifics of the profiles of the reactant concentration along the channel and the dependence of the reaction rate on the parameters. For comparison, the Danckwerts boundary conditions were used as well. [GRAPHICS] .
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| 7. |
- Arvidsson, Adam, 1990, et al.
(författare)
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Metal dimer sites in ZSM-5 zeolite for methane-to-methanol conversion from first-principles kinetic modelling: is the [Cu-O-Cu]2+ motif relevant for Ni, Co, Fe, Ag, and Au?
- 2017
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Ingår i: Catalysis Science and Technology. - : Royal Society of Chemistry (RSC). - 2044-4753 .- 2044-4761. ; 7:7, s. 1470-1477
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Tidskriftsartikel (refereegranskat)abstract
- Direct methane-to-methanol conversion is a desired process whereby natural gas is transformed into an energy-rich liquid. It has been realised at ambient pressure and temperature in metal ion-exchanged zeolites, where especially copper-exchanged ZSM-5 has shown promising results. The nature of the active sites in these systems is, however, still under debate. The activity has been assigned to a [Cu-O-Cu]2+ motif. One remaining question is whether this motif is general and also active in other metal-exchanged zeolites. Herein, we use first-principles microkinetic modelling to analyse the methane-to-methanol reaction on the [Cu-O-Cu]2+ motif, for Cu and other metals. First, we identify the cluster model size needed to accurately describe the dimer motif. Starting from the [Cu-O-Cu]2+ site, the metal ions are then systematically substituted with Ni, Co, Fe, Ag and Au. The results show that activation of Ag and Au dimer sites with oxygen is endothermic and therefore unlikely, whereas for Cu, Ni, Co and Fe, the activation is possible under realistic conditions. According to the kinetic simulations, however, the dimer motif is a plausible candidate for the active site for Cu only. For Ni, Co and Fe, close-to-infinite reaction times or unreasonably high temperatures are required for sufficient methane conversion. As Ni-, Co- and Fe-exchanged ZSM-5 are known to convert methane to methanol, these results indicate that the Cu-based dimer motif is not an appropriate model system for these metals.
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| 8. |
- Carlsson, Per-Anders, 1972, et al.
(författare)
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Bistable mean-field kinetics of CO oxidation on Pt with oxide formation
- 2005
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Ingår i: Applied Surface Science. ; 239, s. 424-31
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Tidskriftsartikel (refereegranskat)abstract
- The bistability of the kinetics of CO oxidation on Pt at sub-atmospheric pressures can be complicated by surface-oxideformation. We present a simple mean-field model making it possible to describe a transition from the low reactive reactionregime occurring via the conventional mechanism of CO oxidation at CO excess, to the high reactive regime including COinteraction with a fully developed surface-oxide overlayer at O2 excess. In the latter case, the oxide is assumed to form islands,the CO2 formation may run primarily on oxide, and in agreement with recent experiments the reaction rate may be several ordersof magnitude lower than the CO adsorption rate on a bare metal surface.
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