Role of Mg:Al ratio and Pt promotion on mitigating the deactivation of Ni-based methane steam reforming catalysts

Ni-based catalysts for CH$_4$ steam reforming require fine tuning to withstand deactivation under dynamic operation conditions relevant to emerging H$_2$-driven technologies. This study investigates the impact of Mg:Al ratio and Pt presence in catalyst composition on the activity and stability of industrially relevant Ni-based mono- and bimetallic catalysts during simulated daily start-up and shut-down cycles in various gas atmospheres. The evolution of the catalyst structure during extensive testing procedures was investigated in detail by complementary electron microscopy, in situ/operando XAS and XRD. The results obtained revealed that the catalyst deactivation is promoted at high Mg:Al ratios and especially affects the monometallic catalysts. By converting CH$_4$ at lower temperatures, Pt regulates Ni oxidation extent and its incorporation into MgO lattice. Further prevention of catalyst deactivation was achieved by optimizing the reactor shut-down procedure to minimize its simultaneous exposure to high temperatures and H$_2$O vapors. By flushing the reactor with N$_2$ only around the reaction extinction temperature, a fraction of Ni species is maintained in metallic state, which is beneficial for the long-term activity and reaction operation economy.