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  • 1. Agrell, J.
    et al.
    Boutonnet, Magali
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Fierro, J. L. G.
    Production of hydrogen from methanol over binary Cu/ZnO catalysts - Part II. Catalytic activity and reaction pathways2003Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 253, nr 1, s. 213-223Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The activity for conversion of methanol into hydrogen was investigated over binary Cu/ZnO catalysts derived from precursors prepared by two different techniques, viz. oxalates formed in microemulsion and hydroxycarbonates formed in aqueous solution. Some distinct differences in the reaction pathways were observed. During partial oxidation of methanol under a sub-stoichiometric oxygen/methanol ratio, the microemulsion materials exhibited considerably higher combustion activity in the low-temperature region than a catalyst prepared in aqueous solution. Over the former, oxygen was quickly converted by methanol combustion, after which steam reforming was initiated, producing hydrogen at the expense of water and gradually decreasing the net heat of reaction. Hence, a reaction sequence for the partial oxidation reaction over microemulsion catalysts is proposed. consisting of consecutive methanol combustion and steam reforming, followed by decomposition when all oxygen has been consumed. Over the hydroxycarbonate catalyst, the reaction ignited at a higher temperature, directly producing hydrogen by partial oxidation of methanol. When the two types of catalysts were evaluated in the steam reforming reaction, all catalysts displayed the typical S-shaped dependence of methanol conversion on temperature. However, there was a downward shift in the temperature at which methanol reached complete conversion, favouring the hydroxycarbonate, material. Hydrogen was produced selectively over all catalysts, but carbon monoxide formation was more pronounced over the microemulsion materials. The differences in catalytic behaviour are discussed in terms of catalyst morphology and the valence state of Cu in the working catalyst.

  • 2. Agrell, J.
    et al.
    Boutonnet, Magali
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Melian-Cabrera, I.
    Fierro, J. L. G.
    Production of hydrogen from methanol over binary Cu/ZnO catalysts - Part I. Catalyst preparation and characterisation2003Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 253, nr 1, s. 201-211Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mixed copper-zinc oxide catalysts (Cu/ZnO) were prepared by two different techniques, i.e. from hydroxycarbonate precursors formed in aqueous solution and from oxalate precursors formed in water-in-oil microemulsion. Their physicochemical properties were characterised by nitrogen adsorption-desorption, N2O chemisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and oxidation (TPO). The BET surface areas ranged from 34 to 87 m(2)/g, depending on the method of preparation. Cu surface areas between 6.6 and 22 m(2)/g were measured. It was a general observation that catalysts prepared by microemulsion technique had lower Cu dispersions than expected (3.4-5.7%), due to a proposed partial embedding of Cu in ZnO. The catalyst prepared by carbonate co-precipitation exhibited a significantly higher Cu dispersion (10.3%). In addition, this catalyst displayed better resistance to successive TPR/TPO than the microemulsion catalysts, which exhibited significant Cu crystallite growth. However, the microemulsion route provided well-mixed materials with a narrow particle size distribution and the possibility to obtain high BET surface areas (up to 87 m(2)/g) by controlling the water/surfactant ratio in the microemulsion. XPS measurements revealed the existence of Cu+ species on the surface of both types of catalysts after exposure to a O-2/CH3OH mixture. The surface composition of the hydroxycarbonate-derived sample was unaffected by reduction in hydrogen and exposure to O-2/CH3OH, while Zn-enrichment on the surface was observed in the microemulsion catalysts after reduction, indicating sintering of the Cu particles. These observations were consistent with the TPR/TPO measurements.

  • 3. Agrell, J.
    et al.
    Germani, G.
    Järås, Sven G.
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Boutonnet, Magali
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Production of hydrogen by partial oxidation of methanol over ZnO-supported palladium catalysts prepared by microemulsion technique2003Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 242, nr 2, s. 233-245Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Selective production of hydrogen by partial oxidation of methanol, using air as oxidant, was studied over a series of ZnO-supported Pd catalysts. Microemulsion-assisted synthesis and conventional impregnation techniques were used for preparation of catalysts containing Pd particles of different sizes. Catalyst characterisation included BET, XRD and TEM analyses. The influence of Pd particle size on catalytic activity and product distribution was studied by carrying out activity measurements at temperatures between 230 and 300 degreesC using a stoichiometric feed composition. All catalysts performed well with respect to methanol conversion and hydrogen yield. Both methanol conversion and hydrogen selectivity increased with increasing reaction temperature, the latter at the expense of water formation. Oxygen conversion was complete throughout the examined temperature range. These selectivity trends, with a strong dependence of hydrogen and carbon monoxide selectivities on methanol conversion and reaction temperature, support a reaction scheme consisting of consecutive methanol combustion, steam reforming and decomposition. More importantly, a correlation between Pd particle size and carbon monoxide selectivity was found. When the microemulsion catalysts are compared, carbon monoxide formation increases with increasing particle size. This was not observed over the impregnated reference catalysts, which exhibited high carbon monoxide-levels throughout the examined temperature range. Bimetallic PdZn particles were detected in spent catalysts by means of XRD and it is suggested that the catalytic activity is dependent on the formation of PdZn, the catalytic function being different from that of Pd-0.

  • 4. Agrell, J.
    et al.
    Hasselbo, K.
    Jansson, K.
    Järås, Sven G.
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Boutonnet, Magali
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Production of hydrogen by partial oxidation of methanol over Cu/ZnO catalysts prepared by microemulsion technique2001Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 211, nr 2, s. 239-250Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Production of hydrogen by partial oxidation of methanol, using air as oxidant. has been studied over a series of Cu/ZnO catalysts prepared by microemulsion technique. The catalytic activity was compared to that of a reference catalyst prepared by conventional co-precipitation. The BET surface areas of the microemulsion catalysts (30-70 wt.% Cu) ranged from 22 to 36 m(2)/g and were considerably lower than that of the reference (60 m(2)/g). Nevertheless, the microemulsion catalysts were more active in the partial oxidation reaction and exhibited high hydrogen and carbon dioxide selectivities. At a molar O-2/CH3OH ratio of 0.1, hydrogen production was initiated at about 185 degreesC over the microemulsion catalysts. Over the reference, hydrogen production began at 215 degreesC under the same conditions. The catalytic activity was Found to be strongly dependent on the partial pressure of oxygen, which also plays an important role in determining the product distribution. By increasing the O-2/CH3OH ratio, the methanol conversion and carbon dioxide selectivity increase. while production of water occurs at the expense of hydrogen. By TEM and TPR, it was observed that Cu is less well-dispersed in the microemulsion catalysts than in the reference. The higher catalytic activity is not expected considering the lower number of exposed Cu sites, i.e, the turnover frequencies are substantially higher over the microemulsion catalysts. It is possible that, a strong interaction between a small part of CuO and the ZnO lattice is responsible for the higher turnover frequencies of the microemulsion catalysts, or that particular crystallographic Cu planes or surface imperfections are the active sites of the reaction.

  • 5.
    Andersson, Robert
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Järås, Sven
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Correlation patterns and effect of syngas conversion level for product selectivity to alcohols and hydrocarbons over molybdenum sulfide based catalysts2012Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 417, s. 119-128Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The focus of the present study was to investigate the effect of the operation conditions, space velocity and temperature, on product distribution for a K-Ni-MoS2 catalyst for mixed alcohol synthesis from syngas. All experiments were performed at 91 bar pressure and constant H-2/CO=1 syngas feed ratio. For comparison, results from a non-promoted MoS2 catalyst are presented. It was found that the CO conversion level for the K-Ni-MoS2 catalyst very much decides the alcohol and hydrocarbon selectivities. Increased CO conversion by means of increased temperature (tested between 330 and 370 degrees C) or decreased space velocity (tested between 2400 and 18,000 ml/(g(cat) h)), both have the same effect on the product distribution with decreased alcohol selectivity and increased hydrocarbon selectivity. Increased CO conversion also leads to a greater long-to-short alcohol chain ratio. This indicates that shorter alcohols are building blocks for longer alcohols and that those alcohols can be converted to hydrocarbons by secondary reactions. At high temperature (370 degrees C) and low space velocity (2400 ml/(g(cat) h)) the selectivity to isobutanol is much greater than previously reported (9%C). The promoted catalyst (K-Ni-MoS2) is also compared to a non-promoted (MoS2) catalyst: the promoted catalyst has quite high alcohol selectivity, while almost only hydrocarbons are produced with the non-promoted catalyst. Another essential difference between the two catalysts is that the paraffin to olefin ratio within the hydrocarbon group is significantly different. For the non-promoted catalyst virtually no olefins are produced, only paraffins, while the promoted catalyst produces approximately equal amounts of C-2-C-6 olefins and paraffins. Indications of olefins being produced by dehydration of alcohols were found. The selectivity to other non-alcohol oxygenates (mostly short esters and aldehydes) is between 5 and 10%C and varies little with space velocity but decreases slightly with increased temperature. Very strong correlation patterns (identical chain growth probability) and identical deviations under certain reaction conditions between aldehyde and alcohol selectivities (for the same carbon chain length) indicate that they derive from the same intermediate. Also olefin selectivity is correlated to alcohol selectivity, but the correlation is not as strong as between aldehydes and alcohols. The selectivity to an ester is correlated to the selectivity to the two corresponding alcohols, in the same way as an ester can be thought of as built from two alcohol chains put together (with some H-2 removed). This means that, e.g. methyl acetate selectivity (C-3) is correlated to the combination of methanol (C-1) and ethanol (C-2) selectivities.

  • 6.
    Andrae, Johan
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Johansson, David
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Bursell, Martin
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Fakhrai, Reza
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Jayasuriya, Jeevan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Manrique Carrera, Arturo
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    High-pressure catalytic combustion of gasified biomass in a hybrid combustor2005Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 293, nr 1-2, s. 129-136Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Catalytic combustion of synthetic gasified biomass was conducted in a high-pressure facility at pressures ranging from 5 to 16 bars. The catalytic combustor design considered was a hybrid monolith (400 cpsi, diameter 3.5 cm, length 3.6 cm and every other channel coated). The active phase consisted of 1 wt.% Pt/gamma-Al2O3 With wash coat loading of total monolith 15 wt.%. In the interpretation of the experiments, a twodimensional boundary layer model was applied successfully to model a single channel of the monolith. At constant inlet velocity to the monolith the combustion efficiency decreased with increasing pressure. A multi-step surface mechanism predicted that the flux of carbon dioxide and water from the surface increased with pressure. However, as the pressure (i.e. the Reynolds number) was increased, unreacted gas near the center of the channel penetrated significantly longer into the channel compared to lower pressures. For the conditions studied (lambda = 46, T-in = 218-257 degrees C and residence time similar to 5 ms), conversion of hydrogen and carbon monoxide were diffusion limited after ignition, while methane never ignited and was kinetically controlled. According to the kinetic model surface coverage of major species changed from CO, H and CO2 before ignition to O, OH, CO2 and free surface sites after ignition. The model predicted further that for constant mass flow combustion efficiency increased with pressure, and was more pronounced at lower pressures (2.5-10 bar) than at higher pressures (> 10 bar).

  • 7.
    Barrientos, Javier
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    González, N.
    Lualdi, Matteo
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Järås, Sven
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    The effect of catalyst pellet size on nickel carbonyl-induced particle sintering under low temperature CO methanation2016Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 514, s. 91-102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Abstract The present work aims to evaluate the effect of catalyst pellet size on deactivation due to nickel carbonyl-induced particle sintering. For that purpose, a γ-Al2O3-supported nickel catalyst was prepared and tested under low temperature and high CO partial pressure. A total of four different pellet sizes were employed in the present study. It was found that the deactivation rate decreases with increasing pellet size. A very severe deactivation was observed when using small pellets. Large pellets exhibited instead a more stable performance. This difference in catalyst stability was explained by X-ray diffraction analyses which revealed that the growth of the nickel particles was very severe when using small pellets. An evaluation of heat and mass transfer phenomena in these four pellets was also conducted. It was found that, under the present low temperature reaction conditions, the temperature at the catalyst external surface can greatly differ from that in the bulk gas when using sufficiently large pellets. It was also shown that, for large pellets, the major part of the interior of the catalyst is exposed to negligible CO partial pressures and high temperatures, fact that can reduce the potential for nickel carbonyl formation.

  • 8.
    Barrientos, Javier
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Lualdi, Matteo
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Järås, Sven
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Deactivation of supported nickel catalysts during CO methanation2014Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 486, s. 143-149Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Deactivation of Ni-based catalysts was investigated during CO methanation over different supported catalysts. X-ray diffraction and temperature-programmed hydrogenation analyses were used to investigate nickel particle sintering and carbon formation during the first 24 h on stream. Titania-supported catalysts presented high resistance towards carbon deposition and nickel particle growth in comparison with the other tested catalysts. Particle size effects on these two deactivation causes were also evaluated. It was shown that carbon formation rates are higher on bigger crystal particles. However, it was found that titania-supported nickel catalysts reduced at high temperatures show the opposite effect. This difference is most probably due to a stronger interaction between nickel and TiOx (x < 2) species on smaller crystals which changes the CO dissociation properties and, in consequence, carbon formation rates.

  • 9.
    Barrientos, Javier
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Lualdi, Matteo
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Suarez Paris, Rodrigo
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Montes, V.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Jaras, S.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    CO methanation over TiO2-supported nickel catalysts: A carbon formation study2015Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 502, s. 276-286Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A systematic study on titania-supported nickel catalysts was performed in order to evaluate the effect of different process conditions on catalyst stability. Reaction tests and temperature-programmed-hydrogenation analyses were used in order to evaluate the effect of temperature, feed composition, water and reduction conditions on catalyst deactivation and carbon deposition. It was shown that high H-2/CO ratios and syngas partial pressures decrease the rate of carbon formation. Moreover, increasing temperature enhanced the formation of more stable carbon species and thus catalyst deactivation. The temperature-programmed hydrogenation analyses also revealed that water reduces the rate of carbon deposition. However, water enhanced catalyst deactivation when the catalysts were reduced at high temperatures. This negative effect of water is probably due to a progressive destruction of the strong-metal-support interaction characteristic of titania-supported nickel catalysts reduced at high temperatures. (C) 2015 Elsevier B.V. All rights reserved.

  • 10. Creaser, Derek
    et al.
    Karatzas, Xanthias
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Lundberg, Bjorn
    Pettersson, Lars J.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Dawody, Jazaer
    Modeling study of 5 kW(e)-scale autothermal diesel fuel reformer2011Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 404, nr 1-2, s. 129-140Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A model was developed that successfully describes key operating features of a 5 kW(e)-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).

  • 11. Danwittayakul, Supamas
    et al.
    Lakshman, K.
    Al-Harthi, S.
    Dutta, Joydeep
    Center of Excellence in Nanotechnology, Asian Institute of Technology, Thailand.
    Enhanced hydrogen selectivity via photo-engineered surface defects for methanol steam reformation using zinc oxide-copper nanocomposite catalysts2014Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 471, s. 63-69Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Methanol steam reformation (MSR) to produce hydrogen (H-2) gas using copper on zinc oxide (Cu/ZnO) supported catalysts is attractive due to the simple and low cost preparation process of the catalyst. H-2 yield from MSR is proportional to total catalyst loading which can be tuned during catalyst preparation. By creating UV-c light induced surface defects on ZnO nanorods, we have shown improved copper (Cu) nano-particle distribution on the ZnO nanorods leading to better H-2 yield. Increase in Cu nanoparticle adsorption is achieved by in situ reduction of Cu ions by photo-generated electrons, facilitated by ZnO surface defects that act as high energy sites favorable for Cu ion adsorption and their subsequent growth into nanoparticles. The modulated Cu/ZnO catalyst increases H-2 selectivity by 57% along with a corresponding increase in CO content, which can be controlled by adjusting H2O:MeOH ratio in the precursor solution.

  • 12.
    Eriksson, Sara
    et al.
    KTH, Tidigare Institutioner, Kemiteknik.
    Nylén, Ulf
    KTH, Tidigare Institutioner, Kemiteknik.
    Rojas, Sergio
    KTH, Tidigare Institutioner, Kemiteknik.
    Boutonnet, Magali
    KTH, Tidigare Institutioner, Kemiteknik.
    Preparation of catalysts from microemulsions and their applications in heterogeneous catalysis2004Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 265, nr 2, s. 207-219Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Microemulsions have a wide range of applications from oil recovery to synthesis of nanoparticles. The first implementation of water-in-oil (w/o) microemulsions for synthesis of nanoparticles was introduced in 1982 and concerns nanoparticles of noble metals for catalytic uses. Since this time, the method has been employed quite extensively in the field of catalysis, from room-temperature reactions such as butene isomerisation to high-temperature reactions such as catalytic combustion of methane.The present review paper will introduce the term microemulsion with emphasis on the microemulsion properties essential for heterogeneous catalyst preparation followed by a general description of the mode of catalytic materials prepared from microemulsions. Several examples of the use of these materials in heterogeneous catalysis are then described. It is shown that nanoparticles obtained from microemulsions have specific properties with respect to size, size distribution and surface structure. Consequently, these particles are in some cases superior regarding catalytic activity and/or selectivity

  • 13.
    Eriksson, Sara
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Rojas, S.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Fierro, J.L.G.
    Effect of Ce-doping on Rh/ZrO2 catalysts for partial oxidation of methane2007Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 326, nr 1, s. 8-16-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The partial oxidation of methane over supported (ZrO2, CeO2-ZrO2) rhodium catalysts was investigated at atmospheric pressure. The effect of temperature, CH4/O-2 ratio, catalyst composition and pre-treatment was studied. Ceria doping of the support material resulted in significant improvements concerning the methane conversion and syngas selectivity, which could be related to a higher noble metal dispersion on the Rh/CeO2-ZrO2 catalyst. In addition, the light-off temperature was decreased by 128 degrees C when using CeO2-ZrO2, as support. X-ray photoelectron spectroscopy revealed the presence of different Rh oxidation states depending on catalyst composition and pre-treatment. A stabilization of partially oxidized (Rh delta+) species by ceria could be detected. An active and stable catalyst behavior could be observed for Rh/CeO2-ZrO2, irrespectively of catalyst pre-treatment, whereas an activation period was required for stabilizing the activity of the Rh/ZrO2 catalyst. The activity tests indicate that the indirect reaction mechanism, consisting of methane combustion followed by steam and dry reforming, prevails under the experimental conditions studied.

  • 14.
    González Arcos, Angélica Viviana
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Rostrup-Nielsen, J.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Engvall, Klas
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Pettersson, Lars J.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Promoted RhPt bimetallic catalyst supported on δ-Al2O3 and CeO2-ZrO2 during full-scale autothermal reforming for automotive applications: Post-mortem characterization2015Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 491, s. 8-16Artikel i tidskrift (Refereegranskat)
    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.

  • 15. Guo, X. W.
    et al.
    Shen, J. P.
    Sun, Licheng
    Song, C. S.
    Wang, X. S.
    Effects of SiO2/Al2O3, MgO modification and hydrothermal treatment on the catalytic activity of HZSM-5 zeolites in the methylation of 4-methylbiphenyl with methanol2004Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 261, nr 2, s. 183-189Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this work is to study the effects Of SiO2/Al2O3 of HZSM-5, MgO modification and hydrothermal treatment on methylation of 4-methylbiphenyl (4-MBP) with methanol under fixed-bed down-flow conditions. The results show that, with an increase in the SiO2/Al2O3 of HZSM-5 (from 50 to 150, molar ratio), the selectivity to 4,4'-dimethylbiphenyl (4,4'-DMBP) increases from 25 to 79%. MgO modification also increases the selectivity to 4,4'-DMBP, but leads as well to low catalyst activity and rapid deactivation. Hydrothermal treatment not only increases the selectivity, but also improves the stability. When CBV1502 (SiO2/Al2O3 = 150) catalyst was hydrothermally treated at 500degreesC, the selectivity to 4,4'-DMBP increased to 85%. The selectivity to 4,4'-DMBP was further improved to about 90% by the increasing in the amount of mesitylene in the feed as solvent.

  • 16. Kumar, N.
    et al.
    Roy, A.
    Wang, Z.
    L'Abbate, Mario Enrico
    KTH.
    Haynes, D.
    Shekhawat, D.
    Spivey, J. J.
    Bi-reforming of methane on Ni-based pyrochlore catalyst2016Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 517, s. 211-216Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Ni-based pyrochlore catalyst was synthesized using the modified Pechini method. In this method, 1 wt% Ni was doped into the La2Zr2O7 pyrochlore structure. The catalyst was characterized by H2-TPR, TPO, XRD, and EXAFS, and tested for its methane reforming activity under bi-reforming reaction conditions; i.e.; in the presence of CO2 and steam: 3CH4+CO2+2H2O⇌4CO+8H2 Repeated TPR/TPO cycles showed that the two consecutive TPR spectra do not change, showing that the catalyst is stable at high temperatures, and that the nickel oxidation/reduction process is reversible. The catalyst showed constant activity with time at all temperatures in the range of 700-950 °C over a cumulative period of 170 h. After this series of bi-reforming tests, TPO of the spent catalyst was carried out, which showed detectable but unquantifiable carbon deposition. The presence of steam in bi-reforming greatly limits carbon deposition compared to directly related dry-reforming tests on this same catalyst.

  • 17.
    Lanza, Roberto
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Canu, P.
    Järås, Sven G.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Methane partial oxidation over Pt-Ru catalyst: An investigation on the mechanism2010Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 375, nr 1, s. 92-100Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanism of the partial oxidation of methane has been investigated over a bimetallic Pt-Ru catalyst. Dedicated experiments aimed to separate and quantify the relative contribution of single reactions included in the so-called "combustion and reforming" mechanism using the same catalyst. The catalyst is 0.5% Ru and 0.5% Pt (w/w) supported on mixture of alumina, ceria and zirconia (75/4.4/20.6%, w/w), washcoated on a ceramic monolith. Steam reforming, dry reforming, direct and reverse water-gas shift reactions were investigated. The temperature range investigated is 300 < T < 800 degrees C, while the space velocity range is 25.000 < GHSV < 100.000 h(-1). Conditions at which single side reactions are expected to occur during the partial oxidation process, were approximated by tuning the reactant composition. The experimental results are also compared with thermodynamic equilibrium calculations. The CO and H-2 yields of partial oxidation have been quantitatively connected with steam and dry reforming, while the persistent water-gas shift reaction always rearranges the products and intermediates.

  • 18.
    Lanza, Roberto
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Canu, P.
    Järås, Sven G.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Microemulsion-prepared ruthenium catalyst for syngas production via methane partial oxidation2008Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 337, nr 1, s. 10-18Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Partial oxidation of methane (POxM) was studied over Ru catalyst supported on alumina (1%, w/w). The catalyst was prepared via microemulsion (ME) and coated onto cordierite monoliths. Samples were characterized by XRD, BET surface area, SEM-EDS and TPR and TPO analyses. The catalyst showed high methane conversion with very good selectivity towards CO and H-2 under every condition tested. The effects of GHSV and heating rate (HR) were investigated, recording composition data both during heating and cooling. This allowed to evidence hysteresis cycles and to obtain additional information on the reactions occurring within the monolith.

  • 19.
    Lanza, Roberto
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Canu, P.
    Järås, Sven G.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Partial oxidation of methane over Pt-Ru bimetallic catalyst for syngas production2008Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 348, nr 2, s. 221-228Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A bimetallic catalyst (Pt-Ru 50/50) has been prepared for methane partial oxidation. Total metal load was 1 wt%. The support was alumina mixed with 25 wt% of a ceria-zirconia mixture. This because of the good performances of alumina for such applications and to exploit the oxygen buffer effect of the ceriazirconia system. The catalyst has been prepared by incipient wetness and characterized by means of XRD, BET surface area, TPR/TPO and SEM-EDS analyses. It showed good activity and high selectivity towards CO and H-2, produced in a ratio suitable for Fisher-Tropsch applications. The effect of spatial velocity (GHSV) has been investigated; ramping temperature up and down, some hysteresis has been evidenced, especially at the highest GHSV, mainly caused by thermal effects. Overall, 100% conversion of methane to H-2 and CO at the appropriate syngas ratio (2/1) can achieved easily and with stability.

  • 20.
    Lanza, Roberto
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Järås, Sven G.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Canu, P.
    Partial oxidation of methane over supported ruthenium catalysts2007Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 325, nr 1, s. 57-67Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Partial oxidation of methane (POM) to synthesis gas was studied over Ru catalysts (1% (w/w)) supported on silica, alumina and ceria-zirconia. Catalyst samples were prepared by incipient wetness and characterized by BET area, XRD, ESEM-EDS, and TPR-TPO analyses. Ru on silica deactivated very fast, while Ru supported on alumina has good activity and selectivity. The mixture CeO2-ZrO2 led to low selectivity towards POM, with a higher selectivity towards complete combustion, common to all the catalysts at lower temperature. Both reduced and non-reduced catalysts were tested resulting in different behaviour in the same temperature range. We investigated the effect of different GHSVs, heating rates and also sequences of heating and cooling cycles. This allowed gaining insight into the sequence of reactions taking place in the reactor and revealed hysteresis for all reaction conditions. This can be explained through a cycling between Ru oxidation states on the surface.

  • 21. Li, Hongliang
    et al.
    Yu, Xinhai
    Tu, Shan-Tung
    Yan, Jinyue
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Energiprocesser.
    Wang, Zhengdong
    Catalytic performance and characterization of Al2O3-supported Pt-Co catalyst coatings for preferential CO oxidation in a micro-reactor2010Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 387, nr 1-2, s. 215-223Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Platinum-cobalt (Pt-Co) catalyst coatings are studied for preferential oxidation of carbon monoxide (PROX) ill hydrogen-rich gas streams. Experimental results show a role for cobalt in improving catalytic activity. The most active catalyst coating can decrease carbon monoxide concentrations from 1% to a value of less than 10 ppm for GHSV values ranging from 40,000 to 120,000 ml g(-1) h(-1). This catalyst coating can work at a wide window of operation ill terms of temperature. Transmission electron microscopy, selected-area electron diffraction, and diffuse reflectance infrared Fourier transform spectroscopy show that the addition of Co forms Pt3Co intermetallic compounds and slightly increases the average particle size. In situ laser Raman spectroscopy reveals the co-existence of Co metal and its oxides on the catalyst surface, due to gradual oxidation of Co by gas phase oxygen within the initial stage of the PROX reaction. The promotional effect of Co during PROX is confirmed and ascribed to this Pt3Co intermetallic compound and the synergetic effect of Co-0 and Co chi+. The high accessibility of the reactant to Pt3Co species appears favorable and crucial for PROX.

  • 22. Lindström, B.
    et al.
    Pettersson, Lars J.
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Menon, P. G.
    Activity and characterization of Cu/Zn, Cu/Cr and Cu/Zr on gamma-alumina for methanol reforming for fuel cell vehicles2002Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 234, nr 02-jan, s. 111-125Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of catalyst properties on the activity and selectivity of hydrogen generation by methanol reforming over copper-based catalysts impregnated on gamma-alumina pellets has been investigated. In the experiments, three sets of copper-based catalysts with various compositions were tested: Cu/Zn/Al2O3, Cu/Cr/Al2O3 and Cu/Zr/Al2O3. The catalysts were characterized using temperature programmed reduction (TPR), temperature programmed oxidation (TPO), SEM-EDS, Brunauer-Emmett-Teller (BET) surface area measurement and X-ray diffraction (XRD). The copper surface area was determined by pulse chemisorption using N2O. We found a correlation between the copper surface area and catalytic activity. The activity tests were performed in a fixed bed reactor with 15 g of spherical catalyst pellets using a gas hourly space velocity (GHSV) of 25,000. The results of the activity tests indicate that the choice of promoter and the catalyst composition greatly influence the activity as well as the selectivity for CO2 formation. The highest conversions were achieved for the zinc-containing catalysts (Cu/Zn/Al2O3) for both steam reforming and the combined reforming process. Complete conversion of methanol was only obtained for the zinc-containing catalysts when running the steam reforming process. The combined reforming process generally yielded A product stream containing lower carbon monoxide concentrations compared to steam reforming at the equivalent reactor temperature for all of the catalysts tested.

  • 23.
    Lopez, Luis
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi. UMSA Universidad Mayor de San Andrés, Bolivia.
    Montes, V.
    Kušar, Henrik
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Cabrera, S.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Järås, Sven
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Syngas conversion to ethanol over a mesoporous Cu/MCM-41 catalyst: Effect of K and Fe promoters2016Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 526, s. 77-83Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transportation fuels such as ethanol can be obtained through thermochemical processing of biomass. Interest in the development of more selective catalysts for the conversion of biomass-derived syngas (H2 + CO) to ethanol is increasing in both academia and industry. In this work, we have evaluated the performances of K and Fe as metal promoters of a mesoporous Cu/MCM-41 catalyst and their effects on the product selectivity and especially on ethanol formation. The metal loading was 29 wt.% Cu, 2 wt.% Fe and 1.6 wt.% K. The catalysts were tested at 300 °C, 20 bar and gas-hourly-space-velocities in the range of 1500–30000 mlsyngas/gcat h; under these conditions the syngas conversion level was between 2 and 11%. The non-promoted Cu/MCM-41 catalyst showed interesting selectivity toward oxygenated compounds, mostly methanol. The addition of K as promoter increases the selectivity toward methanol even more, while the addition of Fe as promoter favors the formation of hydrocarbon compounds. When both K and Fe as promoters are incorporated into the Cu/MCM-41 catalyst, the reaction rate to oxygenated compounds is notably increased, especially for ethanol. The space time yield for ethanol for the Cu/MCM-41 catalyst is 0.3 × 10−5 carbon-mol/gcath which increases to 165.5 × 10−5 carbon-mol/gcath for the Cu-Fe-K/MCM-41 catalyst. From XPS analysis, the Cu-Fe-K/MCM-41 catalyst was found to have the following atomic composition: Cu0.34Fe0.08K0.08Si1.00. The promoting effect of both K and Fe, may be related to an increased reaction rate toward CO non-dissociation and CO-dissociation paths, respectively, which is beneficial for the ethanol formation. Further catalytic results, catalyst characterization and discussion of results are presented in this work.

  • 24.
    Lualdi, Matteo
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Di Carlo, Gabriella
    Lögdberg, Sara
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Järås, Sven
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    La Parola, Valeria
    Liotta, Leonarda Francesca
    Ingo, Gabriel M.
    Venezia, Anna Maria
    Effect of Ti and Al addition via direct synthesis to SBA-15 as support for cobalt based Fischer-Tropsch catalysts2012Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 443-444, s. 76-86Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Different mesoporous SBA-15 supports doped with Ti and Al at 5 and 10 wt% have been synthesized by means of direct synthesis. The supports have been characterized by N 2-adsorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), NH 3-temperature programmed desorption (NH 3-TPD), H 2-chemisorption, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM). Titanium doped materials showed to have much shorter channels than the pristine SBA-15, while aluminum addition did not have a significant effect on channel length. After impregnation with 12 wt% Co, the catalysts were further characterized and tested in the Fischer-Tropsch synthesis at industrially relevant process conditions (483 K, 20 bar, H 2/CO ratio = 2.1, pellet size: 53-90 μm) with and without external water addition. The S C5 + values of the different SBA-supported catalysts were low, especially at low conversion levels (i.e. low water partial pressure), suggesting that CO diffusion limitations increased the H 2/CO ratio inside the 1-dimensional (1D) porous network. The selectivity data showed a correlation between the channel length and the extent of CO-diffusion limitations at much shorter diffusion distances than those for conventional 3D porous supports. Water partial pressure showed to increase the syngas diffusion rate (i.e. removal of diffusion limitations on reactants’ arrival), to have a positive kinetic effect on the rate and to favor longer chain hydrocarbons.

  • 25.
    Lögdberg, Sara
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Walmsley, John C.
    Järås, Sven
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Holmen, Anders
    Blekkan, Edd A.
    Effect of water on the space-time yield of different supported cobalt catalysts during Fischer-Tropsch synthesis2011Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 393, nr 1-2, s. 109-121Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The effect of partial pressure of water on the Fischer-Tropsch (FT) rate of six cobalt-based catalysts supported on three different carrier materials (gamma-Al2O3, alpha-Al2O3, TiO2) with varying Co particle sizes was investigated in a fixed-bed reactor by changing space velocity and by external water vapour addition. A typical catalyst pellet size (<100 mu m) for industrial slurry-bed FT reactors was used. Water was found to have a positive kinetic effect, at least up to moderate amounts, on the FT rate of all catalysts in the present study, including the gamma-Al2O3-supported catalyst with pores smaller than similar to 10 nm. The reason for the apparent negative effect on the space-time yield at a direct exposure of Co supported on narrowpore gamma-Al2O3 to high partial pressures of water is due to a rapid and extensive deactivation. This could be ascribed to formation of hard-to-reduce oxidized cobalt species. The choice of support material was found to have a major effect on the response to changes in partial pressure of water, both with respect to deactivation behaviour and kinetics. However, there is a minor Co-particle size effect on the magnitude of the kinetic effect of water, larger Co particles showing a more positive response. Different extents of mass transfer limitations and/or differences in fugacities of H-2, CO and water among the six catalysts could be ruled out as causes for the observed differences.

  • 26.
    Nylén, Ulf
    et al.
    KTH, Tidigare Institutioner, Kemiteknik.
    Frontela Delgado, Juana
    KTH, Tidigare Institutioner, Kemiteknik.
    Järås, Sven
    KTH, Tidigare Institutioner, Kemiteknik.
    Boutonnet, Magali
    KTH, Tidigare Institutioner, Kemiteknik.
    Low and high-pressure ring opening of indan over 2 wt.% Pt, Ir and bi-metallic Pt25Ir75/boehmite catalysts prepared from microemulsion systems2004Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 262, nr 2, s. 189-200Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A bi-metallic 2 wt.% Pt25Ir75/boehmite catalyst has been synthesized from a microemulsion system and characterized in detail with techniques including TPR, XPS, SEM and TEM-EDX. Additional reduction treatment changes the structural phase of the support as well as the character of the metal particles. TEM-EDX revealed unexpectedly large agglomerates with platinum clusters lying on top of iridium plate-like clusters. The catalytic activity with respect to ring opening of indan was Studied at 325 degreesC and atmospheric pressure and compared with the catalytic performance of corresponding monometallic Pt and Ir/boehmite catalysts. The bi-metallic 2wt.% Pt(25)lr(75)/boehmite catalyst was also tested in a more realistic environment for industrial applications, i.e. at high pressure (40 bar). In essence, the obtained catalytic results indicated superior catalytic activity for the Ir and Pt-Ir catalysts. Concerning selectivity the product distribution varied widely, with hydrogenation and selective ring opening being the most prominent reactions for high pressure and atmospheric pressure conditions, respectively. At atmospheric pressure, all catalysts were slightly deactivated whereas at high pressure, the Pt-Ir catalyst showed a high operating stability with no deactivation.

  • 27.
    Nylén, Ulf
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Pawelec, Bárbara
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Fierro, J.L.G.
    Catalytic ring opening of naphthenic structures: Part II - in-depth characterization of catalysts aimed at upgrading LCO into a high-quality diesel-blending component2006Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 299, s. 14-29Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present paper delves into physical and chemical characterization of surface and bulk properties of the twelve 2 wt.% PtxIry catalysts employed in Part I for ring opening of naphthenic structures. The support materials (ceria, alumina, silica, silica-alumina, zirconia, H-SA and magnesia) were investigated using X-ray diffraction (XRD) for phase identification and adsorption/desorption of nitrogen to obtain the specific surface area and pore size distribution. The catalyst preparation via the incipient wetness technique was closely monitored and the final catalysts were examined by means of X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS) and quantitative TPR followed by dynamic pulse chemisorption of CO, Fourier transform infrared spectroscopy (Fr-IR) of adsorbed CO and NH3-DRIFTS. The XPS analyses are particularly comprehensive and involve all the catalysts in their fresh, reduced and spent states. The combined results from TPR, XPS and Fr-IR of adsorbed CO reveal that metallic Pt-Ir alloys are formed directly upon mild reduction.

  • 28.
    Nylén, Ulf
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Sassu, Lorenzo
    Melis, Stefano
    Järås, Sven
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Catalytic ring opening of naphthenic structures Part I. From laboratory catalyst screening via pilot unit testing to industrial application for upgrading LCO into a high-quality diesel-blending component2006Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 299, s. 1-13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The present investigation shows the most relevant results obtained during a joint academic and industrial effort to develop new effective catalysts for upgrading light cycle oil (LCO) into a high-quality diesel-blending component. Bench-scale atmospheric pressure screening with indan over 12 different Pt-Ir-based ring-opening catalysts prepared by the incipient wetness technique showed that the relative amount of iridium and the choice of support material are factors that mainly influence the activity but also the initial and final product distribution. Moreover, TPO-TG-MS analyses of the spent catalysts revealed that for ceria-based catalysts there is a correlation between the amount of iridium, the amount of coke deposits and the resulting catalytic activity: increasing the iridium load results in less carbonaceous deposits and hence higher catalytic activity due to the intrinsic hydrogenolysis/hydrogenation properties of iridium that effectively destroy coke precursors. The catalytic properties of the chosen catalyst candidate, with the formula 2 wt.% Pt5Ir95/CeO2, were examined more closely in a pilot unit under industrially employed conditions with a tetralin/cetane model feed mixture and the real feed pre-hydrotreated LCO (HDT-LCO). As the operating pressure is increased from atmospheric to industrial high-pressure conditions, i.e. 40 bar, coking tendencies are supressed. Moreover, the dominating reaction pathway for the model feed changes from ring-opening to hydrogenation; still, ring-opening is gradually observed as the temperature exceeds approximately 300 degrees C. Simultaneously with ring-opening, consecutive cracking reactions are observed and these must be closely monitored and carefully balanced in order to reduce liquid yield losses.Results obtained at high pressure employing the HDT-LCO show that catalyst performance is slightly impaired, most likely due to sulphur poisoning. In spite of this, the catalyst candidate shows very promising catalytic properties and as the majority of current and forthcoming diesel quality specifications are exceeded, implementation of this catalyst in industrial operation is feasible.

  • 29. Ojeda, M.
    et al.
    Rojas, Sergio
    KTH, Tidigare Institutioner, Kemiteknik.
    Boutonnet, Magali
    KTH, Tidigare Institutioner, Kemiteknik.
    Perez-Alonso, F. J.
    Garcia-Garcia, F. J.
    Fierro, J. L. G.
    Synthesis of Rh nano-particles by the microemulsion technology - Particle size effect on the CO+H-2 reaction2004Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 274, nr 1-2, s. 33-41Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Several alumina-supported rhodium-based catalysts have been prepared using the microemulsion technology. The change of microemulsion properties led to catalysts with different Rh particle size and narrow size distribution while keeping the same metal loading. The metal particle size was determined by XRD and TEM. These catalysts were tested in the CO hydrogenation reaction in order to investigate the influence of the Rh particle size. The catalytic results indicated that turnover frequency (TOF) increased about four times when the Rh particle size increased approximately from

  • 30. Persson, K.
    et al.
    Thevenin, P. O.
    Jansson, K.
    Agrell, J.
    Järås, Sven G.
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Pettersson, Lars J.
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Preparation of alumina-supported palladium catalysts for complete oxidation of methane2003Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 249, nr 1, s. 165-174Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Alumina-supported palladium catalysts (Pd/Al2O3) have been prepared by incipient wetness (IW), grafting (G) and microemulsion techniques (ME). Two slightly different microemulsion methods have been used (ME1) and (ME2). The catalysts have been calcined at 1000 degreesC for 4 h. The catalysts have then been examined with respect to their activity for the combustion of methane, during heating and cooling ramps. Pd/Al2O3-IW and Pd/Al2O3-ME2 exhibit the highest activity whereas Pd/Al2O3-ME1 and Pd/Al2O3-G are the less active. There is not much of a difference in activity between Pd/Al2O3-IW and Pd/Al2O3-ME2, despite strong differences in palladium particle size observed by TEM analysis. TPO experiments show that Pd/Al2O3-IW and Pd/Al2O3-ME2 present a higher PdO/Pd ratio than the other samples exhibit. The preparation technique affects the reoxidation ability of palladium during cooling, hence the combustion activity of the fresh catalyst, as PdO is more active than Pd for the complete oxidation of methane under lean conditions.

  • 31.
    Regali, Francesco
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Liotta, Leonarda Francesca
    Istituto per lo Studio dei Materiali Nanostrutturati, ISMN CNR, Palermo, Italy.
    Venezia, Anna Maria
    Istituto per lo Studio dei Materiali Nanostrutturati, ISMN CNR, Palermo, Italy.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Järås, Sven
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Hydroconversion of n-hexadecane on Pt/silica-alumina catalysts: Effect of metal loading and support acidity on bifunctional and hydrogenolytic activity2014Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 469, s. 328-339Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bifunctional catalysts based on platinum and amorphous silica-alumina were studied in the hydroconversion of n-hexadecane. The influence of platinum loading and support acidity on activity and selectivity were assessed. The contribution of hydrogenolysis reactions on top of bifunctional hydrocracking was shown to depend not only on metal loading, but also on the effect of support acidity on the intrinsic activity of the platinum sites. The yield of cracking products, and their linear alkane fraction, increased with metal loading, while the isomerization yield was practically independent of the metal content. On a support of high Bronsted acidity, the rate of formation of methane was proportional to the platinum surface area, indicating that dernethylation occurred by metal-cataly ed hydrogenolysis. On the other hand, the methane site-time yield was one order of magnitude lower on a catalyst with negligible Bronsted acidity. Pt-catalyzed hydrogenolysis was also investigated during selective poisoning of acid sites by cofeeding pyridine and comparing the effect of hydrogen partial pressure on reaction rates. In the presence of pyridine, total hydroconversion activity was reduced by one order of magnitude while rates to methane and linear cracking products remained relatively high. These observations indicate that acid sites do not intervene in the mechanism, but that support acidity affects the hydrogenolytic activity of platinum sites.

  • 32. Rojas, S.
    et al.
    Garcia-Garcia, F. J.
    Järås, Sven G.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Martinez-Huerta, M. V.
    Fierro, J. L. G.
    Boutonnet, Magali
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Kemisk teknologi.
    Preparation of carbon supported Pt and PtRu nanoparticles from microemulsion - Electrocatalysts for fuel cell applications2005Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 285, nr 02-jan, s. 24-35Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A series of platinum and platinum ruthenium carbon supported electrocatalyst have been prepared by the microemulsion technique. The influence of parameters such as the preparation route, the metal loading and the PtRu stoichiometry on the morphology of the final nanoparticles has been studied. Irrespective the total metal loading, nanosized particles, displaying a narrow size distribution were obtained. In addition, particle size was found to be independent of the metal loading. Structural characteristics of these systems have been studied by XPS, X-ray diffraction, TEM, and TPR-TPO and their textural parameters by N-2 adsorption. The catalytic performance of the samples was evaluated in the electrochemical oxidation of methanol. The influence of the morphology on the catalytic performance of the catalysts is discussed in terms of their synthesis route. © 2005 Elsevier B.V. All rights reserved.

  • 33. Thevenin, P. O.
    et al.
    Ersson, A. G.
    Kusar, H. M. J.
    Menon, P. G.
    Järås, Sven G.
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Deactivation of high temperature combustion catalysts2001Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 212, nr 02-jan, s. 189-197Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The main objective of catalytic combustion is to attain a flame temperature 300-400 Klower than in thermal or non-catalyzed combustion; this substantially reduces the direct combination of nitrogen and oxygen in air to form the so-called thermal NOx. In this way, catalytic combustion is a preventive solution to the problem of nitrogen oxides emissions. The focus of attention here is its application in gas turbines, both for power production and for transportation by road, sea and air. Any catalyst for catalytic combustion, however, has to face extreme demands: continuous operation above 1000 degreesC in the presence of oxygen and steam for preferably 30,000 h, resistance to poisons in the fuel and/or process air, and ability to withstand large thermal and mechanical shocks. While material/catalyst advances are still inadequate, systems engineering is coming to the rescue by developing multiple-monolith catalyst systems and the so-called hybrid reactors. The deactivation of catalyst supports, washcoats, and active materials is briefly reviewed here: sintering, vaporization, phase transformation, thermal shock and poisoning.

  • 34. Wang, Dongping
    et al.
    Wang, Mei
    Zhang, Rong
    Wang, Xiuna
    Gao, Aiping
    Ma, Jia
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Asymmetric epoxidation of styrene and chromenes catalysed by dimeric chiral (pyrrolidine salen)Mn(III) complexes2006Ingår i: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 315, s. 120-127Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two dimeric chiral (pyrrolidine salen)Mn(III) complexes 3 and 4 were prepared, in which the two (pyrrolidine salen)Mn(III) units are linked either by a p-xylylene or by ap-phthalyl bridge. High yields were attained for asymmetric epoxidation of styrene and substituted chromenes at 0.5-4.0 mol% catalyst loading of 3 and 4 using NaClO/PPNO and m-CPBA/NMO as oxidant systems, with 37-39% ee for styrene and 86-95% ee for substituted chromenes. Dimeric complexes 3 and 4 displayed higher activities than their parent monomeric complexes 1 and 2 of double equiv for epoxidation of substituted chromenes. Complex 3 bearing two tertiary amine units displayed considerably higher activity than analogous dimeric complex 4 containing two carboxamide units in the aforementioned reaction. The effect of excess CH3I on the epoxidation of 6-nitro-2,2-dimethylchromene catalysed by 3 in the aqueous/organic biphasic medium was explored. The recovery and recycling possibilities of the dimeric complexes 3 and 4 were studied.

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