Enhanced photothermal catalytic CO2 hydrogenation: Tuning Ni-ZnO by Ni content and reduction conditions

Abstract

Photothermal catalytic CO₂ hydrogenation is crucial for reducing CO₂ emissions. Herein, metallic Ni, known for its excellent photo-thermal and hydrogen dissociation properties, was deposited onto ZnO for this purpose. 5 wt% Ni/ZnO H₂-reduced at 400 °C achieved a CO₂ conversion of 36.2 % and a CO yield of 16.5 mmol·g_cat⁻¹·h⁻¹ under Xe lamp irradiation at 300 °C, demonstrating an 8.9-fold improvement compared to pristine ZnO. XRD, TEM, XPS, H₂-TPR, and CO₂-TPD analyses revealed that Ni loading above 5 wt% or reduction temperature exceeding 400 °C led to larger Ni particle sizes and decreasing oxygen vacancies, thereby diminishing catalytic activity. UV-Vis DRS, EIS, PL, and DFT studies confirmed that highly dispersed Ni and abundant oxygen vacancies enhanced visible light absorption and prolonged the lifetime of photogenerated charge carriers. These findings highlight the synergy between oxygen vacancies on ZnO and highly dispersed Ni in promoting CO₂ adsorption and activation under visible light illumination.