1- ethanes, oxidation

A catalyst library of 112 catalysts was screened. Seven metal oxides, A1203, Si02, Ti02, ZnO, Ga203, Zr02 and La203 were selected as supports and 16 metal or metal oxides, Mn, Fe, Co, Ni, Ru, Rh, Pd, Ir, Pt, Cu, Zn, Ag, Au, Ga, In and Sn, were selected as additive to support oxides. An additive metal or metal oxide was 

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Although ethylene is produced by various methods as follows, only a few are commercially proven thermal cracking of hydrocarbons, catalytic pyrolysis, membrane dehydrogenation of ethane, oxydehydrogenation of ethane, oxidative coupling of methane, methanol to ethylene, dehydration of ethanol, ethylene from coal, disproportionation of propylene, and ethylene as a by-product. 

A. Kaloyannis, and C.G. Vayenas, Non-Faradaic Electrochemical Modification of Catalytic Activity. 11. Ethane Oxidation on Pt,/. Catal. 171, 148-159 (1997). 

Liu YM, Cong PJ, Doolen RD, Guan SH, Markov V, Woo L, Zeyss S, Dingerdissen U. 2003. Discovery from combinatorial heterogeneous catalysis—a new class of catalyst for ethane oxidative dehydrogenation at low temperatures. Appl Catal A Gen 254 59 -66. 

The palladium-catalyzed asymmetric hydrosilylation of styrenes has been applied to the catalytic asymmetric synthesis of l-aryl-l,2-diols from arylacetylenes (Scheme 6).46 Thus, ( )-l-aryl-2-(trichlorosilyl)ethenes, which are readily generated by platinum-catalyzed hydrosilylation of arylacetylenes, were treated with trichlorosilane and the palladium catalyst coordinated with MOP ligand 12f to give 1 -aryl-1,2-bis(silyl)ethanes, oxidation of which produced the enantiomerically enriched (95-98% ee) 1,2-diols. 

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. 

In the investigation of hydrocarbon partial oxidation reactions the study of the factors that determine selectivity has been of paramount importance. In the past thirty years considerable work relevant to this topic has been carried out. However, there is yet no unified hypothesis to address this problem. In this paper we suggest that the primary reaction pathway in redox type reactions on oxides is determined by the structure of the adsorbed intermediate. When the hydrocarbon intermediate (R) is bonded through a metal oxygen bond (M-O-R) partial oxidation products are likely, but when the intermediate is bonded through a direct metal-carbon bond (M-R) total oxidation products are favored. Results on two redox systems are presented ethane oxidation on vanadium oxide and propylene oxidation on molybdenum oxide. 

Catalytic activity was measured in a 14 mm ID quartz packed-bed reactor, at atmospheric pressure. In ethane oxidation studies on V20s/Si02 the partial pressures were, PCH3CH3 = 13 kPa, P02 = 28 kPa, PH2O = lOkPa,... 

Ethane Oxidation on Supported Vanadium Oxide. Figure 1 shows the rates of production of the major products of ethane oxidation over a series of silica-supported vanadium oxide catalysts. As was described earlier, the structure of the catalyst changed considerably with the active-phase loading (77). The low loading samples (0.3 -1.4%) were shown to consist primarily of 0=V03 monomeric units, while the high loading catalysts (3.5 - 9.8%) were composed of V2O5 crystallites. 

The high activity in ethane oxidation of Rb2Mo04 as compai ed with the other catalysts is very probably connected with its ready reduction (Figure 1). Under the given reaction conditions, this process results only in a higher surface concentration of Mo (or Mo -0 ) species, and not in the further reduction of molybdenum, which would involve the occuiTence of a two-electron transfer. 

It has been demonstrated, however, that the activity of an oxide catalyst for ethane oxidation can be preferentially increased by treating it with chloride or sulfide (14). If a Co-Zr-P-Na-K oxide catalyst was treated with CH3C1, an ethene selectivity of 85% at 55% ethane conversion was obtained at 675°C, compared with 74% selectivity at 32% conversion on the... 

The catalysts used and the temperature for the data shown in Fig. 2 are listed in Table IV. Except for one, the studies were conducted at or below 550°C, which was substantially lower than many experiments for ethane oxidative dehydrogenation. This is because above this temperature, the contribution of homogeneous gas-phase reaction begins to be significant (see, for example, Ref. 28). 

The dependence of selectivity for propene on propane conversion for the better catalysts (Fig. 2) follows a trend similar to that for ethane oxidation. 

The data presented above showed that the oxidative dehydrogenation reactions of the various alkanes share many common features. Thus it is tempting to discuss selectivity for alkane oxidative dehydrogenation with a common scheme. The reaction scheme for ethane oxidation [Eqs. (5)-(7)] provides a useful basis for such a discussion. It shows that the primary reaction of alkane oxidation can take on three different pathways depending on the reaction temperature (Scheme I). The first step in all three pathways is breaking a C—H bond, which is the rate-limiting step. The three pathways are described below. 

M.C. Huff and L.D. Schmidt. Elementary Step Model of Ethane Oxidative Dehydrogenation on Pt-Coated Monoliths. AIChE J., 42 3484-3497,1996. 

T.B. Hunter, T.A. Litzinger, H. Wang, and M. Frenklach. Ethane Oxidation at Elevated Pressures in the Intermediate Temperature Range Experiments and Modeling. Combust. Flame, 104 505-523,1996. 

R. Rota, F. Bonini, A. Servida, M. Morbidelli, and S. Carra. Validation and Updating of Detailed Kinetic Mechanisms The Case of Ethane Oxidation. Ind. Eng. Chem. Res., 33 2540-2553,1994. 

Methane reacts only slowly with oxygen below 400° C. Ethane oxidation was observed by Bone and Hill (S) at 290° to 323° C. Formaldehyde, a reaction product, was found to increase, reach a maximum, and then decrease. Addition in amounts of 1% to a 3 to 1 ethane-oxygen mixture at 316° C. and 720 mm. eliminated the induction period, but other additives such as nitregen dioxide, acetaldehyde, ethyl alcohol, or water, were also more or less effective. 

Perhydroxyl radical, 75 thermal generation from PNA of, 75 Peroxy radical generation, 75 Peroxide crystal photoinitiated reactions, 310 acetyl benzoyl peroxide (ABP), 311 radical pairs in, 311, 313 stress generated in, 313 diundecanyl peroxide (UP), 313 derivatives of, 317 EPR reaction scheme for, 313 IR reaction scheme for, 316 zero field splitting of, 313 Peorxyacetyl nitrate (PAN), 71, 96 CH3C(0)00 radical from, 96 ethane oxidation formation of, 96 IR spectroscopy detection of, 71, 96 perhydroxyl radical formation of, 96 synthesis of, 97 Peroxyalkyl nitrates, 83 IR absorption spectra of, 83 preparation of, 85 Peroxymethyl reactions, 82 Photochemical mechanisms in crystals, 283 atomic trajectories in, 283 Beer s law and, 294 bimolecular processes in, 291 concepts of, 283... 

Table 9.1 S ummary of the performance of selected catalysts in ethane oxidation. 

Symyx entered this competition in 1997 in collaboration with Hoechst with the goal of creating and validating primary and secondary synthesis and screening technologies and the use of this workflow to broadly explore mixed metal oxide compositions so as to discover and optimize new hits . The initial goal was a 10-fold increase in the space-time yield relative to the state-of-the-art MoVNb system for the ethane oxidative dehydrogenation reaction to ethylene. 

Fig. 8.8 Product yields evaluated by PAS detector on catalytic ethane oxidation over N02-treated catalysts. N02 gas was flowed onto each catalyst before reaction to produce active site (reproduced by permission of Elsevier from [20]).

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