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RhPt and Ni based catalysts for fuel reforming in energy conversion
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Technology.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Although current trends in global warming are of great concern, energy demand is still increasing, resulting in increasing pollutant emissions. To address this issue, we need reliable renewable energy sources, lowered pollutant emissions, and efficient and profitable processes for energy conversion. We also need to improve the use of the energy, produced by existing infrastructure. Consequently, the work presented in this thesis aims at investigating current scientific and technological challenges in energy conversion through biomass gasification and the alternative use of fossil fuels, such as diesel, in the generation of cleaner electricity through auxiliary power units in the transport

sector. Production of chemicals, syngas, and renewable fuels is highly dependent on the development and innovation of catalytic processes within these applications. This thesis focuses on the development and optimization of catalytic technologies in these areas. One of the limitations in the commercialization of the biomass gasification technology is the effective catalytic conversion of tars, formed during gasification. Biomass contains high amounts of alkali impurities, which pass on to the producer gas. Therefore, a new material with alkali tolerance is needed.

In the scope of this thesis, a new catalyst support, KxWO3 – ZrO2 with high alkali resistance was developed. The dynamic capability of KxWO3 – ZrO2 to store alkali metals in the crystal structure, enhances the capture of alkali metals "in situ". Alkali metals are also important electronic promoters for the active phase, which usually increases the catalysts activity and selectivity for certain products. Experimental results show that conversion of 1-methylnaphathalene over Ni/KxWO3 – ZrO2 increases in the presence of 2 ppm of gas-phase K (Paper I). This support is considered to contribute to the electronic equilibrium within the metal/support interface, when certain amounts of alkali metals are present. The potential use of this support can be extended to applications in which alkali "storage-release" properties are required, i.e. processes with high alkali content in the process flow, to enhance catalyst lifetime and regeneration.

In addition, fundamental studies to understand the adsorption geometry of naphthalene with increasing temperature were performed in a single crystal of Ni(111) by STM analyses. Chapter 9 presents preliminary studies on the adsorption geometry of the molecule, as well as DFT calculations of the adsorption energy. In relation to the use of clean energy for transport applications, hydrogen generation through ATR for FC-APUs is presented in Papers II to V. Two promoted RhPt bimetallic catalysts were selected in a previous bench scale study, supported on La2O3:CeO2/d – Al2O3 and MgO : Y2O3/CeO2 – ZrO2. Catalyst evaluation was performed in a fullscale reformer under real operating conditions. Results showed increased catalyst activity after the second monolithic catalyst due to the effect of steam reforming, WGS reaction, and higher catalyst reducibility of the RhxOy species in the CeO2 – ZrO2 mixed oxide, as a result of the improved redox properties. The influence of sulfur and coke formation on diesel reforming was assessed after 40 h on stream. Sulfur poisoning was evaluated for the intrinsic activity related to the total Rh and Pt area observed after exposure to sulfur. Sulfur concentration in the aged catalyst washcoat was observed to decrease in the axial direction of the reformer. Estimations of the amount of sulfur adsorbed were found to be below the theoretical equilibrated coverage on Rh and Pt, thus showing a partial deactivation due to sulfur poisoning.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. , xii, 100 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:10
Keyword [en]
RhPt bimetallic catalysts, Ni catalysts, ceria-zirconia, potassium tungsten bronze, zirconium dioxide, autothermal reforming, biodiesel, diesel, sulfur, deactivation, tar reforming, steam reforming, biomass gasification, auxiliary power units, naphthalene
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-160026ISBN: 978-91-7595-440-0 (print)OAI: oai:DiVA.org:kth-160026DiVA: diva2:788144
Public defence
2015-03-05, F3, Lindstedtsvägen 26, KTH, Stokcholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150213

Available from: 2015-02-13 Created: 2015-02-12 Last updated: 2015-11-23Bibliographically approved
List of papers
1. Effect of potassium electrochemical promotion in biomass-tar reforming
Open this publication in new window or tab >>Effect of potassium electrochemical promotion in biomass-tar reforming
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-160027 (URN)
Note

QS 2015

Available from: 2015-02-12 Created: 2015-02-12 Last updated: 2015-02-13Bibliographically approved
2. Autothermal reforming of Fischer-Tropsch diesel over alumina and ceria-zirconia supported catalysts
Open this publication in new window or tab >>Autothermal reforming of Fischer-Tropsch diesel over alumina and ceria-zirconia supported catalysts
2013 (English)In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 107, 162-169 p.Article in journal (Refereed) Published
Abstract [en]

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.

Keyword
Ceria-zirconia, Alumina, Hydrogen, Fischer-Tropsch diesel, Autothermal reforming
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-121105 (URN)10.1016/j.fuel.2013.02.010 (DOI)000316214200016 ()2-s2.0-84878345805 (Scopus ID)
Note

QC 20130422

Available from: 2013-04-22 Created: 2013-04-19 Last updated: 2017-12-06Bibliographically approved
3. 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
Show others...
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 (Scopus ID)
Note
QC 20110415. Updated from submitted to published.Available from: 2011-04-15 Created: 2011-04-15 Last updated: 2017-12-11Bibliographically approved
4. Full-scale autothermal reforming for transport applications: The effect of diesel fuel quality
Open this publication in new window or tab >>Full-scale autothermal reforming for transport applications: The effect of diesel fuel quality
2013 (English)In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 210, 19-25 p.Article in journal (Refereed) Published
Abstract [en]

This study evaluates the feasibility of H-2 production through a fuel flexible reformer, at realistic operating conditions for electricity supply by FC-APUs in the transport sector. The fuel flexibility is evaluated by comparison of autothermal reforming performance with biodiesel (RME), Fischer-Tropsch, low-sulfur diesel (MK1) and European standard diesel (DIN 590). ATR experiments with two monolithic catalysts, Rh1.0Pt1.0Ce10La10/Al2O3 (CAT 1) and Rh1.0Pt1.0Mg4.0Y5.0/CeO2-ZrO2 (CAT 2), sequentially placed in the axial direction of the reformer length were used for full-scale tests. The O-2/C ratio was varied from 0.3 to 0.5 and the H2O/C ratio varied from 2 to 3.5, reaching temperatures in the interval of 700-800 degrees C. The hydrogen production and fuel conversion showed an upward trend from RME < DIN 590 < MK1 < FT with maximum 42 vol.% H-2 and 99% fuel conversion for FT diesel.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Biodiesel, Hydrogen, Autothermal reforming, Multifuel study, APU
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-124959 (URN)10.1016/j.cattod.2012.11.009 (DOI)000320696500004 ()2-s2.0-84878675927 (Scopus ID)
Conference
2nd International Symposium of Catalysis for Clean Energy and Sustainable Chemistry (CCESC), 2012, Alcobendas, Spain
Note

QC 20130802

Available from: 2013-08-02 Created: 2013-08-02 Last updated: 2017-12-06Bibliographically approved
5. Promoted RhPt bimetallic catalyst supported on δ-Al2O3 and CeO2-ZrO2 during full-scale autothermal reforming for automotive applications: Post-mortem characterization
Open this publication in new window or tab >>Promoted RhPt bimetallic catalyst supported on δ-Al2O3 and CeO2-ZrO2 during full-scale autothermal reforming for automotive applications: Post-mortem characterization
2015 (English)In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 491, 8-16 p.Article in journal (Refereed) Published
Abstract [en]

The influence of sulfur and coke formation on the steam reforming of diesel was evaluated for two promoted RhPt bimetallic catalysts, composed of 1:1 Rh:Pt/10:10 La2O3: CeO2/ δ-Al2O3 (CAT 1) and 1:1 Rh:Pt/4:5 MgO: Y2O3/CeO2 − ZrO2 (CAT 2). The intrinsic activity is related to the total Rh and Pt area observed after the exposure to sulfur. Therefore, the degree of deactivation is related to the amount of sulfur deposited on the active metal sites. Sulfur analysis on the aged catalyst washcoat showed a decreasing sulfur concentration in the axial direction of the reformer. The estimated sulfur coverage related to metal surface area after 40 h on stream reached values of 0.145 in CAT 2, below the equilibrated sulfur coverage of 0.19 after tests with DIN 590. Thus, showing a partial deactivation due to sulfur poisoning. Further catalyst characterization on carbon deposits and thermal aging was performed by TPO, TGA, BET, CO chemisorption, and TEM analysis.

Place, publisher, year, edition, pages
Angélica González, 2015
National Category
Natural Sciences
Identifiers
urn:nbn:se:kth:diva-160025 (URN)10.1016/j.apcata.2014.11.035 (DOI)000349731600002 ()2-s2.0-84916600432 (Scopus ID)
Note

QC 20150327

Available from: 2015-02-12 Created: 2015-02-12 Last updated: 2017-12-04Bibliographically approved

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