JNGC 15-2006-247

The Effect of Sulfate Ion on the Isomerization of
n-Butane to iso-Butane

The effect of sulfate ion (SO%-) loading on the properties of Pt/SO:–ZrOz and on the
catalytic isomerization of n-butane to iso-butane was studied. The catalyst was prepared by impregnation
of Zr(0H)A with H2S04 and platinum solution followed by calcination at 600 “C. Ammonia TPD and
FT-IR were used to confirm the distribution of acid sites and the structure of the sulfate species. Nitrogen
physisorption and X-ray diffraction were used to confirm the physical structures of Pt/SO:–ZrO2. XRD
pattern showed that the presence of sulfate ion stabilized the metastable tetragonal phase of zirconia
and hindered the transition of amorphous phase to monoclinic phase of zirconia. Ammonia TPD profiles
indicated the distributions of weak and medium acid sites observed on 0.1 N and 1.0 N sulfate in the
loaded catalysts. The addition of 2.0 N and 4.0 N sulfate ion generated strong acid site and decreased
the weak and medium acid sites. However, the XRD results and the specific surface area of the catalysts
indicated that the excessive amount of sulfate ion collapsed the structure of the catalyst. The catalysts
showed high activity and stability for isomerization of n-butane to iso-butane at 200 “C under hydrogen
atmosphere. The conversion of n-butane to iso-butane per specific surface area of the catalyst increased
with the increasing amount of sulfate ion owing to the existence of the bidentate sulfate and/or polynucleic
sulfate species ((ZrO)zSOz), which acts as an active site for the isomerization.