Browsing by Author "Bai, H"

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Adsorption behavior of moisture over a vanadia/titania catalyst: A study for the selective catalytic reduction process
(2004-09-15)
Lin, CH
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Bai, H
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環境工程研究所
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Institute of Environmental Engineering
A study of the inter-relationship between moisture, vanadia content, operation temperature, and surface acidity for a selective catalytic reduction (SCR) process for nitric oxide (NO) removal was conducted. The effects of operating parameters on the roles of Bronsted and Lewis acids acting in the SCR reaction were specified by the observed NO removal and the spectra of in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results indicated that H2O competed with NH3 molecules to be adsorbed on the pure titania catalyst that contained only Lewis acid sites. However, the competition did not occur over a vanadia-based catalyst on which both Bronsted and Lewis acid sites appeared in the presence of H2O. As compared to that under dry conditions where only Lewis acid sites were found, the catalytic activity was lower under moisturized conditions even though both acids existed and there are fewer reaction sites available. It is concluded that surface acid sites are varied according to different operation conditions. Lewis acidity was dominant under the condition of low vanadia content and in the absence of H2O molecules. It is also less sensitive to temperature. In contrast, Bronsted acidity was dominant under the condition of high vanadia content and in the presence of H2O molecules, and it is highly affected by temperature.
Laboratory evaluation of NH3 injection technology to reduce HCl emissions from incinerators
(1997-04-01)
Bai, H
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Chu, C
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交大名義發表
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環境工程研究所
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National Chiao Tung University
A laboratory-scale experimental study is conducted to investigate the fundamental properties of NH3-HCl reaction in a simulated incinerator duct system. The NH3 injection technology is a dry HCl removal process which produces solid products. The test results showed that under typical incineration operation conditions, the outlet concentration of HCl can meet the emission standards for incinerators in Taiwan. An excessive injection of NH3 above stoichiometric requirement may not lead to the NH3 slip problem. This is because that the excessive amount of NH3 would probably diffuse onto the product particles. However, the enhancement of NH3 utilization is economically not feasible. The outlet concentrations of HCl and NH3 are almost independent of their inlet concentrations for residence time longer than I second. Moisture content and the NH3/HCl injection ratio are two of the most important factors which affect the HCl removal and NH3 utilization.
Sources of sampling error for field measurement of nitric acid gas by a denuder system
(2003-03-01)
Bai, H
;
Lu, C
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Chang, KF
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Fang, GC
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環境工程研究所
Field measurements of atmospheric HNO3 gas by a denuder system equipped with four annular denuders were conducted in Taiwan. The positive errors from interfering N-compounds as well as the negative errors from incompleteness of the apparent absorption of the HNO3 gas. as sampled by one NaCl-denuder, were quantitatively determined and the error sources were identified. It is found that the concentrations of positive error and negative error might cancel each other resulting in less difference between the measured and the true HNO3 concentrations. The atmospheric HNO3 concentration and the ambient temperature were the major factors that influence the degree of negative errors. The apparent absorption efficiency might decrease to less than 80% if the HNO3 gas concentration were lower than 0.3 mug m(-3) or the ambient temperature were over 28degreesC. There are also evidences showed that the positive errors were from both interfering N-containing gases and nitrate-containing particles. (C) 2003 Elsevier Science Ltd. All rights reserved.
Surface acidity over vanadia/titania catalyst in the selective catalytic reduction for NO removal - in situ DRIFTS study
(2003-05-28)
Lin, CH
;
Bai, H
;
環境工程研究所
;
Institute of Environmental Engineering
An in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) study of the selective catalytic reduction (SCR) of NO with NH3 in the presence of O-2 was carried out over vanadia-based catalysts. Vanadia-based catalysts were prepared by impregnation method. The results indicated that the strength of Bronsted acidity positively increased with V2O5 loading, whereas Lewis acidity remained almost constant at a typical SCR operating temperature. Water vapor does not affect the adsorption of Lewis ammonia, but the formation of Bronsted acidity has to be accompanied by water vapor adsorption. Bronsted acidity is decreased with increasing temperature and disappeared at a temperature of around 500degreesC for all testing catalysts, while Lewis acidity slightly decreased with increasing temperature. The disappearance of Bronsted acidity at a high temperature was related to the loss of adsorbed water vapor. (C) 2002 Elsevier Science B.V. All rights reserved.