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

Cr-pillared smectites by intercalation of OH-Cr species in montmorillonite, beidellite, nontronite and saponite smectite clays followed by heating at 450 degreesC in air or nitrogen atmosphere were prepared. The pillaring rea gent containing OH-Cr species was obtained from chromium nitrate solutions by adding NaOH with OH/Cr = 2 and hydrolyzed at 60 degreesC for one day. Th e samples were characterized by X-ray diffraction, by N-2 adsorption-desorp tion isotherms, by acidity measurement and by chemical analysis. The Cr pil lared smectites prepared at 450 IC in nitrogen atmosphere showed interlayer spacing in the range of 13.8-18.8 Angstrom. These values were a function o f the type of smectite members. The micropore surface area, the micropore v olume and the d(001) spacing after pillaring of different smectite members increased with the amount of chromium retentions. Cr-PILCs (pillared interl ayered clays, PILC) showed Lewis (L) and Bronsted (B) acidity characteristi cs and the L/(L + B) ratio was higher in Cr-PILCs prepared from smectites w ith higher tetrahedral negative charge of the structure. The charges and th e composition of the smectite structures influenced considerably the proper ties of the Cr-PILCs. (C) 2001 Elsevier Science B.V. All rights reserved.