Surface properties and cracking activity of delaminated clay catalysts

Abstract

Delaminated clays are solid supports and catalysts characterized by a house-of-card like structure containing, in addition to micropores of the type found in zeolites and pillared clays, mesopores and macropores characteristic of mixed oxides, aluminas and silicas. Electron microscopy results have indicated that only short-range (3 to about 15 units) face-to-face stacking of the silicate layer occurs. These aggregates are believed to contain pillared clay-like microporosity and are held together by cross-linking particles forming a house-of-cards structure containing regions of macroporosity in which large molecules like perfluorotributylamine can be sorbed. Particles less than ≈ 100 nm in size and having lath-shaped morphology have been found to facilitate the preparation of delaminated clay catalysts. Delaminated clays prepared by reacting a synthetic hectorite (Laponite B) with polyoxocations of aluminium are, after a mild heat pretreatment, somewhat less active than pillared clay catalysts, but exhibit greater selectivity to gasoline, light cycle oil (LCGO) and coke make. The improved coke selectivity is probably due to the weaker acidity and the macroporosity of the catalyst which facilitate the desorption of aromatics which otherwise would be retained (occluded) as coke. The lack of Fe 2O 3 impurities is believed to be responsible for the gasoline advantage exhibited by the delaminated clay catalyst. Delaminated clays containing Al 2O 3-clusters are stable to 600 °C in air; however, in the presence of steam their stability is significantly reduced. Therefore, like pillared clays, delaminated clays do not have the hydrothermal stability of zeolite-containing fluid cracking catalysts. However, their thermal stability and macroporous structure could be particularly useful in the preparation of hydrotreating catalysts for the upgrading of heavy oil to useful products.