Carbon Dioxide Reforming of Methane over Mesoporous Alumina Supported Ni(Co), Ni(Rh) Bimetallic, and Ni(CoRh) Trimetallic Catalysts: Role of Nanoalloying in Improving the Stability and Nature of Coking

Abstract

Catalytic dry reforming of methane using carbon dioxide (DRM) to produce CO rich syngas (synthesis gas) over supported nickel catalysts presents major challenges including the carbon deposition and active metal sintering at high operating temperatures. In this work, we have demonstrated that addition of rhodium and cobalt to the nickel phase supported on mesoporous alumina (MAl) to form bimetallic and tri metallic RhNi/MAl, NiCo/MAl, and NiCoRh/MAl catalysts and alloying of Ni was found to enhance the catalyst activity and high resistance toward coking. All these catalysts were synthesized using a triblock copolymer P123 templated precipitation of aluminum isopropoxide and metal precursors, followed by the removal of the template by calcination. The high conversions of CH4 with CO2 into syngas and the nature of carbon formation on these bimetallic catalysts were found to be different from those of the monometallic catalysts, and the ratios of H2 and CO in the syngas were observed to be 0.9–1. The enhanced stability and activity were attributed to the bimetallic phase formation, which was supported by XRD, XPS, TPR, TGA, TEM, and N2-sorption analysis of the fresh and spent catalysts. From these results, a plausible mechanism was proposed to explain the enhanced catalytic activity and stability, which was mainly due to the nature of alloy formation. Nickel was found to form a homogeneous alloy phase with cobalt, while it formed a heterogeneous bimetallic phase with rhodium. Alloying with cobalt moderates the coking in the NiCo/MAl case, while alloying with rhodium increases the carbon gasification by hydrogen spillover effect in the case of NiRh/MAl.