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In this work, the reaction properties of mixed silver-nickel oxide AgNiO2 were investigated in the reaction of CO oxidation ranging from room temperature up to 350 °C. X-ray photoelectron spectroscopy revealed the presence of a single oxidized silver state and the combination of Ni2+ and Ni3+ species on the surface of the as-prepared mixed oxide. It was established that AgNiO2 was able to interact with CO at room temperature. It was accompanied by the simultaneous titration of the lattice (O2−-like) and weakly charged (O−-like) oxygen species. The interaction with CO below 100 °C resulted in the accumulation of carbonate-like species on the AgNiO2 surface. Above 150 °C, the surface structure of mixed oxide was found to be disrupted, resulting in the formation of individual particles of metallic silver and oxidized nickel. [ABSTRACT FROM AUTHOR]

A mixed oxide of silver and nickel AgNiO2 was obtained via co-precipitation in alkaline medium. This oxide demonstrates room temperature activity in the reaction of ethylene epoxidation with a high selectivity (up to 70%). Using the PDF method, it was found that the initial structure of AgNiO2 contains stacking faults and silver vacancies, which cause the nonstoichiometry of the oxide (Ag/Ni < 1). It has been established that on the initial surface of AgNiO2 oxide, silver state can be considered as an intermediate between Ag2O and Ag0 (i.e. Agδ+-like), while nickel is characterized by signs of a deeply oxidized state (Ni3+-like). The interaction of AgNiO2 with C2H4 at room temperature leads to the simultaneous removal of two oxygen species with Eb(O 1s) = 529.0 eV and 530.5 eV considered as nucleophilic and electrophilic oxygen states, respectively. Nucleophilic oxygen was attributed to the lattice oxygen (Ag–O–Ni), while the electrophilic species with epoxidation activity was associated with the weakly bound oxygen stabilized on the surface. According to the TPR-C2H4 data, a large number of weakly bound oxygen species were found on the pristine AgNiO2 surface. The removal of such species at room temperature didn't result in noticeable structural transformation of delafossite. As the temperature of ethylene oxidation over AgNiO2 increased, the appearance of Ag0 particles was first observed below 200 °C followed by the complete destruction of the delafossite structure at higher temperatures. [ABSTRACT FROM AUTHOR]

This paper describes the chemical engineering aspects for the preparation of highly active and stable nanocomposite photocatalysts based on N-doped TiO2. The synthesis is performed using titanium oxysulfate as a low-cost inorganic precursor and ammonia as a precipitating agent, as well as a source of nitrogen. Mixing the reagents under a control of pH leads to an amorphous titanium oxide hydrate, which can be further successfully converted to nanocrystalline anatase TiO2 through calcination in air at an increased temperature. The as-prepared N-doped TiO2 provides the complete oxidation of volatile organic compounds both under UV and visible light, and the action spectrum of N-doped TiO2 correlates to its absorption spectrum. The key role of paramagnetic nitrogen species in the absorption of visible light and in the visible-light-activity of N-doped TiO2 is shown using the EPR technique. Surface modification of N-doped TiO2 with copper species prevents its intense deactivation under highly powerful radiation and results in a nanocomposite photocatalyst with enhanced activity and stability. The photocatalysts prepared under different conditions are discussed regarding the effects of their characteristics on photocatalytic activity under UV and visible light. [ABSTRACT FROM AUTHOR]

Ternary oxide of silver, copper, and manganese (Ag2CuMnO4) was prepared by hydrothermal synthesis in an alkaline solution. The prepared sample was characterized by a delafossite crystal structure without any other crystallized phases. The catalytic properties of Ag2CuMnO4 in oxidation reactions using molecular oxygen were investigated. High catalytic activity was found for Ag2CuMnO4 in the CO oxidation at room temperature, while ammonia oxidation occurred above 100 °C. Ammonia oxidation resulted in the formation of N2O/N2 or NO/NO2 products depending on the reaction temperature. As a result of the reaction exposure on Ag2CuMnO4 during heating up to 400 °C, a modification of surface composition with preservation of the delafossite structure was found. Oxide Ag2CuMnO4 was shown to be operating in wet CO oxidation under ambient conditions. Obtained data emphasize that Ag2CuMnO4 can be considered as a novel and prospective catalytic material with a high potential of application for oxidation processes at low temperatures including ambient conditions. [ABSTRACT FROM AUTHOR]

Ternary oxide of silver, copper, and manganese (Ag2CuMnO4) was prepared by hydrothermal synthesis in an alkaline solution. The prepared sample was characterized by a delafossite crystal structure without any other crystallized phases. The catalytic properties of Ag2CuMnO4 in oxidation reactions using molecular oxygen were investigated. High catalytic activity was found for Ag2CuMnO4 in the CO oxidation at room temperature, while ammonia oxidation occurred above 100 °C. Ammonia oxidation resulted in the formation of N2O/N2 or NO/NO2 products depending on the reaction temperature. As a result of the reaction exposure on Ag2CuMnO4 during heating up to 400 °C, a modification of surface composition with preservation of the delafossite structure was found. Oxide Ag2CuMnO4 was shown to be operating in wet CO oxidation under ambient conditions. Obtained data emphasize that Ag2CuMnO4 can be considered as a novel and prospective catalytic material with a high potential of application for oxidation processes at low temperatures including ambient conditions. [ABSTRACT FROM AUTHOR]

Dependence of NH3 oxidation on the state and dispersion of Pt species in Pt/γ‐Al2O3 catalysts was investigated. Prereduced Pt/γ‐Al2O3 catalysts containing Pt0 nanoparticles exhibited significantly higher activity than preoxidized ones with the same Pt dispersion. The most significant improvement of the catalytic activity (TOF increased by 30 times) was observed when the size of Pt0 particles increased from ∼1 to ∼8 nm. N2 selectivity was found to be mainly determined by the reaction temperature, with a minor influence of Pt particle size. Preoxidized catalysts containing ionic Pt were activated by the reaction medium, while partial deactivation was observed for the prereduced ones. The activity improvement was associated with the presence of Pt4+/Pt2+ species on the surface of preoxidized catalysts. The activity decrease of the prereduced catalysts was due to the partial oxidation and subsequent redispersion of Pt particles. Introduction of H2O and CO2 to the reaction mixture only moderately influenced NH3 oxidation activity shifting NH3 conversion curves by about +15 °C. [ABSTRACT FROM AUTHOR]

Two series of Pt/γ‐Al2O3 catalysts for low temperature NH3 oxidation were prepared using Pt(NO3)4 and H2PtCl6 precursors. Using both precursors results in the formation of small Pt particles (d<1.5 nm), however, Cl‐containing Pt precursors give a higher fraction of highly dispersed Pt species. Such species show high stability against thermal or H2 treatment probably due to the presence of a substantial amount of chlorine on the surface. Treatment of the samples prepared from Pt(NO3)4 with H2 leads to the formation of metallic Pt nanoparticles accompanied by the improvement of catalytic activity in NH3 oxidation at T<200 °C. The main products of ammonia oxidation at temperatures below 250 °C were molecular nitrogen and nitrous oxide with the N2 selectivity reaching 80 %. Operando XANES/EXAFS revealed that even after H2 pretreatment at least 40 % of Pt surface remains in oxidized state under reaction conditions resulting in the appearance of N2O as a by‐product. [ABSTRACT FROM AUTHOR]

Structured composite Ni(Clx)/CeO2/η‐Al2O3/FeCrAl catalysts are developed for the reaction of preferential methanation of carbon monoxide in the presence of carbon dioxide. The use of a FeCrAl alloy wire mesh as a support for Ni(Cl)/CeO2 allows preparation of a heat‐conducting catalyst that is similar in performance and physical‐chemical properties to the highly efficient catalysts in the form of micro pellets, as confirmed by catalytic tests and XRD, XPS, TEM, SEM, EDX characterization techniques. Catalytic tests are carried out in hydrogen‐rich mixture which contains (vol. %): 1 CO, 65 H2, 10 H2O, 20 CO2, He – balance; weight hourly space velocity is 29,000 cm3gcat−1h−1. The structured catalyst with highly dispersed nickel and optimal chlorine content provides CO removal to a level of <10 ppm in the temperature interval of 230–300 °C. XRD, TEM, SEM and EDX analysis confirm the presence of Ni nanoparticles and CeOCl species in the catalytic coating. XPS study of samples after reductive pretreatment (simulating CO preferential methanation reaction conditions) in the preparation chamber of the spectrometer reveals the metallic state of Ni and high concentrations of Cl and Ce3+ on the catalyst surface. [ABSTRACT FROM AUTHOR]

A mixed oxide of silver and nickel AgNiO 2 was obtained via co-precipitation in alkaline medium. This oxide demonstrates room temperature activity in the reaction of ethylene epoxidation with a high selectivity (up to 70%). Using the PDF method, it was found that the initial structure of AgNiO 2 contains stacking faults and silver vacancies, which cause the nonstoichiometry of the oxide (Ag/Ni < 1). It has been established that on the initial surface of AgNiO 2 oxide, silver state can be considered as an intermediate between Ag 2 O and Ag 0 ( i.e. Ag δ + -like), while nickel is characterized by signs of a deeply oxidized state (Ni 3+ -like). The interaction of AgNiO 2 with C 2 H 4 at room temperature leads to the simultaneous removal of two oxygen species with E b (O 1s) = 529.0 eV and 530.5 eV considered as nucleophilic and electrophilic oxygen states, respectively. Nucleophilic oxygen was attributed to the lattice oxygen (Ag-O-Ni), while the electrophilic species with epoxidation activity was associated with the weakly bound oxygen stabilized on the surface. According to the TPR-C 2 data, a large number of weakly bound oxygen species were found on the pristine AgNiO 4 data, a large number of weakly bound oxygen species were found on the pristine AgNiO 2 surface. The removal of such species at room temperature didn't result in noticeable structural transformation of delafossite. As the temperature of ethylene oxidation over AgNiO 2 increased, the appearance of Ag 0 particles was first observed below 200 °C followed by the complete destruction of the delafossite structure at higher temperatures.