J Porous Mater (2006) 13: 319–324 DOI 10.1007/s10934-006-8024-3 Effect of the acid-activated clays on the properties of porous clay heterostructures Fethi Kooli · Png Cheng Hian · Quek Weirong · Solhe F. Alshahateet · Fengxi Chen C  Springer Science + Business Media, LLC 2006 Abstract Porous clay heterostructures (PCHs) are quite a new class of solid acids, and exhibited pore sizes in the rarely observed supermicropore to small mesopore region. They are formed by the surfactant-directed assembly of mesostruc- tured silica within the two dimensional galleries of smectite layered silicates. The acid activation of the smectite clay was an effective way to improve the acidity and the mesoporos- ity of the raw clay mineral. We have studied the effect of the type of clay minerals on the properties of porous acid- activated clay heterostructures (PACHs). Three different raw clays with different cation exchange capacities were selected and acid-activated at an acid/clay ratio of 0.2 (w/w). The syn- thesis of PACHs was achieved and characterized by powder x-ray diffraction, nitrogen adsorption-desorption and acid- ity using cyclohexylamine as probe molecule. A short order in the structure, as revealed by the powder x-ray diffrac- tion of PACH materials was observed, with higher surface areas, pore volumes and acidity for some clays. These prop- erties were not enhanced as we expected, and compared to the PCHs, indicating that the origin or type of clay affects the final properties of the derived materials. By using a soft extraction of the surfactants via chemical way, the stability and the properties of PCH and PACH materials were not improved except for one type of clay. Keywords Montmorillonites . Acid-activated clays . Porous clay heterostructures . Mesoporous materials . Acidity F. Kooli () . P.C. Hian . Q. Weirong . S.F. Alshahateet . F. Chen Institute of Chemical and Engineering Sciences (ICES), 1 Pesek Road, Jurong Island, Singapore 627833 e-mail: fethi kooli@ices.a-star.edu.sg 1. Introduction Pillared clay minerals have been widely studied as porous ad- sorbents and catalysts [1]. The pore sizes of pillared clays fall into micropore size domain, having diameters below 2 nm. The size of the pores depends on the nature of the pillar- ing species and the host clay minerals [2, 3]. The discovery of porous clay hetersotructures (PCHs) has transcended the traditional pore size limitations of pillared clays, leading to materials with uniform pore diameters in the supermicrop- ore to mesopore range (1.5 to 3 nm) [4]. Porous clay het- erostructures are prepared in the first stage, by the expansion of the silicate layers of clay minerals with a long-chained quaternary ammonium cations (usually Q + = cetyltrimethy- lammonium, C16TMA + ) via cation exchange reaction. Neu- tral amine (C n H 2n+1 NH 2 ) molecules are then intercalated along with silica species, which leads to self-assembly of the silica into porous network within the interlayer region [4]. The assembly process is analogous to the surfactant-directed assembly of mesoporous molecular sieves [5], except that the framework silica is constructed in the two-dimentional gallery of the clay mineral, rather than in three dimensions. The surfactants can be removed from the as-synthesized PCH by calcination, producing a stable clay mesoporous silica hy- brid with porosity characteristics similar to those of meso- porous molecular sieves. The pore size characteristics of the PCHs make them potential catalysts for size selective trans- formations of molecules with big diameters, or adsorbents for large organic molecules [6]. The acidity of the PCHs could be tuned and related to the layered host of PCH [4, 7–13]. It is also possible to improve the acidic properties of PCH ma- terials through post synthesis alumination reactions similar to those developed for MCM-41 [11, 15]. The montmorillonite clay is characterized by one Al 3+ octahedral sheets sandwiched between two Si 4+ tetrahedral Springer