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A series of Co-Mn-Al mixed oxide catalysts with different Cs contents (0.5-4.6 wt%) was prepared by calcination of Co-Mn-Al hydrotalcite (Co:Mn:Al = 4:1:1), followed by impregnation by cesium salt (CsNO, CsCO) using the pore filling method. Chemical analysis, N sorption, temperature programmed reduction (TPR)-H, temperature programmed desorption (TPD)-CO and TPD-NH and X-ray photoelectron spectroscopy (XPS) were used to characterize the catalysts. All prepared catalysts were tested for NO catalytic decomposition in inert gas and in the presence of oxygen, water vapor and nitric oxide. The influence of Cs salts used for catalyst preparation and cesium content on catalyst activity were studied. A significant increase in catalytic activity with increasing amount of cesium promoter was observed without respect to the Cs precursor. The strong promotional effect of cesium is electronic in nature and is discussed in term of changes in surface composition and catalyst reducibility. [ABSTRACT FROM AUTHOR]

Highlights: [•] ZnS nanoparticles deposited on montmorillonite forming ZnS-MMT nanocomposite. [•] Catalyst for photocatalytic decomposition of N2O. [•] Better catalytic performance in fluidized bed than fixed bed. [•] Presence of water vapor inhibited N2O decomposition by photocatalysis. [•] Presence of water vapor improved N2O photolysis. [ABSTRACT FROM AUTHOR]

Highlights: [•] N2O conversion decreased in order Cs>Rb>K>Na=Co4MnAlO x >Li. [•] Alkali metals modified electronic properties and acid–base function of surface. [•] Promotional effect of alkali metals is connected with their ionization potential. [•] Charge transfer and a decrease in binding energies was caused by alkali metals. [•] Good stability of K-promoted Co–Mn–Al mixed oxide catalyst in real waste gas [Copyright &y& Elsevier]

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: 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]

[Display omitted] • Co-based mixed oxides with alkali promoters were tested for NO decomposition. • Calcination conditions (temperature, time) strongly influence the stability of catalysts. • Deactivation caused by alkali metals vaporization occurs during first 50 h. • Rearrangement of surface species takes place below the temperature of alkali desorption. Co-Mn-Al mixed oxide and Co 3 O 4 catalysts with alkali metal promoters (K, Cs) were tested for direct NO decomposition with the aim to determine their activity and stability. The catalysts were prepared by coprecipitation with subsequent impregnation by alkali metal salts and characterized by AAS, MP-AES, XRD, N 2 physisorption and species-resolved thermal alkali desorption (SR-TAD). Long-term experiments of NO catalytic decomposition performed above the temperature of alkali metal desorption showed slow deactivation which has not yet been reported by other authors, since only short laboratory tests of NO catalytic decomposition have been presented. The reason for the observed deactivation was identified as volatilization of alkali metal promoters from the catalyst surface, which was revealed by SR-TAD and chemical analysis of alkali metals. Measurements conducted below the temperature of alkali metal desorption yielded an increase in NO conversion during the initial period of measurement, which can be explained by rearrangement of surface species. [ABSTRACT FROM AUTHOR]

The K-doped Co-Mn-Al mixed oxide deN2O catalyst was prepared by calcination of Co-Mn-Al layered double hydroxide, subsequent impregnation with KNO3, and shaping into tablets of 5 mm × 5 mm. Tablets were tested for N2O decomposition in pilot scale reactor connected at the bypassed tail gas from the nitric production plant downstream of the SCR NOx/NH3 catalyst with the aim to perform kinetic measurements. Special attention was paid to study the changes in the catalytic performance, which was monitored using both the long-term catalytic test and the comparison of physical-chemical properties of the fresh and used catalyst. The changes in the surface composition, caused by the time-on-stream operation for 112 days in the pilot reactor, provided stable catalytic performance; average value of N2O conversion of 90 ± 6% at 450 °C was kept (GHSV = 11 000 m³ mbed-3 h-1). The obtained kinetic data were applied in modeling of a full-scale reactor for the N2O emissions abatement and can be used for estimation of the amount of the catalyst necessary for obtaining required N2O conversion in the target plant. [ABSTRACT FROM AUTHOR]

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]