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 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.