ISOMERIZATION OF N-BUTENE TO ISOBUTENE BY FERRIERITE AND MODIFIED FERRIERITE CATALYSTS

n-Butene was isomerized to isobutene over fresh and used ferrierite ca talysts. Activity and selectivity for skeletal isomerization and bipro duct formation were measured and changes following extended use were r elated to changes in ferrierite's aluminum distribution. In its fresh form, ferrierite exhibited high activity for n-butene conversion and h igh selectivity for non-C-4 products with reduced selectivity for isob utene. With time on feed, side-product formation decreased and isobute ne yields reached a maximum, then declined with further time on feed. After several run/regeneration cycles, a marked drop-off in the maximu m achievable isobutene yield was observed and selectivity for non-C-4 products increased. MAS-NMR of the deactivated catalyst showed a decre ase in zeolitic, tetrahedral aluminum and an increase in octahedral al uminum. In order to understand changes occurring following extended us e, ferrierite powders were modified by steam and by steam plus acid-wa sh treatments. A steamed ferrierite catalyst exhibited lower initial n -butene conversion; however, selectivity to non-C, products increased relative to that of the fresh catalyst. XRD peak areas and gravimetric adsorption data indicated excellent crystallinity retention following steam treatment; XRD unit cell determination, and FTIR and NMR analys is suggested significant framework dealumination and the creation of a nonframework aluminum phase. TEM suggested that at least a portion of this phase exists in mesopores created by steam treatment. A steamed- acid-washed ferrierite catalyst also exhibited reduced initial n-buten e conversion but high isobutene selectivity throughout the run. Biprod uct formation was greatly reduced. Characterization indicated that aci d-wash treatment after steaming had no effect on framework aluminum bu t partially reduced the amount of nonframework aluminum. Steamed-acid- washed ferrierite was much less sensitive to subsequent hydrothermal t reatments than was the starting ferrierite. The study suggests a catal ytic role for nonframework alumina, generated upon extended use of unm odified ferrierite and present in steamed ferrierite. Catalytically ac tive, nonframework sites contribute to the production of non-C-4 produ cts and reduced isobutene selectivity. Steamed-acid-washed ferrierite with the active nonframework phase removed exhibits excellent isobuten e selectivity and catalytic stability. (C) 1995 Academic Press, Inc.