Pillaring of different smectite members by chromium species (Cr-PILCs)

Abstract

Cr-pillared smectites by intercalation of OH–Cr species in montmorillonite, beidellite, nontronite and saponite smectite clays followed by heating at 450 °C in air or nitrogen atmosphere were prepared. The pillaring reagent containing OH–Cr species was obtained from chromium nitrate solutions by adding NaOH with OH/Cr=2 and hydrolyzed at 60 °C for one day. The samples were characterized by X-ray diffraction, by N 2 adsorption–desorption isotherms, by acidity measurement and by chemical analysis. The Cr pillared smectites prepared at 450 °C in nitrogen atmosphere showed interlayer spacing in the range of 13.8–18.8 Å. These values were a function of the type of smectite members. The micropore surface area, the micropore volume and the d(0 0 1) spacing after pillaring of different smectite members increased with the amount of chromium retentions. Cr-PILCs (pillared interlayered clays, PILC) showed Lewis (L) and Brönsted (B) acidity characteristics and the L/(L+B) ratio was higher in Cr-PILCs prepared from smectites with higher tetrahedral negative charge of the structure. The charges and the composition of the smectite structures influenced considerably the properties of the Cr-PILCs.