Pd@HyWO3–x Nanowires Efficiently Catalyze the CO2 Heterogeneous Reduction Reaction with a Pronounced Light Effect

The design of photocatalysts able to reduce CO₂ to value-added chemicals and fuels could enable a closed carbon circular economy. A common theme running through the design of photocatalysts for CO₂ reduction is the utilization of semiconductor materials with high-energy conduction bands able to generate highly reducing electrons. Far less explored in this respect are low-energy conduction band materials such as WO₃. Specifically, we focus attention on the use of Pd nanocrystal decorated WO₃ nanowires as a heretofore-unexplored photocatalyst for the hydrogenation of CO₂. Powder X-ray diffraction, thermogravimetric analysis, ultraviolet-visible-near infrared, and in situ X-ray photoelectron spectroscopy analytical techniques elucidate the hydrogen tungsten bronze, H _yWO_{3- x}, as the catalytically active species formed via the H₂ spillover effect by Pd. The existence in H _yWO_{3- x} of Brønsted acid hydroxyls OH, W(V) sites, and oxygen vacancies (V_O) facilitate CO₂ capture and reduction reactions. Under solar irradiation, CO₂ reduction attains CO production rates as high as 3.0 mmol g_cat^-1 hr^-1 with a selectivity exceeding 99%. A combination of reaction kinetic studies and in situ diffuse reflectance infrared Fourier transform spectroscopy measurements provide a valuable insight into thermochemical compared to photochemical surface reaction pathways, considered responsible for the hydrogenation of CO₂ by Pd@H _yWO_{3- x}.