| Significant amounts of natural gas (mainly methane) exist worldwide, and recent discoveries in remote areas suggest that abundant supplies will be available for decades. The traditional exploitation of these carbon resources is not always a viable option because of transportation problems, and flaring of the gas produced is a wasteful alternative. Consequently, the ability to convert methane into easily transportable fuels or chemicals can have a great impact on the economic and energy health of the United States by providing the consumer with a new, previously untapped source of raw materials.; Current processes for the direct conversion of methane rely on thermal activation at extremely high temperatures. Thus, such processes are very energy inefficient. One avenue that offers great promise for directly converting methane to useful products without extensive energy consumption is the catalytic oligomerization of methane.; The conversion of methane to C{dollar}sb2{dollar} hydrocarbons was studied in a tapered reactor using a combination of pulse and flow techniques.; The role of the lead active species has been studied for Pb-Mg-O catalysts in the oxidative coupling of methane. In general, the effect of adding lead to MgO was to increase the rate of total methane conversion. The C{dollar}sb2{dollar} selectivity exhibited a volcano-type pattern with a maximum of 51% being achieved at about 0.4 atom % Pb. This volcano-type behavior is interpreted in terms of an "isolated-site" type mechanism. Addition of PbO in small amounts to a relatively inert MgO matrix results in the formation of a number of isolated strong oxidizing sites which can generate the methyl radicals more efficiently. Since these sites are isolated, the methyl radical has little likelihood of being further oxidized and can desorb into the gas phase where it can couple to form ethane.; A simple kinetic model based on the isolated site mechanism has been developed which explains most of the catalytic features of Pb-Mg-O and Sn-Mg-O catalytic systems. The model predicts an optimum selectivity for C{dollar}sb2{dollar} hydrocarbons as a function of Sn (or Pb) content.; Oxygen exchange experiments and experiments in the pulse mode were used to speculate about the type of oxygen species responsible for methane oxidation. |
