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  • 1.
    Creaser, Derek
    Luleå tekniska universitet.
    Crystal population balance model for nucleation and growth of colloidal TPA-silicalite-11999In: Porous materials in environmentally friendly processes: Proceedings of the 1st International FEZA Conference, Eger, Hungary, 1-4 September, 1999, Amsterdam: Elsevier, 1999, p. 117-124Conference paper (Refereed)
    Abstract [en]

    A model describing the crystallization of colloidal TPA-silicalite-1 is developed and tested. The nucleation rate is approximated from experimental data. Crystal growth is surface-reaction limited and the Gibbs-Thomson effect suppresses growth of small crystals, resulting in an induction period. Slow crystal growth during the nucleation period results in the narrow crystal size distribution typically observed for colloidal TPA-silicalite-1 syntheses.

  • 2.
    Creaser, Derek
    et al.
    Luleå tekniska universitet.
    Andersson, B.
    University of Waterloo.
    Hudgins, R.R.
    Chalmers University of Technology.
    Silveston, P.L.
    Chalmers University of Technology.
    Cyclic operation of the oxidative dehydrogenation of propane1999In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 54, no 20, p. 4437-4448Article in journal (Refereed)
    Abstract [en]

    The cyclic operation of the oxidative dehydrogenation of propane over a V-Mg-O catalyst by the alternate feeding of propane and oxygen gas mixtures was investigated. Generally, the response of the reaction products following a step-change in composition determined the cyclic conditions that resulted in an improved yield of propene. By alternating propane and oxygen with a 1 : 1 cycle split, time-average propene yields higher than steady state could be obtained. The optimal cycle period was about 60 s. This same period provided high propane conversion, as well as high propene selectivity. The cycle split could be varied by shortening the oxygen-feed half of the cycle with little effect on the time-average results. The oxygen half-cycle needed only to be long enough to reoxidize the catalyst. The propane feed scheme was varied by feeding increasing amounts of propane in the oxygen half-cycle. The change in feed scheme caused an increase in the time-average propane conversion that resulted in some further improvement in the propene yield despite some loss in propene selectivity.

  • 3.
    Creaser, Derek
    et al.
    Luleå tekniska universitet.
    Andersson, B.
    Chalmers University of Technology, Department of Chemical Reaction Engineering.
    Hudgins, R.R.
    Department of Chemical Engineering, University of Waterloo.
    Silveston, P.L.
    Department of Chemical Engineering, University of Waterloo.
    Transient kinetic analysis of the oxidative dehydrogenation of propane1999In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 182, no 1, p. 264-269Article in journal (Refereed)
    Abstract [en]

    Oxidative dehydrogenation of propane was studied using various transient techniques. Results support a redox mechanism in which propane reduces the catalyst, which is reoxidized by gas-phase oxygen. Only lattice oxygen participates in propene formation. Desorbable oxygen is a major source of poor selectivity, although lattice oxygen also causes total oxidation. Consequently, propene selectivity in the absence of gas-phase O2is superior to co-feed, steady-state selectivity at the same propane conversion. Propene selectivity is further improved by increasing the degree of catalyst reduction.

  • 4.
    Creaser, Derek
    et al.
    Luleå tekniska universitet.
    Andersson, B.
    Chalmers University of Technology, Department of Chemical Reaction Engineering.
    Hudgins, R.R.
    Department of Chemical Engineering, University of Waterloo.
    Silveston, P.L.
    Department of Chemical Engineering, University of Waterloo.
    Transient study of oxidative dehydrogenation of propane1999In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 187, no 1, p. 147-160Article in journal (Refereed)
    Abstract [en]

    Kinetics and the mechanism of the oxidative dehydrogenation of propane were investigated using various transient techniques. Results support a redox reaction mechanism in which propane and intermediate products react with lattice oxygen, reducing the catalyst surface, which is reoxidized by gas-phase O2. Partial reduction of the catalyst occurs during the start-up to a steady state. Successive pulsing with C3H8 reduced V5+ in the magnesium ortho-vanadate phase to V2+. Carbon-containing species were observed upon interruption of the reaction, although only minute amounts were formed. Cycling increases the amount of the carbon deposited, but this carbon is reactive and most of it is oxidized in the succeeding O2 pulse. Temperature-programmed oxidation (TPO) experiments on the catalyst used in steady-state operation revealed mainly strongly bound carbonaceous matter on the catalyst, but this carbon deposition did not affect catalyst activity. Thus, adsorbed oxygen is an important source of total combustion. Our experiments show, however, that lattice oxygen also produces total oxidation. Propene selectivity of the reaction in the absence of gas-phase O2 was superior to steady-state selectivity, at the same propane conversion. Propene selectivity could be further improved by increasing the degree of reduction of the catalyst

  • 5.
    Creaser, Derek
    et al.
    Luleå tekniska universitet.
    Andersson, Bengt
    Chalmers University of Technology, Department of Chemical Reaction Engineering.
    Hudgins, Robert
    Department of Chemical Engineering, University of Waterloo.
    Silveston, Peter
    Department of Chemical Engineering, University of Waterloo.
    Kinetic modelling of oxygen dependence in oxidative dehydrogenation of propane2000In: Canadian Journal of Chemical Engineering, ISSN 0008-4034, E-ISSN 1939-019X, Vol. 78, no 1, p. 182-193Article in journal (Refereed)
    Abstract [en]

    Several Mars-Van Krevelen-type redox kinetic models were developed for the catalytic oxidative dehydrogenation of propane and examined for their ability to predict high propene yields at low oxygen/propane feed ratios. The intent in this study was to use modelling as a means of extracting further mechanistic insight from experimental data rather than to identify the best model. Thus, a conventional redox model with a consecutive reaction mechanism and a single pathway for the production of carbon oxides predicts higher propene selectivity but only at the expense of low propane conversion. Experimental data indicated, however, that even at the same propane conversion, propene selectivity increased as the oxygen partial pressure was lowered. Models that successfully describe the data had an additional carbon oxide production path involving the reaction of propane with deeply oxidizing surface oxygen species. Kinetic models and experimental data examined do not fully resolve how these deeply oxidizing surface oxygen species are formed. However, they do reflect the accepted view that lattice oxygen selectively produces propene whereas more weakly bound surface adsorbed oxygen reacts to completely oxidize propane.

  • 6.
    Hedlund, Jonas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Noack, M.
    Institute of Applied Chemistry e.V., Rudower Chaussee 5, D-12489, Berlin.
    Kölsch, P.
    Institute of Applied Chemistry e.V., Rudower Chaussee 5, D-12489, Berlin.
    Creaser, Derek
    Luleå tekniska universitet.
    Sterte, Johan
    Caro, J.
    Institute of Applied Chemistry e.V., Rudower Chaussee 5, D-12489, Berlin.
    ZSM-5 membranes synthesized without organic templates using a seeding technique1999In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 159, no 1-2, p. 263-273Article in journal (Refereed)
    Abstract [en]

    Porous α-alumina supports were seeded with colloidal TPA-silicalite-1 crystals and calcined. The supports were treated in a synthesis solution to grow the seed crystals into ZSM-5 films. The synthesis solution was free from organic template molecules in order to avoid the calcination step which often introduces cracks in the synthesized zeolite film. An SEM investigation indicated that the zeolite films on the supports were defect free and that the film thickness was approximately 1.5 μm. XRD data showed that the film consisted of well-crystallized ZSM-5. The permeance in single gas experiments decreased in the order H2O, H2, CO2, O2, N2 and CH4. The difference in permeance between each molecular species in the series was almost one order of magnitude which indicated that the membranes were of a high quality. Molecules larger than CH4 permeated with similar and low rates, independent of their kinetic diameters, indicating a non-selective permeation path through defects in the zeolite films. However, the permeance of these larger molecules was less than 1/10 000 of that for H2O. The highest measured separation factors for binary mixtures of N2/SF6 and H2/i-C4 were 110 and 99.

  • 7.
    Jareman, Fredrik
    et al.
    Luleå tekniska universitet.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Creaser, Derek
    Chalmers University of Technology.
    Sterte, Johan
    Modelling of single gas permeation in real MFI membranes2004In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 236, no 1-2, p. 81-89Article in journal (Refereed)
    Abstract [en]

    A novel permeation model for flow through defects and zeolite pores in real MFI membranes, also accounting for substrate effects has been developed. Defect distributions for two types of MFI membranes were determined from porosimetry data using the model, which incorporated the Horvath Kawazoe (micropores) or the Kelvin equation (mesopores). The narrowest (1.08 nm) and also most common defects were found to be separated with a distance of 10–40 μm according to the model. Diffusion coefficients for hydrogen, helium, nitrogen and SF6 in the zeolite were further determined from single gas permeation data using the model using the independently determined defect distribution. The coefficients are consistent with values previously reported in the literature.

  • 8.
    Lassinantti, Magdalena
    et al.
    Luleå tekniska universitet.
    Jareman, Fredrik
    Luleå tekniska universitet.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Creaser, Derek
    Luleå tekniska universitet.
    Sterte, Johan
    Preparation and evaluation of thin ZSM-5 membranes synthesized in the absence of organic template molecules2001In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 67, no 1-3, p. 109-119Article in journal (Refereed)
    Abstract [en]

    Porous α-alumina supports with a pore size of 100 nm were seeded with colloidal TPA-silicalite-1 crystals with a size of 120 nm. The seeded supports were calcined and treated in a synthesis solution free from organic template molecules to form ZSM-5 films on the supports. According to SEM images, the films were about 2 μm thick and no defects could be found on the as-synthesized membranes. Single gas permeation data was collected and good quality membranes (defined as having a non-detectable permeance of SF6 after drying at 100°C) were further evaluated using binary/ternary gas mixtures. The selectivity for n-butane/i-butane had a maximum value of 17.8 at 220°C. Water was selectively separated from a helium-diluted vaporized water/ethanol azeotrope with a maximum selectivity of 12.4.

  • 9.
    Li, Qinghua
    et al.
    Luleå tekniska universitet.
    Creaser, Derek
    Luleå tekniska universitet.
    Sterte, Johan
    High yield synthesis of collodial crystals of zeolite Y2001In: Zeolites and mesoporous materials at the dawn of the 21st century: proceedings of the 13th International Zeolite Conference, Amsterdam: Elsevier, 2001, p. 140-Conference paper (Refereed)
  • 10.
    Li, Qinghua
    et al.
    Luleå tekniska universitet.
    Creaser, Derek
    Luleå tekniska universitet.
    Sterte, Johan
    The synthesis of small colloidal crystals of TPA-silicalite-1 with short synthesis times and high yields1999In: Studies in Surface Science and Catalysis, ISSN 0167-2991, Vol. 125, p. 133-140Article in journal (Refereed)
    Abstract [en]

    A two-stage varying-temperature crystallization procedure can be used to synthesize particularly small colloidal crystals of TPA-silicalite-1 with reduced synthesis times and high yields. Using this procedure involves starting a synthesis at a reduced temperature which favours the nucleation of a large crystal population. The reduced temperature is maintained throughout the nucleation stage, after which an elevated temperature is used to accelerate the crystal growth and reach higher equilibrium yields favoured by higher temperatures

  • 11.
    Li, Qinghua
    et al.
    Luleå tekniska universitet.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Creaser, Derek
    Luleå tekniska universitet.
    Sterte, Johan
    Zoned MFI films by seeding2001In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 2001, no 6, p. 527-528Article in journal (Refereed)
    Abstract [en]

    The synthesis and characterization of zoned MFI films consisting of intergrown TPA-silicalite-1 and ZSM-5 crystals are described.

  • 12.
    Li, Qinghua
    et al.
    Luleå tekniska universitet.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Sterte, Johan
    Creaser, Derek
    Chalmers University of Technology.
    Bons, Jan-Anton
    European Technology Center.
    Synthesis and characterization of zoned MFI films by seeded growth2002In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 56, no 3, p. 291-302Article in journal (Refereed)
    Abstract [en]

    Supported zoned and sandwiched MFI films were prepared by a two-step crystallization procedure, using seeds. In this work, a zoned MFI film is defined as one assembled by crystals propagating from the support to the film top surface with varying Al content along the length of the crystal. A sandwiched MFI film is referred to as one assembled by at least two layers of crystals. Six types of films were prepared, both zoned and sandwiched, with a high or a low Al-content in the ZSM-5 part and with varying order of the layers, i.e. ZSM-5 coated with silicalite-1 or vice versa. The films were characterized by SEM and TEM. The Al-distribution was measured by cross-sectional EDS, and the preferred orientation of the crystals could be determined by XRD. Truly zoned films are obtained when the compositional difference between the layers is relatively small, and the synthesis conditions are similar or when the first layer is silicalite-1. If the first layer is ZSM-5 and the synthesis conditions and/or the composition vary too much, a discontinuity occurs at the interface between the layers, and sandwiched film results, where nucleation of the second layer is initiated by secondary nucleation or by applying seeds.

  • 13.
    Li, Qinghua
    et al.
    Luleå tekniska universitet.
    Mihailova, Boriana
    Bulgarian Academy of Sciences.
    Creaser, Derek
    Luleå tekniska universitet.
    Sterte, Johan
    The nucleation period for crystallization of colloidal TPA-silicalite-1 with varying silica source2000In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 40, no 1-3, p. 53-62Article in journal (Refereed)
    Abstract [en]

    The effect of varying silica source on the nucleation and crystallization of TPA-silicalite-1 was investigated. A direct experimental method, involving a two-stage varying-temperature synthesis, was used to determine the nucleation period for colloidal crystals of TPA-silicalite-1 with different silica sources, including tetraethoxysilane (TEOS) and amorphous silica (Ludox TM and Ludox LS). For syntheses performed at 60°C with TEOS as silica source, the duration of the nucleation was about 72 h, and a very rapid increase in the crystal population occurred during the initial crystallization time. However, with the amorphous silica sources (Ludox TM or Ludox LS), the duration of the nucleation period was extended to about 120 h, and the nucleation profile consisted of a self-accelerating nucleation rate at the beginning of the nucleation period. The two-stage synthesis method could be used to determine the nucleation profile for the various silica sources. However, this technique overestimated the crystal concentration at the earliest stage of nucleation with amorphous silica. The use of amorphous silica gave rise to a broader crystal size distribution compared to that of TEOS. However, it was found that for both TEOS and amorphous silica the vast majority of the nucleation occurred during an induction period when little or no crystal growth was observed. In addition, Raman spectroscopy revealed structural differences between Ludox TM and Ludox LS which may account for differences in the nucleation processes observed for these two amorphous silicas.

  • 14.
    Li, Qinghua
    et al.
    Luleå tekniska universitet.
    Wang, Zheng
    Luleå tekniska universitet.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Creaser, Derek
    Chalmers University of Technology.
    Zhang, Hong
    Stockholm University.
    Zou, Xiaodong
    Stockholm University.
    Bons, Anton-Jan
    European Technology Center.
    Synthesis and characterization of colloidal zoned MFI crystals2005In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 78, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Colloidal zoned MFI crystals, i.e., continuous crystals with a compositional gradient resulting in a ZSM-5 core covered with a silicalite-1 shell, were synthesized by the addition of ZSM-5 seeds to a silicalite-1 synthesis solution. The effect of the surface aluminum content of the ZSM-5 crystals on the synthesis of the zoned MFI crystals was investigated using SEM, TEM, XPS and XRD. An acid treatment of the ZSM-5 seeds, which removed some of the aluminum at the surface, proved favorable for the synthesis of zoned MFI crystals.

  • 15. Lindmark, Jonas
    et al.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Wirawan, Sang Kompiang
    Creaser, Derek
    Chalmers University of Technology, Department of Chemical and Biological Engineering.
    Li, Mingrun
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Zhang, Daliang
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Zou, Xiaodong
    Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Stockholm University.
    Impregnation of zeolite membranes for enhanced selectivity2010In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 365, no 1-2, p. 188-197Article in journal (Refereed)
    Abstract [en]

    A new method to enhance the selectivity of zeolite membranes for alternative separation tasks has been developed. Calcined MFI membranes were impregnated with a solution of Ca(NO3)2 in methanol and calcined at 600 °C to thermally decompose the nitrate. SEM and EDS data indicated that calcium compounds were evenly distributed in the entire MFI film and in addition, a few crystals of a calcium compound were observed on top of the film in some locations. A HR-TEM investigation showed that calcium compounds were present in low concentration in the sample and that the interiors of the MFI crystals remained fully crystalline after impregnation and calcination. However, the HR-TEM investigation could neither confirm nor rule out the occurrence of calcium compounds in the pores in the interiors of the crystals. In accordance with the SEM and TEM observations, XRD data showed that calcium compounds on top of the film were relatively large CaCO3 crystals and that the zeolite film remained crystalline after impregnation. However, eventual calcium compounds in the pores of the zeolite could not be studied by XRD since these would probably generate a very weak signal of amorphous material. FTIR data indicated that impregnation increased the amount of both physisorbed and chemisorbed CO2, the latter resulting in carbonate species in the film. n-Hexane/helium adsorption branch permporometry showed that the high quality of the membranes remained after modification. The single component permeance ratio CO2/H2 increased from 0.6 to 1.5 after impregnation. Calculations indicated that the increased CO2/H2 single component permeance ratios were both an effect of increased adsorption of CO2 in the film and reduced pressure drop in the support. The dual component separation factor α CO2/H2 at room temperature increased drastically from 0.7 (H2 selective) to 3.4 (CO2 selective) after impregnation. This work shows for the first time that impregnation procedures can be used to tailor the diffusion properties of zeolite membranes in a similar way as impregnation procedures are used to tailor the catalytic performance of catalysts.

  • 16. Mosca, Alessandra
    et al.
    Öhrman, Olov
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Indra, Perdana
    Gadjah Mada University, Yogyakarta.
    Creaser, Derek
    Chalmers University of Technology.
    NO2 and N-2 sorption in MFI films with varying Si/Al and Na/Al ratios2009In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 120, no 3, p. 195-205Article in journal (Refereed)
    Abstract [en]

    MFI crystals or films with controlled thicknesses and different Si/Al ratios were grown on seeded cordierite monoliths using a clear synthesis mixture with template or a template-free gel. The materials were analyzed by scanning electron microscopy, X-ray diffraction, inductively coupled plasma-atomic emission spectrometry, X-ray photoelectron spectroscopy, thermogravimetric analysis and sorption experiments using N2 or NO2 adsorbates. The films were uniformly distributed over the support surface. As expected, the specific monolayer N2 adsorption capacity (mol/gzeolite) was constant and independent of film thickness. The specific molar NO2 adsorption capacity was significantly lower than the specific molar monolayer N2 adsorption capacity, indicating that NO2 is adsorbed at specific sites rather than evenly distributed in a monolayer. A number of NO2 adsorption sites with varying strengths were observed by TPD experiments. At 30 °C, the amount of adsorbed NO2 in the MFI films increased with increasing Al and Na content as opposed to the N2 adsorption capacity, which was independent of these parameters. At 200 °C, the adsorbed amount of NO2 was lower than at 30 °C and apparently independent on Al concentration in the Na-MFI films. These results indicate that different mechanisms are involved in NO2 adsorption. NO2 may adsorb weakly on Na+ cations and also react with silanol groups and residual water in the zeolite, the latter two results in more strongly bound species. Upon NO2 adsorption, formation of NO was observed. This work represents the first systematic study of the effects of Al and Na content on NO2 adsorption in MFI films.

  • 17.
    Perdana, Indra
    et al.
    Chalmers University of Technology, Department of Chemical and Biological Engineering.
    Creaser, Derek
    Chalmers University of Technology, Department of Chemical and Biological Engineering.
    Lindmark, Jonas
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Influence of NOx adsorbed species on component permeation through ZSM-5 membranes2010In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 349, no 1-2, p. 83-89Article in journal (Refereed)
    Abstract [en]

    A thin ZSM-5 film was grown on an α-alumina support, resulting in a composite membrane. The membranes were characterized by SEM and adsorption branch n-hexane/helium permporometry. In addition, the permeation of gas mixtures containing NO2, NO, N2 and argon was evaluated. The effect of temperature and gas mixture composition on the component permeation and selectivity was investigated. It was found that NOx permeation through the ZSM-5 membrane was partially surface concentration dependent and was thermally activated. However, transport by gas translational diffusion seemed to dominate at the conditions studied. The presence of various NOx adsorbed species appeared to influence diffusion of NO2 in ZSM-5 and reduced transport of other inert and weakly adsorbed components over a wide temperature range (20 to 400 °C). Strongly adsorbed surface nitrate species formed in the presence of gas phase NOx should be responsible for the reduced transport of these components at the elevated temperature. The findings are of interest for possible applications of ZSM-5 membranes for component separation at high temperature.

  • 18.
    Perdana, Indra
    et al.
    Chalmers University of Technology, Department of Chemical Reaction Engineering.
    Creaser, Derek
    Chalmers University of Technology, Department of Chemical Reaction Engineering.
    Öhrman, Olov
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    A comparison of NOx adsorption on Na, H and BaZSM-5 films2007In: Applied Catalysis B: Environmental, ISSN 0926-3373, E-ISSN 1873-3883, Vol. 72, no 1-2, p. 82-91Article in journal (Refereed)
    Abstract [en]

    NOx adsorption in ZSM-5 films containing Na+, H+ or Ba2+ as counter ions was studied. NaZSM-5 films showed a superior NOx adsorption capacity over the entire temperature range (30-350 °C) in comparison with the other films. Besides the possibility to form strongly bound surface nitrate species, the presence of the Na+ ions in ZSM-5 resulted in a large enhancement of various weakly adsorbed species. In the HZSM-5 film, the NOx adsorption was mainly due to physisorption, surface nitric acid and nitrosium ion (NO+) formation. Besides weakly adsorbed species and surface nitric acid, the NOx adsorption in BaZSM-5 films also resulted in formation of strongly bound surface nitrate species. The nitrate species in the BaZSM-5 film were found to be resistant to NO exposure and were mainly formed through an NO2 disproportionation pathway.

  • 19.
    Perdana, Indra
    et al.
    Chalmers University of Technology, Department of Chemical Engineering and Environmental Science.
    Creaser, Derek
    Chalmers University of Technology, Department of Chemical Engineering and Environmental Science.
    Öhrman, Olov
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    NOx adsorption over a wide temperature range on Na-ZSM-5 films2005In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 234, no 1, p. 219-229Article in journal (Refereed)
    Abstract [en]

    NOx adsorption over a wide temperature range (30–350 °C) on monolith supported Na-ZSM-5 films were studied with a gas flow reactor. The nature of the adsorbed species was further investigated by in situ infrared spectroscopy. Depending on the adsorption temperature, three different ranges of thermally stable species were observed on Na-ZSM-5 films. In addition to the role of cationic sites and residual hydroxyl groups in zeolite frameworks, it was found that the formation of nitric acid plays an important role in NO2 adsorption. Nitrate species were formed during adsorption by two mechanisms. The nitrates formed via nitric acid and involving NO formation had lower thermal stability than those formed through an NO2 disproportionation reaction

  • 20.
    Qinghua, Li
    et al.
    Luleå tekniska universitet.
    Boriana, Mihailova
    Bulgarian Academy of Sciences.
    Creaser, Derek
    Luleå tekniska universitet.
    Sterte, Johan
    Aging effects on the nucleation and crystallization kinetics of colloidal TPA-silicalite-12001In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 43, no 1, p. 51-59Article in journal (Refereed)
    Abstract [en]

    A direct experimental method, involving a two-stage varying-temperature synthesis, was utilized to investigate the effects of aging on the nucleation kinetics for the synthesis of nanosized TPA-silicalite-1 with various silica sources, including tetraethoxysilane (TEOS) and amorphous silica Ludox TM. For TEOS aging had only a mild influence on the nucleation and crystallization kinetics, whereas for Ludox TM dramatic changes occurred. After extended aging periods, the nucleation kinetics for syntheses with Ludox TM became similar to those for syntheses with TEOS, leading to increasing similarities in the properties of the products of the crystallization. Independent of aging time and silica source, the nucleation processes occurred over a substantial period of time, extending over the induction period, but were completed before crystal growth was detected. With increased aging, the nucleation period was gradually decreased and tended to be completed earlier in the induction period. Raman spectra revealed that with Ludox TM, aging enhanced the interaction between TPA+ and the silica species, leading to an increase in the concentration of precursor species for nucleation, which in turn accelerated the nucleation rate.

  • 21.
    Qinghua, Li
    et al.
    Luleå tekniska universitet.
    Creaser, Derek
    Luleå tekniska universitet.
    Sterte, Johan
    An investigation of the nucleation/crystallization kinetics of nanosized colloidal faujasite zeolites2002In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 14, no 3, p. 1319-1324Article in journal (Refereed)
    Abstract [en]

    two-stage varying-temperature technique was utilized to study the nucleation/crystallization kinetics of nanosized faujasite zeolites from clear solutions. At 100 C, the nucleation period of zeolite Y was determined to be about 6.5 days, which extended over almost the whole period of crystal growth. The crystallization kinetics of colloidal zeolite Y differed from those for another clear solution, colloidal zeolite system, namely, TPA-silicalite-1, where the nucleation and crystal growth were found to occur as separate processes. Despite the occurrence of simultaneous nucleation and crystal growth, the colloidal zeolite Y product had a crystal size distribution similar to that for TPA-silicalite-1. In addition, the influence of the growth-limiting nutrient (Na+) on the crystallization of zeolite Y was investigated. The sodium concentration in the synthesis solution could be controlled below a critical level to avoid the nucleation of zeolite A.

  • 22. Sterte, Johan
    et al.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Creaser, Derek
    Luleå tekniska universitet.
    Öhrman, Olov
    Wang, Zheng
    Luleå tekniska universitet.
    Lassinantti, Magdalena
    Li, Quinghua
    Luleå tekniska universitet.
    Jareman, Fredrik
    Luleå tekniska universitet.
    Application of the seed-film method for the preparation of structured molecular sieve catalysts2001In: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308, Vol. 69, no 1-4, p. 323-329Article in journal (Refereed)
    Abstract [en]

    The seed-film method has been applied for the preparation of various materials of potential interest as structured molecular sieve catalysts. The method has proven to be very flexible and allows for the reproducible preparation of a number of molecular sieve–substrate combinations as well as the control of the materials’ properties of importance in catalytic applications such as zeolite loading, film thickness, film density and crystal orientation. The preparation of thin molecular sieve films on ceramic foams, α-alumina pellets and porous alumina supports as well as various metal surfaces is described. The preparation of zoned coatings with a compositional gradient is also discussed.

  • 23. Wirawan, Kompiang
    et al.
    Creaser, Derek
    Lindmark, Jonas
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Bendiyasa, I Made
    Gadjah Mada University, Yogyakarta.
    Sediawan, Wahyudi Budi
    Gadjah Mada University, Yogyakarta.
    H2/CO2 permeation through a silicalite-1 composite membrane2011In: Journal of Membrane Science, ISSN 0376-7388, E-ISSN 1873-3123, Vol. 375, no 1-2, p. 313-322Article in journal (Refereed)
    Abstract [en]

    Single and binary H2/CO2 gas permeation was studied through a silicalite-1 composite membrane consisting of a thin zeolite film (< 1 μm) supported on α-alumina. The temperature range for permeation measurements was 25 to 300 °C. To determine the quality of the membrane, i.e the quantity and size of defects, n-hexane/helium permporometry measurements were performed. In general, single component fluxes decreased with increasing temperature whereas binary component fluxes showed a maximum value followed by a continuous decrease. A mass transport model that takes into account the surface diffusion and gas translational diffusion in the zeolite pores, Knudsen diffusion in defects, as well as viscous flow and Knudsen diffusion in the support material was developed to simulate the single and binary gas permeation measurements. Simulation results show that the surface diffusion was the dominant mass transport mechanism in the membrane. In addition, the transport resistance of the support material was not negligible and it was found to influence the permeation selectivity. The model adequately described the experimental results for both single and binary permeation. The model predictions indicated that a CO2/H2 separation factor exceeding 9.8 and a CO2 flux exceeding 4 mol/(m2·s) could be obtained at 0 °C and a feed pressure of 10 bar and atmospheric permeate pressure.

  • 24. Öhrman, Olov
    et al.
    Nordgren, U.
    Luleå tekniska universitet.
    Creaser, Derek
    Luleå tekniska universitet.
    Sterte, Johan
    Zeolite ZSM-5 coatings on inert packing materials2001In: Zeolites and mesoporous materials at the dawn of the 21st century: proceedings of the 13th International Zeolite Conference, Amsterdam: Elsevier, 2001, p. 292-Conference paper (Refereed)
1 - 24 of 24
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