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  • 1.
    Grahn, Mattias
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Faisal, Abrar
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik. Department of Chemical Engineering, COMSATS University Islamabad, Lahore Campus, Lahore, Pakistan.
    Öhrman, Olov G.W
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik. RISE ETC - Energy Technology Center, SE-941 28 Piteå, Sweden.
    Zhou, Ming
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Signorile, Matteo
    Department of Chemistry, NIS and INSTM Reference Centre, Università di Torino, Torino, Italy.
    Crocellà, Valentina
    Department of Chemistry, NIS and INSTM Reference Centre, Università di Torino, Torino, Italy.
    Nabavi, Mohammad Sadegh
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Hedlund, Jonas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Small ZSM-5 crystals with low defect density as an effective catalyst for conversion of methanol to hydrocarbons2019Inngår i: Catalysis Today, ISSN 0920-5861, E-ISSN 1873-4308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work presents the synthesis of nearly defect-free ZSM-5 nanosized crystals, prepared in fluoride medium by seeding with silicalite-1. This material was carefully characterized and its catalytic performances in the methanol to hydrocarbons (MTH) reaction were assessed. Such fluoride-based material was compared to a reference ZSM-5, produced through a conventional alkaline synthesis but from the same seeding. Despite both the materials show closely identical morphology and they have a comparable acid site population, the catalyst prepared using the fluoride route showed significantly longer lifetime in MTH compared to the catalyst prepared using conventional synthesis at high pH. The slower deactivation for the samples prepared using the fluoride route was ascribed, thanks to a thorough in situ IR spectroscopy study, to its lower density of internal defects. According to the UV-Raman characterization of coke on the spent catalyst, the fluoride-based ZSM-5 catalyst produces less molecular coke species, most probably because of the absence of enlarged cavities/channels as due to the presence of internal defects. On the basis of these observations, the deactivation mechanism in the ZSM-5 synthesized by fluoride medium could be mostly related to the deposition of an external layer of bulk coke, whereas in the alkali-synthesized catalyst an additional effect from molecular coke accumulating within the porous network accelerates the deactivation process.

  • 2.
    Korelskiy, Danil
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Ye, Pengcheng
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Nabavi, Mohammad Sadegh
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Hedlund, Jonas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Selective blocking of grain boundary defects in high-flux zeolite membranes by cokin2017Inngår i: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, nr 16, s. 7295-7299Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Commercial application of zeolite membranes has been hindered by the challenge of preparing defect-free membranes. Herein, we report a facile method able to selectively plug grain boundary defects in high-flux MFI zeolite membranes by coking of iso-propanol at 350 °C. After modification, the permeance via defects was reduced by 70%, whereas that via zeolite pores was reduced by only 10%.

  • 3.
    Nabavi, Mohammad Sadegh
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Defects in Zeolite Catalysts and Membranes2020Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    ZSM-5 is one of the most well-known zeolites. It has been synthesized for many different applications, including as catalyst for catalytic reactions and as a membrane in separation processes.  The main goal of this thesis is to investigate and characterize the defects in crystal and film growth of ZSM-5 for modification purposes.

    Primarily, ZSM-5 crystals with carefully controlled thickness were synthesized in fluoride and hydroxide media. These synthesized catalysts were then characterized and the two synthesis routes were compared with each other in terms of stability. Then, in the synthesized catalysts, the role of defects during reaction was investigated. Furthermore, the growth of ZSM-5 nanocrystals and subsequent film formation was investigated to better understand how particles formed in synthesis solution (a hydrolyzed mixture of H2O-TEOS-TPAOH), followed by how these crystals interact to form a zeolite film. Finally, pre- and post-production modification of ZSM-5 and PHI membranes was investigated. Since, the roughness surface of the support could play a crucial role in having an even film, it was done as a pre-treatment technique for membrane synthesis. Additionally, a technique was developed in an attempt to plug the defects of grain boundaries to increase the membrane performance.

     

  • 4.
    Nabavi, Mohammad Sadegh
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Zhou, Ming
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Mouzon, Johanne
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Grahn, Mattias
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Hedlund, Jonas
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Kemiteknik.
    Stability of colloidal ZSM-5 catalysts synthesized in fluoride and hydroxide media2019Inngår i: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 278, s. 167-174Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    ZSM-5 zeolite crystals with carefully controlled thicknesses in the range 20–110 nm, i.e. in the colloidal domain, were synthesized in fluoride and hydroxide media. The crystals were treated in steam at high temperature to evaluate the stability and evaluated by SEM, XRD, NMR and NH3-TPD. The results showed that the framework of crystals synthesized in fluoride media was more stable than the framework of crystals synthesized in hydroxide media. This should be an effect of lower concentration of structural defects and silanol groups in the former zeolites as reported by other groups. However, independently of the synthesis conditions, all crystals dealuminated rapidly when treated with steam at the conditions investigated in the present work.

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