No abstract

This work was aimed to design efficient catalysts for N 2 O decomposition at low temperatures. Cobalt oxide (Co 3 O 4) was prepared by hydrothermal, precipitation and combustion methods and tested for N 2 O decomposition. It was found that the catalysts prepared by solution combustion synthesis were most active for this reaction. Subsequently, a series of ceria (CeO 2) supported Co 3 O 4 catalysts (xCeCo) were prepared by solution combustion method and used them for N 2 O decomposition. All the catalysts were characterized by analytical methods like XRD, TEM, BET, XPS, UV-Vis, Raman and H 2-TPR. It was found that 10 and 20 wt..% loading of CeO 2 on Co 3 O 4 promoted the activity of Co 3 O 4 towards N 2 O decomposition, whereas, higher loading of CeO 2 reduced the activity. Typical results indicated that addition of CeO 2 increases the surface area of Co 3 O 4 , and improves the reduction of Co 3+ to Co 2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step for the N 2 O decomposition over Co 3 O 4 spinel catalysts. Optimal CeO 2 loading can increase both dispersion and surface area of Co 3 O 4 catalysts and weaken the CoO bond strength to promote N 2 O decomposition.

Degradation of phenol in water was examined in a non‐thermal plasma reactor combined with CeO2, Fe2O3/CeO2, and ZrO2/CeO2 catalysts. Plasma reactor was operated in a dielectric barrier discharge configuration, whereas, catalysts were characterized by XRD, BET, and Raman spectroscopy. The effect of applied voltage, phenol concentration and catalyst addition was studied. Typical results indicated that the degradation efficiency increases with increasing voltage, whereas, the best energy yield was obtained at lower applied voltage. Total organic carbon analyzer confirmed the mineralization of phenol, which was further enhanced by the catalyst addition up to 47.3%. The intermediate compounds formed during the plasma decomposition were identified by gas chromatography mass spectrometry (GC–MS).

Direct decomposition of nitrous oxide (N2O) was studied in a non‐thermal plasma (NTP) dielectric barrier discharge (DBD) reactor operated under ambient conditions. Influence of various parameters like discharge gap, input power, residence time, and N2O concentration were studied to achieve high conversions. The conversion decreased with increasing flow rate and N2O concentration. Typical results indicated that N2O decomposition may be efficient at high residence time and low concentrations. The degree of N2O decomposition varied between 30 and 100% with the power variation between 0.5 and 2.7 W. Interesting observation is that packing the discharge volume with dielectric materials (ceramic, glass, and Al2O3 beads) improved the conversion. Under the same experimental conditions, the effect of the dielectric materials followed the order: ceramic beads > glass beads > Al2O3 beads > no packing. It was concluded that packed bed plasma reactor may be an efficient way for the reduction of N2O emissions.

Low-cost activated carbons were prepared by physical activation of bio-waste rice husk. Various physicochemical characterization techniques confirmed the high surface area and oxygen functional groups on the surface. It has been confirmed that activation under humidified carbon dioxide followed by ozonation resulted the highest number of surface functional groups on activated carbon. Nitrogen adsorption-desorption isotherms confirmed the highest surface area (417 m 2 /g), whereas elemental analysis ensured the increasing oxygen content after activation. Temperature-programmed decomposition quantified these surface oxygen functional groups, and it was concluded that ozonation increased both acidic and basic groups. The developed activated carbons were tested during the removal of a model dye methylene blue from aqueous medium in the concentration range 10-30 mg/L. Typical results indicated that adsorption studies are consistent with the Langmuir isotherm model with maximum monolayer adsorption capacity of 28.5 mg/g, and the dimensionless separation factor (R L ) values between 0.006 and 0.030 confirmed a favorable adsorption. Methylene blue adsorption followed pseudo-second order kinetics indicating MB was adsorbed onto the surface via chemical interaction.