THE ROLE OF SODIUM AND STRUCTURE ON THE CATALYTIC BEHAVIOR OF ALUMINA.1. ISOPROPANOL DEHYDRATION ACTIVITY

Three different transitional aluminas were doped with controlled and m easured amounts of Na and were tested for 2-propanol dehydration activ ity. These alumina samples were activated by heating at 773 K in situ before use. In order to examine the sites responsible for the reaction , simultaneous temperature-programmed desorption (TPD) and thermogravi metric analysis (TGA) measurements of 2-propanol were performed on the samples. A typical gamma-alumina sample adsorbed ca. 2 . 10(18) molec ules of 2-propanol per m(2). When 400 ppm (0.04 wt.-%) of Na was added to this sample, the reactivity fell by 75%. Since the Na level corres ponds to 0.07 . 10(18) atoms/m(2), this suggests that the active sites are much fewer in number than the number of adsorption sites. Besides affecting the active sites, Na also modifies the adsorption sites cau sing a fraction of the adsorbed 2-propanol to desorb before reaction i n the TPD experiment. The effect of added Na was contrasted with the e ffect of alumina form (gamma, delta and alpha). These alumina samples were also characterized by IR spectroscopy in a companion study (part II of this paper, Appl. Catal. A, 000 (1995) 000) where we found that the added Na impurities affected the hydroxyl groups and adsorbed pyri dine. This study provides a comprehensive picture of how Na impurities modify the catalytic behavior of transitional alumina.