CeO2 doping boosted low-temperature NH3-SCR activity of FeTiOx catalyst: A microstructure analysis and reaction mechanistic study

• CeO₂ doping significantly improved low-temperature NH₃-SCR activity on FeTiO_x. • The crystallinity of FeTiO_x was decreased dramatically after CeO₂ doping. • Unique Ce-O-Fe structure in FeCe_0.2TiO_x accounted for its superior redox property. • Facile activation of NH₃ to-NH₂ on FeCe_0.2TiO_x promoted the DeNO_x efficiency. FeTiO_x has been recognized as an environmental-friendly and cost-effective catalyst for selective catalytic reduction (SCR) of NO_x with NH₃. Aimed at further improving the low-temperature DeNO_x efficiency of FeTiO_x catalyst, a simple strategy of CeO₂ doping was proposed. The low-temperature (<250℃) NH₃-SCR activity of FeTiO_x catalyst could be dramatically enhanced by CeO₂ doping, and the optimal composition of the catalyst was confirmed as FeCe_0.2TiO_x, which performed a NO_x conversion of 90% at ca. 200℃. According to X-ray diffraction (XRD), Raman spectra and X-ray absorption fine structure spectroscopy (XAFS) analysis, FeCe_0.2TiO_x showed low crystallinity, with Fe and Ce species well mixed with each other. Based on the fitting results of extended X-ray absorption fine structure (EXAFS), a unique Ce-O-Fe structure was formed in FeCe_0.2TiO_x catalyst. The well improved specific surface area and the newly formed Ce-O-Fe structure dramatically contributed to the improvement of the redox property of FeCe_0.2TiO_x catalyst, which was well confirmed by H₂-temperature-programmed reduction (H₂-TPR) and in situ XAFS experiments. Such enhanced redox capability could benefit the activation of NO and NH₃ at low temperatures for NO_x removal. The detailed reaction mechanism study further suggested that the facile oxidative dehydrogenation of NH₃ to highly reactive-NH₂ played a key role in enhancing the low-temperature NH₃-SCR performance of FeCe_0.2TiO_x catalyst.     

Degradation of gas-phase propylene glycol monomethyl ether acetate by ultraviolet/ozone process: A kinetic study

A pilot-scale plug-flow reactor was built to investigate its performance in treating airborne propylene glycol monomethyl ether acetate (PGMEA) via ozonation, ultraviolet (UV) photolysis and UV/O3 technologies. Governing factors, such as the initial molar ratio of ozone (O3) to PG-MEA, UV volumetric electric power input, and moisture content in the influent airstream, were investigated. A 1-L batch reactor was used to investigate some photodegradation characteristics of PGMEA in advance. Experiments were conducted at a fixed influent PGMEA concentration of approximately 50 ppm and an ambient temperature of 26 degrees C. A gas space time of 85 sec in the plug-flow reactor was kept for either ozonation or photolysis reaction, whereas a gas space time of 170 sec was used for the UV/O3 degradation. Results show that an initial molar ratio of O3 to PGMEA of >2.91 and an UV volumetric electric input power of 0.294 W/L(-1) sufficed to obtain PGMEA decompositions of >90% by UV/O3. Kinetic analyses indicate that all types of PGMEA decomposition are pseudo-first order with respect to its concentration. Moisture content (relative humidity = 15-99%) and UV volumetric electric input power (0.147 and 0.294 W/L(-1)) were major factors that strongly affect the PGMEA degradation rate.     

Source identifications of PM10 aerosols depending on hourly measurements of soluble components characterization among different events in Taipei Basin during spring season of 2004

Continuous measurements of hourly PM10 soluble ions were performed by the in situ IC technology in order to assess the impact of Asian outflows on local air quality. The intensive aerosol observation was carried in Taipei from 11 February 22:00 to 7 April 19:00, 2004. Concentrations of the water-soluble ions (Cl(-), NO(-)(2), NO(-)(3), SO(2-)(4), Na(+), NH(+)(4), K(+), and Ca(2+)) were measured in a total of 3,300 samples. The characteristics of air pollutant events in Taipei Basin were classified as frontal dust, dust, northeast monsoon, south wind and sea/land breeze according to the hourly meteorology and air pollutant concentrations. Factor analysis was conducted based on hourly data for 13 variables to find the group of variables with similar behavior. According to the source characteristics of high loading species, the possible sources of PM10 aerosols in each group were identified. Three to four factors were identified for each event. The total variances of frontal dust, dust, northeast trade, south wind, and sea/land breeze events were explained about 85%, 86%, 76%, 77%, and 80%, respectively, indicating that the identified factors were satisfactory.