Partial oxidation of methane to formaldehyde

Develop the energy equation as an enthalpy balance for the partial oxidation of methane to formaldehyde, occurring nonisothermally in a PFR, according to the reaction network of Spencer and Pereira (1987) in Example 5-8. 

Silica-Supported MoO and V20 Catalysts in Partial Oxidation of Methane to Formaldehyde... 

The partial oxidation of methane to formaldehyde with molecular O2 has been investigated on bare Si02, 4%Mo03/Si02 and... 

In this paper we present a comparative study of the catalytic properties of bare Si02, 4% Mo03/Si02 and 5% V205/Si02 catalysts in the partial oxidation of methane to formaldehyde. The role of the acidic properties and reduced sites, evaluated in steady state conditions, is addressed. A co-operative reaction path-... 

Catalytic Activity. The world-wide interest focused in the catalytic partial oxidation of methane to formaldehyde has led to a great variety of conflicting results (9), The main reason of such discrepancies lies in the lack of a generally valid rule for evaluating and comparing the proposed catalytic systems. In effect, this reaction involves a very complex pathway since the desired partial oxidation product, HCHO, exhibits a limited thermal stability at T>4(X)°C and can be oxidized to more easily than CH itself. Hence, a suitable reactor device and appropriate operating conditions result to be of fundamental importance in order to attain reliable data unaffected by experimental artefacts. 

Kinetic expressions for the three step pathway given above for the partial oxidation of methane to formaldehyde over a vanadium oxide-silica catalyst were determined by Spencer and Periera [17]. The kinetic parameters... 

Sun, Q., Jehng, J.-M., Hu, H. Herman, R.G., Wachs, l.E. and Klier, K. (1997) In situ Raman spectroscopy during the partial oxidation of methane to formaldehyde over supported vanadium oxide catalysts. Journal of Catalysis, 165 (1), 91-101. 

Cull Is et studied the partial oxidation of methane to formaldehyde over a Cl-poisoned Pd-catalyst. 

A more precise analysis and characterization of the M0O3 crystallites shape have shown that in fact the better plane for propene oxidation to acrolein corresponds to the (IkO) plane as schematised in fig. 1 [7]. It is then suggested that the propene activation (H abstraction) into the 3t-allyl intermediate occurs on the side (100) plane while the O atom insertion occurs on the (010) basal plane. As a matter of fact it is worth noting that due to the layered structure of M0O3, the lattice oxide ions are much more labile in the (OkO) plane than in the others. Recently such a structure sensitivity was also derived for the partial oxidation of methane to formaldehyde 8],... 

A kinetic study has been carried out on the partial oxidation of methane to formaldehyde over a silica-supported vanadia catalyst. The results indicate that oxygen was adsorbed on the catalyst and took part in the reaction in an Eley-Rideal or Mars-van Krevelen maimer. The nature of the interaction with the catalyst was dependent on whether the reaction took place in methane rich (pcH4 = 80 kPa) or lean (po,4 = 4 kPa) conditions. A reaction mechanism for the partial oxidation of methane to formaldehyde is proposed, which is consistent with the data reported here. Methanol oxidation experiments over this catalyst suggested that it was not an intermediate under the conditions employed during this study. 

In recent years there has been much interest in the conversion of methane to value added products, such as ethane/ethylene [1], methanol [2], formaldehyde [3-5] and synthesis gas [6]. Many studies have been carried out on the partial oxidation of methane to formaldehyde over silica [7], and over molybdena [8,9], vanadia [5,10] supported on silica, or FeNbB-0 [11] with nitrous oxide [7-9] or oxygen [7,10] as the oxidant. 

An Eley-Rideal/Mars-van Krevelen type of mechanism was found for the partial oxidation of methane to formaldehyde. The differences in the rate equations were due to differences in the amounts of oxygen present in methane rich and lean conditions. Methanol was not an intermediate in the reaction. Methanol oxidation experiments indicated that methanol was oxidised sequentially to formaldehyde, carbon monoxide and hence to carbon... 

Baldwin, T. and Burch, R., Partial oxidation of methane to formaldehyde on chlorine promoted catalysts, Appl. Catal., 75 153—178 (1991). 

Mann, R. S. and Dosi, M. K., Partial oxidation of methane to formaldehyde over halogen modified catalysts, J. Chem. Tech. Biotechnol., 29 467—479, (1979). 

Kinetic coupling at the steady state does not only affect the rate of chain reactions in parallel or in series (ref. 5, Chapter 5), but more importantly, the coupling affects selectivity. As an example, consider the partial oxidation of methane to formaldehyde followed by the oxidation of formaldehyde to carbon monoxide. Both radical chain cycles are kinetically coupled as shown in Figure 4. At the steady state, the coupling steps between the chain cycles above and below must proceed at the same rate so that ... 

It seems likely that the use of IMR-P for a consecutive reaction can have beneficial effects on selectivity. Indeed, using the partial oxidation of methane to formaldehyde as the test reaction, the selectivity was found to be higher than... 

Coupling of catalytic reactions is caused by competition for active centers. Since chain reactions are essentially catalytic in nature, coupling should also affect their rates and selectivity. But, as mentioned before, chain reactions have some characteristics that warrant a separate treatment. This treatment will now be undertaken for reactions both in parallel and in series. As examples of coupling between chain reactions running in parallel, we shall examine copolymerization and co-oxidation. The partial oxidation of methane to formaldehyde and carbon monoxide will be taken up in the next section as a typical case of coupling between chain reactions in series. 

Spencer, N. (1988). Partial Oxidation of Methane to Formaldehyde by Means of Molecular Oxygen, J. Catal, 109, pp. 187-197. 

Initially, supported MoOx and VO species were proposed as active and relatively selective in the partial oxidation of methane to formaldehyde. The nature of metal oxide support and the V- or Mo-content strongly influence the dispersion of molybdenum and vanadium species, which is a key factor for obtaining better selectivity to formaldehyde. At the moment, the highest productivity to formaldehyde, in terms of space-time yields, seems to be obtained over a vanadium oxide supported on mesoporous silica synthesized by a novel method. In this case, the best results have been achieved with a water pressure of 8 kPa, suggesting that water mainly influences the number of accessible active sites and only weakly affects the catalytic properties of these sites. 

Moreover, other transition metal oxides have been investigated in the last ten years. Supported iron oxide catalysts have also been reported as active and relatively selective for partial oxidation of methane to formaldehyde. In general, the nature... 

Nguyen, L., Loridant, S., Launay, H., efa/. (2006). Study of New Catalysts Based on Vanadium Oxide Supported on Mesoporous Silica for the Partial Oxidation of Methane to Formaldehyde Catalytic Properties and Reaction Mechanism, J. Catal., 237, pp. 38-48. 

Parmahana, A., Sokolovskii, V., Miceli, D., Arena, F, and Giordano, N. On the nature of the catalytic activity of silica-based oxide catalysts in the partial oxidation of methane to formaldehyde with O2. J. Catal 1994, 148, 514-523. 

ParmaUana, A., Arena, R, Frusteri, R, Martinez-Arias, A., Lopez-Granados, M., and Fierro, J.L.G. Effect of Fe-addition on the catalytic activity of silicas in the partial oxidation of methane to formaldehyde. Appl. Catal. A Gen. 2002, 226, 163-174. 

Smith, M.R. and Ozkan, U.S. The partial oxidation of methane to formaldehyde — Role of different crystal planes of M0O3. J. Catal. 1993, 141, 124-139. 

Yang, C., Xu, N.R and Shi, J. (1998) Experimental and modeling study on a packed-bed membrane reactor for partial oxidation of methane to formaldehyde. Industrial Engineering Chemistry Research, 37, 2601-2610. 

The catalytic partial oxidation of methane to formaldehyde, considered in many comprehensive reviews — see, e.g., [57] — is not the subject of the present analysis, limited only to... 

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