C, H, N-elemental analyzer. and NH3-TPD, FTIR, XPS and reactor system are used to investigate the function of hydrogen in n-butane isomerization over the N-promoted (3 mol% as Al2O3) sulfated zirconia catalyst (Al/SZ). Findings show relatively stable Al/SZ catalyst activity at 250 degrees C with 1-12 introduction; however it decreases very quickly when N-2 replaces H-2. Deactivation is attributed to coke formation. The main components of coke are graphite and polymeric hydrocarbons. Activity call be recovered about 70% when H-2 is admitted again. Conversely, catalytic activity is lower but more stable in the presence of H-2 (hall ill that of N-2 at 150 degrees C. Findings also show that activity cannot be restored if n-butane conversion is down to zero (i.e., the catalyst is completely deactivated). This study infers that H-2 reacts with coke at 250 degrees C. but inhibits isobutane formation and cannot react with coke at 150 degrees C. Catalytic activity restoration is via the reaction between coke and adsorbed hydrogen oil the Bronsted acid sites. Although many researchers report that decayed Sulfated zirconia regenerates by burning coke off with oxygen, this work finds that the fouled catalyst regenerates, though not completely, by hydrogen, provided it is not fully deactivated. (C) 2009 Elsevier B.V. All rights reserved.