Design of Ni-FAU Zeolite Bifunctional Materials for Integrated Carbon Dioxide Capture and Methanation: Construction of ultrafine NiO nanoparticles.

The Integrated Carbon Dioxide (CO2) Capture and Methanation (ICCU-Met) technology has emerged as a promising strategy for reducing CO2 emissions while producing methane (CH4) fuel. However, a significant challenge in this process is the absence of bifunctional materials (DFMs) that simultaneously possess highly dispersed metal sites and stable adsorbent structures under variable temperature conditions. This is particularly problematic because existing nickel-based (Ni) bifunctional materials are prone to metal sintering and structural degradation at high temperatures. In this study, highly dispersed ultrafine Ni metal confined in Faujasite (FAU) zeolite support bifunctional materials were synthesized with remarkable CO2 capture capacity of 2.77 mmol CO2/g and CH4 yield of 654.4 μmol CH4/g in the ICCU-Met reaction. Notably, the 8Ni-FAU DFMs maintained their initial activity after 10 drastic heating-cooling cycles between 70 °C and 300 °C. Moreover, the CO2 adsorption, CH4 yield, and CH4 selectivity of 8Ni-FAU DFMs under simulated real flue gas atmosphere were 0.43 mmol/g, 264.3 μmol/g, and 99.5 %, respectively. This stability is attributed to the successful immobilization of ultrafine NiO nanoparticles within the FAU zeolite pores, which enhanced the metal-support interactions and promoted the formation of oxygen vacancies. These features facilitated the efficient adsorption and decomposition of CO2, as well as the activation and dissociation of H2. Both in situ DRIFTs experiments and density functional theory (DFT) calculations confirmed that the 8Ni-FAU DFMs proceed via the formate pathway. Additionally, it was found that the strong interaction between the active Ni metal and the FAU support reduces the CO2 adsorption energy and lowers the energy barrier for the generation of formate (HCOO*) active intermediates, thus guiding the ICCU-Met reaction.