Alkanes partial oxidation

Mechanistic studies of alkane partial oxidation reactions on nickel oxide by modem surface science techniques ... 

Examples Oxidative coupling of methane (OCM), oxidative dehydrogenation of C -C4 alkanes, partial oxidation of methane to synthesis gasa, combined oxidative coupling of methane and toluene to styrene Surface-stabilized combustion, partial oxidation of methane to synthesis gasa, synthesis of cyanic acid from methane, ammonia, and oxygen3... 

Another possible solution of the problem is to perform the reaction at a very low initial oxygen concentration. Although in the case of alkane partial oxidation this is not favorable for obtaining high yields of target products (oxygenates, olefins, synthesis gas), an almost uniform temperature field can be achieved. 

Williams, KA, Schmidt, LD. Catalytic autoignition of higher alkane partial oxidation on rhodium coated foams. Appl. Catal. A Gen. 2006399 30-45. 

Figure 24.2. Structure of the most studied catalysts in alkane partial oxidation (a) vanadyl pyrophosphate (VPO) (b) VSbO rutile phase (c) orthorhombic bronze, so-called Ml phase, i.e MoVTe(Sb)NbO (d) Keggin molybdophophoiic acid structure.

One of the key aspects in the catal5dic behavior for alkane partial-oxidation catalysts seems to be related to the coordination number (Fig. 24.3), the aggregation degree, and the oxidation state of the vanadium species as active sites. It fact, it has been shown that the V-environment plays an important role in catalytic behavior. 

Many molecules undergo partial oxidation on adsorption and many alkanes and alkenes are believed to yield an adsorbed CHO group on adsorption (Petrii, 1968). These processes usually lead to the complete oxidation of the organic molecule to carbon dioxide and few workers have attempted to halt the reaction at an intermediate stage. Hence, although there are undoubtedly possibilities for using dissociative chemisorption for synthetic reactions, this chapter will not consider these processes further. 

We have summarized below recent results concerning spectroscopic / flow reactor investigations of hydrocarbons partial and total oxidation on different transition metal oxide catalysts. The aim of this study is to have more information on the mechanisms of the catalytic activity of transition metal oxides, to better establish selective and total oxidation ways at the catalyst surface, and to search for partial oxidation products from light alkane conversion. 

Iron N,N -bis(2-pyridinecarboxamide) complexes encaged in zeolite Y were used for the partial oxidation of alkanes.99 Epoxidation with manganese N,N -bis(2-pyridinecarboxamide) complexes encapsulated in zeolite Y was also reported.100... 

The selective oxidation of alkanes is cuiTently one of the most widely studied classes of catalytic reactions. This work mainly concentrates on the oxidative dehydrogenation of methane, with some attention paid to the partial oxidation of the product of this reaction, ethane. As regards the latter reaction, higher yields of pai tial oxidation products (acetaldehyde and ethylene) were achieved when N2O was used instead of O2 (1-6). 

The catalytic homogeneous oxidation at low temperatures is therefore economically interesting, but also very difficult to achieve due to the high stability of CH-bonds. Partial oxidation is particularly hard in alkanes as classical oxidation procedures tend to over oxidize them. In the case of methane this would result in the formation of CH2O, CO and CO2. Low valent transition metals, however, are capable of activating the CH bond and rendering that problem less important as the difference in reactivity between the CH bond in methane and methanol is not that big. 

Substrates which can undergo partial oxidation are characterized by a 7T-electron system or unshared electrons olefins and aromatics contain the first, methanol, ammonia and sulphur dioxide the second. Alkanes do not contain such electrons. Their selective oxidation appears to demand (thermal or catalytic) dehydrogenation to alkenes as the initial process. 

The synthesis of intermediates and monomers from alkanes by means of oxidative processes, in part replacing alkenes and aromatics as the traditional building blocks for the chemical industry [2]. Besides the well-known oxidation of n-butane to maleic anhydride, examples of processes implemented at the industrial level are (i) the direct oxidation of ethane to acetic acid, developed by Sabic (ii) the ammoxidation of propane to acrylonitrile, developed by INEOS (former BP) and by Mitsubishi, and recently announced by Asahi to soon become commercial (iii) the partial oxidation of methane to syngas (a demonstration unit is being built by ENI). Many other reactions are currently being investigated, for example, (i) the... 

Alkanes, which are the principal components of natural gas and crude oil, are still the preferred energy source of our society. In regard to the prime importance of alkanes as feedstock for the chemical industry, it appears a waste of resources simply to burn these precious raw materials. Unfortunately, attempts to transform alkanes into more valuable products are hampered by their low reactivity, as best illustrated by the use of alkanes as inert solvents. For example, the cracking process requires temperatures of about 1000 °C in order to convert long-chain alkanes into short-chain alkanes. Controlled conversion of hydrocarbons is difficult to achieve and limited to partial oxidations, such as the conversion of butane into acetic acid. It is obvious that processes that would enable efficient functionalization to occur at low temperature would have enormous potential application. Achievements towards this goal will almost certainly rely on the use of catalysts, which will have to activate the stable C-H bond (375-440 kf mol-1) in order to induce its scission. 

The overall partial oxidation reaction of alkanes can be written as follows ... 

Goetsch DA, Schmidt LD. Microsecond catalytic partial oxidation of alkanes. Science. 1996 271(5255) 1560-1562. 

Fournier et al. (1992) Heteropolymolybdates, vanadium substituted Phase stability, dehydration + + n.a Partial oxidation of C3 and C4 alkanes... 

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