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- Arve, Kalle, et al.
(författare)
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Did Chemisorption Become an Obsolete Method With Advent of Tem? Comparison of Mean Particle Size and Distribution of Silver on Alumina
- 2011
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Ingår i: Catalysis Letters. - : Springer Science and Business Media LLC. - 1572-879X .- 1011-372X. ; 141:5, s. 665-669
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Tidskriftsartikel (refereegranskat)abstract
- Silver particle size and dispersion on a Ag/Al2O3 for HC-SCR were examined by means of chemisorption and TEM. Experimental results showed that determination of the accurate mean particle size (mps) is challenging and that the both applied methods have specific characteristics increasing the inaccuracy in the results which has to be taken into account in evaluation of catalytic activity. The results from TEM imaging were found to depend highly on the mode in which the surface was scanned (bright field versus dark field). Generally the point resolution was higher in dark field but the obtained mps did not increased along with the increasing silver loading. The main limitation with the O-2-chemisorption was related to the choice of the stoichiometric factor between the adsorbent and silver atoms. However, together these techniques support each other and help to give a more realistic picture of the mean silver particle size, distribution and indications of the oxidation states on the alumina support.
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| 3. |
- Azis, Muhammad Mufti, 1983, et al.
(författare)
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Kinetic modeling of H2-assisted C3H6 selective catalytic reduction of NO over silver alumina catalyst
- 2015
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 278, s. 394-406
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Tidskriftsartikel (refereegranskat)abstract
- A global kinetic model was developed for C3H6-SCR consisting of NO oxidation, C3H6 oxidation and C3H6-SCR reactions with and without H-2 over Ag-Al2O3. The model is based on a dual role of H-2 to remove inhibiting nitrates from the active sites as well as to modify/form new active Ag sites. For model development, a range of temperature programmed reaction (TPR) and transient feed experimental conditions were used. The proposed model was eventually also validated with additional transient experimental data. The kinetic model proposed in this study predicts the experimental data well for a wide-range of feed conditions. Evaluation of mass transfer resistance in the washcoat indicated that during H-2-assisted C3H6-SCR, mild internal mass transfer resistance for NO was predicted to be important already at 250 degrees C.
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| 4. |
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| 5. |
- Azis, Muhammad Mufti, 1983, et al.
(författare)
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Microkinetic modeling of H2-assisted NO oxidation over Ag-Al2O3
- 2013
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947. ; 221, s. 382-397
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Tidskriftsartikel (refereegranskat)abstract
- A microkinetic model has been assembled to investigate the mechanism for NO oxidation over a monolith-supported Ag–Al2O3 catalyst both in the presence and absence of H2. The effect of H2 examined in the kinetic model was to reduce self inhibiting surface nitrate species on active silver sites. A reduced factorial design of inlet experimental conditions was used to generate transient experimental data. The kinetic model was developed based on a single channel reactor model which accounted for mass and heat transfer between gas and catalyst washcoat as well as mass transport resistance in the washcoat. In general, the modeling results could reproduce the transient experimental data well with correct levels of outlet concentrations and time scales for transient responses. It was found that the effect of increased NO and NO2 inlet concentration had a negative correlation with the NO oxidation conversion, which in the model was considered related to the formation of nitrate surface species. In addition, the model in agreement with experiments, clearly showed that H2 promoted the NO oxidation mainly at low temperature and this effect tended to decrease at elevated temperatures. When H2 was present in the feed, the kinetic model showed that H2 was consumed rapidly in the front part of the monolith. This was also seen in the experiments where in all cases H2 was entirely consumed. The rapid reaction of H2 along with resulting transport limitations indicated that the H2 promotion of the NO oxidation reaction may have been isolated to only a portion of the catalyst.
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| 6. |
- Azis, Muhammad Mufti, 1983, et al.
(författare)
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On the role of H2 to modify surface NOx species over Ag-Al2O3 as lean NOx reduction catalyst: TPD and DRIFTS studies
- 2015
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Ingår i: Catalysis Science and Technology. - 2044-4753 .- 2044-4761. ; 55:1, s. 296-309
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Tidskriftsartikel (refereegranskat)abstract
- Formation and stability of surface NOx species related to the promotional effect of H2 over Ag–Al2O3 as NOx reduction catalyst were investigated with temperature-programmed desorption and DRIFT spectroscopy. Formation of two groups of surface NOx species was found: a less thermally stable group of “low temperature (LT) species” and a more thermally stable group of “high temperature (HT) species”. The LT NOx was attributable to the decomposition of surface NOx species formed on the active sites where its elimination by addition of H2 or thermal decomposition correlated with higher NO oxidation and NOx reduction conversion. Under reaction conditions, these possibly inhibiting LT NOx species were stable up to about 300 °C and their formation depended on donation of oxygen from surface oxides. Removal of LT nitrate species by H2 accounted for only a fraction of the increased NO oxidation and NOx reduction conversion by co-feeding H2. Furthermore, it was also found that H2 facilitates formation of HT NOx that primarily corresponded to the decomposition of spectator species on the Al2O3 support identified as monodentate nitrate species. From TPD studies of C3H6-SCR, it was shown that H2 not only eliminated LT NOx but also promoted formation of greater quantities of adsorbed hydrocarbons.
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