Light alkane isomerization with sulfated zirconia - From mechanistic insight to new catalysts

An experimental study was made of the isomerization of n-butane on sulfated zirconia. Butene species were the main intermediates during n-butane isomerization on sulfated zirconia. The active sites were formed by labile sulfate species formed by sulfur trioxide sulfation on zirconia preheated at 673 K. The discussion covers introduction; experimental; results (evidence for butene formation by temperature programmed desorption of n-butane; determination of water formed by in situ IR spectroscopy; the key component for the active sites of sulfated zirconia: labile sulfate species); and conclusions. N-butane was isomerized in an 8 mm dia quartz microtube reactor at 1 atm. The reactor was filled with 0.2 g, 355-710 μm zirconia pellets, activated in situ at 673 K for 2 hr in helium flow of 10 mL/min, then cooled to 373 K. Then the reactant mixture of 5% n-butane in helium at a total flow rate of 20 mL/min passed through the catalyst bed. Prior to the reaction, the Messer 99.5% n-butane passed through an olefin trap containing 20 g activated HY zeolite to remove olefin impurities and traces of water before it was mixed with helium. There was no detectable trace of butenes in the reactant mixture after purification. The reaction products were analyzed by GC-FID. At steady state, butenes were not detected in the reaction products such that TPD was used to give direct evidence of alkenes formed by suppressing subsequent reactions of the reactive alkenes.