Metal-exchanged zeolite systems

ASPECTS OF CATALYST DEVELOPMENT FOR MOBILE UREA-SCR SYSTEMS - FROM VANADIA-TITANIA CATALYSTS TO METAL-EXCHANGED ZEOLITES... 

However, if transition metal exchanged zeolites are active materials in NH3-SCR, N2O emission can be also observed. N2O emission constitutes one of the main drawbacks of this system. For instance, Wilken et al. [112] reports a maximum N2O production at 200 °C over Cu-Beta zeolite. Mechanism of N2O emission is proposed to proceed through the decomposition of ammonium nitrates (reaction 19.28) ... 

Information published during thepast few years about the faujasite class of zeolites indicated that they present a possibly unique system in which the necessary conditions might be met. Sherry (4, 5) reported that rare earths, as compared with alkali or alkaline earth metals, are readily exchanged into Linde X from dilute aqueous solutions, and that they strongly favor the zeolite phase. When such an exchanged zeolite is dehydrated by heating to 350-700° C, the lanthanide ions move into the small pore system (6>, 7) after which they are not readily exchanged back out of the crystal. Smith (8) has reviewed the structure of lanthanide X and Y zeolites. 

The ESR spectrum observed when TNB was adsorbed on metal-exchanged Y zeolite was essentially a singlet (Co-, Ni-, La-exchanged) or a singlet with additional hyperfine structure (Ca exchanged). These systems are being further investigated. 

Zeolites are attractive host materials as they present regular channel systems, providing crystallographic defined locations for metal clusters. Hence, the size of the clusters inside the zeolites can be limited by the dimensions of their channels and cages. Zeolite-supported noble metal catalysts were extensively studied due to their wide application as catalysts in petroleum industry.Reduction of silver in zeolite hosts has been carried out by /-irradiation.The intermediate paramagnetic (charged) silver clusters formed in /-irradiated silver-exchanged zeolites have been studied by electron spin resonance (ESR)... 

Copper-exchanged zeolite ZSM-5 have received considerable attention of researchers over last several years because of their ability to promote both the total oxidation of alkanes and the decomposition of NOj [1 - 12]. However, little is known about the possibility of the CuH-ZSM-5 system modification as a result of the introduction of ions of the second active transition metal. A high and stable catalytic activity of Co/H-ZSM-5 in total oxidation of CH, was demonstrated recently [13]. Therefore, the mutual influence of two active components stabilized by H-ZSM-5 matrix is of interest. 

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