Direct Production of Formaldehyde by Partial Oxidation of Methane

催化剂寿命评估及失活机理研究：在本项目研究之初，我们认为催化剂失活可能是由于催化剂表面碳的沉积和积聚所致。但目前认为催化剂失活是由于催化剂升温至反应温度和反应温度为600℃时钼化合物的损失所致。部分钼化合物以α-MoO_3为主，容易升华出反应器并沉积在与反应器相连的管壁上。因此，防止钼化合物在前处理和高温反应过程中升华的催化剂的设计是催化剂长寿命的关键。由于分散在二氧化硅载体外的钼化合物被迅速去除，我们认为最重要的技术是催化剂的制备，将钼化合物包裹在二氧化硅载体的微孔内。甲烷转化为含氧物的活化机理的研究：在本研究中，我们使用分散在二氧化硅上的SMA(H_4SiMo_&lt；12&gt；O_&lt；40&gt；)作为甲烷部分氧化制含氧物的催化剂。SMA的特点之一是在1个SMA分子中含有4个质子。在本项目的研究中，经常使用KOH处理的二氧化硅载体，其中SMA分子中的H^+离子被K^+离子取代。结果表明，K~+取代的SMA/SiO_2催化剂活性较低，进料中的甲烷几乎全部留在反应器出口。这意味着SMA中的质子对甲烷活化为含氧物具有重要作用。现在。我们认为在SMA/SiO_2催化剂上，H~+与CH_4反应生成的CH_5~(++)是甲烷部分氧化的重要反应中间体。

Studies on the evaluation of catalyst life and the mechanism of catalyst deactivation :At the beginning of this project research, we thought that the catalyst deactivation was likely caused by the deposition and accumulation of carbon over the catalyst surface. But now it is probed that the catalyst deactivation comes from the loss of molybdenum compounds during heating the catalysts to the reaction temperature and during the reaction at 600 ℃. A part of Mo compounds, mainly consisted of α- MoO_3, easily sublimated out of the reactor and deposited on the wall of tubes connected with the reactor. So, the key technique for a long life lies in the design of catalysts against sublimation of Mo compounds during both pretreatments and reaction at high temperature. Since Mo compounds dispersed out side of the silica support were found to remove rapidly, we believe that the most important technique is in the catalyst preparation to entrap the Mo compounds inside the micro-pores of silica supports.Study on the activation mechanisms of methane into oxygenates :In the present study, we use SMA (H_4SiMo_<12>O_<40>) dispersed on silica as catalysts for partial oxidation of methane into oxygenates. One of the features of SMA is to possess 4 protons in 1 SMA molecule. In this project research KOH treated silica supports were often used, where H^+ ions in SMA molecules were substituted with K^+ ions. It was found that the K^+-substituted SMA/silica catalysts showed a low activity, and that almost all of the methane in the feed remained at the outlet of the reactor. This means that the protons in SMA have an important role for the activation of methane into oxygenates. Now. we are thinking about the presence of CH_5^+, generated by the reaction of H^+ on SMA and CH_4, as an important reaction intermediate for partial oxidation of methane on SMA/Si0_2 catalysts.