Catalytic transformation of methane into

A. Catalytic Transformation of Methane into Aromatics Under Non-OxiDATiVE Conditions... 

Even aliphatic hydrocarbons are susceptible to oxidative carbonylation. From an industrial point of view, the most important process concerns the direct conversion of methane into acetic acid. This transformation has been achieved with Rh(III)-based catalysts using oxygen as the oxidizing agent [149-153], and it is still object of investigations aimed at developing more efficient catalytic systems working under mild conditions. 

This is a major achievement, mainly due to Basset and his group, in surface organometallic chemistry because it has been thus possible to prepare single site catalysts for various known or new catalytic reactions [53] such as metathesis of olefins [54], polymerization of olefins [55], alkane metathesis [56], coupHng of methane to ethane and hydrogen [57], cleavage of alkanes by methane [58], hydrogenolysis of polyolefins [59] and alkanes [60], direct transformation of ethylene into propylene [61], etc. These topics are considered in detail in subsequent chapters. 

G.V. Echevsky, E.G. Kodenev, O.V. Kikhtyanin, V.N. Parmon, Direct Insertion of Methane into C3-C4 Paraffins Over Zeolite Catalysts a Start to the Development of New One-Step Catalytic Processes for Gas to Liquid Transformation, 258, Applied Catalysis A General, 159-171, (2004). 

Transformations of methane [77] and other lower alkanes [78] into aromatic hydrocarbons, e.g., benzene, are very interesting. Table III.6 presents some catalytic systems for nonoxidative methane dehydrogenation over transition metal ion-loaded zeohtes [77d]. 

Having set out the properties of tantalum and zirconium hydride toward C-H bond activation of alkanes we now describe the catalytic hydrogenolysis of C-C bonds. It was previously shown in the laboratory that supported-hydrides of group 4 metals, and particularly of zirconium, catalyze the hydrogenolysis of alkanes [21] and even polyethylene [5] into an ultimate composition of methane and ethane. However, to our initial surprise, these zirconium hydrides did not cleave ethane. (=SiO)2Ta-H also catalyzes the hydrogenolysis of acyclic alkanes such as propane, butane, isobutane and neopentane. But, unlike the group 4 metals, it can also cleave ethane [10], Figure 3.7 illustrates this difference of behavior between (=SiO)2Ta(H) and [(=SiO)(4.j,)Zr(H) ], x= or 2). With Ta, propane is completely transformed into methane by successive reactions, while with Zr only equimolar amounts of methane and ethane are obtained. 

The model of deactivation describes the transformations of two boundary forms of the carbonaceous deposits during the catalytic hydrogenation of CO2. These are the hydrocarbon-formed active deposit (CH) and the graphitic inactive one (C)n. Thus deactivation is based on dehydrogenation of the active deposit into the inactive one that blocks active centers for hydrogenation. The active deposit, a product of polymerization of surface methane precursors (CH ), is simultaneously their consumer and producer. The mass balance of the active intermediates derived from the model assumptions gave the kinetic equation which quantitatively describes the deactivation. 

The C-H activation of alkanes is known as a difficult chemical process [11]. By the chemical method, severe conditions and/or expensive catalysts have been used to activate the C-H bond [12]. However, the biological system achieves such a difficult reaction very easily at room temperature [13]. Methane monooxygenase (MMO) catalyzes an oxidation of methane to methanol in methanotrophs, a methane-utilizing bacteria [eq. (2)] [14,15]. In the catalytic reaction of MMO, one oxygen atom of O2 is incorporated into a substrate and another oxygen atom is transformed into water. 

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