Oxygen vacancies coupled with surface silicide facilitate CO2 activation at near-room temperature for efficient methane productivity on Ni-oxide supported Pd nanoparticles

Abstract

The catalytic conversion of carbon dioxide (CO₂) into valuable commodities such as methane (CH₄) via CO₂ methanation stands as a promising avenue for addressing both energy and environmental challenges. Considering the exothermic nature of the CO₂ methanation reaction, low temperature is beneficial for high CH₄ productivity. However, the high stability of linear CO₂ molecules demands highly active catalysts for activation at low temperatures. In response, we have developed binary catalysts comprising tetrahedral symmetric Ni-oxide-supported Pd nanoparticles with a surface coating of silicide (NiO_TPdX-T, X = Pd/Ni ratio). The as-prepared NiO_TPdX-T catalyst with a Pd/Ni ratio of 1.5 (hereafter denoted as NiO_TPd15-T) initiates CO₂ methanation at an unprecedentedly low temperature of 50 °C with 100% CH₄ selectivity and achieves an outstanding CH₄ productivity of ∼6858 mmol g⁻¹ h⁻¹ at 300 °C temperature, surpassing its monometallic counterparts (NiO_T-T (∼3899 mmol g⁻¹ h⁻¹) and Pd-T (∼331 mmol g⁻¹ h⁻¹)) by several fold. With insights from comprehensive physical and electrochemical investigations along with ambient pressure X-ray photoelectron spectroscopy (APXPS) observations, we demonstrated that the remarkably high CH₄ productivity of the NiO_TPd15-T catalyst originates from the local cooperation between oxygen vacancies (O^V)s in the Ni-oxide support, surface silicide and adjacent Pd nanoparticles. During CO₂ conversion, the O^Vs and surface silicide facilitate CO₂ activation, while Pd nanoparticles and metallic Ni domains promote hydrogen splitting. We envision that the obtained results will open new perspectives for designing high-performance catalysts possessing multiple active sites for the CO₂ reduction reaction.