NEOPENTANE CRACKING CATALYZED BY IRON-PROMOTED AND MANGANESE-PROMOTEDSULFATED ZIRCONIA

Cracking of neopentane was catalyzed by a sulfated oxide of zirconium promoted with iron and manganese. Reaction at 300-450 degrees C, atmos pheric pressure, and neopentane partial pressures of 0.00025-0.005 bar gave methane as the principal product, along with C-2 and C-3 hydroca rbons, butenes, and coke. The order of reaction in neopentane was dete rmined to be 1, consistent with a monomolecular reaction mechanism and with the formation of methane and t-butyl cations; the latter was pre sumably converted into several products, including only little isobuty lene. At 450 degrees C and a neopentane partial pressure of 0.005 bar, the rate of cracking at 5 min onstream was 5 x 10(-8) mol/(g of catal yst s). Under the same conditions, the rates observed for unpromoted s ulfated zirconia and USY zeolite were 3 x 10(-8) and 6 x 10(-9) mol/(g of catalyst s), respectively. The observation that the promoted sulfa ted zirconia is not much more active than the other catalysts is contr asted to published results showing that the former catalyst is more th an two orders of magnitude more active than the others for n-butane is omerization at temperatures<100 degrees C. The results raise a questio n about whether the superacidity attributed to sulfated zirconia as a low-temperature butane isomerization catalyst pertains at the high tem peratures of cracking.