Effect of the acid-activated clays on the properties of porous clay heterostructures

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 mesostructured 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 mesoporosity of the raw clay mineral. We have studied the effect of the type of clay minerals on the properties of porous acidactivated 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 synthesis of PACHs was achieved and characterized by powder x-ray diffraction, nitrogen adsorption-desorption and acidity using cyclohexylamine as probe molecule. A short order in the structure, as revealed by the powder x-ray diffraction of PACH materials was observed, with higher surface areas, pore volumes and acidity for some clays. These properties 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.