Partial oxidation, of methane to synthesis

Partial oxidation of methane to synthesis gas over Ru/Ti02 catalysts... 

Concerning the reaction pathway, two routes have been proposed the sequence of total oxidation of methane, followed by reforming of the unconverted methane with CO2 and H2O (designated as indirect scheme), and the direct partial oxidation of methane to synthesis gas without the experience of CO2 and H2O as reaction intermediates. The results obtained by Schmidt and his co-workers [4, 5] indicate that the direct reaction scheme may be followed in a monolith reactor when an extremely short contact time is employed at temperatures in the neighborhood of 1000°C. However, the majority of previous studies over numerous types of catalysts show that the partial oxidation of methane follows the indirect reaction scheme, which is supported by the observation that a sharp temperature spike occurs near the entrance of the catalyst bed, and that essentially zero CO and H2 selectivity is obtained at low methane conversions (<25%) where oxygen is not fully consumed [2, 3]. A major problem encountered... 

Controlled elimination of mass and heat transport resistances is an important prerequisite for obtaining intrinsic kinetic parameters of the fast exothermic reaction of partial oxidation of methane to synthesis gas. It has been demonstrated that under conditions of strong transport limitations erroneous conclusions concerning the reaction scheme can be derived [7-9]. It was determined in this laboratory that transport limitations are practically absent over a wide range of operating conditions if one portion of the catalyst (< 40 pm) is diluted with -5 portions of an... 

Co and Fe catalysts have also been studied for the partial oxidation of methane to synthesis gas. Their potential relies on the fact that Co and Fe have higher melting and vaporizing points than Ni. Lower performances were mostly observed, however, which is probably related to the higher activity of CoO and FC2O3 for the complete oxidation of methane [121, 132, 133]. The recognized order of reactivity for partial oxidation is in fact Ni Co > Fe. However, it was observed that the performance of Co improves when a promoter is added. An extensive study of the catalytic partial oxidation of methane over CO/AI2O3 catalysts with different metals (0.1 wt% of Ni, Pt,... 

These values of A Hr are standard state enthalpies of reaction (aU gases in ideal-gas states) evaluated at 1 atm and 298 K. 7VU values of A are in kilojoules per mole of the first species in the equation. When A Hr is negative, the reaction hberates heat, and we say it is exothermic, while, when A Hr is positive, the reaction absorbs heat, and we say it is endothermic. Tks Table 2-2 indicates, some reactions such as isomerizations do not absorb or liberate much heat, while dehydrogenation reactions are fairly endothermic and oxidation reactions are fairly exothermic. Note, for example, that combustion or total oxidation of ethane is highly exothermic, while partial oxidation of methane to synthesis gas (CO + H2) or ethylene (C2H4) are only slightly exothermic. 

Hamakawa S, Shiozaki R, Hayakawa T, Suzuki K, Murata K, Takehira K, Koizumi M, Nakamura J, and Uchijima T. Partial oxidation of methane to synthesis gas using Ni/Cao.8Sro.2Ti03 anode catalyst. J. Electrochem. Soc. 2000 147 839-844. 

Ostrowski T, Giroir-Fendler A, Mirodatos C, and Mleczko L. Comparative study of the partial oxidation of methane to synthesis gas in fixed-bed and fiuidized-bed membrane reactors Part 11—development of membranes and catalytic measurements. Catal Today 1998 40(2-3) 191-200. 

At relatively low temperatures (< 800 °C), over most catalysts investigated, the catalytic partial oxidation of methane to synthesis gas is thought to follow the so-called indirect scheme, according to which initially methane is combusted until all... 

Nakagawa, K., Ikenaga, N., Teng, Y., Kobayashi, T., and Suzuki, T. Partial oxidation of methane to synthesis gas over iridium-nickel bimetallic catalysts. Applied Catalysis. A, General, 1999, 180, 183. 

Otsuka, K., Wang, Y., Sunada, E., and Yamanaka, I. Direct partial oxidation of methane to synthesis gas by cerium oxide. Journal of Catalysis, 1998, 175, 152. 

S. Pei, M.S. Kleefisch, T.P. Kobylinski, K. Faber, C.A. Udovich, V. Zhang-McCoy, B. Dabrowski, U. Balachandran, R.L. Mieville and R.B. Poeppel, Failure mechanisms of ceramic membrane reactors in partial oxidation of methane to synthesis gas. Catal. Lett., 30 (1995) 210-212. 

Wang HY, Ruckenstein (1999) Catalytic partial oxidation of methane to synthesis gas over g-AljO -supported rhodium catalysts. Catal Lett 59 121-127... 

Pavlova SN, Sazonova NN, Ivanova JA, Sadykov VA, Snegurenko OI, Rogov VA, Zolotarskii IA, Moroz EM (2004) Partial oxidation of methane to synthesis gas over supported catalysts based on Pt-promoted mixed oxides. Catal Today 91-92 299-303... 

Enger BC, Lodeng R, Holmen A (2008) A review of catalytic partial oxidation of methane to synthesis gas with emphasis on reaction mechanism over transition metal catalysts. Appl Catal A 346 1-27... 

Passos FB, de Oliveira ER, Mattos LV, Noronha FB (2005) Partial oxidation of methane to synthesis gas on Pt/CexZri xO2 catalysts the effect of the support reducibility and of the metal dispersion on the stability of the catalysts. Catal Today 101 23-30... 

Caro J, Schiestel T, et al., Perovskite hoUow-fiber membranes in the partial oxidation of methane to synthesis gas in a membrane reactor, Desalination 2006 129 415-417. 

The mechanism of the partial oxidation of methanol to Hj and CO2 can be very complex due to the possibility of many different reactions occurring simultaneously. Some of these processes are the methanol decomposition, combustion, water gas shift, etc. The residence time studies indicated that possible reactions taking place primarily are the combustion forming CO2 and H2O and the decomposition to CO and H2. There is no evidence to dispute that the partial oxidation of methanol can occur as a primary reaction. In this respect, the partial oxidation of methanol is similar to the partial oxidation of methane to synthesis gas (CH4 -b 1/2 O2 CO... 

PARTIAL OXIDATION OF METHANE TO SYNTHESIS GAS IN A FAST FLOW MEMBRANE REACTOR. 

Sustainable Ni/BaTi03 Catalysts for Partial Oxidation of Methane to Synthesis Gas... 

The major advantages of this route over the steam reforming are the H /CO ratio of ca. 2 suitable for downstream processes and the exothermicity of the reaction which eliminates the need for a fuel gas [2]. Many catalysts for the partial oxidation of methane to synthesis gas, consisting of supported metals such as Ni, Co and Fe and noble metals Pd, Ir, Rh, Ru, Pt, etc have been described in the literature [2-9],... 

This work suggests that the high activity and selectivity of the catalysts Gd-Co-O and Sm-Co-O for the partial oxidation of methane to synthesis gas is due to the stability of the cobalt in its reduced state over the sesquioxides Gd,0, and Sm,0,. In the case of La-Co-O and Nd-Co-O reoxidation of cobalt to the original perovskite structure causes loss of activity and selectivity. TPO experiments with reduced Ln-Co-0 (Ln = La, Nd, Sm and Gd) catalysts indicated that reoxidation takes place in two steps first oxidation of the supported Co to the spinel Co,04 (Co- Co, 04) and further the oxidation of the Co-" to Co with a simultaneous solid state reaction with Ln,0, regenerating the perovskite structure. It was observed that the temperature for the second oxidation step is strongly dependent on the nature of the lanthanide increasing in... 

The combination of reactions (2) and (5) may be considered as a scheme for direct methane oxidation to synthesis gas (CO -f H2). Similar reactions may determine the high efficiency of mixed catalysts containing Ni and rare-earth oxides for the partial oxidation of methane to synthesis gas [9]. This mechanism does not require a preliminary total oxidation of methane followed by its reforming with CO2 and/or water which was considered as the main route for synthesis gas formation [10,11]... 

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