Development of liquid-phase oxidation processes by use of highly dispersed metal-metal oxide catalysts

我们的目标是开发新的催化剂体系，促进烃类的部分氧化。在液相条件下，由于反应物/产物的扩散限制，TS-1分子筛晶体的尺寸对催化剂的活性有很大的影响。合成了含钒催化剂VS-2，并证明其对氧化端碳和内碳都具有活性。通过自旋捕集实验发现VS-2催化烷烃氧化体系中有烷基自由基生成。通过在金属硅酸盐中引入金属组分，实现了以氧代替H_2O_2的利用，该催化剂似乎是一个双功能体系。当温度高于50 ℃时，由于H_2O_2的氢解作用，氧化速率随温度的升高而降低。我们已经成功地将该系统扩展到气相氧化。以Pd/TS-1为催化剂，在H_2和O_2存在下，甲烷氧化为甲醛。在不加H_2的情况下，完全氧化生成CO_2。在含过渡金属的介孔催化剂上也进行了类似的甲醛合成。水热法合成的含钼MCM-41对甲烷和氧气生成甲醛的选择性最好。含钒MCM-41在甲烷深度氧化反应中表现出良好的活性。应注意，水热合成的介孔金属硅酸盐比用金属盐浸渍的介孔硅酸盐更具选择性。甲醛的选择性是急剧依赖于沸石/分子筛的孔径，这是解释在一次形成的甲醛内的相对较小的孔的连续分解。

We aimed at developing new catalyst systems which promote the partical oxidation of hydrocarbons. In the liquid phase conditions we have found that the size of the zeolite TS-1 crystals have a great influence on the activity of the catalyst because of the diffusion limitation of the reactants/products. The V-containing catalyst VS-2 was synthesized and proved to be active in the oxidation terminal carbons as well as internal carbons. By spin trapping experiments the formation of alkyl radical was detected for the alkane oxidation systems catalyzed by VS-2. The utilization of oxygen instead of H_2O_2 was attained by introducing metallic components incorporated inside the metallosilicates ; the catalyst seems to act as a bifunctional system. However, the rate of oxidation decreased with increasing temperature up to > 50ﾟC because of the promotion of the hydeogenolysis of H_2O_2. We have been successful in extending the system to gas phase oxidation. Methane was oxidized to formaldehyde over Pd/TS-1 in the presence of H_2 and O_2. Without addition of H_2 the complete oxidation occurred to give CO_2. Similar formaldehyde synthesis was also carried out over the mesoporous catalysts containing transition metals. Hydrothermally synthesized Mo-containing MCM-41 was found most selective for formaldehyde formation from methance and O_2. Vanadium-containing MCM-41 was active in the deep oxidation of methane. It is to be noted that the hydrothermally synthesized mesoporous metallosilicates were more selective than the mesoporous silicates impregnated with metal salts. The selectivity for formaldehyde was sharply dependent on the pore size of the zeolites/molecular sieves, which was interpreted in terms of the successive decomposition of once formed formaldehyde inside the relatively small pores.