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macrostructure, high porosity and low thermal expansion are used as supports in automotive catalytic converters and as diesel particulate filters (DPF) [16, 17]. Monolith substrates may be wash-coated, dip-coated, slip-coated, slurry-coated or extruded directly into catalytic bodies using appropriate materials [18, 19]. Due to the difficulty in washcoating the zeolite, a binder material is needed, which causes a reduction in the accessible surface area of the zeolite coating and increases the diffusion resistance of the adsorbing species. Due to surface tension effects of the washcoat during manufacturing, more material is deposited at the corners of the monolith channels, consequently increasing the diffusion path of the adsorbing species [18]. However, the performance of a zeolite coating is dependent on its morphology. A perfect, smooth film without intercrystalline pores will have other transport properties than a coating comprised of a multilayer of crystals with intercrystalline porosity. For well defined zeolite films, the mass transfer resistance can be controlled by varying the film thickness. This was demonstrated recently by our group [20], where thin ZSM-5 zeolite films without binder material were grown on 400 cells per square inch (cpsi) cordierite monoliths by first depositing a monolayer of colloidal zeolite seed crystals on the monoliths and then growing the crystals to thin films. The catalytic activity of the films was subsequently evaluated by p- xylene isomerisation, and the effect of film thickness on mass transfer was clearly demonstrated. As opposed to washcoated monoliths, these films had an even thickness i.e. no effects of surface tension in the corners. Growth of zeolite films without binder material on ceramic cordierite supports was previously also reported by Zamaro et al. [46] (mordenite) and our group [30] (faujasite). In another work, the adsorption and diffusion of CO2 in a carbon monolith adsorbent were studied with the Zero Length Column (ZLC) method by Brandani et al. [21]. The ZLC data showed that the dispersion in the monolith was controlled by mass transfer resistance rather than axial mixing. Zeolite monoliths consisting of 5A zeolite and Na-bentonite with square lattice channels and a wall thickness of 0.98 mm were prepared by Li et al. [14, 19, 22]. The 64PDF Image | Structured Zeolite Adsorbents for PSA Applications
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