还原温度对Ir/ZrO_2催化剂上巴豆醛选择性加氢的影响

Effects of Reduction Temperature on Selective Hydrogenation of Crotonaldehyde over Ir/ZrO_2 Catalyst

采用浸渍法制备了负载型Ir/ZrO2催化剂,详细考察了H2还原温度对Ir/ZrO2催化剂上气相巴豆醛选择性加氢反应性能的影响.结果表明,随着还原温度的升高,Ir/ZrO2催化剂上巴豆醛转化率和巴豆醇选择性均先升后降.400°C下还原时,Ir/ZrO2催化剂性能最佳,巴豆醛转化率和巴豆醇选择性分别达32.2%和74.3%.X射线光电子能谱结果表明,催化剂表面系Ir0和Ir3+共存,且随着还原温度的升高,Ir0的比例逐渐增加,至600oC时,表面Ir物种大部分以Ir0存在.NH3程序升温脱附结果表明,随着还原温度的升高,催化剂表面Lewis酸中心的数目减少,强度下降.这是由于催化剂中Cl含量下降所致.Ir0和Ir3+共存和中等强度的表面Lewis酸中心有利于提高巴豆醇选择性.

The Ir/ZrO2 catalyst was prepared by impregnation,and the effect of reduction temperature on its catalytic performance for hydrogenation of crotonaldehyde in gas phase was measured.With increasing reduction temperature,the crotonaldehyde conversion and selectivity for crotyl alcohol over the Ir/ZrO2 catalyst first increase and then decrease.The catalyst reduced at 400 oC exhibits the highest crotonaldehyde conversion,reaching a value as high as 32.2%,and the selectivity for ctotyl alcohol is 74.3%.The results of X-ray photoelectron spectroscopy indicated that both Ir0 and Ir3＋ species coexist on the catalyst surface after reduction at 400 oC.With increasing reduction temperature,the ratio of Ir0/Ir3＋ increases,and the surface Ir species exists mainly as Ir0 when the reduction temperature is 600 oC.Additionally,NH3 temperature-programmed desorption indicated that the amount and intensity of Lewis acid sites show a downward trend with increasing reduction temperature,which is attributed to the decline of Cl element in the catalyst.Therefore,it is concluded that the coexistence of Ir0 and Ir3＋ and moderate-intensity of surface Lewis acid help improve the yield and selectivity of crotyl alcohol.