Synthesis and catalytic evaluation of zoned MFI films

• Alumina and quartz supports were coated with well-defined precursor ZSM-5 films ranging from 350 nm to 2300 nm in thickness. The precursor samples were subsequently treated with hydrochloric acid and hydrothermally treated in a silicalite-1 synthesis solution in order to obtain zoned MFI films. A dense, but rougher, silicalite-1 film was formed on top of the smooth precursor ZSM-5 film after two hydrothermal treatments. Defects such as open grain boundaries and cracks were observed by SEM and in concert, mesopores were detected by gas adsorption in the precursor and zoned films. The mesopore volume per gram film increased after acid treatment and zoning, probably due to that a small fraction of the zeolite film dissolved in this process. As expected, the aluminum concentration at the surface of the un-calcined zoned film was lower compared to that at the surface of the calcined precursor ZSM-5 film. However, after calcination of the zoned film, the concentration of aluminum at the surface increased, probably due to aluminum migration from the precursor film to the surface of the zoned film during calcination. The aluminum concentration at the surface of the calcined zoned film was even higher than at the surface of the calcined precursor ZSM-5 film. Consequently, the triisopropylbenzene cracking rate constant did not decrease as expected after zoning, probably due to the increased amount of defects and/or aluminum migration. The p-xylene diffusivity increased after zoning, probably due to the formation of defects, whereas the xylene isomerization rate constants were unaffected, as expected.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Kemiteknik -- Kemiska processer (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering -- Chemical Process Engineering (hsv//eng)

Nyckelord

Chemical Technology

Kemisk teknologi

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