Metal hydroxide assisted integrated direct air capture and conversion to methane with Ni/Al2O3 catalysts

Abstract

Methods to synthesize sustainable and renewable methane are becoming of growing interest to relieve humankind from its reliance on fossil and finite natural gas reserves. Metal hydroxide salts are able to capture CO₂ from dilute sources including ambient air in the form of carbonate and bicarbonate salts. We report herein the direct conversion of such inorganic carbonate salts into methane in yields of up to 100% utilizing both Ni/Al₂O₃ and Ni/CaAl₂O₄ catalysts. This conversion is achieved in 48 hours with 50 bar of hydrogen at a relatively moderate temperature of 225 °C under batch conditions. Water was also shown to improve the conversion of the carbonate salt to methane and the Ni/Al₂O₃ catalyst retained 99% of its activity in the alkaline media after five consecutive hydrogenation cycles. Remarkably, the metal hydroxide was also regenerated during the reaction and was reused to capture CO₂ for subsequent reactions. Compared to the conventional sequential approach involving the capture of CO₂ followed by the release of CO₂ and its hydrogenation to methane in the Sabatier reaction, the integrated route presented here can offer a number of energetic and economic benefits that could pave the way for a robust carbon capture and conversion process.