Search

The reduction of Co-based oxides doped with Al3+ ions has been studied using in situ XRD and TPR techniques. Al3+-modified Co3O4 oxides with the Al mole fraction Al/(Co + Al) = 1/6; 1/7.5 were prepared via coprecipitation, with further calcination at 500 and 850 °C. Using XRD and HAADF-STEM combined with EDS element mapping, the Al3+ cations were dissolved in the Co3O4 lattice; however, the cation distribution differed and depended on the calcination temperature. Heating at 500 °C led to the formation of an inhomogeneous (Co,Al)3O4 solid solution; further treatment at 850 °C provoked the partial decomposition of mixed Co-Al oxides and the formation of particles with an Al-depleted interior and Al-enriched surface. It has been shown that the reduction of cobalt oxide by hydrogen occurs via the following transformations: (Co,Al)3O4 → (Co,Al)O → Co. Depending on the Al distribution, the course of reduction changes. In the case of the inhomogeneous (Co,Al)3O4 solid solution, Al stabilizes intermediate Co(II)-Al(III) oxides during reduction. When Al3+ ions are predominantly on the surface of the Co3O4 particles, the intermediate compound consists of Al-depleted and Al-enriched Co(II)-Al(III) oxides, which are reduced independently. Different distributions of elemental Co and Al in mixed oxides simulate different types of the interaction phase in Co3O4/γ-Al2O3-supported catalysts. These changes in the reduction properties can significantly affect the state of an active component of the Co-based catalysts. [ABSTRACT FROM AUTHOR]

In this work, new photocatalysts based on Cd1−xMnxS sulfide solid solutions were synthesized by varying the fraction of MnS (x = 0.4, 0.6, and 0.8) and the hydrothermal treatment temperature (T = 100, 120, 140, and 160 °C). The active samples were modified with Pt and NiS co-catalysts. Characterization was performed using various methods, including XRD, XPS, HR TEM, and UV-vis spectroscopy. The photocatalytic activity was tested in hydrogen evolution from aqueous solutions of Na2S/Na2SO3 and glucose under visible light (425 nm). When studying the process of hydrogen evolution using an equimolar mixture of Na2S/Na2SO3 as a sacrificial agent, the photocatalysts Cd0.5Mn0.5S/Mn(OH)2 (T = 120 °C) and Cd0.4Mn0.6S (T = 160 °C) demonstrated the highest activity among the non-modified solid solutions. The deposition of NiS co-catalyst led to a significant increase in activity. The best activity in the case of the modified samples was shown by 0.5 wt.% NiS/Cd0.5Mn0.5S (T = 120 °C) at the extraordinary level of 34.2 mmol g−1 h−1 (AQE 14.4%) for the Na2S/Na2SO3 solution and 4.6 mmol g−1 h−1 (AQE 2.9%) for the glucose solution. The nickel-containing samples possessed a high stability in solutions of both sodium sulfide/sulfite and glucose. Thus, nickel sulfide is considered an alternative to depositing precious metals, which is attractive from an economic point of view. It worth noting that the process of photocatalytic hydrogen evolution from sugar solutions by adding samples based on Cd1−xMnxS has not been studied before. [ABSTRACT FROM AUTHOR]

The nanoscale Co–Mg–O oxide sample (15 wt% in terms of Co 3 O 4) was prepared from the corresponding xerogel synthesized by the modified sol-gel method. The hydrolysis of as-prepared Mg(OCH 3) 2 was carried out using the aqueous solution of Co(NO 3) 2 precursor. The CoO x nanocrystallites of about 10–20 nm in size were shown to be uniformly distributed within the MgO matrix. The reduction of Co–Mg–O in H 2 flow was found to proceed in two separate stages within the temperature ranges of 200–350 °C and 350–600 °C. The prepared binary Co–Mg–O system was demonstrated to possess completely reproducible reduction behavior in the consecutive reduction/reoxidation cycles. The phase composition of the sample exposed to both the reducing and oxidative environment was followed by an in situ X-ray diffraction analysis performed at temperatures of 25, 300, 500 and 700 °C. The determined lattice parameters for MgO (a = 4.219 Å) and Co 3 O 4 (a = 8.110 Å) were found to be slightly increased as compared with the values from Powder Diffraction File, so that the formation of joint non-stoichiometric (Mg 1-x Co x)O and (Co 3-x Mg x)O 4 phases was suggested. The strong chemical interaction of cobalt oxide with MgO matrix was also evidenced by the data of a diffuse reflectance UV–vis spectroscopy. Image 1 • The nanoscale Co–Mg–O oxide system was prepared by the modified sol-gel method. • CoO x species of 10–20 nm in size are uniformly distributed within the MgO matrix. • The prepared Co–Mg–O system possesses completely reproducible reduction behavior. • Strong interaction between Co and Mg oxides was proved by DR UV–vis spectroscopy. [ABSTRACT FROM AUTHOR]

Two types of nickel-modified Cd1−xZnxS-based photocatalysts, CdxZn1−xNiySy+1 (mol% Ni = 0.05–0.5; x = 0.8) and yNiS/CdxZn1−xS (mol% Ni = 0.1–1.0; x = 0.8), were prepared via a simple two-stage technique. The samples were characterized by XRD, UV–vis spectroscopy, and XPS techniques. The activity of the synthesized photocatalysts were tested in the gas-phase photocatalytic reduction of CO2 under visible light (λ = 450 nm). It has been shown that both CdxZn1−xNiySy+1 and yNiS/CdxZn1−xS samples with ultra-low content of nickel sulfide have improved activity in the carbon dioxide reduction in comparison to bare CdxZn1−xS solid solutions. Also, it has been demonstrated that the addition of the reducing agent—hydrogen—into the system does not lead to a positive effect: the rate of CO2 reduction either remains unchanged or decreases. [ABSTRACT FROM AUTHOR]

A series of solid solutions of cadmium and manganese sulfides, Cd1−xMnxS (x = 0–0.35), and composite photocatalysts, CdS-β-Mn3O4-MnOOH, were synthesized by precipitation with sodium sulfide from soluble cadmium and manganese salts with further hydrothermal treatment at 120 °C. The obtained photocatalysts were studied by the X-ray diffraction method (XRD), UV-vis diffuse reflectance spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N2 low temperature adsorption. The photocatalysts were tested in hydrogen production using a Na2S/Na2SO3 aqueous solution under visible light (λ = 450 nm). It was shown for the first time that both kinds of photocatalysts possess high activity in hydrogen evolution under visible light. The solid solution Cd0.65Mn0.35S has an enhanced photocatalytic activity due to its valence and conduction band position tuning, whereas the CdS-β-Mn3O4-MnOOH (40–60 at% Mn) samples were active due to ternary heterojunction formation. Further, the composite CdS-β-Mn3O4-MnOOH photocatalyst had much higher stability in comparison to the Cd0.65Mn0.35S solid solution. The highest activity was 600 mmol g−1 h−1, and apparent quantum efficiency of 2.9% (λ = 450 nm) was possessed by the sample of CdS-β-Mn3O4-MnOOH (40 at% Mn). [ABSTRACT FROM AUTHOR]