The Experts below are selected from a list of 198 Experts worldwide ranked by ideXlab platform
Heriberto Pfeiffer - One of the best experts on this subject based on the ideXlab platform.
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microstructural and co2 Chemisorption analyses of li4sio4 effect of surface modification by the ball milling process
Thermochimica Acta, 2013Co-Authors: Issis C Romeroibarra, Jose Ortizlanderos, Heriberto PfeifferAbstract:a b s t r a c t The ball milling process was used to modify microstructurally the Li4SiO4, and different structural and microstructural analyses were performed, followed by an analysis of the CO2 Chemisorption process. In comparison to previous reports, the Li4SiO4 modified sample exhibited very important dif- ferences and improvements during the dynamic CO2 Chemisorption process. Additionally, an analysis of the Li4SiO4-CO2 Chemisorption products showed that the Li2CO3-Li2SiO3 external shell exhibits a degree of mesoporosity at T < 500 ◦C, which is favorable for diffusion processes. Finally, the CO2 Chemisorption-desorption process was analyzed at 550 ◦ C during 10 cycles. The ball milled Li4SiO4 sam- ple showed a stable performance during the CO2 Chemisorption-desorption test and presented better efficiencies than the solid-state sample. The mechanical milling technique proved to be an effective method for modifying the microstructural properties of the ceramic absorbent by enhancing the CO2 Chemisorption-desorption process without further sintering effects.
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analysis and perspectives concerning co2 Chemisorption on lithium ceramics using thermal analysis
Journal of Thermal Analysis and Calorimetry, 2012Co-Authors: Jose Ortizlanderos, Tatiana L Avalosrendon, Carlos Gomezyanez, Heriberto PfeifferAbstract:CO2 removal from flue gas has been proposed as one of the most reliable solutions to mitigate global greenhouse emissions. Lithium ceramics are among several materials that have potential applications in CO2 removal. Lithium ceramics are able to chemisorb CO2 in a wide temperature range, presenting several interesting properties. All lithium ceramics present a similar CO2 Chemisorption reaction mechanism that has been described at the micrometric scale. However, there are several issues that have not been fully elucidated. The aim of this study is to re-analyze different experiments related to the CO2 Chemisorption on lithium ceramics and to propose how different factors control this process. This study focuses on diffusion controlled CO2 Chemisorption, which has been shown to be the limiting step of the CO2 Chemisorption process. Diffusion controlled CO2 Chemisorption appears to be mainly influenced by the chemical composition of a product’s external shell.
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thermokinetic analysis of the co2 Chemisorption on li4sio4 by using different gas flow rates and particle sizes
Journal of Physical Chemistry A, 2010Co-Authors: Rafael Rodriguezmosqueda, Heriberto PfeifferAbstract:Lithium orthosilicate (Li4SiO4) was synthesized by solid-state reaction and then its CO2 Chemisorption capacity was evaluated as a function of the CO2 flow rate and particle size. Initially, a Li4SiO4 sample, with a total surface area of 0.4 m2/g, was used to analyze the CO2 Chemisorption, varying the CO2 flow between 30 and 200 mL/min. Results showed that CO2 flows modify the kinetic regime from which CO2 capture is controlled. In the first moments and at low CO2 flows, the CO2 capture is controlled by the CO2 diffusion through the gas-film system, whereas at high CO2 flows it is controlled by the CO2 Chemisorption reaction rate. Later, at larger times, once the carbonate−oxide external shell has been produced the whole process depends on the CO2 Chemisorption kinetically controlled by the lithium diffusion process, independently of the CO2 flow. Additionally, thermokinetic analyses suggest that temperature induces a CO2 particle surface saturation, due to an increment of CO2 diffusion through the gas-fi...
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co2 absorption on na2zro3 a kinetic analysis of the Chemisorption and diffusion processes
Journal of Physical Chemistry C, 2008Co-Authors: Itzel Alcerrecacorte, Esteban Fregosoisrael, Heriberto PfeifferAbstract:The kinetics analysis of carbon dioxide (CO2) Chemisorption on sodium zirconate (Na2ZrO3), which implies a sodium diffusion process, was investigated. Initially, Na2ZrO3 was analyzed by X-ray diffraction, scanning electron microscopy, and N2 adsorption, to characterize the material. Finally, the material was thermally analyzed under a CO2 flux. Later, different isothermal experiments were performed under a CO2 flux to study kinetically the CO2 Chemisorption on Na2ZrO3. Results showed that there is a sintering effect of the sample during the heating process. This effect produced, at low temperatures, a decrease in the CO2 Chemisorption efficiency. However, at high temperatures, once the sodium diffusion was activated, the sintering effect did not interfere with the CO2 Chemisorption process. Modeling the CO2 Chemisorption on Na2ZrO3 (in terms of a double process: Chemisorption and sodium diffusion) allowed us to estimate the activation energy for these processes, 33 866 J/mol (Chemisorption) and 48 009 J/...
Charles B Mullins - One of the best experts on this subject based on the ideXlab platform.
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Dynamics of precursors in activated dissociative Chemisorption systems
The Chemical Physics of Solid Surfaces, 2020Co-Authors: S.m. Mcclure, M.i. Reichman, D.c. Seets, P.d. Nolan, G.o. Sitz, Charles B MullinsAbstract:Publisher Summary This chapter discusses the dynamics and mechanisms involved in precursor-mediated dissociative Chemisorption, with a particular emphasis on the dynamics of precursors in “activated” dissociative Chemisorption systems. It defines the facile and activated systems and other items relevant to the discussion of dissociative Chemisorption. It provides a review of the existing literature regarding the precursor-mediated Chemisorption for facile systems. It also discusses the dynamics of precursors in activated Chemisorption systems. In particular, research and results by various investigators on the CH 4 /Ir and O 2 /Pt systems is presented and the various conclusions drawn are compared and contrasted. For a variety of the adsorption systems investigated in the literature, it has been demonstrated that Chemisorption proceeds, primarily, by two mechanisms: a direct dissociative mechanism and a precursor-mediated mechanism. Direct dissociative Chemisorption occurs when an impinging gas molecule possesses enough kinetic energy to overcome the reaction potential energy barrier to dissociate and chemisorb directly to the surface. Thus, through this pathway, the probability of dissociative Chemisorption to be primarily a function of energy of the molecule is seen, increasing as the energy of the molecule increases. In precursor-mediated Chemisorption, the impinging gas molecule loses enough energy upon impact to become trapped in a precursor state, typically within the physical adsorption potential well of the surface.
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dissociative Chemisorption of methane on ir 111 evidence for direct and trapping mediated mechanisms
Journal of Chemical Physics, 1997Co-Authors: D.c. Seets, C T Reeves, B A Ferguson, M C Wheeler, Charles B MullinsAbstract:Molecular beam and bulb gas techniques were employed to study dissociative Chemisorption of methane on Ir(111). The initial dissociative Chemisorption probability (S0) was measured as a function of incident kinetic energy (Ei), surface temperature, and angle of incidence (θi). As the incident kinetic energy increases, the value of S0 first decreases and then increases with Ei indicating that a trapping-mediated Chemisorption mechanism dominates methane dissociation at low kinetic energy, and a direct mechanism dominates at higher kinetic energies. The values of the reaction probability determined from molecular beam experiments of methane on Ir(111) are modeled as a function of Ei, θi, and surface temperature. These fits are then integrated over a Maxwell–Boltzmann energy distribution to calculate the initial Chemisorption probability of thermalized methane as a function of gas and surface temperature. The calculations are in excellent agreement with results obtained from bulb experiments conducted with r...
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Direct dissociative Chemisorption of methane and ethane on Ir(110) : isotope effects and vibrationally assisted Chemisorption
Surface Science, 1994Co-Authors: R.w. Verhoef, Charles B Mullins, D. Kelly, W. H. WeinbergAbstract:We have investigated the direct dissociative Chemisorption of methane and ethane on the reconstructed Ir(110) surface using supersonic molecular beams. We have considered the direct Chemisorption of both CH4 and C2H6 and their fully deuterated isotopes at beam energies between 1 and 35 kcal/mol, and have observed a substantial kinetic isotope effect, both in the translational energy required for the onset of measurable Chemisorption, and for the initial probability of dissociative Chemisorption at a given translational energy. The translational energy needed for a measurable (> 0.01) probability of Chemisorption varies between 6 and 11 kcal/mol for the four molecules. The initial probability of dissociative Chemisorption increases rather linearly with beam energy above this onset up to the highest beam energies employed. We obtain reasonable agreement between the experimental data and a model of tunneling through an Eckart barrier. The tunneling model gives a barrier height of 36 kcal/mol for both methane and ethane, with ethane having a slightly more narrow barrier width (0.13 A) than methane (0.15 A). We have also investigated the effect of vibrational energy on dissociative Chemisorption by using vibrationally hot molecular beams. The results show that there is substantial vibrational assistance for CD4 and C2D6 (~ 0.05), but that there is no measurable effect for CH4 and C2H6 (< 0.02). We show that these results are most consistent with attributing the enhanced Chemisorption probability to the asymmetric C-D and C-H stretching modes, although it is possible that other vibrational modes are contributing to the observed enhancement. We also observe a lowering of the translational energy required for measurable Chemisorption of the vibrationally hot beams by approximately 4 kcal/mol. Such an effect is again shown to be consistent (although not uniquely) with the asymmetric C-D stretching mode. We have also measured the variation of the initial probability of Chemisorption with the polar angle of incidence between the beam and the surface. In all cases, alkane Chemisorption is shown to obey normal-energy scaling, within experimental error. Finally, we report that there is no observable dependence of the initial probability of direct Chemisorption on surface temperature between 550 and 1150 K under the conditions investigated here, which is consistent with the traditional picture of direct dissociative Chemisorption.
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Isotope effects for the direct dissociative Chemisorption of methane and ethane on Ir(110) and vibrationally assisted Chemisorption
Surface Science, 1993Co-Authors: R.w. Verhoef, Charles B Mullins, D. Kelly, W. H. WeinbergAbstract:We have investigated the direct dissociative Chemisorption of methane and ethane and their fully deuterated isotopes on the Ir(110) surface using supersonic molecular beams. There is a substantial kinetic isotope effect over a wide range of translational energies. The translational energy threshold for an observable (> 0.01) probability of Chemisorption varies between 6 and 11 kcalmol for the four molecules. We have also investigated the effect of vibrational energy on dissociative Chemisorption by using vibrationally hot molecular beams. The results show that there is substantial vibrational assistance for CD4 and C2D6 (∼ 5%), but no measurable effect for CH4 and C2H6 (< 2%). These results are most consistent with attributing the enhanced Chemisorption probability to the asymmetric CD and CH stretching modes. Consistent with this interpretation, we observe a lowering of the translational energy threshold for the Chemisorption of the vibrationally hot beams by approximately 4 kcalmol.
Felix Studt - One of the best experts on this subject based on the ideXlab platform.
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exploring scaling relations for Chemisorption energies on transition metal exchanged zeolites zsm 22 and zsm 5
Chemcatchem, 2016Co-Authors: Samira Siahrostami, Hanne Falsig, Pablo Beato, Poul Georg Moses, Jens K Norskov, Felix StudtAbstract:Copper exchange on all the different T sites of ZSM-22 and ZSM-5 is considered and the Chemisorption energies of dioxygen, OH, and O species are studied. We show that for different T sites the adsorption energies vary significantly. The oxygen adsorption energy on copper-exchanged zeolites is quite similar to those of the most selective catalysts for oxidation reactions, that is, Ag and Au surfaces. The Chemisorption energies of oxygen, carbon-, and nitrogen-containing species on different transition metals exchanged in ZSM-22 are also investigated. The study covers three different oxidation states, that is, 1+, 2+, and 3+ for the transition-metal exchanges. Scaling relations are presented for the corresponding species. Chemisorption of O scales with Chemisorption of OH for all three considered exchanges, whereas there are essentially rough correlations for NH2 and N as well as CH3 and C.
Hui Zhang - One of the best experts on this subject based on the ideXlab platform.
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A MODEL FOR THE MUTUAL INFLUENCE OF Chemisorption AND MULTILAYER SEGREGATION
Surface Review and Letters, 1996Co-Authors: Hui Zhang, Shulin CongAbstract:The Green function method and the Chemisorption theory of Einstein and Schrieffer are used to calculate the Chemisorption energies of O and CO on the multilayer segregated Ni-Cu disordered binary alloy within the many-coupled self-consistent coherent potential approximation. In general cases, the Chemisorption-induced surface segregation can change the surface component and the Chemisorption property to varying degrees. When the mutual influence of Chemisorption and multilayer segregation is considered, the changes appear slightly mild. The Chemisorption energy for O/Ni-Cu (CO/Ni-Cu) depends sensitively on O(CO) coverage θ, and decreases with increasing θ.
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The mutual influence of Chemisorption and surface segregation: calculation of the Chemisorption energy of O or CO on Ni-Cu alloy
Journal of Physics: Condensed Matter, 1992Co-Authors: Hui ZhangAbstract:The Green's function method and the Chemisorption theory of Einstein and Schrieffer are used to calculate the Chemisorption energy of O or CO on a Ni-Cu disordered binary alloy surface using the average T-matrix approximation. The change of surface segregation due to Chemisorption is investigated in detail. From the Chemisorption point of view, the behaviour of O resembles that of CO to a certain extent. The calculated results show that the Chemisorption of O/Ni-Cu and CO/Ni-Cu systems can all constrain surface segregation, resulting in more stable Chemisorption.
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The mutual influence of Chemisorption and surface segregation : calculation of the Chemisorption energy of O or CO on Ni-Cu alloy : Surface and interface science
Journal of Physics: Condensed Matter, 1992Co-Authors: Hui ZhangAbstract:The Green's function method and the Chemisorption theory of Einstein and Schrieffer are used to calculate the Chemisorption energy of O or CO on a Ni-Cu disordered binary alloy surface using the average T-matrix approximation. The change of surface segregation due to Chemisorption is investigated in detail. From the Chemisorption point of view, the behaviour of O resembles that of CO to a certain extent. The calculated results show that the Chemisorption of O/Ni-Cu and CO/Ni-Cu systems can all constrain surface segregation, resulting in more stable Chemisorption
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The Chemisorption energy of CO on a disordered binary alloy
Surface Science, 1992Co-Authors: Hui ZhangAbstract:Abstract The one-dimensional tight-binding model and the one-electron Chemisorption theory are used to calculate the Chemisorption energy of CO on a NiCu disordered binary alloy surface, in which the coherent-potential approximation and the technique of complex-energy-plane integration are adopted. The change of surface segregation due to Chemisorption is also investigated. The Chemisorption of the CO/NiCu system can change the surface component concentration drastically, thereby influencing the Chemisorption energy. The result shows that the Chemisorption of the system strongly constrains surface segregation, resulting in Chemisorption properties more like those of CO/Ni rather than those of CO/Cu.
Chien-to Hsieh - One of the best experts on this subject based on the ideXlab platform.
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Activation Energy for Oxygen Chemisorption on Carbon at Low Temperatures
Industrial & Engineering Chemistry Research, 1999Co-Authors: Hsisheng Teng, Chien-to HsiehAbstract:The kinetics of oxygen Chemisorption on resin chars were investigated in this study. The Elovich equation was employed to facilitate the interpretation of the Chemisorption process. It was found that the activation energy for Chemisorption is not constant and varies with surface coverage. This observation can be explained by a distributed kinetic parameter model, here implemented as a distributed activation energy model. The energy distribution model reveals that the amount of mass uptake obtained in a typical Chemisorption study does not involve full coverage of all of the active sites on carbon. It is concluded that the information on active sites obtained from low-temperature Chemisorption cannot be directly applied to gasification at higher temperatures.