Frustrated Lewis Pairs Boosting CO2 Capture and In Situ Methanation over Ni/CaO Dual-Functional Materials

Abstract

In this study, a Ni/CaO dual-functional material with a frustrated Lewis pair (FLP) structure was synthesized through the codoping of Al and Zr for integrated CO₂ capture and methanation applications. The formation of FLPs was confirmed using CO₂-TPD, EPR, and NH₃-TPD, which showed enhanced acid–base properties due to the creation of oxygen vacancies (acting as Lewis bases) and the introduction of Zr⁴⁺ (acting as a Lewis acid). This unique acid–base environment facilitated efficient CO₂ activation and proton transfer. In situ diffuse reflectance infrared Fourier transform spectroscopy identified key intermediates such as CO*, indicating that in situ methanation follows a dissociation path. DFT calculations demonstrated that the FLP structure lowers the energy barrier for COOH* to CO* conversion, while Zr⁴⁺ accelerated the C–H bond formation. Compared to the pristine Ni/CaO material without FLP structures, the Ni₁₀Ca₈₀Al₅Zr₅ material with FLP structures exhibits a significant enhancement in performance, with CO₂ adsorption capacity increasing from 9.89 to 12.51 mmol/g and CH₄ yield rising from 3.68 to 7.46 mmol/g. Over 20 cycles, the CO₂ conversion rate and CH₄ selectivity of Ni₁₀Ca₈₀Al₅Zr₅ only slightly decreased by 0.45 and 4.6%, respectively. The CO₂ adsorption capacity decreased to 9.35 mmol/g in the first 15 cycles and then remained stable. This study demonstrates that Al and Zr codoping improves the cyclic stability and methanation activity of Ni/CaO dual-functional materials.