The role of H 2 in n-butane isomerization over Al-promoted sulfated zirconia catalyst

Abstract

C, H, N-elemental analyzer, and NH 3-TPD, FTIR, XPS and reactor system are used to investigate the function of hydrogen in n-butane isomerization over the Al-promoted (3 mol% as Al 2O 3) sulfated zirconia catalyst (Al/SZ). Findings show relatively stable Al/SZ catalyst activity at 250 °C with H 2 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 can be recovered about 70% when H 2 is admitted again. Conversely, catalytic activity is lower but more stable in the presence of H 2 than in that of N 2 at 150 °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 °C, but inhibits isobutane formation and cannot react with coke at 150 °C. Catalytic activity restoration is via the reaction between coke and adsorbed hydrogen on the Brønsted 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.