Na-W-Mn/SiO_2催化剂中的组分协同效应

Synergic Effect of Active Components in Na W Mn/SiO_2 Catalyst

利用ＸＲＤ，ＳＥＭ 和Ｒａｍａｎ 光谱等手段对ＮａＷＭｎ／ＳｉＯ２ 催化剂中形成的物相、活性组分在载体表面的分散度以及催化剂表面的金属中心结构进行了研究． 结果表明，组分间的相互作用对各活性组分在催化剂中的存在形式有重要影响． 在无定形氧化硅表面， Ｗ 以八面体六配位ＷＯ３ 形式存在，在α方石英表面， Ｗ 以四面体四配位的ＷＯ４ 形式存在． 没有组分Ｎａ 时， Ｗ 或Ｍｎ 在催化剂表面以氧化物颗粒形式存在； Ｎａ 的加入不仅可大大提高Ｗ或Ｍｎ 在催化剂表面的分散度，而且可使ＷＯ４ 四面体的结构变得十分均一． 反应性能研究还表明， Ｎａ 和Ｍｎ 之间存在很强的电子相互作用，对于含Ｍｎ 催化剂的选择性具有重要影响．

The bulk phase, dispersion state and structure form of active components in Na W Mn/SiO 2 catalyst were studied by using XRD, SEM and Raman spectroscopy. The results showed that the interaction among the components has significant effect on their existing form. Tungsten exists as octahedral WO 3 with six coordination on amorphous silica but as tetrahedral WO 4 with four coordination on α cristobalite. When tungsten or/and manganese is loaded without sodium, they exist as congregated oxide particles. Addition of sodium makes not only the dispersion of tungsten and manganese be greatly improved, but also the WO 4 structure becomes very uniform. There exists strong interaction between sodium and manganese. Mn O sites are very active, but addition of sodium will strongly suppress their activity. The Na Mn interaction is very important for the high selectivity of the manganese containing catalyst.