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n-HEPTANE HYDROISOMERIZATION OVER BIFUNCTIONAL ZEOLITE CATALYSTS
[Thesis]. Manchester, UK: The University of Manchester; 2012.
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Abstract
Isomerization is an industrially important process which involves converting less desirable n-alkanes into more desirable iso-alkanes. Increased iso-alkanes are preferred in gasoline to increase the octane number and to help meet the demand for more efficient automotive engines. Bifunctional catalysts containing noble metals such as Pt on USY zeolites has been widely used in the petroleum refining for the isomerization process.This research was carried out to study the n-heptane hydroisomerization over bifunctional monometallic (Ni or Pt) and bimetallic (Pt-Ni) catalysts supported on a commercial CBV-712 zeolite. Catalysts were prepared by ion exchange and competitive ion exchange in order to determine any positive catalytic effect of Pt and Ni over 1% Pt-USY. Five metal-loaded CBV-712 USY zeolite catalysts, with varying levels of both metals (Pt and Ni), were first characterized with ICP-OES, XRD, SEM and TEM. After in-situ activation, all catalysts were tested for the hydroisomerization of n-heptane co-fed with hydrogen. The liquid and gas products were analyzed using GC-FID and GC-MS, and the coke content on the catalyst was determined using TGA.For short times-on-stream, the Pt-Ni catalysts were more active than the Pt catalysts as described in the literature. However, the bi-metallic catalysts deactivated to different degrees dependent on the method of ion exchange used.In addition, the results tended to indicate that after longer periods-on-stream, the bimetallic tended to behave similar to the 1 wt% Pt only. However, the 1 wt% Pt 2 wt% Ni remained more active and appeared stable even up to 6000 minutes-on-stream. This is the first time these results are reported in the literature. Another finding in this dissertation indicates the control of pH throughout the ion exchange procedure is essential as the resultant metal cluster size impacts on the catalytic performance and stability.