Controllably tailoring external surface sites of nanosheet HZSM-5 for maximizing light olefins in catalytic cracking of n-decane

Abstract

A series of triphenylethoxysilane (TPEOS)-modified nanosheet HZSM-5 catalysts (ZN-x, x = 4%, 8% and 16%, mass) were synthesized by chemical liquid deposition to selectively change external acidity distributions. TPEOS modification was found to passivate some external Brønsted and Lewis acid sites by 37.8%, in which Brønsted acid sites (BAS) were found more easily sacrificed by breaking the surface AlO bond of bridging hydroxyl groups and forming SiOSi bonds. The selectivity of ZN-8 catalyst for light olefins (ethylene, propylene and butene) in n-decane catalytic cracking is up to 26% (450 °C, WHSV = 10.95 h−1), which is ca. 78% higher than that of parent one. The better performance was attributed to the appropriate external acid density in ZN-8, which inhibits bimolecular hydrogen transfer reaction of light olefins on the adjacent acid sites, resulting in more olefins, few coke precursors and thus an excellent catalytic stability.