Alkali Resistant Fe-Zeolite Catalysts for SCR of NO with NH3 in Flue Gases

Abstract

Fe-zeolite catalysts were prepared by ionexchange and characterized by nitrogen physisorption, electron paramagnetic resonance (EPR) spectroscopy, NH 3 -temperature programmed desorption (TPD), H 2 -temperature programmed reduction (TPR) and Energy dispersive X-ray spectroscopy (EDX) methods. The effect of potassium doping on the acidic and redox properties of the Fe-zeolite catalysts were studied. The prepared catalysts showed high surface area and surface acidity. This is essential for increased alkali resistivity in comparison with conventional metal oxide supports like, e.g. TiO 2 and ZrO 2 , towards e.g. potassium salts in flue gases from biomass fired power plants. These properties allowed both undoped and potassium doped Fe-zeolite catalysts to posses high activity during the selective catalytic reduction (SCR) of NO with NH 3 . The extent of deactivation of the Fe-zeolite catalysts was further compared with commercial V 2 O 5 -WO 3 -TiO 2 catalyst (VWT) with various levels of potassium poisoning. While VWT catalysts severely deactivated at relative low potassium concentration levels the Fe-zeolite catalysts also showed superior alkali resistivity even at high potassium loadings.

A “Smart” Hollandite DeNOx Catalyst: Self‐Protection against Alkali Poisoning

“…The exchange reactions occur readily at normal NH 3 -SCR operating temperatures because alkali species, such as KCl and K 2 SO 4 , are mobile in view of their low Tamman temperatures (T Tam ). [9][10][11] The K + loading had almost no influence on the catalytic activity of HMO, and all HMO catalysts tested exhibited almost the same activity.For reference, a conventional deNO x catalyst (V 2 O 5 -WO 3 / TiO 2 ) with different K + loadings was also tested in the NH 3 -SCR reactions under the same conditions ( Figure 1). [9-11, 13, 14] However, this approach can not completely alleviate alkali poisoning because, to a great extent, alkali-metal ions and reactants compete for the same sites.…”

“…[2] An associated issue, which is often encountered in the control of NO x emissions from the alkali-rich stack gas of power plants (co-)fuelled by biomass, is the severe deactivation of conventional V 2 O 5 -WO 3 /TiO 2 catalysts in the selective catalytic reduction of NO by NH 3 (NH 3 -SCR). [4][5][6][7][8][9][10][11] For example, Zheng et al [8] proposed a deactivation mechanism by proton exchange at catalytically active Brønsted acid sites with alkali-metal ions. [4][5][6][7][8][9][10][11] For example, Zheng et al [8] proposed a deactivation mechanism by proton exchange at catalytically active Brønsted acid sites with alkali-metal ions.…”

“…[4][5][6][7][8][9][10][11] For example, Zheng et al [8] proposed a deactivation mechanism by proton exchange at catalytically active Brønsted acid sites with alkali-metal ions. [7][8][9][10][11] Figure 1 shows the catalytic activity of HMO with different K + loadings in NH 3 -SCR reactions at 350 8C as expressed in terms of the rate constant for the conversion of NO. [12] On the basis of this deactivation mechanism, a possible approach to the development of an alkali-resistant catalyst is to increase the number of catalytically active sites and "alkaliactive" sites (for trapping alkalis), for example, by using a support with the property of high or super acidity or by increasing the concentration of active elements.…”

“…[7][8][9][10][11] Figure 1 shows the catalytic activity of HMO with different K + loadings in NH 3 -SCR reactions at 350 8C as expressed in terms of the rate constant for the conversion of NO. [7][8][9][10][11] Figure 1 shows the catalytic activity of HMO with different K + loadings in NH 3 -SCR reactions at 350 8C as expressed in terms of the rate constant for the conversion of NO.…”

“…[3,4] This deactivation is predominately caused by the strong interaction of alkali-metal ions with catalytically active sites. [4][5][6][7][8][9][10][11] For example, Zheng et al [8] proposed a deactivation mechanism by proton exchange at catalytically active Brønsted acid sites with alkali-metal ions. The exchange reactions occur readily at normal NH 3 -SCR operating temperatures because alkali species, such as KCl and K 2 SO 4 , are mobile in view of their low Tamman temperatures (T Tam ).…”