Alkane isomerization over sulfated zirconia solid acid system

Abstract

Summary Sulfated zirconia (SZ) and its modified versions attract great interest in recent years, because of their promising potential in n‐alkane isomerization. The oxidative and protonation routes are active and interactional in n‐alkane activation over SZ catalysts. The bimolecular reaction becomes dominant with increasing the density of active sites on SZ surface and decreasing the carbon chain of feed. Pentane and hexane are mainly isomerized by protonated cyclopropane mechanism, while which is thermodynamically unflavored for n‐butane isomerization. The deactivation of SZ catalysts is primarily caused by the loss of superacidity and oxidizing ability, resulted from the structure changes of sulfate species. Several strategies for improving the activity of SZ are reviewed. The intrinsic structure‐reactivity relationship of SZ catalysts in alkane isomerization is updated to illuminate the prerequisite for the highly active catalysts and the mechanism of active sites formation. The applications of Pt/SZ in fixed‐bed and unmodified SZ in circulating fluidizing bed in light alkanes isomerization are compared with the conventional technologies based on the chlorinated alumina catalysts. Finally, the future study of SZ catalysts is outlooked from the academic investigations to the industrial applications.

Butane Isomerization as a Diagnostic Tool in the Rational Design of Solid Acid Catalysts

“…The carbenium intermediates are then neutralized by hydrogen transfer from other species, to form neutral products. These computational findings showed excellent agreement with experimental values, confirming this mechanism [19,31]. [19,31].…”

“…Currently there are over 85 Butamer plants operating worldwide, making it the primary butane isomerization process [16]. To date a range of commercial processes exist, typically focussing on either chlorinated alumina or sulfated zirconia catalysts (Table 1) [17][18][19][20].…”

“…Comparing commercial butane isomerization processes. Adapted from [19] and [21][22][23]. This list is by no means exhaustive, with the pool of companies developing their own isomerization catalysts constantly increasing, including Axens (ATIS-1L), Shell (Hysomer) and Clariant (Hysopar 6000) [8].…”

“…Initially it was believed that this carbenium ion then formed a methyl-cyclopropane intermediate, as observed in pentane and hexane isomerization. However, it has since been shown that such a species is actually a transition state, that leads to carbon scrambling, and not isobutane [19,31]. Instead a methyl shift may occur, resulting in a tertiary isobutyl carbenium ion (Figure 3).…”

“…The method by which the metal is loaded onto the catalyst has been seen to affect the activity of the catalyst. A comparison of ion exchange and impregnation methods of Pd/H-ZSM-5 shows greater selectivity when the Pd is loaded by ion exchange and when treated with a strong acid to increase acid site density [19]. The choice of dopant precursor can also influence the systems reactivity.…”