Characterization of sulfur on Pt-alkali metal/Al2O3 catalysts treated with H2S by a temperature-programmed reaction using deuterium and its role in the dehydrogenation of isobutane

Article abstract of DOI:10.1246/bcsj.73.759

Increased demand for isobutylene, used for the production of MTBE, has generated interest in the catalytic conversion of isobutane to isobutylene. Isobutylene is predominantly obtained from C4 fractions of ethylene plants or FCC units, but since the supply of isobutylene from these sources depends on the demand for the primary products, other processes have been studied. In the dehydrogenation of isobutane to isobutylene on Pt/Al₂O₃ catalyst, the isobutylene yield is lowered due to the occurrence of by-reactions, e.g., coking, cracking, and skeletal isomerization. A study of enhancing the selective dehydrogenation of isobutylene by inhibiting these by-reactions showed that the isobutane dehydrogenation selectivity on reduced Pt-Li₂O/Al₂O₃, Pt-Na₂O/Al₂O₃, and Pt-K₂O/Al₂O₃ catalysts increased with treatment with H₂S. The orders of selectivity were Pt-Na₂O/Al₂O₃ > Pt-K₂O/Al₂O₃ > Pt-Li₂O/Al₂O₃. The optimum reaction temperature for increasing the selectivity was 773 K, because a cracking reaction preferentially took place at temperatures above the optimum. Most of the reversibly adsorbed sulfur was HS^- and the reversibly adsorbed sulfur bridged between the PtS_ir and the Na₂S_ir. The factor that increased the selectivity would correlate with the bridging sulfur species and interact with the hydrogen in the adsorbed isobutane.