Shape selectivity in linear paraffins hydroconversion in 10-membered-ring pore zeolites

Pd/zeolite-catalyzed hydroconversion of n-hexadecane (n-C16) and n-heptane (n-C7) was studied for 10MR (ZSM-5, ZSM-22), 12MR (ZSM-12), and EMM-23 (21MR x 10MR) zeolites. The catalytic activity depended on the Bronsted acidity and the crystalline domain size. n-C16 hydroconversion benefited from short diffusion lengths in ZSM-5 nanosheets compared to bulk ZSM-5. In general, over-cracking is dominant in ZSM-5 with a cracked product distribution skewed to C4 products, to be explained by a snug fit of particular dibranched isomers at zeolite intersections. This effect is less pronounced for the 1D 10MR pores in ZSM-22, which lacks intersections. Although large pores in ZSM-12 offer relatively high activity, those in EMM-23 do not. Based on selectivity patterns, EMM-23 behaves like ZSM-5, probably because of the trilobe shape of its 21MR pores acting as 10MR pores. Only ZSM-12 offers operation in the ideal hydrocracking regime, in the sense of impediments neither by hydrogenation nor by diffusion. Faster intrazeolite diffusion of n-C-7 in comparison to n-C-16 leads to a higher yield of isomers for the nanostructured zeolites. Overall, the hydroconversion of the smaller alkane is more substantially impacted by variations in the crystalline zeolite domain size. (c) 2020 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

The hydroconversion of n-hexadecane and n-heptane catalyzed by Pd/zeolite is influenced by the Bronsted acidity and crystalline domain size. Smaller alkanes are more significantly impacted by variations in the zeolite domain size.