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Clay Minerals (1991) 26, 49-60 PREPARATION OF POROUS MATERIALS BY CHEMICAL ACTIVATION OF THE LLANO VERMICULITE H. SUQUET, S. CHEVALIER, C. MARCILLY* AND D. BARTHOMEUF Laboratoire de Rgactivitd de Surface et Structure, URA 1106, Universitg P. et M. Curie, 4 Place Jussieu, 75252-Paris Cddex 05, and * lnstitut Fran~ais du Pdtrole, B P 311, 92506-Rueil-Malmaison, France (Received 1 March 1990; revised 12 July 1990) A B S T R A C T: A mild acid attack of the Llano vermiculite produces porous materials suitable for use as cracking catalysts and/or catalysts supports. After HCI attack at 80~ (1 M), the number of acid sites measured by the Hammett indicator method is ~0.50/nm 2, and the specific surfaces are 245 m2/g after calcination at 550~ (4 h), and 55 m2/g after steaming at 750~ (4 h). The performance of leached (1 M HCI) vermiculite has been compared with another hydrocarbon cracking catalyst- y-AI203. The leached vermiculite produces a definite higher conversion and higher C3, C4 and gasoline yields, but much lower coke production. By electron microscopy, infrared spectroscopy, X-ray powder diffraction and thermal analysis, it has been shown that the leached vermiculite samples are composed of more or less attacked layers retaining their original platy morphology, and non-crystalline hydrated silica. Chemical analyses indicate that octahedral cations are dissolved first. Since the 1973 petroleum crisis, catalytic cracking of heavy oil fractions has become financially important. As zeolites have been used to crack the small molecules (<8/k), scientific research is striving to obtain a suitable catalyst to pre-crack the heavier fractions (i. e. larger molecules). Such a solid would need to have a minimum shape selectivity while being very selective with respect to coke formation. It should also (i) have sufficient thermal and hydrothermal stability to withstand the conditions within a FCC (Fluid Catalytic Cracking) regenerator, and (ii) possess sufficient acid sites to ensure carbocation formation. The 2 : 1 phyllosilicates present acidic sites in the interlayer area but above 200~ the layers are dosed and the acidic sites inaccessible. To maintain the porosity of phyllosilicates at cracking temperatures they must be chemically activated, creating "holes" in layers. This method was extensively studied in the 1960s using montmorillonites (Rupert et al., 1987). We have applied this method to vermiculites, which are more thermally stable because the octahedral sheet is complete (the dehydroxylation temperature of the layers is 100~ higher than that for montmorillonites). From among the vermiculites, that from Llano has been chosen because of its low iron content (0.03% FeO) since according to some authors (Tichit et al., 1988), the iron gives rise to coke formation. EXPERIMENTAL Materiojs The Llano vermiculite was supplied by the CMS Source Clays Repository at the University of Missouri. The sample was formed by the surface weathering of phlogopite in a dolomitic and magnesitic marble (Clabaugh & Barnes, 1959). The crystals (more or less ?9 1991 The Mineralogical Society