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Communication Dans Un Congrès Année : 2014

Methane removal from air in a plasma-catalytic hybrid reactor

Résumé

Methane oxidation has been investigated in a plasma-catalytic hybrid reactor. A comparison between catalyst without plasma (catalytic), plasma-alone (without catalyst materials), catalyst after-plasma (PPC) and catalyst in-plasma (IPC) was systematically made in the temperature range of 25-500°C. Pd-supported on Al2O3 spheres, with different diameters (1.0 and 1.8 mm) and different Pd amount (0.5 and 1wt.%Pd), were used as catalysts. The N2 adsorption/desorption analysis show that both the BET surface area and the total pore volume increases with the alumina sphere diameter, corresponding to mesoporous materials. XRD patterns suggest the formation of alumina phase with presence of the characteristic peaks for -Al2O3 phase. XRD analysis also confirms a small Pd metal peak to be present along with the major PdO peaks. However, XPS analyzes shows only the Pd2+ peak, corresponding to the PdO phase, probably because the amount of exposed Pd metal is too small to be picked up by XPS. Thus, one can expect that the exchange or equilibration should occur on the surface of PdO at lower temperatures, being the PdO quite stable and does not easily change oxidation state of a metal. XPS results also showed the formation of palladium species in a higher oxidation state, probably PdO2, inducing the formation of new interfacial sites for the oxidation reaction. CH4 catalytic oxidation shows that Al2O3, by itself, does not exhibit any catalytic activity for CH4 conversion at temperature lower than 500ºC. Moreover, the catalytic activity increases by decreasing the particle size and increasing the Pd amount, according to the following sentences: 1wt% Pd/Al2O3 (1.0 mm) > 1wt% Pd/Al2O3 (1.8 mm) ~ 0.5wt% Pd/Al2O3 (1.0 mm) > 0.5wt% Pd/Al2O3 (1.8 mm). These results could be attributed to the high surface exposure of the active sites related to a better dispersion of Pd particles on the small diameter support, and the greater number of active sites present on the catalyst to increase the amount of Pd loaded. For plasma-alone experiments, CH4 conversion reached a maximum of 67% with CO, CO2, O3, and HNO3 as main products. The plasma-catalytic results revealed the benefit effect of plasma on the oxidation of CH4 even at low temperature. Results clearly show that, at room temperature, the plasma could activate both alumina and Pd/Al2O3 catalysts: CH4 conversion up to 5% was measured. In plasma-catalytic systems, the CH4 conversion curves were shifted toward lower temperature as the plasma specific input energy increased. Catalytic performances were significantly enhanced when plasma is used. Compared with plasma-off case, improvements of 200% and 40% were measured at 300 and 350°C, respectively. Although the difference is weak, the in-plasma catalysis configuration seem to be more efficient compared with post-plasma catalysis. In all cases, the reaction using Pd/Al2O3 catalyst becomes more selective in carbon dioxide formation than the reaction in plasma alone and, at high temperature O3 and HNO3 disappears in favor of NOx.
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Dates et versions

hal-01059357 , version 1 (29-08-2014)

Identifiants

  • HAL Id : hal-01059357 , version 1

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Thien Pham Huu, Sonia Gil, Patrick da Costa, Anne Giroir-Fendler, Ahmed Khacef. Methane removal from air in a plasma-catalytic hybrid reactor. GECAT, Apr 2014, Cluny, France. ⟨hal-01059357⟩
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