Xuehua Zou

The effect of hydroxyl groups and surface area of hematite derived from annealing goethite for phosphate removal

Synthetic goethite and thermally treated goethite at different temperatures were used to remove phosphate from sewage. The effect of annealing temperature on phosphate removal over time was investigated. X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption and desorption (BET), and infrared emission spectrum (FT-IES) were utilized to characterize the phase, morphology, specific surface area, pore distribution, and the surface groups of samples. The results show that annealed products of goethite at temperatures over 250°C are hematite with the similar morphology as the original goethite with different hydroxyl groups and surface area. Increasing temperature causes the decrease in hydroxyl groups, consequential increase in surface area at first and then experiences a decrease (14.8-110.4-12.6 m(2)/g) and the subsequent formation of nanoscale pores. The variation rate of hydroxyl groups and surface area based on FT-IES and BET, respectively, are used to evaluate the effect of annealing temperature on phosphate removal. By using all of the characterization techniques, it is concluded that the changes of phosphate removal basically result from the total variation rate between hydroxyl groups and surface area.

V2O5/hematite catalyst for low temperature selective catalytic reduction of NOx with NH3

Abstract A series of V 2 O 5 /hematite (V/H) catalysts were prepared by impregnation of goethite with NH 4 VO 3 solution and used in the selective catalytic reduction (SCR) of NO with NH 3 . The catalysts were characterized by X-ray diffraction, transmission electron microscopy, N 2 adsorption, H 2 temperature-programmed reduction, and NH 3 temperature-programmed desorption. The effects of V 2 O 5 loading and calcination temperature on the SCR activity were investigated. The NO conversion over 3% V/H catalysts calcined at 300 °C exceeded 95% at 250–300 °C. Neither H 2 O nor SO 2 (0.01%) had any adverse impact on the activity, but a decrease of SCR activity was observed after high concentrations (0.03% and 0.05%) of SO 2 were introduced. Cutting off the SO 2 supply resulted in activity restoration. The simultaneous addition of 5% H 2 O and 0.03% SO 2 led to a synergistic poisoning effect, but when these gases were switched off, the activity was recovered. SO 2 adsorption on the catalyst surface led to the decrease in SCR activity.

The functionalization of limonite to prepare NZVI and its application in decomposition of p-nitrophenol

Nano zero valent iron (NZVI) was prepared by reducing natural limonite using hydrogen. X-ray fluorescence, thermogravimetry, X-ray diffraction, transmission electron microscope, temperature programmed reduction (TPR), field emission scanning electron microscope/energy disperse spectroscopy (FESEM/EDS) were utilized to characterize the natural limonite and reduced limonite. The ratios of Fe:O before and after reducing was determined using EDS. The reactivity of the NZVI was assessed by decomposition of p-nitrophenol (p-NP) and was compared with commercial iron powder. In this study, the results of TPR and FESEM/EDS indicated that NZVI can be prepared by reducing natural limonite using hydrogen. Most importantly, this NZVI was proved to have a good performance on decomposition of p-NP and the process of p-NP decomposition agreed well with the pseudo-first-order kinetic model. The reactivity of this NZVI for decomposition of p-NP was greatly superior to that of commercial iron powder.

Performance of selective catalytic reduction of NO with NH3 over natural manganese ore catalysts at low temperature

ABSTRACT Natural manganese ore catalysts for selective catalytic reduction (SCR) of NO with NH3 at low temperature in the presence and absence of SO2 and H2O were systematically investigated. The physical and chemical properties of catalysts were characterized by X-ray diffraction, Brunauer–Emmett–Teller (BET) specific surface area, NH3 temperature-programmed desorption (NH3-TPD) and NO-TPD methods. The results showed that natural manganese ore from Qingyang of Anhui Province had a good low-temperature activity and N2 selectivity, and it could be a novel catalyst in terms of stability, good efficiency, good reusability and lower cost. The NO conversion exceeded 85% between 150°C and 300°C when the initial NO concentration was 1000 ppm. The activity was suppressed by adding H2O (10%) or SO2 (100 or 200 ppm), respectively, and its activity could recover while the SO2 supply is cut off. The simultaneous addition of H2O and SO2 led to the increase of about 100% in SCR activity than bare addition of SO2. The formation of the amorphous MnOx, high concentration of lattice oxygen and surface-adsorbed oxygen groups and a lot of reducible species as well as adsorption of the reactants brought about excellent SCR performance and exhibited good SO2 and H2O resistance.