还原-氧化预处理对双孔道钴基催化剂催化性能的影响

Influence of reduction-oxidation pretreatment on the performance of bi-modal structure Co-based catalysts in Fischer-Tropsch synthesis

以双介孔分布MCM-41分子筛为载体,采用等体积浸渍法制备了钴基催化剂,并考察了还原-氧化预处理方式对催化剂结构及费托合成催化性能的影响。新鲜催化剂经预处理之后,XRD结果显示钴物种主要以单质钴形式存在,且主要以面心立方钴晶型出现,晶粒粒径由原来的8.4 nm增加到22.6 nm,由于晶粒粒径的增大,拉曼峰呈现蓝移特征。SEM及TEM表征表明,预处理后催化剂中钴物种在载体中有较好的分散性。H2-TPR结果表明,新鲜催化剂经还原-氧化预处理后钴物种的还原温度降低,钴物种-载体间作用力增强。费托合成反应结果显示,经预处理后催化剂较新鲜催化剂活性低,甲烷选择性提高,但C5～18的选择性明显提高,尤其是C5～11的选择性可达到新鲜催化剂的两倍。

Co-based catalyst supported on bi-modal MCM-41 molecular sieves was prepared by incipient-wetness impregnation method;the influence of reduction and oxidation pretreatment on the catalyst structure and its performance in Fischer-Tropsch synthesis（FTS） was investigated.XRD results showed that the cobalt species in the catalyst after the pretreatment is in the form of metal cobalt with face centered cubic crystal phase and the crystallite size is increased from 8.4 nm to 22.6 nm,compared with the untreated one;due to the increase of crystallite size,the Raman characteristic peak shows a blue shift.SEM and TEM results indicated that the cobalt species exhibits good dispersibility.H2-TPR results indicated that the reduction temperature is reduced and the interaction between metal and support is strengthened after the pretreatment.As a result,the pretreated-catalyst exhibits lower FTS activity and higher selectivity to methane than the fresh catalyst;however,the selectivity to C5~18 products over the pretreated-catalyst is improved obviously,especially,the selectivity to C5~11,which is about twice as that over the untreated one.