| 1. |
- Mihai, Oana, 1975, et al.
(author)
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Evaluation of an Integrated Selective Catalytic Reduction-Coated Particulate Filter
- 2015
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 54:47, s. 11779-11791
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Journal article (peer-reviewed)abstract
- In this study, an SCR-coated particulate filter with soot loaded from engine bench experiments was evaluated. Prior to soot loading, the sample was hydro-thermally aged at 850 degrees C. Flow reactor measurements were performed under various reaction conditions to examine the impact of soot in an SCR-coated diesel particulate filter (DPF) on standard SCR, fast SCR, NH3 oxidation, and NO oxidation. In the presence of soot, NOx conversion was slightly lower at 200-300 degrees C due to the blocking of active sites. However, at higher temperatures, the NOx conversion was somewhat higher with soot, indicating that soot more strongly inhibited the oxidation of NH3 than the SCR reaction. When feeding equal amounts of NO and NO2 together with NH3, ammonium nitrates on the sample were formed. The presence of soot significantly decreased the formation or the stability of ammonium nitrate, resulting in higher conversion with soot. To further understand this interesting aspect, ammonium nitrate formation and decomposition experiments using model Cu/BEA catalyst with and without soot were performed. It was observed that less N2O was formed in the presence of soot, and this in combination with COx formation during the ammonium nitrate formation step suggested that soot reacted with the ammonium nitrates, and we propose that this occurs on CuO species on the outside of the zeolite particles.
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| 2. |
- Mihai, Oana, 1975, et al.
(author)
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The effect of soot on ammonium nitrate species and NO2 selective catalytic reduction over Cu-zeolite catalyst-coated particulate filter
- 2016
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In: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences. - : The Royal Society. - 1364-503X .- 1471-2962. ; 374:2061
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Journal article (peer-reviewed)abstract
- A selective catalytic reduction (SCR)-coated particulate filter was evaluated by means of dynamic tests performed using NH3, NO2, O-2 and H2O. The reactions were examined both prior to and after soot removal in order to study the effect of soot on ammonium nitrate formation and decomposition, ammonia storage and NO2 SCR. A slightly larger ammonia storage capacity was observed when soot was present in the sample, which indicated that small amounts of ammonia can adsorb on the soot. Feeding of NO2 and NH3 in the presence of O-2 and H2O at low temperature (150, 175 and 200 degrees C) leads to a large formation of ammonium nitrate species and during the subsequent temperature ramp using H2O and argon, a production of nitrous oxides was observed. The N2O formation is often related to ammonium nitrate decomposition, and our results showed that the N2O formation was clearly decreased by the presence of soot. We therefore propose that in the presence of soot, there are fewer ammonium nitrate species on the surface due to the interactions with the soot. Indeed, we do observe CO2 production during the reaction conditions also at 150 degrees C, which shows that there is a reaction with these species and soot.
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| 3. |
- Andonova, Stanislava, 1977, et al.
(author)
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The effect of iron loading and hydrothermal aging on one-pot synthesized Fe/SAPO-34 for ammonia SCR
- 2016
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In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 180, s. 775-787
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Journal article (peer-reviewed)abstract
- The current commercially-available technique for NOx reduction for diesel engines is the selective catalytic reduction (SCR) of NOx with NH3 over Cu zeolites. One of the problems of this technique is their limited ability to convert NOx at diesel particulate filter (DPF) regeneration temperatures. In addition, during regeneration of the DPF there is a risk of thermally deactivating the SCR catalyst. Thus, the aim of the current work was the development of a catalytic system that can reduce NOx both at low as well as high temperature and in addition is stable at high temperature. In order to reach this goal, a Fe/SAPO-34 with chabazite (CHA) structure was combined in a system with a commercial Cu/CHA catalyst. Earlier studies have shown that it is difficult to ion-exchange Fe into CHA structures due to steric hindrance, and we have therefore used a novel synthesis procedure which incorporated iron directly into the zeolite structure. Fe/SAPO-34 with three different Fe-loadings (0.27; 0.47 and 1.03 wt.% Fe) were synthesized and the catalysts were characterized using inductively coupled plasma atomic spectroscopy (ICP-AES), N-2 adsorption-desorption isotherms, BET area measurements and X-ray diffraction (XRD). The chemical composition, porous and crystalline structure of the parent SAPO-34 sample were found to be only slightly affected by addition of small amounts of Fe in the framework zeolite structure. However, more visible changes in the crystallinity were observed in the Fe/SAPO-34 catalysts with higher Fe content, which were attributed to the unit cell size expansion provoked by integration of higher amounts of Fe into the zeolite SAPO-34 framework. The Fe/SAPO-34 with the lowest Fe-loading (0.27 wt.%) was found to be the best catalyst when considering activity as well as high temperature stability. The synthesized Fe/SAPO-34 catalyst demonstrated a significantly improved NOx reduction performance at high temperatures (600-750 degrees C) when compared to a commercial Cu/CHA SCR system, and the combined system (Fe/SAPO-34+ Cu/CHA) exhibited a very good performance in a large temperature interval (200-800 degrees C) that encompasses most diesel exhaust gas conditions.
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| 4. |
- Doronkin, D. E., et al.
(author)
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Study of the "Fast SCR"-like mechanism of H2-assisted SCR of NOx with ammonia over Ag/Al2O3
- 2012
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In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 113, s. 228-236
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Journal article (peer-reviewed)abstract
- It is shown that Ag/Al2O3 is a unique catalytic system for H-2-assisted selective catalytic reduction of NOx by NH3 (NH3-SCR) with both Ag and alumina being necessary components of the catalyst. The ability of Ag/Al2O3 and pure Al2O3 to catalyse SCR of mixtures of NO and NO2 by ammonia is demonstrated, the surface species occurring discussed, and a "Fast SCR"-like mechanism of the process is proposed. The possibility of catalyst surface blocking by adsorbed NOx and the influence of hydrogen on desorption of NOx were evaluated by FTIR and OFT calculations.
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| 5. |
- Ojagh, Houman, 1976, et al.
(author)
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Effect of Dimethyl Disulfide on Activity of NiMo Based Catalysts Used in Hydrodeoxygenation of Oleic Acid
- 2017
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 56:19, s. 5547-5557
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Journal article (peer-reviewed)abstract
- Alumina supported NiMo catalysts were synthesized. The prepared NiMo catalysts were activated by DMDS in a sulfidation process and characterized. The sulfided NiMo catalysts were next used in hydrodeoxygenation (HDO) of oleic acid in a batch reactor. Afterward, the NiMo catalysts were recovered and used in another set of HDO reactions of oleic acid under the same conditions used in the previous HDO reactions. After the HDO experiments, the active phase and deposited coke on spent catalysts were characterized. The results indicated that higher concentrations of DMDS promoted the production of heptadecane (C-17) but had no effect on the production of octadecane (C-18). Moreover, the XPS results revealed the promotional effect of DMDS concentration on maintenance of the sulfidity of the catalysts. In addition, the results for the experiments with the second run catalyst revealed a clear deactivation due to increased coke depositions. Furthermore, after two repeated experiments with first run and second run catalysts, it was observed that coke formation decreased when the concentration of DMDS was increased. These results dearly indicate a correlation between the concentration of DMDS and coke formation.
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| 6. |
- Ojagh, Houman, 1976, et al.
(author)
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Effect of Thermal Treatment on Hydrogen Uptake and Characteristics of Ni-, Co-, and Mo-Containing Catalysts
- 2015
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 54:46, s. 11511-11524
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Journal article (peer-reviewed)abstract
- Nonsulfided alumina supported Ni, Co, Mo, NiMo, and CoMo hydrotreating catalysts were synthesize. The TEM results indicated low dispersions of the active metals for Mo, NiMo, and CoMo, samples but significantly higher dispersion for the Ni sample. The effect of calcination and reduction on the hydrogen uptake capacity of the samples was investigated. The H-2-chemisorption and XPS results together showed that the precalcination step had a detrimental effect on the hydrogen absorption of the Ni sample formation of stable metal oxides. The XPS results revealed that the metal oxides of all calcined samples reached with the alumina support to form very stable spinels. Futher, the positive effects of a hydrogen atmosphere during the reduction, on the hyderogen uptake of the samples were cinfirmed by H-2-chemisorption measurements. Finally, the heats of adsorption (Delta H) of hydrogen for the Ni and Co samples were calculated to be 140 and 98 kJ mol(-1), respectively.
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| 7. |
- Salam, Muhammad Abdus, 1983, et al.
(author)
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Influence of bio-oil phospholipid on the hydrodeoxygenation activity of NiMoS/Al2O3 catalyst
- 2018
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In: Catalysts. - : MDPI AG. - 2073-4344. ; 8:10
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Journal article (peer-reviewed)abstract
- Hydrodeoxygenation (HDO) activity of a typical hydrotreating catalyst, sulfided NiMo/γ-Al2O3for deoxygenation of a fatty acid has been explored in a batch reactor at 54 bar and 320°C in the presence of contaminants, like phospholipids, which are known to be present in renewable feeds. Oleic acid was used for the investigation. Freshly sulfided catalyst showed a high degree of deoxygenation activity; products were predominantly composed of alkanes (C17 and C18). Experiments with a major phospholipid showed that activity for C17 was greatly reduced while activity to C18 was not altered significantly in the studied conditions. Characterization of the spent catalyst revealed the formation of aluminum phosphate (AlPO4), which affects the active phase dispersion, blocks the active sites, and causes pore blockage. In addition, choline, formed from the decomposition of phospholipid, partially contributes to the observed deactivation. Furthermore, a direct correlation was observed in the accumulation of coke on the catalyst and the amount of phospholipid introduced in the feed. We therefore propose that the reason for the increased deactivation is due to the dual effects of an irreversible change in phase to aluminum phosphate and the formation of choline.
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| 8. |
- Sjöblom, Jonas, 1968, et al.
(author)
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Modelling of non uniform washcoat in catalytic monolith reactors
- 2019
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Conference paper (other academic/artistic)abstract
- For advances in the design of exhaust aftertreatment systems, modelling can be a valuable tool. There have been various efforts in modelling the diesel oxidation catalyst (DOC) with varying degree of complexity. The simplest 1D models discretize the monolithic channel axially and use an effectiveness factor to account for different washcoat geometries. The more complex 1+1D models also resolve the catalyst washcoat which makes them able to better predict efficiency of e.g. layered catalysts. However, the vast majority of these 1+1D models assume the washcoat to be a uniform slab with homogeneous properties. Thus, they cannot identify tangential washcoat variations which have been found to have substantial effects on washcoat diffusivity (1). In this work a new parallel 1+1D reactor model has been developed. Similar to the sectionalizing method presented by Papadias et al (2), the washcoat is sliced into multiple tangential sections based on an evenly distributed angle. The model then solves each section of the washcoat independently – assuming that no mass is transferred between each section. Preliminary results (see figure 1) compare NO light-off simulations using the original 1+1D model and the parallel model using 3 sections. If the washcoat properties for each section are kept constant, then the conversion efficiency of the parallel model is slightly decreased because of the increased diffusive resistance of the thicker corners. However, if including the local porosity of each section (where the corners show a 13% increase in local porosity based on SEM images), the conversion efficiency of the parallel model is significantly higher because of the increased pore diffusivity in the corners. The proposed methodology enables analysis of local washcoat properties. The results are important for high performance modelling towards zero emission vehicles.
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| 9. |
- Sjöblom, Jonas, 1968, et al.
(author)
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Robust parameter estimation methodology for heterogeneous catalytic reactors
- 2022
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Conference paper (other academic/artistic)abstract
- Modeling of Exhaust-Gas Aftertreatment Systems is an important tool for improved understanding and thus improved performance and durability. The challenges for accurate modeling of the multi-scale reactor are many and one important challenge is the interplay between mass transfer and kinetics. Although intrinsic kinetics (without effects from mass transfer) are possible to obtain by analysis of the washcoat separately, many challenges (e.g. washcoat distribution, ageing effects) are best studied using the monolith reactor structure. In this study, a 1+1D diesel oxidation catalyst model was tuned to synthetic catalyst activity test (SCAT) bench data using a robust parameter estimation algorithm based on response surface methodology (RSM). The final residuals (SSE) were compared with experimental uncertainties to enable a statistical F-test to assess the model fit. Two different design of experiment (DoE) design matrices were compared to evaluate potential interaction effects between parameters. While the choice of DoE had different benefits, problems with each design could easily be circumvented. Several parameter estimation cases were compared to investigate the importance of some key algorithm choices: (a) the choice of a weight function for the residual calculation. A weight function sensitive to the experimental observation distribution obtained different fits with different parameter sets. (b) The importance of carefully designed experimental observations. Simulations with catalysts containing an inert washcoat layer proved invaluable for tuning of internal mass transfer coefficients. (c) The importance of experimentally measured constants as initial guesses. The use of intelligent gravimetric analysis (IGA) showed to give a much more suitable initial guess for tortuosity compared to literature data. For all cases, the model fit gave insignificant F-test values (experimental uncertainties were larger than the model residuals), rendering that none of the parameter sets could be rejected. To demonstrate the significance of the different cases, the final parameter set for each case were compared through comparison of ratios of classical timescales, showing the experimental conditions for the various controlling regions of mass transfer and kinetics.
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| 10. |
- Tamm, Stefanie, 1975, et al.
(author)
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A kinetic model of the hydrogen assisted selective catalytic reduction of NO with ammonia over Ag/Al2O3
- 2013
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In: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 59:11, s. 4325-4333
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Journal article (peer-reviewed)abstract
- A global kinetic model which describes H2-assisted NH3-SCR over an Ag/Al2O3 monolith catalyst has been developed.The intention is that the model can be applied for dosing NH3 and H2 to an Ag/Al2O3 catalyst in a real automotiveapplication as well as contribute to an increased understanding of the reaction mechanism for NH3-SCR. Therefore, the model needs to be simple and accurately predict the conversion of NOx. The reduction of NO is described by a global reaction, with a molar stoichiometry between NO, NH3 and H2 of 1:1:2. Further reactions included in the model are the oxidation of NH3 to N2 and NO, oxidation of H2, and the adsorption and desorption of NH3. The model was fitted to the results of an NH3-TPD experiment, an NH3 oxidation experiment, and a series of H2-assisted NH3-SCR steady-state experiments. The model predicts the conversion of NOx well even during transient experiments.
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