【摘 要】
：
以二氧化硅担载铁氧化物(1wt％Fe/SiO2)为探针,结合XRD、XANES以及EXAFS分析结果首次从表面配位几何的观点讨论了钠助剂对Fe/SiO2催化剂结构及其甲烷氧化偶联反应性能所产生的
【机 构】
：
北京化工大学可控化学反应科学与技术基础教育部重点实验室,北京大学化学与分子工程学院北京
论文部分内容阅读
以二氧化硅担载铁氧化物(1wt％Fe/SiO2)为探针,结合XRD、XANES以及EXAFS分析结果首次从表面配位几何的观点讨论了钠助剂对Fe/SiO2催化剂结构及其甲烷氧化偶联反应性能所产生的影响.XRD分析表明,Fe/SiO2经800℃焙烧后仍保持无定形特征,添加钠助剂并经800℃焙烧后,Na-Fe/SiO2已转化为α-方石英结构.Fe/SiO2的EXAFS拟合结果显示,铁中心被5个近邻氧环绕,平均Fe-O键长为0.194 nm.与Fe/SiO2相比,Na-Fe/SiO2的径向结构函数谱中最强峰的相对强度提高了1/4,表明形成了一个更加密集的Fe-O壳层.拟合结果表明围绕中心铁原子0.189 nm处平均有4.1个氧近邻.Fe K-边XANES谱表明钠的参与使催化剂的活性组分由配位不饱和的八面体位逐渐向四配位四面体位迁移.甲烷氧化偶联反应结果显示,添加钠助剂后甲烷转化率有所下降,但是C2烃的选择性提高了近42个百分点,Cox的选择性则明显下降.说明钠的引入使催化剂的表面结构发生变化,所形成的多数四面体/少数八面体混合结构有效地抑制了甲烷的深度氧化,乙烯乙烷的选择性明显提高.
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