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Rhodium diesel-reforming catalysts for fuel cell applications
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Heavy-duty diesel truck engines are routinely idled at standstill to provide cab heating or air conditioning, and in addition to supply electricity to comfort units such as radio and TV. Idling is an inefficient and unfavorable process resulting in increased fuel consumption, increased emissions, shortened engine life, impaired driver rest and health, and elevated noise. Hydrogen-fueled, polymer-electrolyte fuel-cell auxiliary power unit (PEFC-APU) as a silent external power supply, working independently of the main engine, is proposed as viable solution for better fuel economy and abatement of idling emissions. In a diesel PEFC-APU, the hydrogen storage problem is circumvented as hydrogen can be generated onboard from diesel by using a catalytic reformer. In order to make catalytic diesel PEFC-APU systems viable for commercialization research is still needed. Two key areas are the development of reforming catalyst and reformer design, which both are the scope of this thesis. For diesel-reforming catalysts, low loadings of Rh and RhPt alloys have proven to exhibit excellent reforming and hydrogen selectivity properties. For the development of a stable reforming catalyst, more studies have to be conducted in order to find suitable promoters and support materials to optimize and sustain the long-term performance of the Rh catalyst. The next step will be full-scale tests carried out at realistic operating conditions in order to fully comprehend the overall reforming process and to validate promising Rh catalysts. This thesis can be divided into two parts; the first part addresses the development of catalysts in the form of washcoated cordierite monoliths for autothermal reforming (ATR) of diesel. A variety of catalyst compositions were developed containing Rh or RhPt as active metals, CeO2, La2O3, MgO, Y2O3 as promoters and Al2O3, CeO2-ZrO2, SiO2 and TiO2 as support materials. The catalysts were tested in a bench-scale reactor and characterized by using N2-BET, XRD, H2 chemisorption, H2-TPR, O2-TPO, XPS and TEM analyses. The second part addresses the development and testing of full-scale reformers at various realistic operating conditions using promising Rh catalysts.

The thesis shows that a variety of Rh on alumina catalysts was successfully tested for ATR of diesel (Papers I-IV). Also, zone-coating, meaning adding two washcoats on specific parts of the monolith, was found to have beneficial effects on the ATR catalyst performance (Paper II). In addition, RhPt supported on CeO2-ZrO2 was found to be one of the most active and promising catalyst candidates for ATR of diesel. The superior performance may be attributed to higher reducibility of RhiOx species and greater dispersion of Rh and Pt on the support (Paper IV). Finally, two full-scale diesel reformers were successfully developed and proven capable of providing high fuel conversion and hydrogen production from commercial diesel over selected Rh catalysts (Papers II-III, V-VI).

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , x, 81 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:28
Keyword [en]
Autothermal reforming, auxiliary power unit, BET, chemisorption, diesel, fuel cell, hydrogen, monolith, reforming catalyst, reformer design, Rh, RhPt alloy, TEM, TPO, TPR, XRD, XPS, zone coating
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-32647ISBN: 978-91-7415-945-5OAI: oai:DiVA.org:kth-32647DiVA: diva2:411319
Public defence
2011-04-29, KTH - Sal F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110418Available from: 2011-04-18 Created: 2011-04-18 Last updated: 2011-04-18Bibliographically approved
List of papers
1. Microemulsion and incipient wetness prepared Rh-based catalyst for diesel reforming
Open this publication in new window or tab >>Microemulsion and incipient wetness prepared Rh-based catalyst for diesel reforming
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2011 (English)In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 175, no 1, 515-523 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Autothermal reforming, Diesel, Incipient wetness, Platinum, Reverse microemulsion, Rhodium
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-32504 (URN)10.1016/j.cattod.2011.02.042 (DOI)000295735400072 ()2-s2.0-80054860735 (ScopusID)
Note
QC 20110415Available from: 2011-04-15 Created: 2011-04-15 Last updated: 2012-01-26Bibliographically approved
2. Zone-coated Rh-based monolithic catalyst for autothermal reforming of diesel
Open this publication in new window or tab >>Zone-coated Rh-based monolithic catalyst for autothermal reforming of diesel
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2011 (English)In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 101, no 3-4, 226-238 p.Article in journal (Refereed) Published
Abstract [en]

In this work we present results of hydrogen generation from diesel via autothermal reforming (AIR) obtained with monolithic catalysts consisting of either one or two layers of monometallic Rh and bimetallic RhPt washcoats. The Rh metal loading of the monometallic washcoats was varied between 0.5, 1.0 and 3.0 wt%, while the weight ratio of Rh:Pt in the bimetallic washcoats was kept constant at 1:1. Furthermore, non-doped and CeLa-doped catalysts were also tested to detect differences in catalyst activity. The catalysts consisting of two layers of washcoats were termed zoned catalysts and each layer was applied to some given length in the axial direction of the monolith. All catalysts were prepared by impregnation using the incipient wetness technique with delta-Al2O3 B as support and deposited onto 400 cpsi cordierite monoliths. A total of eight catalysts, including both single layered and zone-coated, were tested in a bench-scale reactor using low-sulfur diesel as fuel at operating conditions H2O/C=2.5, O-2/C=0.49 (lambda = 0.33), GHSV 17,000 h(-1) and P = 1 atm. The results showed that the zoned catalyst, covered with the two washcoats Rh1.0Pt1.0-Ce10La5.0/delta-Al2O3 and Rh-3.0-Ce10La10/delta-Al2O3, respectively, was most active in terms of fuel conversion and hydrogen production. The zoned catalyst's long-term performance and stability was also evaluated in a full-scale reactor using low-sulfur and Fischer-Tropsch diesels at operating conditions H2O/C = 2.5, O-2/C = 0.49 (lambda =0.33), GHSV= 10,800 h(-1), P = 1 atm, and at H2O/C = 2.4, 02/C = 0.39 (lambda=0.26), GHSV- 10,200 h(-1), P = 1 atm. respectively. The results showed that high fuel conversion and hydrogen production were obtained from both fuels. 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. Fresh and aged samples of the catalysts were characterized by N-2-BET, H-2 chemisorption, XRD, H-2-TPR, O-2-TPO and XPS analyses.

Keyword
Autothermal reforming, Diesel, Rhodium, Zone-coated monolithic catalyst
Identifiers
urn:nbn:se:kth:diva-31649 (URN)10.1016/j.apcatb.2010.09.027 (DOI)000287068400009 ()2-s2.0-78650307598 (ScopusID)
Note
QC 20110321Available from: 2011-03-21 Created: 2011-03-21 Last updated: 2011-04-18Bibliographically approved
3. Hydrogen generation from n-tetradecane, low-sulfur and Fischer-Tropsch diesel over Rh supported on alumina doped with ceria/lanthana
Open this publication in new window or tab >>Hydrogen generation from n-tetradecane, low-sulfur and Fischer-Tropsch diesel over Rh supported on alumina doped with ceria/lanthana
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2011 (English)In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 164, no 1, 190-197 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Autothermal reforming, Ceria, Cordierite monolith, Diesel, Lanthana, Rhodium
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-32507 (URN)10.1016/j.cattod.2010.10.019 (DOI)000289716300035 ()2-s2.0-79955064483 (ScopusID)
Note
QC 20110415Available from: 2011-04-15 Created: 2011-04-15 Last updated: 2012-08-22Bibliographically approved
4. Autothermal reforming of low-sulfur diesel over bimetallic RhPt supported on Al2O3, CeO2-ZrO2, SiO2 and TiO2
Open this publication in new window or tab >>Autothermal reforming of low-sulfur diesel over bimetallic RhPt supported on Al2O3, CeO2-ZrO2, SiO2 and TiO2
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2011 (English)In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 106, no 3-4, 476-487 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Alumina, Ceria-zirconia, Diesel reforming, Rhodium-platinum, Silica, Titania
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-32521 (URN)10.1016/j.apcatb.2011.06.006 (DOI)000294092400024 ()2-s2.0-79960835892 (ScopusID)
Note
QC 20110415. Updated from submitted to published.Available from: 2011-04-15 Created: 2011-04-15 Last updated: 2015-02-13Bibliographically approved
5. Assessing the adaptability to varying fuel supply of an autothermal reformer
Open this publication in new window or tab >>Assessing the adaptability to varying fuel supply of an autothermal reformer
2008 (English)In: Chemical Engineering Journal, ISSN 1385-8947, Vol. 142, 309-317 p.Article in journal (Refereed) Published
Abstract [en]

The present paper describes the study of an autothermal reformer and its fuel-flexible capabilities. Experiments have been performed in a reactor designed to generate hydrogen by autothermal reforming for a 1-5 kW(e) polymer electrolyte fuel cell. Both logistic fuels (diesel, gasoline, and E85) and alternative fuel candidates (methanol, ethanol, and dimethyl ether) were tested in the reformer. The same catalyst composition, Rh supported on Ce/La-doped gamma-Al2O3 and deposited on cordierite monoliths, was used for all fuels. The practical feasibility of reforming each fuel in the present reactor design was tested and evaluated in terms of fuel conversion and selectivity to hydrogen and carbon dioxide. Temperature profiles were studied both in the axial and radial direction of the reformer. It was concluded from the experiments that the reformer design was most suitable for use with hydrocarbon mixtures Such as diesel, gasoline, and E85, where it represents a good basis for an optimized multifuel-reformer design.

Keyword
hydrogen; multifuel autothermal reformer; auxiliary power unit; Rh catalyst
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-10021 (URN)10.1016/j.cej.2008.02.026 (DOI)000259555500009 ()2-s2.0-49649087235 (ScopusID)
Note
QC 20100804Available from: 2009-03-04 Created: 2009-03-04 Last updated: 2011-04-18Bibliographically approved
6. Characterization and optimization of an autothermal diesel and jet fuel reformer for 5 kW(e) mobile fuel cell applications
Open this publication in new window or tab >>Characterization and optimization of an autothermal diesel and jet fuel reformer for 5 kW(e) mobile fuel cell applications
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2010 (English)In: Chemical Engineering Journal, ISSN 1385-8947, Vol. 156, no 2, 366-379 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Autothermal reformer, Diesel, Fuel flow, Fuel preheating, Jet fuel, Monolithic catalyst, catalytic partial oxidation, auxiliary power units, liquid, hydrocarbons, hydrogen, sulfur, performance, scale, technologies
National Category
Chemical Engineering Other Environmental Engineering
Identifiers
urn:nbn:se:kth:diva-19239 (URN)10.1016/j.cej.2009.10.039 (DOI)000274771400018 ()2-s2.0-73249135810 (ScopusID)
Note
QC 20110210Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-04-18Bibliographically approved

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