High surface area bulk molybdenum nitride catalysts were synthesized via temperature-programmed ammonolysis of an ammonium heptamolybdate and citric acid (CA) composite. The synthesized materials were tested for CO_x-free H₂ production via ammonia decomposition for fuel cell application. Cobalt was added at different loadings (1, 3, and 5 wt%) as a promoter for the bulk molybdenum nitrides. The chemical composition and surface morphology of the nitride catalysts were studied by means of XRD, XPS, SEM-EDAX and TEM techniques. Addition of cobalt increased the formation of the γ-Mo₂N phase and cobalt existed as the Co₃Mo₃N phase, which was uniformly distributed over Mo₂N as evidenced by TEM and SEM analyses. A drastic increase in Mo₂N crystal size was observed when the Co loading exceeded 3 wt%, which in turn decreased the catalyst activity for ammonia decomposition reaction. All catalysts exhibit higher activity than the reported nitride catalysts at low temperatures. All catalysts showed stable activity for 30 hours. The activation energy calculated for ammonia decomposition was decreased drastically from 131.2 to 99 kJ mol⁻¹ by the addition of cobalt (1 wt%) in Mo₂N preparation.

Using anthropogenic carbon dioxide (CO₂) as a feedstock for the production of synthetic fuel has gained significant attention in recent years. Among the various CO₂ conversion pathways, the production of synthetic natural gas via CO₂ methanation holds promise because of its potential for both carbon recycling and renewable energy storage. Nickel (Ni) and ruthenium (Ru) are the dominant metals employed as catalysts in the CO₂ methanation reaction. This review summarizes the research landscape of Ni- and Ru-based catalysts over the last ten years. Bibliometric analysis revealed that China has the highest number of publications, the Chinese Academy of Sciences is the foremost academic institution, and the International Journal of Hydrogen Energy is the leading journal in this area of research. The publication trend revealed that research on Ni-based catalysts is published at almost four times the rate of Ru-based catalysts. Despite growth in research, problems with catalyst stability and kinetics still exist. The latest research on various catalytic systems, including supported, bimetallic, and single-atom catalysts and the fundamental challenges associated with the CO₂ methanation process are reviewed. This review provides a new angle for future studies on catalysts based on non-noble Ni and noble Ru metals and opens the way for additional research in this area.