氧化铝载体对Pt-Sn-K/γ-Al2O3催化剂上异丁烷脱氢性能的影响

Effect of alumina support on the performance of Pt-Sn-K /γ-Al_2O_3 catalyst in the dehydrogenation of isobutane

采用盐酸回流法和氨水沉淀法合成了氧化铝载体,并通过络合真空浸渍法制备了不同来源氧化铝负载的Pt-Sn-K/γ-Al2O3催化剂。利用N2物理吸附、CO脉冲吸附、H2程序升温还原、NH3程序升温脱附、热重等手段对Pt-Sn-K/γ-Al2O3催化剂进行了表征,以异丁烷脱氢为探针反应研究了氧化铝载体对该催化剂脱氢性能的影响。结果表明,与由盐酸回流法合成的载体制备的催化剂相比,采用氨水沉淀法合成的氧化铝载体制备的Pt-Sn-K/γ-Al2O3催化剂表面具有较小的Pt颗粒和较弱的酸性分布,其脱氢活性及异丁烯选择性更优。14 d的连续运行数据显示,由氨水沉淀合成的载体制备的催化剂,其抗积炭能力更强,反应后催化剂的积炭石墨化程度更低,因而具有更好的稳定性;在该催化剂上,异丁烷初始转化率为56.67%,14 d后仍能达到34.71%,异丁烯初始选择性为80%,7 d后维持在94%左右。

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.