Supported nickel catalysts for low temperature methane steam reforming: comparison between metal additives and support modification

The effect of Ag (1 wt%) and Au (1 wt%) on the catalytic properties of Ni/Al2O3 (7 wt% Ni) for methane steam reforming (MSR) was studied in parallel with the effect of CeO2 (6 wt%) and La2O3 (6 wt%) addition. The addition of 1 wt% Ag to the alumina supported nickel catalyst drastically decreased its catalytic properties at temperatures lower than 600 degrees C, due to the blockage of metal catalytic centers by silver deposition. The addition of Au and CeO2 (La2O3) to the nickel catalyst improved the methane conversion, CO2 selectivity and hydrogen production at low reaction temperatures (t < 600 degrees C). At 700 degrees C under our working conditions, the additives have no important effect in hydrogen production by MSR. The best hydrogen production at low temperatures was obtained for Ni-Au/Al2O3, due to the higher CO2 selectivity, cumulated with slightly higher methane conversion in comparison with Ni/CeO2-Al2O3. At high temperature, Ni/CeO2-Al2O3 is stable for 48 h on stream. Ni-Au/Al2O3 and Ni-Ag/Al2O3 are mainly deactivated due to the temperature effect on Au and Ag nanoparticles and less through coke formation. On Ni/Al2O3 and Ni/La2O3-Al2O3, crystalline, graphitic carbon was deposited after 48 h of reaction leading to catalyst partial deactivation. On the Ni/CeO2-Al2O3 surface, a porous amorphous form of deposited carbon was found, which does not decrease its catalytic activity after 48 h of reaction.