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Abstract: TiO2 and Ag-TiO2 (0.05, 0.25 and 1wt% of Ag) thin films were prepared by the sol–gel method. The prepared films were characterized using SEM-EDAX, XRD, Raman spectroscopy, atomic force microscopy and UV–Vis spectrometry. Photocatalytic decomposition of N2O was performed in an annular batch reactor illuminated with an 8W Hg lamp (254nm wavelength). The photoreactivity of Ag-TiO2 increases with the Ag amount to 0.25wt% Ag. Further increase of Ag loading to 1wt% Ag did not change N2O conversion. The Ag particles deposited on the TiO2 surface can act as electron–hole separation centers. The presence of water vapor and oxygen in the reaction mixture slightly improved N2O conversion. [Copyright &y& Elsevier]

Abstract: Paper deals with design of pilot reactor for low temperature N2O decomposition in off-gases from HNO3 production. Pseudo-homogeneous one-dimensional model of an ideal plug flow reactor was used for modeling of N2O decomposition in a laboratory fixed bed reactor filled with grains or pellets of a Co–Mn–Al mixed oxide catalyst. Increase in inlet pressure up to 0.6MPa did not influence the effective diffusion coefficient, but improved the achieved N2O conversion. Based on the laboratory data of N2O decomposition over Co–Mn–Al mixed oxide pellets, catalyst bed of 3400kg was estimated for target 90% N2O conversion (30000m3 h−1 of exhaust gases from HNO3 plant containing 0.1molar% N2O, 0.01molar% NO, 0.01molar% NO2, 3molar% H2O, 5molar% O2) at 420°C and 600kPa inlet pressure. [Copyright &y& Elsevier]

Abstract: A series of Co–Mn–Al mixed oxides was prepared by a thermal treatment of coprecipitated layered double hydroxide precursors modified with different amount of potassium (0–3wt.%) and tested in N2O catalytic decomposition. Chemical analysis, XRD, XPS, surface area measurements, SEM, and contact potential difference measurements were used for bulk and surface characterization of the catalysts. The Co–Mn–Al mixed oxide with 1.1–1.8wt.%K exhibited the highest conversion of N2O and minimum value of the catalyst surface work function. Direct correlation between the work function values and the activity of the catalysts demonstrates that N2O decomposition over K-promoted Co–Mn–Al mixed oxides proceeds via the cationic redox mechanism and controlled modification of surface electronic properties provides the essential factor for catalyst optimization. [Copyright &y& Elsevier]

Abstract: Catalytic decomposition of N2O over calcined Co–Mn–Al layered double hydroxide (LDH) modified with slight amount of alkali (Li, Na, K), rare earth (La, Ce), or noble metals (Pd, Pt) was studied. Two methods of promoter addition were applied: impregnation of LDH-related Co–Mn–Al mixed oxide by a promoter-containing solution and incorporation of the promoter during coprecipitation of the LDH precursor. The method of preparation affected the reducibility of the obtained mixed oxide catalysts but its effect on the surface area (with the exception of a cerium-contained sample) and N2O conversion was less evident. The modification of the Co–Mn–Al mixed oxide with K or Na increased N2O conversion, while no effect or a decrease in the N2O conversion was observed over the other examined catalysts. Alkali metals act as electron promoters; therefore, the differences in catalytic activity may be related to changes of oxygen-transition metal bond strength. The Co–Mn–Al mixed oxides with 1.8wt% K exhibited a high catalytic activity even under the simultaneous presence of O2, H2O and NOx. The laboratory stability test revealed maintenance of the beneficial effect for 360h. [Copyright &y& Elsevier]

Abstract: A series of catalysts was prepared by thermal treatment (500°C) of the coprecipitated Co–Mn–Al layered double hydroxide (Co:Mn:Al molar ratio of 4:1:1) doped with various amount of potassium (0–3wt%). Obtained spinel-like mixed oxides were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, BET surface area measurements, temperature-programmed H2 reduction, and temperature-programmed CO2 and NH3 desorption. The prepared catalysts were tested for N2O decomposition to determine the effect of K addition on the catalytic activity in the presence of O2, NO x and H2O. An optimum K content of ca. 0.9–1.6wt% was found to achieve a high catalytic activity in the presence of O2 and H2O, while the non-modified Co–Mn–Al mixed oxide was the most active catalyst in the presence of O2 and NO x . The addition of potassium to the Co–Mn–Al mixed oxide apparently results in a modification of both electronic properties of active metals and acid-base function of the catalyst surface. [Copyright &y& Elsevier]

Abstract: Pure TiO2 anatase particles with a crystallite diameters ranging from 4.5 to 29nm were prepared by precipitation and sol–gel method, characterized by X-ray diffraction (XRD), BET surface area measurement, UV–vis and scanning electron microscopy (SEM) and tested in CO2 photocatalytic reduction. Methane and methanol were the main reduction products. The optimum particle size corresponding to the highest yields of both products was 14nm. The observed optimum particle size is a result of competing effects of specific surface area, charge–carrier dynamics and light absorption efficiency. [Copyright &y& Elsevier]

Abstract: Kinetics of N2O decomposition over catalyst prepared by calcination of Co–Mn hydrotalcite was examined in integral fixed-bed reactor () at various N2O and O2 initial partial pressure at temperature range of 330–450°C. Kinetic data were evaluated by linear and non-linear regression method, 15 kinetic expressions were tested. Based on the obtained results a redox model of N2O decomposition was proposed. At low pressures of O2, adsorbed oxygen is formed by the N2O decomposition; the N2O chemisorption is considered as the rate-determining step. On the contrary, at high O2 pressure it could be assumed that adsorbed oxygen species appear as a result of O2 adsorption and the Eley–Rideal mechanism is the rate determining. N2O decomposition is well described by the 1st rate law at N2O and O2 concentrations typical for waste gases. [Copyright &y& Elsevier]

Abstract: The Co–Mn–Al mixed oxide catalysts were prepared by thermal decomposition of hydrotalcite-like precursors with Co/(Mn+Al) molar ratio of 2 and Mn/Al molar ratio varying from 0 to 2. The obtained catalysts were characterized by powder XRD, XPS, BET surface area and TPR measurements and tested in N2O decomposition. The most active Co4MnAl catalyst exhibited both the optimum Mn/Al molar ratio and the optimum amount of components reducible in the temperature region in which the catalytic reaction proceeds (350–450°C). [Copyright &y& Elsevier]

Abstract: The decomposition of the nitrous oxide over catalysts prepared by thermal decomposition of Ni-(Mg)-MIII (MIII =Al or Mn) hydrotalcite-like precursors was studied. The mixed oxides obtained at 500°C were characterized using various techniques—X-ray diffraction (XRD), BET surface area measurements, temperature-programmed desorption (TPD) and temperature-programmed reduction (TPR). The N2O decomposition was performed in the temperature range 300–450°C, at 0.05–0.15mol% inlet N2O concentrations; oxygen and nitrogen dioxide were added in some runs. The Ni-Al and Mg-Mn catalysts exhibited high catalytic activity but those containing both transition metal cations (i.e. Ni and Mn) were less active. Their lower activity was interpreted in terms of different oxidation states of manganese and nickel in the mixed oxide systems. Up to a certain value of oxygen pressure the presence of oxygen in the reaction mixture caused an inhibition of the reaction rate, while at higher oxygen pressures the N2O conversion remained nearly constant. The correlation between the observed oxygen inhibition and the proposed N2O decomposition mechanism as well as the relationship between the observed activity and the amount of reducible components determined from TPR experiments are discussed. [Copyright &y& Elsevier]

Abstract: Pure TiO2 and various silver-enriched TiO2 powders were prepared by the sol–gel process controlled in the reverse micellar environment. The catalysts were tested in CO2 photocatalytic reduction and characterized by X-ray diffraction (XRD), nitrogen adsorption measurement and UV–vis. Methane and methanol were the main reduction products. The yield of methane and methanol increases when modifying the TiO2 by silver incorporation is caused by two mechanisms: up to 5% of Ag in TiO2 the Ag impurity band inside the TiO2 bandgap decreases the absorption edge and increases so the electron–hole pair generation, above 5% of Ag in TiO2 Ag metallic clusters are formed in TiO2 crystals with Shottky barrier at the metal–semiconductor interface, which spatially separates electron and holes and increases their lifetime (decreases probability of their recombination). [Copyright &y& Elsevier]

Highlights: [•] Synthesis of micro-mesoporous zeolitic materials by non-templating method [•] Deposition of zeolite nanoseeds on the SBA-15 surface [•] N2O conversion over Fe-modified micro-mesoporous zeolitic catalysts [Copyright &y& Elsevier]

Abstract: Catalysts with various Ag loading (0.7–5.2wt%) in the powder form were prepared by the sol–gel process controlled in the reverse micellar environment. X-ray diffraction (XRD), nitrogen adsorption measurement, UV–vis and elemental analysis were employed for characterization of catalysts. Effect of various silver loadings on photocatalytic activity of TiO2 catalysts in N2O photocatalytic decomposition was studied. Photocatalytic decomposition of N2O was performed in annular batch reactor illuminated with 8W Hg lamp (254nm wavelength). Reaction kinetic corresponds to first-order reaction rate which is in agreement with plausible reaction mechanisms. The highest N2O conversion of 77% after 24h was reach over TiO2 modified by 3.4wt% Ag. The Ag metal clusters could provoke a decrease in the electron–hole recombination rate. [Copyright &y& Elsevier]

Abstract: A series of Co–Mn–Al/TiO2 catalysts with different Co+Mn loading (5–24wt.%) was prepared by impregnation of TiO2 support. Bulk Co–Mn–Al mixed oxides were prepared by different methods. The prepared catalysts were characterized by chemical analysis, surface area measurement, temperature programmed techniques (TPR, TPD) and tested for N2O catalytic decomposition. TiO2 acted only as a catalytic support and did not contribute to the catalytic activity. The N2O conversion over TiO2-supported Co–Mn–Al catalysts was increasing with Co+Mn loading, and was proportional to the amount of easily reducible components. Comparing the catalysts with identical amount of active components, the highest catalytic activity was achieved on the calcined precursors having carbonates in their molecules (layered double hydroxides Co–Mn–Al-HT-ex and Co–Mn–Al-carb), the lowest one on the calcined Co–Mn–Al nitrates due to the lower surface area, less advantageous porous structure and worse reducibility. [Copyright &y& Elsevier]

Abstract: The kaolinite/TiO2 composite was prepared using thermal hydrolysis of kaolinite/titanyl sulphate suspension and characterized by XRFS, XRPD, SEM and N2 physical adsorption. Its photocatalytic properties were evaluated by photocatalytic reduction of CO2 by water and compared with commercial TiO2 photocatalyst Degussa P25. Results showed that the yields of CO2 photocatalytic reduction products methane and methanol were higher over a kaolinite/TiO2 composite than over commercial TiO2 (Degussa P25) in spite of smaller proportion of TiO2 in the composite. Introducing of TiO2 nanoparticles into the kaolinite structure caused a decrease of anatase crystallite size. Kaolinite can also change acidobasic properties of catalyst surface, inhibit the recombination of electron–hole pairs and prevent the formation of TiO2 aggregates in suspension. These facts can contribute to the observed higher photocatalytic efficiency of kaolinite/TiO2 compared to the commercial TiO2 photocatalyst. [Copyright &y& Elsevier]

Copper-containing mixed metal oxides are one of the most promising catalysts of selective catalytic oxidation of ammonia. These materials are characterized by high catalytic efficiency; however, process selectivity to dinitrogen is still an open challenge. The set of Cu-Zn-Al-O and Ce/Cu-Zn-Al-O mixed metal oxides were tested as catalysts of selective catalytic oxidation of ammonia. At the low-temperature range, from 250 °C up to 350 °C, materials show high catalytic activity and relatively high selectivity to dinitrogen. Samples with the highest Cu loading 12 and 15 mol.% of total cation content were found to be the most active materials. Additional sample modification by wet impregnation of cerium (8 wt.%) improves catalytic efficiency, especially N 2 selectivity. The comparison of catalytic tests with results of physicochemical characterization allows connecting the catalysts efficiency with the form and distribution of CuO on the samples' surface. The bulk-like well-developed phases were associated with sample activity, while the dispersed CuO phases with dinitrogen selectivity. Material characterization included phase composition analysis (X-ray powder diffraction, UV-Vis diffuse reflectance spectroscopy), determination of textural properties (low-temperature N 2 sorption, scanning electron microscopy) and sample reducibility analysis (H 2 temperature-programmed reduction).

Ionic liquids are increasingly used for their superior properties. Four water-immiscible ionic liquids (butyltriethylammonium bis(trifluoromethylsulfonyl)imide, octyltriethylammonium bis(trifluoromethylsulfonyl)imide, dodecyltriethylammonium bis(trifluoromethylsulfonyl)imide, butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and their water miscible precursors (bromides) were synthesized in a microwave reactor and by conventional heating. The best conditions for microwave-assisted synthesis concerning the yield and the purity of the product are proposed. The heating in the microwave reactor significantly shortened the reaction time. Biocide and ecotoxic effects of synthesized ionic liquids and their precursors were investigated. All tested compounds had at least a little effect on the growth or living of microorganisms (bacteria or mold). The precursor dodecyltriethylammonium bromide was found to be the strongest biocide, but posed a risk to the aquatic environment due to its relatively high EC 50 value in the test with Vibrio fischeri . We assumed that apart from the alkyl chain length, the solubility in water, duration of action, or type of anion can influence the final biocide and ecotoxic effect.

TiO2 as nanostructured powders were prepared by (1) sol-gel process and (2) hydrothermal method in combination with (A) the processing by pressurized hot water and methanol or (B) calcination. The subsequent synthesis step was the modification of prepared nanostructured TiO2 with nitrogen using commercial urea. Textural, structural, surface and optical properties of prepared TiO2 and N/TiO2 were characterized by nitrogen physisorption, powder X-ray diffraction, X-ray photoelectron spectroscopy and DR UV-vis spectroscopy. It was revealed that TiO2 and N/TiO2 processed by pressurized fluids showed the highest surface areas. Furthermore, all prepared materials were the mixtures of major anatase phase and minor brookite phase, which was in nanocrystalline or amorphous (as nuclei) form depending on the applied preparation method. All the N/TiO2 materials exhibited enhanced crystallinity with a larger anatase crystallite-size than undoped parent TiO2. The photocatalytic activity of the prepared TiO2 and N/TiO2 was tested in the photocatalytic reduction of CO2 and the photocatalytic decomposition of N2O. The key parameters influencing the photocatalytic activity was the ratio of anatase-to-brookite and character of brookite. The optimum ratio of anatase-to-brookite for the CO2 photocatalytic reduction was determined to be about 83 wt.% of anatase and 17 wt.% of brookite (amorphous-like) (TiO2-SG-C). The presence of nitrogen decreased a bit the photocatalytic activity of tested materials. On the other hand, TiO2-SG-C was the least active in the N2O photocatalytic decomposition. In the case of N2O photocatalytic decomposition, the modification of TiO2 crystallites surface by nitrogen increased the photocatalytic activity of all investigated materials. The maximum N2O conversion (about 63 % after 18 h of illumination) in inert gas was reached over all N/TiO2.

The aim of this study was to remove ammonia from an aqueous solution by its decomposition to valuable products such as H2 and harmless N2 under UV light. The decomposition of ammonia by photocatalytic process represents an emerging and interesting way of its removal since beside the need of its reduction from the drinking and wastewaters with the respect to its negative impact on human and mammals health, it can lead to generation of hydrogen as an alternative fuel. A laboratory-synthesized Pt/TiO2-ZrO2 photocatalyst was studied and its photocatalytic activity was compared with the activity of commercial TiO2 Evonik P25. The Pt/TiO2-ZrO2 photocatalyst was prepared by combining a sol-gel process controlled within reverse micelles of nonionic surfactant Triton X-114 in cyclohexane, impregnation under vacuum and calcination. Explored photocatalysts were characterized by organic elementary analysis, nitrogen physisorption, XRD, FESEM and UV-Vis spectroscopy. The real platinum content in the Pt/TiO2-ZrO2 photocatalyst was determined by ICP-MS. The photocatalytic decomposition of ammonia was investigated in the time range of 0-12 h. During the first two hours the generation of hydrogen was almost negligible. The generation of hydrogen increased after 4 h of irradiation. Based on time dependences of ammonia decomposition the kinetic rate constants for Pt/TiO2-ZrO2 and TiO2 Evonik P25 photocatalysts were calculated. The ammonia photocatalytic decomposition was described well by the first order kinetic equation. The photocatalytic ammonia decomposition over the platinized TiO2-ZrO2 photocatalyst was proving 2 times higher photocatalytic performance than Evonik P25 (1241 μmol/g(cat) and 665 μmol/g(cat), respectively).