The heightened interest in liquid organic hydrogen carriers encourages the development of catalysts suitable for multicycle use. To ensure high catalytic activity and selectivity, the structure–reactivity relationship must be extensively investigated. In this study, high-loaded Ni–Cu catalysts were considered for the dehydrogenation of methylcyclohexane. The highest conversion of 85% and toluene selectivity of 70% were achieved at 325 °C in a fixed-bed reactor using a catalyst with a Cu/Ni atomic ratio of 0.23. To shed light on the relationship between the structural features and catalytic performance, the catalysts were thoroughly studied using a wide range of advanced physicochemical tools. The activity and selectivity of the proposed catalysts are related to the uniformity of Cu distribution and its interaction with Ni via the formation of metallic solid solutions. The method of introduction of copper in the catalyst plays a crucial role in the effectiveness of the interaction between the two metals.

A series of Mn−Co mixed oxides with a gradual variation of the Mn/Co molar ratio were prepared by coprecipitation of cobalt and manganese nitrates. The structure, chemistry, and reducibility of the oxides were studied by X-ray diffraction (XRD), X-ray absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR). It was found that at concentrations of Mn below 37 atom %, a solid solution with a cubic spinel structure is formed. At concentrations above 63 atom %, a solid solution is formed on the basis of a tetragonal spinel, while at concentrations in a range of 37−63 atom %, a two-phase system, which contains tetragonal and cubic oxides, is formed. To elucidate the reduction route of mixed oxides, two approaches were used. The first was based on a gradual change in the chemical composition of Mn−Co oxides, illustrating slow changes in the TPR profiles. The second approach consisted in a combination of in situ XRD and pseudo-in situ XPS techniques, which made it possible to directly determine the structure and chemistry of the oxides under reductive conditions. It was shown that the reduction of Mn−Co mixed oxides proceeds via two stages. During the first stage, (Mn, Co) 3 O 4 is reduced to (Mn, Co)O. During the second stage, the solid solution (Mn, Co)O is transformed into metallic cobalt and MnO. The introduction of manganese cations into the structure of cobalt oxide leads to a decrease in the rate of both reduction stages. However, the influence of additional cations on the second reduction stage is more noticeable. This is due to crystallographic peculiarities of the compounds: the conversion from the initial oxide (Mn, Co) 3 O 4 into the intermediate oxide (Mn, Co)O requires only a small displacement of cations, whereas the formation of metallic cobalt from (Mn, Co)O requires a rearrangement of the entire structure.

A series of Pt/TiO 2 photocatalysts was prepared by impregnation of fresh and thermal-activated titania (commercial Evonik Aeroxide P25 TiO 2 ) with an aqueous solution of H 2 PtCl 6 followed by reduction in an aqueous solution of NaBH 4 . The thermal activation was performed by annealing in air. The photocatalytic activity of the Pt/TiO 2 catalysts was measured for the hydrogen production from a mixture of glycerol under UV radiation. It was found that the activation at 300-600 °C provides an increase in the photoreactivity of resulting Pt/TiO 2 photocatalysts in the production of hydrogen while its structural and textural properties do not change. This effect is due to formation of cationic vacancies that limits fast electron-hole recombination. Keywords photocatalysis • XPS • NEXAFS • XRD • nanoparticles Catalysis Letters Catalysis LettersNaBH 4 (Acros Organics, 98%) at room temperature [7]. The photocatalysts were referred to as "T300", "T400", "T500", "T600", "T700", and "T800", respectively. The photocatalyst prepared without the thermal activation was referred to as "RT". Platinum content was approximately 1 wt% in all the photocatalysts. All the chemical reagents used in the experiments, excluding distilled water, were obtained from commercial sources as guaranteed-grade reagents and were used without further purification and treatment. MethodsThe photocatalysts were examined by UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) spectroscopy, and X-ray diffraction (XRD) and N adsorption techniques. The diffuse reflectance UV-vis spectra were obtained using a Shimadzu UV-2501 PC spectrophotometer with an ISR-240A diffuse reflectance unit. The specific surface area (SSA) was calculated by the Brunauer-Emmett-Teller method using nitrogen adsorption isotherms measured at liquid nitrogen temperatures with an automatic Micromeritics ASAP 2400 sorptometer. XRD patterns were recorded on a Bruker D8 Advance diffractometer in the 2θ range from 20° to 80° using the Cu Kα radiation. The mean sizes of crystallites in the samples were estimated from the full width at half maximum of corresponding peaks using the Scherrer formula. The phase composition of the photocatalysts was quantitatively analyzed using the Rietveld refinement method.The XPS study was performed using an X-ray photoelectron spectrometer (SPECS Surface Nano Analysis GmbH, Germany) equipped with a PHOIBOS-150 hemispherical electron energy analyzer, a XR-50M X-ray source, and an ellipsoidal crystal monochromator FOCUS-500. The core-level spectra were obtained under ultrahigh vacuum conditions using the monochromatic Al Kα radiation. The charge correction was performed by setting the Ti2p 3/2 peak at 459.0 eV [12]. In this case, the main peak in the C1s spectra was observed at 285.2±0.1 eV. Relative concentrations of elements were determined from the integral intensities of the core-level spectra using the cross sections according to Scofield [13]. For detailed analysis, the spectra were fitted in...

The oxidation of CO has been studied over FeÀ Al and CuÀ FeÀ Al oxide nanocomposite catalysts prepared by melting of copper, iron, and aluminum nitrates. It was shown that the addition of copper significantly increases the catalytic activity of the FeÀ Al nanocomposites. The catalysts were characterized by lowtemperature nitrogen adsorption, X-ray diffraction (XRD), and Xray photoelectron spectroscopy (XPS). It was found that the catalysts contain Fe 2 O 3 with the hematite structure modified by aluminum. Copper in the three-component catalyst is in the Cu 2 + state, forming CuO and CuFeO x clusters on the catalyst surface. An increase in the copper content leads to the formation of a Cu x Al y Fe 3-x-y O 4 spinel phase. In situ XPS study showed that a treatment of the catalysts in a CO flow leads to the reduction of both copper and iron cations into the metallic state. In contrast, a treatment in a CO/O 2 flow leads only to partial reduction of Cu 2 + to Cu 1 + , while Fe 3 + are not reduced. The tests of catalytic activity performed in a flow fixed bed reactor using a CO pulse technique showed that the light-off temperature in the oxidation of CO over the CuÀ FeÀ Al nanocomposite catalysts depends on the copper content. The minimal light-off temperature was achieved over the catalyst containing 5 wt% CuO. In addition, we performed kinetic measurements in a differential reactor and obtained the activation energy and the reaction orders with respect to the reactants. The reaction mechanism of the catalytic oxidation of CO and the origin of active species are discussed.

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