Ethane selective oxidation

Interest in ethane selective oxidation to acetic acid has been rising in the last few years due to the low cost of ethane which is now easily available from the large sources of namral gas which have recently been discovered. Although different catalytic systems have been proposed, Pd-doped MoVNbO mixed oxides are one of the more promising catalysts. " ... 

A = Lao.8Bao 2) catalysts for ethane-selective oxidation to ethane. Appl. Catal. A Gen. 2001,213,91-102. 

A topic of current interest is that of methane activation to give ethane or selected oxidation products such as methanol or formaldehyde. Oxide catalysts are used, and there may be mechanistic connections with the Fischer-Tropsch system (see Ref. 285). 

Li/MgO(100) Mo(lOO) thin film (selective oxidation of methane to ethane) (7)... 

In this paper selectivity in partial oxidation reactions is related to the manner in which hydrocarbon intermediates (R) are bound to surface metal centers on oxides. When the bonding is through oxygen atoms (M-O-R) selective oxidation products are favored, and when the bonding is directly between metal and hydrocarbon (M-R), total oxidation is preferred. Results are presented for two redox systems ethane oxidation on supported vanadium oxide and propylene oxidation on supported molybdenum oxide. The catalysts and adsorbates are stuped by laser Raman spectroscopy, reaction kinetics, and temperature-programmed reaction. Thermochemical calculations confirm that the M-R intermediates are more stable than the M-O-R intermediates. The longer surface residence time of the M-R complexes, coupled to their lack of ready decomposition pathways, is responsible for their total oxidation. 

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). 

As previous studies had suggested that the selective oxidation of ethane might occur through the formation and further reaction of ethoxide, it seemed useful to investigate the effects of these molybdate catalysts in the decomposition of ethanol. The decomposition of ethanol at 603 K yielded acetaldehyde (64-69%), ethane (25-26%), ethylene (3-5%) and small amounts of methane and CO. A decay in catalytic activity was observed for all catalysts. At the steady state, neither the activity nor the selectivity differed significantly for these molybdates. 

In general, the ethylene to ethane selectivity is governed by the relative rates of the processes shown in Scheme 3.1. Here, combination of methyl radicals (step 2) is a homogeneous process, but all other steps can be both homogeneous and heterogeneous.294 It was also found that further oxidation of the C2 products (steps 4 and 6) becomes important only with increasing C2 concentration in the system.327... 

Combinatorial methods were also applied in the discovery of new catalysts for the low-temperature oxidation213 and oxidative dehydrogenation of propane.214 A 144-member catalyst library was screened by photothermal deflection spectroscopy and mass spectrometry to find the most active compositions of V-Al-Nb and Cr-Al-Nb oxides for the oxidative dehydrogenation of ethane.215 The ternary combination V(45)-Sn(45)-Mo(10)-O selected by laser-induced fluorescence imaging gave much higher yield than did V205 in the selective oxidation of naphthalene to naphthoquinone.216... 

The difference in reactivity of the butadiene precursor toward 02 and NzO is interesting. N20 is known to be active in selective oxidation (16). For example, on molybdenum oxide (16) and cobalt magnesium oxide (17), NzO decomposes at room temperature to form an O adsorbed species which is very active in the oxidative dehydrogenation of ethane. The results presented above suggest that the degradation of butadiene precursor on a-iron oxide requires an 02 and not an 0" species. This implies that the degradation proceeds via a peroxide intermediate. 

The selective oxidation of C—H bonds in alkanes under mild conditions continues to attract interest from researchers. A new procedure based upon mild generation of perfluoroalkyl radicals from their corresponding anhydrides with either H2O2, m-CPBA, AIBN, or PbEt4 has been described. Oxidation of ethane under the reported conditions furnishes propionic acid and other fluorinated products.79 While some previously reported methods have involved metal-mediated functionalization of alkanes using trifluoroacetic acid/anhydride as solvent, these latter results indicate that the solvent itself without metal catalysis can react as an oxidant. As a consequence, results of these metal-mediated reactions should be treated with caution. The absolute rate constants for H-abstraction from BU3 SnH by perfluorinated w-alkyl radicals have been measured and the trends were found to be qualitatively similar to that of their addition reactions to alkenes.80 a,a-Difluorinated radicals were found to have enhanced reactivities and this was explained as being due to their pyramidal nature while multifluorinated radicals were more reactive still, owing to their electrophilic nature.80... 

The field is defined here around the activation of butane, propane and ethane plus the oxidation of propene. The reason for this boundary is the similarity of the chemistry and the great need to understand the mechanism of selectivity of activated oxygen in these multi-step reactions. The processes cannot be conducted at high temperatures such as with methane activation as the target products are not stable under conditions where alkane activation is fast. The selective oxidation of... 

Micro structured wells (2 mm x 2 mm x 0.2 mm) on the catalyst quartz wafer were manufactured by sandblasting with alumina powder through steel masks [7]. Each well was filled with mg catalyst. This 16 x 16 array of micro reactors was supplied with reagents by a micro fabricated gas distribution wafer, which also acted as a pressure restriction. The products were trapped on an absorbent plate by chemical reaction, condensation or absorption. The absorbent array was removed from the reactor and sprayed with dye solution to obtain a color reaction, which was then used for the detection of active catalysts by a CCD camera. Alternatively, the analysis was also carried out with a scanning mass spectrometer. The above-described reactor configuration was used for the primary screening of the oxidative dehydrogenation of ethane to ethylene, the selective oxidation of ethane to acetic acid, and the selective ammonoxidation of propane to acrylonitrile. 

Volpe, A. F., Weinberg, W. H., Woo, L., Zysk, J., Combinatorial heterogeneous catalysis oxidative dehydrogenation of ethane to ethylene, selective oxidation of ethane to acetic acid, and selective ammonoxidation of propane to acrylonitrile, Top. Catal. 2003, 23, 65-79. 

Rare earth oxides are useful for partial oxidation of natural gas to ethane and ethylene. Samarium oxide doped with alkali metal halides is the most effective catalyst for producing predominantly ethylene. In syngas chemistry, addition of rare earths has proven to be useful to catalyst activity and selectivity. Formerly thorium oxide was used in the Fisher-Tropsch process. Recently ruthenium supported on rare earth oxides was found selective for lower olefin production. Also praseodymium-iron/alumina catalysts produce hydrocarbons in the middle distillate range. Further unusual catalytic properties have been found for lanthanide intermetallics like CeCo2, CeNi2, ThNis- Rare earth compounds (Ce, La) are effective promoters in alcohol synthesis, steam reforming of hydrocarbons, alcohol carbonylation and selective oxidation of olefins. 

Platinum(II), for example, K2PtClt, in an aqueous medium in the presence of 02, oxidizes ethane selectively to ethanol and ethylene glycol, whereas metallic Pt is required for the further oxidation of alcohols to carboxylic acids. Platinum metal also catalyzes the oxidation of alkenes to 1,2-diols. The presence of CO prevents further oxidation of the alcohol products.155... 

Regular pulses of pure ethane on bulk V2O5 maintained at 823 K in a microcalorimeter linked to a gas chromatograph provided kinetic data of theoretical significance, as weU as an insight into the mechanism of the reduction process. The results of this work carried out using mainly calorimetric techniques led to the conclusion that diffusion of oxygen from the bulk is predominant in the selective oxidation of ethane and that the redox process plays a more important role than the acidic sites in the case of unsupported vanadium pentoxide. 

MgO-supported vanadium catalysts have been proposed as active and selective catalysts for the ODH of propane and n-butane [1,2], while AljOg-supported vanadium catalysts present a high selectivity to ethene during selective oxidation of ethane [3],... 

We shall first show that it is still far fiom clear which are the families of catalysts to be used for the various reactions mainly oxidative dehydrogenation or oxidation to oxygen-containing molecules of ethane, propane or isobutane. Much research is still necessary for understanding the mechanisms leading to high selectivity. In this context, we shall suggest that many concepts inherited from the development in selective oxidation and ammoxidation of olefins are probably of little use. 

Catalysts based on transition metal oxides are the principal materials investigated in alkane ODH. Ethane is oxidatively dehydrogenated to ethylene with high conversion and selectivity over bulk metal oxide catalysts containing... 

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