Enhanced methane decomposition over nickel-carbon-B₂O₃ core-shell catalysts derived from carbon dioxide

Nickel-carbon-B₂O₃ nanocomposites (Ni@C-B₂O₃s) were synthesized from a single-step reaction of CO₂ with NaBH₄ at 1bar and investigated as catalysts for methane decomposition. These catalysts exhibited an unprecedented activity for producing hydrogen and graphitic carbon nanoonions (CNOs) without any generation of carbon oxides (CO_x), despite of the absence of a catalyst reduction step by hydrogen. Around 90% of methane conversion with 61mmolmin^-1g_Ni^-1 was achieved using 13wt% nickel-containing Ni@C-B₂O₃ (13Ni@C-B₂O₃) at 850°C under 46.15 LCH4h-1gNi-1. The uncompromising activity of the catalyst comes from the two major contributions: the absence of nickel oxide eliminates the formation of carbon oxides and the amorphous core-shell structure of Ni@C-B₂O₃s facilitates nano-sized nickel cores to escape the CNOs and directly decompose methane. This was verified by various microscopic and spectroscopic investigations. The generated CNOs on 13Ni@C-B₂O₃ were partially oxidized by CO₂ as a mild oxidant with the production of CO. The catalytic activity of 13Ni@C-B₂O₃ was maintained for 15 cycles, providing a potential of enabling the cyclic process of CH₄ decomposition/CO₂ regeneration. By synthesizing Ni@C-B₂O₃s from CO₂ and using them to the cyclic operation, not only was CO₂ converted to the valuable catalyst, but hydrogen, CNOs, and CO were also produced from the greenhouse gases of methane and CO₂.