Effect of interactions between Ni and Mo on catalytic properties of a bimetallic Ni-Mo/Al₂O₃ propane reforming catalyst

The effect of promoting a 15 wt.% Ni/Al2O3 catalyst with small amounts of Mo (0.1 and 0.5 wt.%) to produce H2 via propane oxidative steam reforming was investigated. Activity and stability experiments run at 450 °C showed that the 0.1 wt.% Mo-promoted catalyst had higher propane conversion, higher H₂ yields and showed superior performance in terms of resisting deactivation by coking. Different characterization techniques show that the impact on activity, selectivity and stability are driven by an electronic effect of Mo on Ni, even with such small amounts. For example, oxygen storage capacity measurements revealed higher oxygen mobility over the promoted catalyst surface. This high O₂ mobility led to higher gasification rates of carbonaceous species, leading to higher H2 yields and preventing coking of the catalyst. In-situ DRIFTS experiments also showed that the addition of Mo affected the stability of adsorbed reaction intermediates on the catalyst surface. Higher CO yields over the Mo-promoted catalyst resulted from weak adsorption or rapid desorption of CO in the presence of these small amounts of Mo. These changes in intermediate species stabilities affected some pathways in the general propane oxidative steam reforming scheme. Weak adsorption of CO also decreased the amount further oxidized to CO₂ while the increased oxidation of CHx species lowered the amount hydrogenated to CH₄.