Photocatalytic decomposition of nitrous oxide using TiO2 and Ag-TiO2 nanocomposite thin films

TiO2 and Ag-TiO2 (0.05, 0.25 and 1 wt% 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 8 W Hg lamp (254 nm wavelength). The photoreactivity of Ag-TiO2 increases with the Ag amount to 0.25 wt% Ag. Further increase of Ag loading to 1 wt% 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.Web of Science20917517

Photocatalytic reduction of CO2 over TiO2 based catalysts

At present, carbon dioxide is considered the largest contributor among greenhouse gases. This review covers the current state of problem of carbon dioxide emissions from industrial and combustion processes, the principle of photocatalysis, existing literature related to photocatalytic CO2 reduction over TiO2 based catalysts and the effects of important parameters on the process performance including light wavelength and intensity, type of reductant, metal-modified surface, temperature and pressure.Web of Science6219

N2O emissions from production of HNO3

Nitrous oxide (N2O) belongs to greenhouse gases and damages the stratospheric ozone. Production of HNO3 is the main industry source of N2O emissions. Mechanism of formation of N2O have been described and the results of measurements of N2O emission have been presented from several HNO3 plants differing by the pressure of the ammonia combustion and NOx abatement technologies.Podtlenek azotu (N2O) jest zaliczany do grupy gazów cieplarnianych, który uszkadza warstwę ozonową. Największym przemysłowym źródłem emisji N2O jest produkcja kwasu azotowego. Opisano mechanizm powstawania N2O i wyniki pomiarów jego emisji N2O z wybranych technologii produkcji HNO3, które różnią się ciśnieniem w procesie spalania amoniaku i technologią denitryfikacji

Effect of temperature, pressure and volume of reacting phase on photocatalytic CO2 reduction on suspended nanocrystalline TiO2

The effect of temperature, pressure and volume of reactant solution on the photocatalytic reduction of CO2 at suspended TiO2 was studied in an annular batch photoreactor. Reaction products in the liquid phase (methanol, formaldehyde) and in the gas phase (methane, ethane, carbon monoxide, molecular oxygen and hydrogen) were analysed by gas chromatography. The photocatalytic reduction of CO2 was not sensitive significantly to small temperature variations within 10 K. The CO2 pressure at carbonation of the solution influenced the selectivity of the CO2 conversion to methane and methanol, while the dihydrogen yield was higher by two orders of magnitude and independent of the pressure. The dependence of the product yields on the volume of the liquid phase confirmed the fact that the requirement for perfect mixing was difficult to fulfil for the annular configuration of the reactor

Comparison of the pure TiO2 and kaolinite/TiO2 composite as catalyst for CO2 photocatalytic reduction

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

Application of calcined layered double hydroxides as catalysts for abatement of N2O emissions

The results of catalytic decomposition of N2O over mixed oxide catalysts obtained by calcination of layered double hydroxides (LDHs) are summarized. Mixed oxides were prepared by thermal treatment (500 °C) of coprecipitated LDH precursors with general chemical composition of MII1-xMIIIx(OH)2(CO3)x/2·yH2O, where MII was Ni, Co, Cu and/or Mg, MIII was Mn, Fe and/or Al, and the MII/MIII molar ratio was adjusted to 2. The influence of chemical composition of the MII-MIII mixed oxide catalysts on their activity and stability in N2O decomposition was examined. The highest N2O conversion was reached over Ni-Al (4:2) and Co-Mn-Al (4:1:1) catalysts. Their suitability for practical application was proved in simulated process stream in the presence of O2, NO, NO2 and H2O. It was found that N2O conversion decreased with increasing amount of oxygen in the feed. The presence of NO in the feed caused a slight decrease in N2O conversion. A strong decrease in the reaction rate was observed over the Ni-Al catalyst in the presence of NO2 while no N2O conversion decrease was observed over the Co-Mn-Al catalyst. Water vapor inhibited the N2O decomposition over all tested catalysts. The obtained kinetic data for N2O decomposition in a simulated process stream over the Co-Mn-Al catalyst were used for a preliminary reactor design. The packed bed volume necessary for N2O emission abatement in a HNO3 production plant was calculated as 35 m3 for waste gas flow rate of 30 000 m3 h-1

Catalytic decomposition of nitrous oxide over oxides derived from hydrotalcite-like compounds

Mixed oxide-based catalysts prepared by the thermal decomposition of M(II)-Al hydrotalcite-like compounds (M(II) = Co, Cu, Ni, or Mg) were used in catalytic decomposition of nitrous oxide into nitrogen and oxygen. The prepared hydrotalcites as well as calcined products were characterized by the thermal analysis (TG/DTA), X-ray powder diffraction, infrared spectroscopy, and BET surface area measurements. The catalytic reaction was performed in a fixed-bed reactor at 1000 ppm N2O inlet concentration in the temperature range 330-450degreesC, the space velocity was 60 000 cm(3) g(-1) h(-1). Ni- and Co-containing catalysts showed high activity in nitrous oxide decomposition. A very poor activity for Mg-Al mixed oxide catalyst was observed

Study of the catalytic activity of calcined Ni/Mg/Al (Mn) hydrotalcites for N2O decomposition

Mixed oxide-based catalysts prepared by thermal decomposition of Ni-(Mg)-M(III) hydrotalcite-like compounds (M(III) = Al, Mn) were used in catalytic decomposition of nitrous oxide in order to describe the catalytic activity of multicomponent catalysts and to study the effect of Mg2+ presence in the catalysts structure. Although the catalytic activity of prepared Ni-Al and Mg-Mn calcined hydrotalcites was high, the simultaneous presence of both transition metal cations Ni2+ and Mn3+ in the catalyst structure caused a decrease of N2O conversion and specific surface area. The N2O conversions decrease with increasing content of Mg in the Ni-Al system and increase in the Ni-Mn system. The rise of Mg content in the catalysts resulted in larger surface area and higher thermal stability of both Ni-(Mg)-Al and Ni-(Mg)-Mn samples. The prepared hydrotalcites as well as calcined products were characterized by the thermal analysis (TG/DTA), powder X-ray diffraction (XRD), and BET surface area measurements