Effect of alumina support on the performance of Pt-Sn-K/γ-Al₂O₃ catalyst in the dehydrogenation of isobutane

Alumina supports were synthesized by hydrochloric acid reflux and ammonia precipitation methods; after that the Pt-Sn-K/γ-Al₂O₃ catalysts were prepared by complex impregnation method under vacuum with alumina of different sources as the supports. The catalysts were characterized by N₂ physisorption, CO pulse chemisorption, H₂ temperature-programmed reduction, NH₃ temperature-programmed desorption and thermogravimetric analysis; the effect of the alumina support on the performance of Pt-Sn-K/γ-Al₂O₃ catalysts in the dehydrogenation of isobutane was investigated. Compared with the catalyst supported on Al₂O₃ from hydrochloric acid reflux, the catalyst supported on the Al₂O₃ from ammonia precipitation is provided with smaller platinum particle size and weaker acidic distribution, and then exhibits higher activity and selectivity to isobutene in isobutane dehydrogenation. Moreover, the catalyst with Al₂O₃ synthesized by ammonia precipitation as the support exhibits better resistance against coke deposition and the coke deposited also has a lower degree of graphitization, which endues the catalyst with better stability. During a long term test of 14 d over the catalyst with Al₂O₃ synthesized by ammonia precipitation as the support, the conversion of isobutane is initially 56.67% and then decreased to 34.71% after 14 d; meanwhile, the initial selectivity to isobutene is 80% and it remains approximate 94% after 7 d.