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| 2. |
- Mosca, Alessandra, et al.
(författare)
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NO2 and N2 sorption in MFI films with varying Si/Al and Na/Al ratios
- 2009
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 120:3, s. 195-205
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Tidskriftsartikel (refereegranskat)abstract
- MFI crystals or films with controlled thicknesses and different Si/Al ratios were grown on seeded cordierite monoliths using a clear synthesis mixture with template or a template-free gel. The materials were analyzed by scanning electron microscopy, X-ray diffraction, inductively coupled plasma-atomic emission spectrometry, X-ray photoelectron spectroscopy, thermogravimetric analysis and sorption experiments using N 2 or NO 2 adsorbates. The films were uniformly distributed over the support surface. As expected, the specific monolayer N 2 adsorption capacity (mol/g zeolite ) was constant and independent of film thickness. The specific molar NO 2 adsorption capacity was significantly lower than the specific molar monolayer N 2 adsorption capacity, indicating that NO 2 is adsorbed at specific sites rather than evenly distributed in a monolayer. A number of NO 2 adsorption sites with varying strengths were observed by TPD experiments. At 30 °C, the amount of adsorbed NO 2 in the MFI films increased with increasing Al and Na content as opposed to the N 2 adsorption capacity, which was independent of these parameters. At 200 °C, the adsorbed amount of NO 2 was lower than at 30 °C and apparently independent on Al concentration in the Na-MFI films. These results indicate that different mechanisms are involved in NO 2 adsorption. NO 2 may adsorb weakly on Na + cations and also react with silanol groups and residual water in the zeolite, the latter two results in more strongly bound species. Upon NO 2 adsorption, formation of NO was observed. This work represents the first systematic study of the effects of Al and Na content on NO 2 adsorption in MFI films. © 2008 Elsevier Inc. All rights reserved.
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| 3. |
- Perdana, Indra, 1973, et al.
(författare)
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A comparison of NOx adsorption on Na, H and BaZSM-5 films
- 2007
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 72, s. 82-91
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Tidskriftsartikel (refereegranskat)abstract
- NOx adsorption in ZSM-5 films containing Na+, H+ or Ba2+ as counter ions was studied. NaZSM-5 films showed a superior NOx adsorption capacity over the entire temperature range (30-350ºC) in comparison with the other films. Besides the possibility to form strongly bound surface nitrate species, the presence of the Na ions in ZSM-5 resulted in a large enhancement of various weakly adsorbed species. In the HZSM-5 film, the NOx adsorption was mainly due to physisorption, surface nitric acid and nitrosium ion (NO+) formation. Besides weakly adsorbed species and surface nitric acid, the NOx adsorption in BaZSM-5 films also resulted in formation of strongly bound surface nitrate species. The nitrate species in the BaZSM-5 film were found to be resistant to NO exposure and were mainly formed through an NO2 disproportionation pathway.
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| 4. |
- Perdana, Indra, 1973, et al.
(författare)
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Effect of external mass transport on permeation in a Wicke-Kallenbach cell
- 2009
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Ingår i: Chemical Engineering Research and Design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 87:10, s. 1438-1447
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Tidskriftsartikel (refereegranskat)abstract
- Wicke-Kallenbach (WK) cells are often used for studying separation and component transport in porous material. In order to obtain important transport parameters, mathematical models are frequently developed but they generally consider the fluid phase in the WK compartments to be free of concentration gradients and thus external mass transport resistance is neglected. The present work is a detailed study of how the external transport influences permeation through porous material in a WK cell. External mass transfer effects were demonstrated experimentally and they were further studied from three-dimensional (3-D) model simulations. Film theory was applied to develop an appropriate Sherwood number correlation for the external mass transport coefficient. It was shown that the flow in the compartment and geometrical factors of the WK cell had significant influences on the permeation. It was found that introducing the proposed external mass transport correlation into a simplified one-dimensional (1-D) model was adequate to reproduce results from both the experimental data and the 3-D model.
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| 5. |
- Perdana, Indra, 1973, et al.
(författare)
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Influence of NOx adsorbed species on component permeation through ZSM-5 membranes
- 2010
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 1873-3123 .- 0376-7388. ; 349:1-2, s. 83-89
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Tidskriftsartikel (refereegranskat)abstract
- A thin ZSM-5 film was grown on an alpha-alumina support, resulting in a composite membrane. The membraneswere characterized by SEM and adsorption branch n-hexane/helium permporometry. In addition,the permeation of gas mixtures containing NO2, NO, N2 and argon was evaluated. The effect of temperatureand gas mixture composition on the component permeation and selectivity was investigated.It was found that NOx permeation through the ZSM-5 membrane was partially surface concentrationdependent and was thermally activated. However, transport by gas translational diffusion seemed todominate at the conditions studied. The presence of various NOx adsorbed species appeared to influencediffusion of NO2 in ZSM-5 and reduced transport of other inert and weakly adsorbed components overa wide temperature range (20–400◦C). Strongly adsorbed surface nitrate species formed in the presenceof gas phase NOx should be responsible for the reduced transport of these components at the elevatedtemperature. The findings are of interest for possible applications of ZSM-5 membranes for componentseparation at high temperature.
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| 6. |
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| 7. |
- Perdana, Indra, 1973, et al.
(författare)
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Modelling NOx adsorption in a thin NaZSM-5 film supported on a cordierite monolith
- 2007
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 62:15, s. 3882-3893
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Tidskriftsartikel (refereegranskat)abstract
- Transient two dimensional (2-D) and three dimensional (3-D) single channel models (SCMs) describing transport of NOx into a NaZSM-5 film and kinetics for reactions forming nitrate species were developed. The film consisted of a continuous thin layer of inter-grown NaZSM-5 crystals supported on a cordierite monolith support. The 2-D model which included a comprehensive transport model was developed for studying the adsorption kinetics, whereas the more rigorous 3-D model was used to provide a better picture of radial and axial concentration and velocity variations in the monolith channel and the film. The overall adsorption-desorption mechanism, consisting of two competing reaction schemes for nitrate formation, was sufficient to predict the dynamic development of surface nitrate species. The simulation results showed that the adsorption is strongly influenced by transport resistance in the NaZSM-5 film. Also, the effective diffusion of NOx in the NaZSM-5 film is apparently surface nitrate concentration dependent.
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| 8. |
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| 9. |
- Perdana, Indra, 1973
(författare)
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NOx Adsorption and Transport in ZSM-5 Films
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present work dealt with a fundamental study of NOx adsorption-desorption and transport in ZSM-5 as films supported on cordierite monolith and as a part of composite membranes. The adsorption-desorption study was focused on developing a mechanistic understanding of NOx adsorption in ZSM-5 films including the effects of counter-ions, Si/Al ratios and film thicknesses on the adsorption. NOx adsorption-desorption measurements were carried out in a continuous flow reactor using binder-free ZSM-5 films grown on a cordierite monolith. Temperature programmed desorption (TPD) was used to determine thermal stability of the adsorbed species. To obtain detail information about the character of the adsorbed species, in-situ diffuse reflectance infrared spectroscopy measurements were carried out. It was found that various NOx adsorbed species with different thermal stabilities could be formed in the ZSM-5 depending on the counter-ions present and adsorption temperature. Si/Al and Na/Al ratios determined the adsorption capacity and mass transport resistance was observed to be of importance during transient adsorptions. The proposed adsorption mechanism combined with a mathematical transport model for NOx adsorption in a ZSM-5 film supported on a monolith support was able to reproduce the observed NOx adsorption-desorption phenomena which in turn offered a better insight into the NOx adsorption process in a thin ZSM-5 film. In addition, NOx transport in ZSM-5 films was further studied with the use of composite membranes in a Wicke-Kallenbach (WK) cell. It was found that the NOx transport in the ZSM-5 micropores was thermally activated and was influenced by surface adsorbed species. The presence of the adsorbed NO2 could hinder diffusion of non adsorbing components over a wide temperature range of 20C to 400C. The present work also showed that the measurement of component permeation through a membrane in the WK cell could be influenced by fluid dynamics and gas phase transport in the WK cell. However, the external mass transport correlation proposed through the present work can be useful to simplify the development of accurate transport models.
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| 10. |
- Perdana, Indra, 1973
(författare)
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NOx Adsorption in ZSM-5 Films - Experimental studies and mathematical modeling
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work dealt with studies of NOx adsorption in films of ZSM-5. The study was interesting due to its significant contribution to develop a detailed understanding of NOx transport and adsorption in ZSM-5 which is of interest for catalyst or membrane applications. The adsorption study was focused on developing a mechanistic understanding of NOx adsorption in ZSM-5 films. NOx adsorption measurements and temperature programmed desorption (TPD) were carried out in a continuous flow reactor using binder-free ZSM-5 films grown on a cordierite monolith. The TPD measurements were used to determine the thermal stability of the various adsorbed species. To obtain more information about the character of the adsorbed species formed, in-situ diffuse reflectance infrared spectroscopy experiments were also carried out. It was found that various NOx adsorbed species with different thermal stabilities were present in the ZSM-5 depending on the counter-ions present and adsorption temperature. Also, mass transport resistance was observed to be of importance during transient adsorptions. In addition to the experimental work, mathematical modeling of NOx adsorption in a ZSM-5 film supported on a monolith support was also addressed, where both adsorption kinetics and mass transport resistances are important issues. A proposed adsorption mechanism combined with a transport model was able to reproduce the observed NOx adsorption-desorption phenomena which in turn offered a better insight into the NOx adsorption process in a thin ZSM-5 film.
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