CaH2-promoted activity of Ni-carbonate interface for CO2 methanation

Abstract

Transition metal-carbonate interfaces often act as active sites in heterogeneous catalytic reactions. The interface between transition metal and metal carbonate exhibits a dynamic equilibrium during the CO₂ hydrogenation reaction, involving surface carbonate hydrogenation and CO₂ chemisorption. Nonetheless, there have been few reports on engineering the activity of the interface between transition metal and alkaline earth metal carbonate for catalytic CO₂ conversion. This work demonstrated that the incorporation of CaH₂ in Ni/CaCO₃ enhances the CO₂ methanation activity of the catalysts. The CO₂ conversion for Ni/CaH₂-CaCO₃ reached 68.5% at 400 °C, which was much higher than that of the Ni/CaCO₃ (31.6%) and Ni/CaH₂-CaO (42.4%) catalysts. Furthermore, the Ni/CaH₂-CaCO₃ catalysts remained stable during the stability test for 24 h at 400 °C and 8 bar. Our research revealed that CaH₂ played a crucial role in promoting the activity of the Ni-carbonate interface for CO₂ methanation. CaH₂ could modify the electronic structure of Ni and tune the structural properties of CaCO₃ to generate medium basic sites (OH groups), which are favorable for the activation of H₂ and CO₂. In-situ Fourier transform infrared spectroscopy (FTIR) analysis combined with density functional theory calculations demonstrated that CO₂ activation occurs at the hydroxyl group (OH) on the CaH₂-modified Ni-carbonate surface, leading to the formation of CO₃H* species. Furthermore, our study has confirmed that CO₂ methanation over the Ni/CaH₂-CaCO₃ catalysts proceeds via the formate pathway.