HYDROGEN EFFECT ON N-BUTANE ISOMERIZATION OVER SULFATED ZIRCONIA-BASED CATALYSTS

Iron- and manganese-promoted sulfated zirconia (SFMZ) has been tested as an n-butane isomerization catalyst in the temperature range of 35 t o 180 degrees C, The catalytic activity exhibits an induction period w hose length is dependent on the reaction conditions, The presence of H -2 in the feed stream strongly suppresses n-butane conversion over unp romoted sulfated zirconia (SZ) and over Pt-containing SFMZ (PtSFMZ). H owever, hydrogen had no effect on n-butane isomerization over SFMZ. Th ese findings were interpreted on the basis of a bimolecular mechanism where unsaturated intermediates (carbenium ions and/or butene) are for med during the break-in period, The role of promoters (Fe and Mn) is n ot only facilitating the formation of hydrogen-deficient intermediates and their accumulation on the catalyst surface, but also enhancing th eir stability. The negative effect of hydrogen over PtSFMZ is attribut ed to the occurrence of atomic hydrogen via the dissociative adsorptio n Of H-2 on Pt. (C) 1997 Academic Press.