The selectivity changes in 1-hexene isomerization and its relation to acid properties of Pd/SAPO-11, SAPO-11, HZSM-5, and H-mordenite catalysts

Abstract

The activity and selectivity patterns for l-hexene isomer~'zation have been compared in the temperature range of 150-450~ fo) four different kinds of acidic zeolites (H-mordenite, HZSM-5, SAPO- 11 and PdtSAPO-I 1) differing both ir acid properties and geometric structure. At lower reaction temperatures (150-175~ the predominant reaction pathway was double bond shift(DBS) and was not influenced by the type of catalyst. At higher temperatures significant shifts in selectivity were observed from DBS to cracking (C) or skeletal rearrangement (SR) depending on the type of catalyst. Temperature programmed desorption {TPD) patterns of chemisorbed NH3 were also determined. Three different peaks were found for the most of TPD patterns. The first peak might be associated with Lewis acid- site, and the other two peaks at higher temperatures might be associated with Br6nsted acid-sites. It was found that significant loss of strong Br6nsted acidity upon Pd loading on SAPO-I 1. A selectivity correlation at 350~ showed strong dependence of DBS and cracking on total acidity. The reaction seems well suited for in- vestigation of the interrelation between pore st)ucture and surface acidity in terms of these selectivity factors.