| 1. |
- Creaser, Derek, 1966, et al.
(författare)
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Modeling study of 5 kWe-scale autothermal diesel fuel reformer
- 2011
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Ingår i: Applied Catalysis A: General. - : Elsevier BV. - 1873-3875 .- 0926-860X. ; 404, s. 129-140
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Tidskriftsartikel (refereegranskat)abstract
- A model was developed that successfully describes key operating features of a 5 kWe-scale autothermal diesel fuel reformer with an engineered monolith-supported Rh based catalyst. The model consisted of a kinetic model comprised of four overall reactions including total oxidation, fuel steam reforming, methane formation via fuel decomposition and the water–gas shift reaction. The model also accounted for heat and mass transport effects that were of importance when coupling the exothermic oxidation reactions with endothermic steam reforming reactions in a full-scale reformer. According to the model, the total oxidation and steam reforming reactions occurred simultaneously, however the heat effects of the oxidation reaction dominated near the reactor inlet resulting in a local hot spot. Transport resistances were found to hinder the rates of the main reactions, especially at higher temperature operating conditions. The model was primarily based on experimental data for a commercial low-sulphur diesel fuel (MK1), however it was found to also reasonably well describe the operation of the reactor with a diesel surrogate (n-tetradecane).
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| 2. |
- DAWODY, JAZAER, 1959, et al.
(författare)
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E4-Mistra, a research program for the development of an energy efficient low emission exhaust aftertreatment system for heavy duty vehicles
- 2012
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Ingår i: World Renewable Energy Forum, WREF 2012, Including World Renewable Energy Congress XII and Colorado Renewable Energy Society (CRES) Annual Conference. - : American Solar Energy Society. - 9781622760923 ; , s. 4530-4536
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Konferensbidrag (refereegranskat)abstract
- This paper presents a unique system approach applied in a joint academic - industrial research program, E4 Mistra, to reach the goals of energy efficiency and low emissions exhaust aftertreatment system for heavy duty vehicles. The high energy efficiency is achieved by heat recuperation, on-board hydrogen production for use in both an auxiliary power unit and for NOx reduction and by finding new solutions for making the after-treatment system active at low exhaust temperatures. To reach low particulate emissions a mechanical filter using a sintered metal filter is developed. Low NOx emissions are achieved by an efficient NOx reduction catalyst. The system is based on four technological advances: Thermoelectric material s for heat recuperation, catalytic reduction of NOx over innovative catalyst substrates using hydrocarbons from the fuel and H2 from a high efficiency fuel reformer, and particulate filtration over a porous metal filter.
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| 3. |
- Gonzalez, Angelica V., et al.
(författare)
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Autothermal reforming of Fischer-Tropsch diesel over alumina and ceria-zirconia supported catalysts
- 2013
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 107, s. 162-169
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Tidskriftsartikel (refereegranskat)abstract
- Autothermal reforming (ATR) of synthetic Fischer-Tropsch diesel has been carried out to evaluate the fuel reformer and the catalyst performance at realistic operating conditions. Hydrogen was produced via ATR in a full-scale reformer (ID = 84 mm, L = 400 mm) at 650-750 degrees C. The two monolithic catalysts were sequentially located in the reformer and simultaneously tested. The catalysts were composed of 1:1 wt% Rh:Pt as active metals; CeO2, MgO, Y2O3, and La2O3 were used as promoters. The first catalytic monolith was supported on delta-Al2O3 and the second on CeO2-ZrO2. Fresh samples were characterized by N-2-BET, XRD and H-2-TPR analyses. Catalyst activity was evaluated at O-2/C similar to 0.34-0.45 and H2O/C similar to 2-3. Results show an increased catalyst activity after the second monolithic catalyst due to the effect of steam reforming, water-gas shift reaction (WGS) and higher catalyst reducibility of RhxOy species on the CeO2-ZrO2 mixed oxide as a result of the improved redox properties. Hydrogen concentrations of 42 vol% and fuel conversion of 98% after the CeO2-ZrO2-supported catalyst was obtained at O-2/C = 0.42 and H2O/C = 2.5.
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| 4. |
- Kannisto, Hannes, 1979, et al.
(författare)
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Efficient low temperature lean NOx reduction over Ag/Al2O3-A system approach
- 2011
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 104:1-2, s. 74-83
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on lean NOx reduction (LNR) by n-octane using silver-alumina based catalysts, with the addition of hydrogen. The work takes a system approach, where parameters such as temperature, reformate gas composition, fuel penalty and realistic monolith samples are considered. The LNR catalyst samples were prepared by impregnation and sol-gel methods and the NOx reduction performance was characterized by flow-reactor experiments, where realistic engine-out gas compositions were used. The hydrogen feed over the LNR catalyst samples was determined via data achieved by autothermal reforming experiments over a rhodium based catalyst, using real diesel as feedstock. The LNR catalyst samples generally show an enhanced NOx reduction when hydrogen is added to the gas feed. In particular, a 2 wt% silver-alumina sample with the addition of minute amounts of platinum, shows a high increase in NOx reduction when hydrogen is added to the feed. The addition of CO, a potential poison in the reaction and a by-product from the reforming, did not show any significant effect on the LNR catalyst performance at the conditions used. This is beneficial, since it renders a CO clean-up step in the reformer system unneeded. Ammonia formation is discussed in terms of a possible dual-SCR system. Finally, the fuel penalty for hydrogen production and hydrocarbon addition is taken into consideration. It is found that an addition of 1000 ppm H-2 leads to unacceptable fuel penalties. (C) 2011 Elsevier B.V. All rights reserved.
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| 5. |
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| 6. |
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| 7. |
- Karatzas, Xanthias, et al.
(författare)
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Autothermal reforming of low-sulfur diesel over bimetallic RhPt supported on Al(2)O(3), CeO(2)-ZrO(2), SiO(2) and TiO(2)
- 2011
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Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 106:3-4, s. 476-487
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this paper is to study and clarify the role of selected supports (both reducible and non-reducible) on the activity, selectivity and stability of RhPt-based catalyst for diesel reforming. Autothermal reforming (AIR) of low-sulfur diesel (S similar to 6 ppm, C/H similar to 6.43 (w/w)), H(2)O/C similar to 2.5, O(2)/C similar to 0.49, was tested at bench scale to detect differences in activity for catalysts consisting of 1 wt% Rh and 1 wt% Pt supported on alumina, ceria-zirconia (17.5 wt% ceria), silica and titania. Promoters in the form of MgO. Y(2)O(3), La(2)O(3), CeO(2) and ZrO(2), ranging from 4 wt% to 10 wt%, were also added onto the supports to detect differences in catalyst activity in terms of diesel conversion, CO(2) selectivity, and hydrogen and ethylene production. All metals were added sequentially onto the support by the incipient wetness technique and washcoated on 400 cpsi cordierite monolithic carriers with dimensions d = 17.8 mm, l=30.5 mm. The product gas analysis, using FTIR and NDIR, showed that RhPt/CeO(2)-ZrO(2) was found to be most active for AIR of diesel since a fuel conversion close to 98% was obtained. Furthermore, the catalyst activity of the unpromoted samples, in terms of diesel conversion, increased in the following order: RhPt/SiO(2) < RhPt/TiO(2) < RhPt/Al(2)O(3) < RhPt/CeO(2)-ZrO(2). The addition of promoters was found to be insignificant as well as having a negative impact on the catalyst performance in most cases, except for the alumina-promoted sample. The addition of 10 wt% La(2)O(3) on RhPt/Al(2)O(3) was found to enhance diesel conversion, hydrogen productivity as well as lower the ethylene concentration from 3700 ppm to less than half that value. The latter observation was confirmed by O(2)-TPO analysis of aged powder samples where lower loads of coke were present than on the La-promoted sample. The morphology, surface and bulk properties of RhPt/CeO(2)-ZrO(2) were closely examined in order to provide a possible correlation between the activity and characterization results. N(2)-BET analysis showed that the surface area of RhPt/CeO(2)-ZrO(2) was 64 m(2)/g, while the silica samples exhibited the highest area, similar to 137-185 m(2)/g. Hence, the difference in the surface areas was not enough to explain the trends observed in the activity measurements. XRD analysis of RhPt/CeO(2)-ZrO(2) showed crystalline phases characteristic of zirconia, most likely tetragonal. Also, the diffractogram did not reveal any Rh or Pt peaks indicating that the noble metal particles are highly dispersed on the support. In contrast, peaks ascribed to metallic Pt (similar to 30-46 nm) were clearly visible on the XRD patterns taken from all the other supported samples. H(2)-TPR analysis of RhPt/CeO(2)-ZrO(2) showed reduction peaks ascribed to Rh(i)O(x) species as well as a minor hydrogen spillover effect on the support to be present at T=120 degrees C and 450 degrees C, respectively. Also, the hydrogen consumption of the Rh(i)O(x) species was the highest compared to the other supported RhPt samples. TEM analysis performed on fresh RhPt/CeO(2)-ZrO(2) showed that the Rh(i)O(x) and Pt particles were highly dispersed on the support, both with particle sizes in the vicinity of similar to 5-15 nm. Rh species was found on ceria and zirconia, while Pt was present mainly on the ceria layer possibly in the form of Pt-O-Ce bonds. H(2)-chemisorption analysis measured at T similar to 40 degrees C shows similar Rh dispersion results. To summarize, the higher activity results of RhPt/CeO(2)-ZrO(2) for AIR of diesel, compared to other supported catalysts, may be ascribed to the higher reducibility of Rh(i)O(x) species as well as the superior Rh and Pt dispersion. Also, the support contribution, in particular ceria, is believed to promote water gas-shift activities as well as reduce coke deposits on the catalyst surface.
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| 8. |
- Karatzas, Xanthias, et al.
(författare)
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Characterization and optimization of an autothermal diesel and jet fuel reformer for 5 kW(e) mobile fuel cell applications
- 2010
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Ingår i: Chemical Engineering Journal. - : Elsevier BV. - 1385-8947 .- 1873-3212. ; 156:2, s. 366-379
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Tidskriftsartikel (refereegranskat)abstract
- The present paper describes the characterization of an autothermal reformer designed to generate hydrogen by autothermal reforming (ATR) from commercial diesel fuel (similar to 10 ppm S) and jet fuel (similar to 200 ppm S) for a 5 kW(e) polymer electrolyte fuel cell (PEFC). Commercial noble metal-based catalysts supported on 900 cpsi cordierite monoliths substrates were used for ATR with reproducible results. Parameters investigated in this study were the variation of the fuel inlet temperature, fuel flow and the H2O/C and O-2/C ratios. Temperature profiles were studied both in the axial and radial directions of the reformer. Product gas composition was analyzed using gas chromatography. It was concluded from the experiments that an elevated fuel inlet temperature (>= 60 degrees C) and a higher degree of fuel dispersion, generated via a single-fluid pressurized-swirl nozzle at high fuel flow, significantly improved the performance of the reformer. Complete fuel conversion, a reforming efficiency of 81% and an H-2 selectivity of 96% were established for ATR of diesel at P=5kW(e), H2O/C = 2.5, O-2/C = 0.49 and a fuel inlet temperature of 60 degrees C. No hot-spot formation and negligible coke formation were observed in the reactor at these operating conditions. The reforming of jet fuel resulted in a reforming efficiency of only 42%. A plausible cause is the coke deposition, originating from the aromatics present in the fuel, and the adsorption of S-compounds on the active sites of the reforming catalyst. Our results indicate possibilities for the developed catalytic reformer to be used in mobile fuel cell applications for energy-efficient hydrogen production from diesel fuel.
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| 9. |
- Karatzas, Xanthias, et al.
(författare)
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Hydrogen generation from n-tetradecane, low-sulfur and Fischer-Tropsch diesel over Rh supported on alumina doped with ceria/lanthana
- 2011
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 164:1, s. 190-197
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Tidskriftsartikel (refereegranskat)abstract
- The present study demonstrates the use of rhodium-based monolithic catalyst for onboard reforming of diesel fuels. Experimental results from hydrogen generation of n-tetradecane, low-sulfur and Fischer-Tropsch diesel, via autothermal reforming (ATR), were acquired with a catalyst consisting of 3 wt% Rh supported on alumina doped with Ce/La. The catalyst was prepared by impregnation using the incipient wetness technique, and deposited onto a 400 cpsi cordierite monolith. Furthermore, the catalyst was tested over ranges of oxygen-to-carbon and water-to-carbon feed ratios, both in a bench-scale and a full-scale reactor. Fresh powder samples of the catalyst were characterized by XRD, N(2)-BET, H(2) chemisorption, H(2)-TPR and XPS analyses. The activity results showed that high fuel conversions and hydrogen production could be achieved with 3 wt% Rh for all fuels. Furthermore, the highest formation of CO and C(2)H(4) was found in the product gas stream from the low-sulfur diesel. In addition, partial oxidation and steam reforming reactions were identified by closely studying the distribution of the analyzed product gas composition and the temperature measurements. The characterization results showed the presence of finely dispersed Rh particles in the support. Furthermore, bulk and surface rhodium oxides were detected, which have been suggested to be one of the major active phases for ATR of diesel. Bulk and surface cerium oxides (CeO(2)) and surface La in the dispersed phase were also found to be present in the catalyst composition. These promoters are believed to improve the catalyst activity and durability.
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| 10. |
- Karatzas, Xanthias, et al.
(författare)
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Microemulsion and incipient wetness prepared Rh-based catalyst for diesel reforming
- 2011
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 175:1, s. 515-523
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Tidskriftsartikel (refereegranskat)abstract
- The role of the catalyst preparation technique was investigated for diesel reforming. Reverse microemulsion (ME) and incipient wetness (IW) techniques were used for the preparation of Rh-based monolithic catalysts that were employed for hydrogen generation of low-sulfur diesel via autothermal reforming (ATR). The washcoat of the tested catalysts consisted of 0.5 wt% Rh, 1 wt% Rh, and 1: 1 wt% Rh: Pt supported on gamma-alumina. All washcoats were deposited on 400 cpsi cordierite monoliths. The reaction condition was T(feed) = 650 degrees C, H(2)O/C similar to 2.5, O(2)/C similar to 0.49, TOS = 3 h, GHSV similar to 13 000 h(-1) and P = 1 atm. Fresh and aged powder samples of the catalyst were characterized by N(2)-BET, H(2) chemisorption, XRD, H(2)-TPR, O(2)-TPO and TEM. The activity results established that Rh and RhPt formulations, prepared by ME and IW, are highly active for ATR of diesel where fuel conversions above 92% were obtained. FTIR and NDIR analysis also showed that the highest formation of ethylene was found in the product gas stream from the bimetallic samples indicating that RhPt/Al(2)O(3) is less resistant towards carbon deposition. The latter observation was confirmed by O(2)-TPO analysis of the aged samples where high loads of coke were found both on the active metals and on the support. Interestingly, these effects were less significant on the ME samples. The characterization results clearly showed differences in morphology between the ME and the IW samples. N(2)-BET analysis showed that higher surface area, similar to 268-285 m(2)/g, was obtained with the ME samples. Also, H(2) chemisorption analysis showed that the rhodium dispersion was similar to 10% higher for the ME samples (H/Rh similar to 60-66%). XRD analysis showed that crystalline phases of gamma-alumina were present on all samples. The diffractograms also showed small traces of metallic Pt (similar to 16-30 nm) in the bimetallic samples. H(2)-TPR analysis, showed peaks ascribed to bulk rhodium oxides and rhodium aluminates. It was also noted that the addition of Pt on the support lowered the reducibility of the different rhodium species. TEM analysis performed on the fresh and aged ME and IW bimetallic samples showed mainly Rh(x)Pt(1-x) alloys with an average particle size of similar to 20-50 nm were present on the alumina support. Also, for the aged samples, no sintering effects were noted. Furthermore, rhodium was found to switch oxidation state from e. g. Rh(3+) to Rh(0) while Pt remained in the metallic state.
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