Pd@H_yWO_3–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, HyWO3–x, as the catalytically active species formed via the H2 spillover effect by Pd. The existence in HyWO3–x of Brønsted acid hydroxyls OH, W(V) sites, and oxygen vacancies (Vo) facilitate CO2 capture and reduction reactions. Under solar irradiation, CO2 reduction attains CO production rates as high as 3.0 mmol gcat–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@HyWO3–x

Crystal Structure and High-Temperature Thermoelectric Properties of the Mo3−x Ru x Sb7 Compounds

Zintl phases are currently receiving great attention for their thermoelectric potential typified by the discovery of a high ZT value in Yb 14MnSb 11-based compounds. Herein, we report on the crystallographic characterization via neutron and x-ray diffraction experiments, and on the thermoelectric properties measured in the 300 K to 1000 K temperature range, of Mo 3Sb 7 and its isostructural compounds Mo 3-x Ru x Sb 7. Even though Mo 3Sb 7 displays rather high ZT values given its metallic character, the partial substitution of Mo by Ru substantially improves its thermoelectric properties, resulting in a ZT value of ∼0.45 at 1000 K for x = 0.8. © 2009 TMS

Neutron Diffraction and Ab initio Studies of Te Site Preference in Mo₃Sb_7-xTe_x

Band structure calculations based on the KKR-CPA method have been undertaken on the Mo3Sb7-xTex and Re 3As7-xGex systems as well as neutron diffraction analysis on the polycrystalline Mo3Sb7 and Mo3Sb5.4Te1.6 compounds. Both results strongly suggest that the Te atoms are located only on the 12d crystallographic site, whereas the Ge atoms are located on the 16f site as previously experimentally underlined from neutron diffraction study. From an electronic point of view, this site preference in the Mo3Sb7-xTex samples is well-supported by total energy estimation and is presumably related to the reduction of the overall valence p states of Te with respect to those of the 12d Sb site. © 2008 American Chemical Society