Ammonia is synthesized directly from water and N at room temperature and atmospheric pressure in a flow electrochemical cell operating in gas phase (half-cell for the NH synthesis). Iron supported on carbon nanotubes (CNTs) was used as the electrocatalyst in this half-cell. A rate of ammonia formation of 2.2×10 gNH3  m h was obtained at room temperature and atmospheric pressure in a flow of N , with stable behavior for at least 60 h of reaction, under an applied potential of -2.0 V. This value is higher than the rate of ammonia formation obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with a total Faraday efficiency as high as 95.1 % was obtained. Data also indicate that the active sites in NH electrocatalytic synthesis may be associated to specific carbon sites formed at the interface between iron particles and CNT and able to activate N , making it more reactive towards hydrogenation.

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Ammonia is synthesized directly from water and N2 at room temperature and atmospheric pressure in a flow electrochemical cell operating in gas phase (half‐cell for the NH3 synthesis). Iron supported on carbon nanotubes (CNTs) was used as the electrocatalyst in this half‐cell. A rate of ammonia formation of 2.2×10−3 gNH3  m−2 h−1 was obtained at room temperature and atmospheric pressure in a flow of N2, with stable behavior for at least 60 h of reaction, under an applied potential of −2.0 V. This value is higher than the rate of ammonia formation obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with a total Faraday efficiency as high as 95.1 % was obtained. Data also indicate that the active sites in NH3 electrocatalytic synthesis may be associated to specific carbon sites formed at the interface between iron particles and CNT and able to activate N2, making it more reactive towards hydrogenation.

The nature, thermal stability, and reducibility in H2 of sulfate species on copper-on-alumina and their mechanism of formation during interaction of the sorbent-catalyst with S02-containing flows were studied in a flow microreactor and by Fourier-transform infrared spectroscopy. Spectra of the sulfate species formed on A1203, CuO, CuAl204, and Cu0/A1203 samples either by impregnation with various amounts of sulfate salts or by direct sulfation with S02 + 02 are compared. The results indicate that, on pure alumina, two types of surface sulfate species form, one more stable at low surface coverage attributed to a type with only one double S=0 bond and the second less stable and more easily decomposed by water vapor, attributed to a S03 group linked to an Al-0 pair site or to an oligomer species as S207. Sulfation of CuO leads to bulklike CuS04, whereas sulfation of copper aluminate leads to three types of sulfate species, one linked to Al3+ ions, another to Cu2+ ions, and the third to sulfate species in interaction both with Al3+ and Cu2+ ions. The latter species does not appear in the spectra of Cu supported on A1203. The analysis of the formation of sulfate species on copper-on-alumina sorbent-catalysts suggests the following mechanism: in the presence of gaseous oxygen, copper performs catalytically the first step of oxidation of S02 to S03 which then forms a stable surface sulfate at either the copper site or the aluminum site. During the first cycle of interaction of the sorbent catalyst with the S02-containing flow, a sulfate linked mainly to aluminum sites forms in an amount (about 300-400 jtmol/g) equivalent to the limiting value of sulfate species on pure A1203. This species is more stable against reduction than the other sulfate species and is not reduced by H2 at 420 °C. During the first cycle of reduction, copper aluminate sites are reduced to metallic copper which, in the consecutive step of interaction with the S02 + 02 containing flow, give rise to the formation of surface species mainly on copper that are completely regenerated in the consecutive treatment with H2 at 420 °C.