Influence of nitrogen impurity for steam methane reforming over noble metal catalysts

• The NH3 by-production for CH4 SR containing N2 over metal catalysts was studied.
• A relatively large amount of NH3 was produced over commercial Ni and Ru catalysts.
• Over Rh, Pt, and Ir catalysts, the amount of NH3 formed was quite low (< 0.1 ppm).

Ammonia by-production for steam methane reforming over alpha alumina (α-Al2O3) supported noble metal catalysts was investigated using the methane containing nitrogen feedstock for residential fuel cell. Ammonia is poisonous substance for carbon monooxide preferential oxidation (CO-PROX) catalyst, Pt elctrode, and proton exchange membrane (PEM) in the polymer electrolyte fuel cell system. The ammonia concentrations in the reformed gases at 700 °C under SV = 10,000 h−1 condition over commertial Ni and Ru catalysts were 20 ppm and 81 ppm, respectively. In the case of the Ru catalyst, ammonia concentration almost reached the chemical equilibrium value at 700 °C. Ammonia formation performance over 0.5 wt% metal (Rh, Pt, Ir, and Ru) supported on α-Al2O3 catalyst prepared by the impregnation method was compared at 700 °C under SV = 2,500 h−1 condition; the ammonia concentrations in the reformed gases over the Rh, Pt, and Ir catalysts were below 0.1 ppm. The order of ammonia formed amount over the catalysts was as follows: Ru > > Rh, Pt, Ir. The ammonia formation can be substantially suppressed during steam reforming of methane containing nitrogen over the Rh, Pt, and Ir catalysts.

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