Wei-guo Pan

Liquid Phase Oxidation and Absorption of NO from Flue Gas: A Review

NO (nitric oxide) is one of the main air pollutants emitted from coal-fired power plants. During the past several decades, capture of NO by liquid phase oxidation and the absorption process has drawn much attention for its advantages of low cost and co-capture of other pollutants. This paper provides a comprehensive review of recent development of liquid phase oxidation and the absorption process for NO capture. The process chemistry, effect of reaction parameters on absorption efficiency, and simultaneous capture with other pollutants in flue gas are critically summarized and reviewed. And the future development of this process is also referred to and discussed in brief.

Deactivation of Mn/TiO2 catalyst for NH3-SCR reaction: effect of phosphorous

The deactivation mechanism of phosphorous on a Mn/TiO2 catalyst for selective catalytic reduction of NO with NH3 was investigated in this study. It was found that the NH3-SCR reaction over the Mn/TiO2 catalyst obeyed the Langmuir–Hinshelwood mechanism. From the characterization results, it could be found the addition of phosphorous on the Mn/TiO2 catalyst would decrease its reducibility and inhibit the adsorption of chemisorbed oxygen and NOx species on its surface. As a result, the P-doped Mn/TiO2 catalyst was deactivated.

The Absorption Kinetics of NO into Weakly Acidic NaClO Solution

NO is a major air pollutant from coal-fired power plants. A combined removal of SO2 and NO is a prospective process. In this paper, the absorption kinetics of NO into weakly acidic NaClO solution was studied in a stirred tank reactor. It was proven that the absorption process occurred under the fast pseudo-mth reaction regime, and the reaction was found to be first-order with respect to both NO and NaClO. When the initial pH value of NaClO solution is 5.5, it has the best performance for NO absorption. The frequency factor and the average activation energy of this reaction were 7.96 × 108 m3/(mol s) and 28.15 kJ/mol, respectively. The absorption rate of NO increased with increasing reaction temperature.

Absorption of NO from simulated flue gas by using NaClO2/(NH4)2CO3 solutions in a stirred tank reactor

Experiments were performed in a stirred tank reactor to study the absorption kinetics of NO into aqueous solutions of NaClO2/(NH4)2CO3 solutions. The absorption process is a fast pseudo-reaction, and the reaction was found to be second-order with respect to NO and first-order with respect to NaClO2, respectively. The frequency factor and the average activation energy of this reaction were 4.56×1011 m6/(mol2 s) and 33.01 kJ/mol respectively. The absorption rate of NO increased with increasing reaction temperature, but decreased with increasing (NH4)2CO3 solution.

A CeFeOx catalyst for catalytic oxidation of NO to NO2

Abstract Catalytic oxidation of NO into NO 2 is a promising method for NO x emission control. The aim of this study was to develop an economic and environmental-friendly catalyst for NO catalytic oxidation. Herein a CeFeO x complex oxide catalyst for catalytic oxidation of NO was prepared by coprecipitation method. After that the catalytic performance of this catalyst was measured on a fixed-bed reactor. It was found that the intrinsic activity of CeFeO x was higher than that of CeO x and FeO x . The characterization techniques of Brumauer-Emmett-Teller (BET), X-ray diffraction (XRD), temperature programmed reduction with H 2 (H 2 -TPR), temperature programmed desorption with NO+O 2 (NO+O 2 -TPD) and X-ray photoelectron spectroscopy (XPS) were performed to investigate the surface area, crystal structure, redox property and NO x adsorption behavior of the catalyst samples. From the characterization results, it was concluded that the low crystallinity of CeFeO x promoted the dispersion of active species, as a result, enhancing the redox ability and NO adsorption capacity of CeFeO x catalyst, which is favorable to NO catalytic oxidation. Furthermore, the presence of much chemisorbed oxygen on CeFeO x catalyst also made a great contribution to its good catalytic performance.

The enhanced resistance to P species of an Mn–Ti catalyst for selective catalytic reduction of NOx with NH3 by the modification with Mo

Phosphorous has a deactivation effect on an SCR catalyst. In this study, the effect of Mo modification on the resistance to P species of a Mn–Ti catalyst for selective catalytic reduction of NOx with NH3 was investigated. It was found that the addition of Mo could greatly improve the P species tolerance of the Mn–Ti catalyst. From the characterization results of BET, XRD, H2-TPR, NH3-TPD and XPS, it could be concluded that the modification of the Mn–Ti catalyst by Mo could enhance its specific surface area, redox ability and NH3 adsorption capacity, along with the generation of more surface chemisorbed oxygen species, as a result, greatly enhancing the P species resistance of the Mn–Ti catalyst. The results of an in situ DRIFT study indicated that the NH3-SCR reactions over Mn–Ti and Mn–Mo–Ti catalysts were governed by L–H mechanism (≤200 °C) and E–R mechanism (>200 °C) respectively.

The enhanced performance of a CeSiOx support on a Mn/CeSiOx catalyst for selective catalytic reduction of NOx with NH3

A series of Mn/CeSiOx catalysts were prepared by the wet impregnation method and used for selective catalytic reduction of NO with NH3. As can be seen from the experimental results, the Mn/CeSiOx catalyst with a Ce/Si molar ratio of 2/1 showed excellent low-temperature SCR activity, high N2 selectivity and excellent SO2 and H2O tolerance. The relationship between the CeSiOx support and the SCR performance of Mn/CeSiOx (2 : 1) catalyst was investigated based on the characterization results of N2 adsorption, XRD, XPS, H2-TPR, NH3-TPD and in situ DRIFT. The strong interaction between Ce and Si resulted in the good dispersion of Mn species on the support; correspondingly, the redox ability and NH3 adsorption capacity were greatly enhanced. The results of in situ DRIFT study revealed that the NH3-SCR reactions over Mn/CeO2 and Mn/CeSiOx (2 : 1) mainly obeyed both the E–R mechanism and the L–H mechanism. Furthermore, the formation of more Mn4+ and chemisorbed oxygen greatly facilitates the oxidation of NO to NO2, as a result, promoting the low-temperature SCR performance of Mn/CeSiOx (2 : 1).

CHARACTERIZATION OF FLY ASH FROM COAL-FIRED POWER PLANT AND THEIR PROPERTIES OF MERCURY RETENTION

Recent research has shown that fly ash may catalyze the oxidation of elemental mercury and facilitate its removal. However, the nature of mercury-fly ash interaction is still unknown, and the mechanism of mercury retention in fly ash needs to be investigated more thoroughly. In this work, a fly ash from a coal-fired power plant is used to characterize the inorganic and organic constituents and then evaluate its mercury retention capacities. The as-received fly ash sample is mechanically sieved to obtain five size fractions. Their characteristics are examined by loss on ignition (LOI), scanning electron microscope (SEM), energy dispersive X-ray detector (EDX), X-ray diffraction (XRD), and Raman spectra. The results show that the unburned carbon (UBC) content and UBC structural ordering decrease with a decreasing particle size for the five ashes. The morphologies of different size fractions of as-received fly ash change from the glass microspheres to irregular shapes as the particle size increases, but there is no correlation between particle size and mineralogical compositions in each size fraction. The adsorption experimental studies show that the mercury-retention capacity of fly ash depends on the particle size, UBC, and the type of inorganic constituents. Mercury retention of the types of sp2 carbon is similar to that of sp3 carbon.

Low-temperature selective catalytic reduction of NO on CeO2–CuO/Al2O3 catalysts prepared by different methods

CeO2–CuO/Al2O3 catalysts were prepared by three different methods and their activities for selective catalytic reduction (SCR) of NO with NH3 were investigated. As can be seen from the experimental results, the catalyst prepared by the single-step sol–gel (SG) method showed the best SCR activity and resistance to SO2 and H2O. In order to investigate the relationship between the preparation method and the performance of SCR catalysts, the catalysts were characterized by using Brunauer–Emmett–Teller, X-ray diffraction, temperature programmed reduction with hydrogen, temperature programmed desorption with ammonia, X-ray photoelectron spectroscopy, Fourier transform infrared and thermo-gravimetric analysis techniques. It was found that the excellent performance of CeO2–CuO/Al2O3 catalyst prepared by the single-step SG method should be resulted from its large surface area, low crystallinity, high oxygen storage capacity, high NH3 adsorption capacity, high concentration of surface chemisorbed oxygen, weak sulphation process and weak water absorption.

Absorption of NO by Aqueous Solutions of KMnO4/H2SO4

The absorption of NO in aqueous solutions of KMnO4 and H2SO4 was carried out in a stirred tank reactor under atmosphere pressure. The results indicated that the absorption process was under a fast pseudo-m th reaction regime. The reaction between NO and aqueous solutions of KMnO4/H2SO4 was found to be first-order with respect both to NO and to KMnO4. The addition of H2SO4 to KMnO4 solutions increased the absorption rate of NO and increasing reaction temperature was also favorable to the absorption of NO.