CH4 and CO2 conversions

The stability but also the catalytic activity of nickel-based perovskite was improved with a low amount of magnesium or rhodium in the structure. The solubility of Mg in the perovsldte structure is limited phases such as NiO and MgO are evidenced by XRD when >0.1 in LaNii Mg >,03 [24]. High catalytic activity was reached at 700 °C, with LaNio.9Mgo.1O3 under severe reaction conditions 10 mg of catalysts, CH4/CO2 50/50 ml/min without dilution gas. The CH4 and CO2 conversion were respectively equal to 57 and 67% and maintained during 15 h on stream even if carbon deposition was detected by thermogravimetric analysis at the end of the reaction (27 wt%). 

Fig. 12. Conversions of CH4 and CO2 and selectivities for formation of CO and H2 as a function of time on stream for C02 reforming of CH4 catalyzed by 17 wt% Ni/La203. Before reaction, the catalyst was reduced in flowing H2 at 773 K for at least 5 h and then at 1023 K for 2 h. Reaction conditions pressure, 1 atm temperature, 1023 K feed gas molar ratio, CH4 /C02 = 1 /1 GHSV is unknown (228).

The preparation method also affects the Ni/La203 catalysts (231). The conversions of CH4 and CO2 in the CO2 reforming of CH4 catalyzed by Ni/La203... 

The reactions involved in acetate conversion to CH4 and CO2 as well as the thermodynamic data are given in Fig. 10 and Table 4. Acetate is activated in Methanosarcina to... 

Acetate conversion to CH4 and CO2 is strictly dependent on Na ions [110]. Cell suspensions of Methanosarcina barkeri have been shown to generate a Na gradient ([Na ]out/[Na ]in 5) across the cytoplasmic membrane [230]. The sites of Na dependence and of Na translocation in acetate conversion to CH4 and CO2 are not known. Both the reduction of CH3-S-C0M to CH4 and the oxidation of CO to CO2 are not dependent on Na [230,235]. Recent evidence indicates that CH3-H4MPT H-S-CoM methyltransferase is a Na" -dependent membrane protein, which catalyzes primary Na ... 

Figure 5, Methane and CO2 conversions over 1% Rh/Alumina at 800 C, CH4/CO2 = 2, and 8atm.

For example the conversion of cellulose was studied in autoclaves with residence times of up to 1 h at 200-400 °C and 8-18 MPa [138, 139]. It was found that sodium carbonate as a catalyst suppresses the formation of char and oil and mainly water-soluble products were formed. At 400 and with a Ni catalyst, CH4 and CO2 were found as major products in the gas phase. Batch reactor experiments [140, 141] used for the formation of a CH4-rich gas from biomass, waste model compounds and real waste waters, were also carried out at 350 °C, 20 MPa, and reaction times of 60-120 min. It was shown that aromatic and aliphatic hydrocarbons as well as oxygenates are converted to a CH4-rich fuel gas in the presence of hydrogenation catalysts. The results were confirmed in continuous-flow reactor experiments with residence times of 10 min and longer for conversions of 90 % or more. In any case, without the high reactivity of biomass in and with near-critical water, methane formation at low temperatures would not be possible. 

Initial monitoring of the catalytic activity was performed using as-synthesized perovskites without any reduction step. In the case of conventional LaNiOs, very low values of conversions were observed for both CH4 and CO2 until 800 °C. For nanocast LaNiOs, comparatively higher conversions (approximately 40%) were... 

Figure 3.8 CH4 and CO2 dry reforming conversion as a function of time on stream at 700 °C over Ni/La20s catalysts derived from nanocast (LN-NCR) and bulk...

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