PREPARATION AND CHARACTERIZATION OF THE PORE STRUCTURE AND ACIDITY OFHYDROXY-CR SMECTITES

Hydroxy-chromium smectites were prepared using hydroxy-chromium soluti ons with a OH/Cr content of about 1 and 2 aged for six weeks at 313 K. To study the thermal stability and oxidation resistance of hydroxy-ch romium, interlayers materials were calcined at 473 K and 573 K in air. The extent of intercalation was evaluated using X-ray diffraction. Th e structural parameters such as surface areas, micropore volumes, and mesopore size distributions were evaluated from sorption of nitrogen. The surface chemistry was described in terms of the pK(a) distribution s calculated from potentiometric titration data using the SAIEUS proce dure. The results obtained demonstrate that the properties of final ma terials depend on the OH/Cr content in the intercalating solution. Whe n OH/Cr was about 1 the materials with a developed surface area and mi croporosity were obtained. The thermal stability and oxidation resista nce of hydroxy-Cr smectites differ significantly. The sample obtained using OH/Cr about 1 is more oxidation resistant compared to this obtai ned with OH/Cr about 2. The differences in the observed behavior are l ikely related to the orientation and organization of hydroxy-chromium oligomers within the interlayer space of smectite.