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Supported Pt catalyst hydrogen selective catalytic reduction of NO

Author: YangShuFang
Tutor: WangXinPing
School: Dalian University of Technology
Course: Physical and chemical
Keywords: Nitrogen oxides H2-SCR Ferrierite Steam Hydrotalcite
CLC: X13
Type: Master's thesis
Year: 2011
Downloads: 125
Quote: 1
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Abstract


Nitrogen oxides (NOx) is an air pollutant harmful to human health, but also the formation of acid rain and thus endanger crops, buildings the main pollutants. Selective catalytic reduction (SCR) is an effective way to eliminate NOx. H2 selective catalytic reduction NOx (H2-SCR) because of its low-temperature characteristics of high activity aroused interest in the study. This paper studies the Pt H2-SCR reaction, discusses the type of carrier on the activity. Depth study of the Pt / HFER catalyst reactivity and mechanism of the system investigated the effect of water vapor. And hydrotalcite material as a carrier Pt H2-SCR catalysts were studied. Compared under the same conditions of Pt were supported on the HFER, ZSM-5, A12O3 obtained on the reaction of H2-SCR catalyst performance. The results show that, HFER and ZSM-5 zeolite Pt ratio Al2O3 as carrier, can catalyst has better H2-SCR reaction performance. The reason can be presumed, Zeolite Pt supported on the support can make more active state exists in the metal. Thus better able to activate H2, H2-SCR reaction in favor. In the Pt / HFER the catalyst, showed that: (1) the catalyst for the catalytic activity of the NO oxidation above 150 ℃ above to be able to emerge, and to eliminate the catalyst NOx conversion rate maximum (87.9%) occurred at 110 ℃ . (2) increase the reaction system, the proportion of NO2 in NOx, but reduces the NOx conversion rate to eliminate; (3) elimination of the NOx conversion rate lower temperatures, and even lead to an increase in the concentration of NO2 at the outlet of the reactor the concentration of NO higher than the corresponding inlet concentration phenomenon. Based on the above experimental facts, combined with in situ infrared results, first proposed and demonstrated in the reaction system of NO2 and surface nitrate species is not the Pt / HFER catalyst H2-SCR reaction intermediate species, and adsorbed species on Pt NOδ it may be the catalyst for the reaction of H2-SCR key active species. For the 0.5% Pt / HFER the H2-SCR catalyst reaction, increasing the H2 concentration in the system, not only can significantly improve the elimination of NOx conversion rates, but also significantly improved the conversion rate of H2. To explain this anomaly, the system studied by pre-oxidation of water vapor partial H2 after H2-SCR reaction. The results showed that a small amount of water vapor in the system (0.2% -0.8%) to be added not only to improve the conversion rate of NOx and H2, N2 selectivity also increased. Based on the above experimental facts, the first non-reactive with the surface water and competitive adsorption of nitrate species, a reasonable explanation of the mechanism of the reactor inlet, the lower H2 concentration in the H2-SCR reaction conversion rate of H2 obtained in this experiment phenomenon but smaller. Research paper also examines the hydrotalcite material as a carrier Pt, Pd catalysts H2-SCR reaction, reached the following conclusions: hydrotalcite after calcination at 500 ℃ generated composite oxide with a layered structure material before calcination, compared Pt is more suitable as a carrier for the H2-SCR reaction; Pt / Mg-Al-O catalyst was pretreated H2/N2 temperature can increase its H2-SCR reaction activity, the reduction of low valence Pt species H2-SCR reaction The active species; compared with Pd on hydrotalcite calcination at 500 ℃ in terms of the resulting composite oxide carrier, Pt is better H2-SCR active ingredient.

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