Co-Ni on zirconia and titania catalysts for methane decomposition to hydrogen and carbon nanomaterials: The role of metal-support interactions

Cobalt and nickel-based bimetallic catalysts supported over titanium dioxide and zirconia were synthesized using the mechanical mixing method and investigated for catalytic methane decomposition reaction. The total contents of both metals were kept at 15 wt% and the ratio between cobalt and nickel remained one. The catalyst characterization prior to reaction showed that zirconia-supported nickel and cobalt-based catalysts represented as ZNC exhibited weaker metal-support interaction as well as easily reducible active species while titania-supported nickel and cobalt-based catalysts denoted as TNC had relatively stronger metal-support interaction. The activity results revealed that ZNC activated at 500 °C (ZNC-500) catalysts performed better with a maximum hydrogen production rate of 7.26 mol/g_M/s than their TNC counterparts i.e., TNC-500 (5.83 mol/g_M/s). The elevated activation temperature resulted in the loss of activity that was assigned to metal particle agglomeration. Moreover, elevated activation temperature caused the reduction of surface oxide species without allowing the reduction of bulk oxide species. The extent of interaction between the metal and the support, reducibility, and the degree of metal particle aggregation have significantly influenced the catalytic activity as well as carbon growth mechanisms of the catalysts. The characterization of spent catalysts using SEM and TEM discovered that carbon nanomaterials were formed over the surface of the catalysts and each catalyst followed either base-growth and/or tip-growth mechanism.