Preparation, characterization and surface acid catalytic activity of microporous clays pillared with Al1-xFexOy (x=0.00 to 1.00) oxidic species

Montmorillonite was pillared with mixed oxidic species of the form Al1-xFex Oy where x = 0.00, 0.05, 0.15, 0.25, 0.50, 0.75 and 100. The pillaring agen t was an alkaline solution of the corresponding quantities of metal nitrate s so as to obtain a final ratio (Al + Fe)/OH = 1:2. The specific surface ar ea (BET) of the samples dried at 500 degrees C was found to be 230 +/- 10 m (2) g(-1) for x = 0.00 - 0.50 and similar to 139 +/- 8 m(2) g(-1) for x = 0 .75-1.00. The XRD results obtained at low angles from samples oriented alon g the (001) axis showed gallery heights of the heated solids of 16-17 Angst rom for x = 0.00 - 0.50 and 9.9 - 9.8 Angstrom for x = 0.75 - 1.00. The aci dity of the samples, checked by TPD of NH3, varied from similar to 12 x 10( 17) sites m(-2) (x greater than or equal to 0.25) to similar to 9 x 10(17) sites m(-2) (x less than or equal to 0.75). The acid catalytic activity of the solids was checked using the isopropanol (IPA) decomposition as a probe reaction. The main products observed were propene (selectivity greater tha n or equal to 80%) and di-iso-propyl ether (DIPE) (selectivity less than or equal to 20%). The apparent activation energies for the TPA conversion wer e calculated, and the selectivity dependence on temperature was kinetically modelled. From this, a mechanism was derived to account for the reactions of one or two IPA molecules towards propene or DIPE, respectively, and the dependence of the selectivity on the Al/Fe ratio and the acidity of the sol ids. (C) 1999 Elsevier Science B.V. All rights reserved.