Surface properties and porous texture of montmorillonite-(Ce or Zr) phosphate cross-linked compounds

In this work, pore texture characteristics of a series of Ce(IV) or Zr(IV) montmorillonite phosphate cross-linked compounds obtained by precipitation of cerium or zirconium phosphate with dilute H₃PO₄ on the micelles of an aqueous montmorillonite suspension, previously submitted to ion-exchange processes to replace its exchange ions with Ce(IV) or Zr(IV), are studied. Surface areas and pore volumes of the different materials prepared are determined by N₂ adsorption at 77 K and mercury porosimetry techniques. Analysis of the N₂ adsorption isotherms by the t-De Boer and Dubinin-Radushkevich methods, revealed the presence of a certain degree of microporosity in all the materials studied. Moreover, analysis of the Hg intrusion data permitted to determine the contribution of the macro- and mesopores to the total surface area and pore volume of the prepared compounds. The results reveal a greater specific surface area for these compounds than for montmorillonite and the evolution of this parameter with thermal treatment is related to the nature and content of phosphate in the different samples. However, the changes recorded in the V_p and S/V_p parameters during the thermal process suggest that surface diffusion is the dominant transport mechanism in the sintering process.