Activity in methanation

Fe, and B SI, Tl, Th, and Ce). The transforaed materials exhibit high specific activity In methanation, ammonia synthesis, and ethylene hydrogenation reactions. The similarity between the industrial methanation catalysts and catalysts obtained by decomposition of various Intermetallics Is striking. Most catalysts obtained by decomposition of a binary alloy Involve an associative combination of... 

Alifanti, M Auer, R Kirchnerova, J Thyrion, F Grange, P Delmon, B. Activity in methane combustion and sensitivity to sulfur poisoning of LauxCexMni.yCoyOs perovskite oxides. Appl. Catal, B Environmental, 2003, Volmne 41, Issues 1-2, 71-81. 

CP/MAS NMR study of CH4 activation on [(=SiO)2Ta(H)J shows the formation even at 150 °C of methyUdene and methyUdyne species by an a-H elimination process on several sites that should correspond to the tris-hydride on other sites a methyl group is transferred to the surface, leading to the formation of (=Si-Me) and of [(=SiO)3Ta]. Correlation with EXAFS suggests that the tris-hydride should exist on surface sites (=20%) quite distant from siloxy bridges whereas methyl transfer to the surface should happen on the specific sites (=80%) close to the siloxy bridges. The latter, which are formally 10 electrons species, exhibit a moderate to weak activity in methane C-H activation. To the best of our knowledge, this is the first observation of methyl group transfer on a surface (Scheme 2.18). 

OS3(CO)l2 Amorphous carbon black Adsorption from solution and thermal treatment under H2 Os particles active in methanation [71]... 

Ni-Pd. Moss et al. (252) reported that 60% Pd (in bulk) catalysts (i.e., those which have almost 100% Pd in the surface) had almost the same activity in ethane hydrogenolysis as pure Ni, although pure Pd itself is not very active. This might be an indication that for this reaction mixed ensembles of Pd-Ni can operate. In this respect it is interesting that Driessen recently found that in contrast to this, a 75% Pd (bulk) catalyst [the exchange reaction detected (255) the presence of some Ni in the surface of a catalyst of this composition] showed no activity in methanation, compared to Ni. 

For the purpose of studying the effect of the inorganic matrix origin on iron protoporphyrin biomimic activity in methane oxidation to methanol the above-mentioned carriers of the acidic-basic type were used. According to data in Tables 7.4 and 7.5, mimics derived from them simultaneously simulate catalase reaction and monooxygenase function of cytochrome P-450. 

It was found that almost all transition metals (d-metals) exhibit catalytic activity toward methane decomposition reaction to some extent, and some demonstrate remarkably high activity. It should be noted, however, that there is no universal agreement among different groups of researchers regarding the choice of the most efficient metal catalyst for methane decomposition. For example, it was demonstrated that the rate of methane activation in the presence of transition metals followed the order Co, Ru, Ni, Rh > Pt, Re, Ir > Pd, Cu, W, Fe, Mo.20 Other researchers have found Pd to be the most active catalyst for methane decomposition,18-21 whereas still others found Ni was the catalyst of choice,22 or Fe and Ni.23-24 Finally, Co catalyst demonstrated highest activity in methane decomposition reaction.25... 

Ruthenium supported on oxides is a catalyst of various reactions. It is active in methanation reactions [e.g. 1, 2, 3], in Fischer-Tropsch synthesis [e.g. 4, 5, 6], in CO oxidation [7, 8], in the synthesis of methyl alcohol [9], 1" the redu ction of NO to nitrogen CIO] and in hydrogenolysis of ethane [11] and of butane [12]. Ru supported on carbon is supposed to replace the iron in ammonia synthesis [13]. Lately ruthenium supported on oxides is intensively investigated as a potential... 

CH4 oxidation has been experienced for ceria supported on a barium hexaaluminate, an heat resistant support. Preparation by a new reverse microemulsion method leads to ceria nanoparticles deposited on support and having a BET area close to 100 mVg after calcination at 1000 0 [72]. Such ultrahigh disperse nanoparticles show exceptional thermal resistance the authors mentioned that ceria particles prepared with a size of 6 nm sinters only to 18 nm after a calcination at 1IOO°C under a water containing atmosphere. Of course excellent activity in methane combustion has been observed. According to their experimental conditions calculated specific activity expressed as mol(CH4).h. m was estimated to 6.4x10 at 500°C whereas Bozo [44J reported a value of 1.5x1 O at the same temperature both values look similar. Thus the difference in methane conversion may be related to BET area only which is spectacularly preserved using the reverse micro-emulsion method for synthesis. 

Similar results were found by Bozo [44]. Palladium deposited onto ceria-zirconia Ceo67Zro3302 solid solution showed very high activity in methane combustion (T50 close to 300 C) but similar to that of palladium deposited onto alumina. Like for the case of platinum a deactivation is observed during tests at temperatures comprised between 200°C and 400 C (Fig. 13.3). However when aged at 1000 C under an air+water mixture this catalysts showed superior resistance compared to classical catalysts as far as activity is considered. Despite a severe sintering of both metal (dispersion is now 1%) and support, whose surface area is close to 4 mVg, T50 was shifted to 420 C, i.e. 120°C only, still much lower for platinum deposited on the same support which showed a TSO close to 620°C. Calculation of specific activities in the 200-300°C range have clearly evidenced that ceria-zirconia support does not have any influence upon performance of PdO in... 

An interesting aspect of supported palladium is the fact that palladium oxide is the thermodynamically stable phase below 1052 K, whereas the metallic palladium is stable above this temperature. It was found that the oxidic form was much more active in methane combustion than the metallic form [51,52]. This phenomenon is actually used in controlling the catalyst temperature in one of the proposed combustor concepts (See Section IV.B) and is treated in more depth in Section III.A. 

In summary, it is evident that Mo does not a lter intrinsic activity in methane reforming. It docs, however, markedly increase the thioiesistance of that phase. 

Figure 1 shows the plots of methane conversion vs. temperature for catalysts supported on alumosilicate ceramics. It is seen that the highest activity in methane oxidation has the sample with the active component 0,4%Pt + 0,2%Pd (T " = 440°C). The lowest activity is exhibited by the sample containing only 0,3%Pt (T ° = 55o"C). 

The results presented in this paper have confirmed the fact that the zeolite type catalysts which are highly active in methane oxidation reaction, are also highly active in NOx reduction reaction. 

Magnesium oxide has been reported to be active in methane complete oxidation by Berg and Jaras. The activity was somewhat lower compared with a Ba-substituted hexa-aluminate. The difference between the two catalysts decreased after calcination to 1500 °C. 

The deactivation of these catalysts is probably due to the formation of highly stable species, such as barium sulfate. In addition to the possible encapsulation of Pd particles, the migration of barium from the bulk to the surface of the support is probably responsible for the lower activity in methane oxidation. The possible formation of barium or lanthanum sulfate covering Pd particles will be further investigated. 

Wang, Y., Ren, J., Wang, Y., Zhang, F., Liu, X., Guo, Y., and Lu, G. (2008) Nanocasted synthesis of mesoporous LaCo03 perovskite with extremely high surfece area and excellent activity in methane combustion. /, Phys. Chem. C, 112 (39), 15293-15298. 

B. (2002) Evidence of phase cooperation in the LaCoOs-Ce02-Co304 catalytic system in relation to activity in methane combustion. Appl Catal A- Gen, 231 (1-2), 65-80. 

Wang, Y, Wang, Y, Liu, X.,etal. (2009). Nanocasted Synthesis of the Mesostructured LaCo03 Perovskite and Its Catalytic Activity in Methane Combustion, J. Nanosci. Nanotechno., 9, pp. 933-936. 

The activation of C-H bond in methane is a crucial hrst step in its combustion for power and heat generation. Once the hrst bond has been broken, sequential oxidation reactions to CO2 and H2O are relatively easy. A basic understanding of the activation of C-H bonds in methane is of vital importance since it permits one to assess the inhuence of catalytic and process parameters on the rate and efficiency of its catalytic combustion [29]. Several types of catalysts — including nonreducible oxides, reducible oxides, and metals — are capable of oxidizing methane with varying efficiencies. It is harder for C-H bonds to be activated in methane than in other hydrocarbons, due to the weaker adsorption of methane on oxides or on oxidized metal surfaces [30]. Strong adsorption of a saturated hydrocarbon is a prerequisite for combustion, but factors other than the strength of the C-H bond also affect the rate of combustion. 

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