Low-temperature steam reforming of jet fuel in the absence and presence of sulfur over Rh and Rh–Ni catalysts for fuel cells

This work is a comparative study on low-temperature steam reforming of jet fuel over Rh and Rh–Ni loaded on CeO2-modified Al2O3 support in the absence and presence of different amounts of organic sulfur. Rh loaded on CeO2–Al2O3 support can promote reforming of sulfur-free or desulfurized jet fuel at <520 °C with >97% conversion to syngas and CH4. However, monometallic Rh/CeO2–Al2O3 catalyst deactivates by S poisoning. During the reforming of liquid fuel with >10 ppmw S, catalytic activity rapidly decreases when the amount of sulfur in the fuel flown over the catalyst reaches the level corresponding to a Sfuel:Rhsurf atomic ratio of 0.28–0.30 (for which the amount of surface Rh is based on H2 and CO pulse chemisorption analysis). Methane formation is even more sensitive (than conversion) to sulfur poisoning. At a Sfuel:Rhsurf ratio of 0.15, methane selectivity over the Rh/CeO2–Al2O3 catalyst begins to decline. Addition of Ni by co-impregnation into the Rh/CeO2–Al2O3 catalyst leads to much higher sulfur tolerance. Ni acts as a protective and sacrificial metal for Rh in the Rh–Ni/CeO2–Al2O3 catalyst. Ni surface saturation of sulfur was found to occur at a Sfuel:Nisurf ratio of 0.59–0.60, corresponding to a Sfuel:Rhsurf ratio of 1.1 for 2% Rh–10% Ni/CeO2–Al2O3. The bimetallic Rh–Ni/CeO2–Al2O3 catalyst allows for successful low-temperature reforming of a JP-8 jet fuel containing 22 ppm sulfur for 72 h with >95% conversion. TPR and XPS analysis reveals close Rh–Ni metal–metal interactions. The presence of Ni increases the temperature for Rh reduction in TPR, whereas Rh helps maintain Ni in a reduced state in an oxidative atmosphere.