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系统，以促进碳氢化合物的颗粒氧化。在液相条件下，由于反应物/产物的扩散限制，TS-1分子筛的晶粒度对催化剂的活性有很大的影响。合成了含钒催化剂VS-2，并对氧化末碳和内碳进行了活性测定。通过自旋捕捉实验检测到VS-2催化的烷烃氧化体系生成了烷基自由基。利用氧气代替H_2O_2是通过在金属硅酸盐中引入金属组分来实现的，催化剂似乎是一个双功能体系。然而，由于H_2O_2的氢解促进了H_2O_2的氢化分解，在&gt；50ﾟC以下，氧化速率随着温度的升高而降低。我们已成功地将该体系扩展到气相氧化。在Pd/TS-1催化剂上，甲烷在H_2和O_2存在下被氧化成甲醛。在没有H_2的情况下，甲烷被完全氧化生成CO_2。含有过渡金属的介孔催化剂上也进行了类似的甲醛合成。水热合成的含钼MCM-41对甲烷和氧气生成甲醛的选择性最高。含钒的MCM-41对甲烷的深度氧化具有较高的活性。值得注意的是，水热合成的介孔金属硅酸盐比浸渍金属盐的介孔硅酸盐具有更高的选择性。对甲醛的选择性很大程度上依赖于沸石/分子筛的孔径大小，这可以用相对较小的孔径内曾经形成的甲醛的连续分解来解释。

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.