Promoting the photocatalytic conversion of carbon dioxide to methanol on molybdenum dioxide using sodium species†

Mimicking natural photosynthesis to convert CO₂ into small energy molecules (e.g., CH₄ and CH₃OH) is of great significance for carbon neutralization. However, achieving catalytic reactions with high selectivity in the absence of sacrificial reagents or extra photosensitizers remains a huge challenge. Here, we demonstrated that sodium species on MoO₂ (Na/MoO₂) can act as an effective photocatalyst for selectively converting CO₂ into CH₃OH under visible light irradiation. Na/MoO₂ showed good catalytic activity, exhibiting a rate of 82.7 μmol h⁻¹ g⁻¹ of CH₃OH formation in a 16-h reaction with 79.4% selectivity to CH₃OH compared to CO evolution when 10 mg of the catalyst was applied. The catalytic activity and selectivity of Na/MoO₂ are much higher than those of pure MoO₂, which only showed 3.5 mol h⁻¹ g⁻¹ of CH₃OH formation in a 1-h reaction with 39.7% selectivity to CO, without the need for a sacrificing agent or photosensitizer. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and theoretical calculations explained that the Na atom on the (100) crystal plane could lower the CO₂ activation energy barrier by reducing the reaction energy of the rate-determining path from COOH* to COH₂* from 1.47 eV to 0.75 eV. Therefore, this work provides a novel view for promoting the activity of photocatalysts by introducing alkaline metal species onto metal oxides.