Copper ion exchange

From the comparison of the results, it can be inferred that copper ions exchanged in the ZSM-5 zeolites assumes a bidentate (sites 12 and II) or tridentate coordination (sites M5, Z6, and M7). These two groups differ also in the molecular properties (Table 2.2). The I-centers are characterized by lower values of the valence index and greater partial charges, QCu, in comparison to the M and Z centers, which is associated with the deeper laying HOMO and LUMO levels. In the M5, Z6, and M7 sites Cu1 ions exhibit more covalent character, and the frontier orbitals have less negative energies. As a result, the chemical hardness of the I-centers, located at the channel intersections, is smaller than those located on the walls of the ZSM-5 zeolite. 

Iwamoto, M., Mizuno, N. and Yahiro, H. (1991) Removal of nitrogen monoxide over copper ion-exchanged zeolite catalysts, Sekiyu Gakkaishi, 34, 375. 

Ishihara, T., Kagawa, M., Hadama, F. et al. (1997) Copper ion-exchanged SAPO-34 as a thermostable catalyst for selective reduction of NO with C3H6, J. Catal., 169, 93. 

Iwamoto, M Yahiro, H Tanda, K Mizuno, N Mine, Y Kagawa, S. Removal of nitrogen monoxide through a novel catalytic process. 1. Decomposition on excessively copper-ion-exchanged ZSM-5 zeolites. J., Phys. Chem., 1991, Volume 95, 3727-3730. 

Long, R. Q. and Yang, R. T. Selective Catalytic reduction of nitric oxide with ethylene on copper ion-exchanged Al-MCM-41 catalyst, Ind. Eng. Chem. Res., 1999, Volume 38, Issue 3, 873-878. 

Copper Ion-exchanged Zeolites as Active Catalysts for Direct Decomposition of Nitrogen Monoxide... 

The catalytic properties of a copper ion-exchanged ZSM-5 zeolite (Cu-ZSM-5) can be compared with others. 

Copper ions exchanged microporous molecular sieves, in particular Cu-ZSM-5, are active catalysts for the selective catalytic reduction of NO and N2O with hydrocarbons in the presence of O2 (HC-SCR). It has been reported that the catalytic activity may be controlled by intra-crystalline diffiisivity and by geometry-limited diffusion depending on the hydrocarbon molecular size and the zeolite pore size [1]. Therefore, it is of interest to prepare Cu-Al-MCM-41 mesoporous molecular sieves and to compare their activity with that of Cu-ZSM-5. 

As regards the Cu-Al-MCM-41 (Si/Al=30 and 150) and Cu-ZSM-5 (Si/Al=25) catalysts, the copper ion exchange is related to the presence of both Bronsted Si-OH-Al acid sites and internal silanols. In the case of Cu-ZSM-5 (Si/Al=25) it appears that only the Bronsted acid sites are responsible for the ion exchange (Cu/Al 0.5). The fact that the copper loading of Cu-Al-MCM-41 (Si/Al=30) is similar to that of Cu-MCM-41 and less than that of Cu-Al-MCM-41 (Si/Al=150) may be an indication of the presence of extra-framework octahedral A1 species with no ion exchange capacity (vide infra). 

The Al insertion causes loss of crystallinity and less ordered mesopore structure. By comparing the copper ion exchange capacity of Cu-MCM-41 and Cu-Al-MCM-41 it turns out that for low Al insertion (Si/Al=150) most of Al is framework, whereas in the sample with Si/Al=30 a large part of the aluminum species are extra-framework with no ion exchange capacity and different catalytic behavior. 

Methanol Conversion over Copper Ion-Exchanged Silicate Minerals"... 

Dimerizations of aryldiazomethanes to 1,2-diarylethylenes were reported to be catalyzed by cerium(IV) ammonium nitrate (4J), lithium bromide (42), copper(II) salts (43), and rhodium(II) acetate (44) and to be induced by photolysis (45). Catalysis of copper ion-exchanged zeolite (CuNaY) was compared with reactions of copper salts supported on AI2O3 and a homogeneous catalyst, Cu(C104)2, for the dimerization [Eq. (11)] of aryldiazomethane (Table XIII) (-/6). 

In nucleophilic substitutions performed in the liquid phase, copper ) is presumed to be the actual catalyst [1]. It is very likely that this is also the active site in vapour-phase reactions, as the reaction mechanism seems comparable [2]. Copper-zeolites usually are prepared in the copper(II) form upon heating, copper(II) can be reduced to copper(I), accompanied by a loss of molecular oxygen [6]. Presumably this phenomenon is related to the decomposition of the copper-oxygen species formed during the copper ion exchange [7]. In our experiments, a pretreatment with ammonia -a well-known method to reduce copper(II) to copper(I) at elevated temperatures [8,9]- has been applied to increase the copper(I) level. 

Two copper containing ZSM-5 catalysts with Si/Al ratio of 24 and 66 and Cu/Al ratio of 0,5 and 1, respectively, have been prepared by conventional ion exchange of sodium with coppor. The third catalyst was a copper ion exchanged dinoptilolite, a natural zeolite of small pore size. 

Zhang, Y., and M. Flytzani-Stephanopoulos, 1994, Catalytic decomposition of nitric oxide over promoted copper-ion-exchanged ZSM-5 zeolites, in Environmental Catalysis, ed. J.M. Armor, Vol. 552 of ACS Symposium Series (American Chemical Society, Washington, DC) pp. 7-21. 

Natural clinoptilolite originates from Caimanes deposit (Moa, Cuba). We denote these samples as blank Cli. Copper ion exchange was carried out from 0.1 M... 

The activity of copper-exchanged zeolite catalysts in direct decomposition was influenced by (i) the degree of copper ion-exchange [7] (no decomposition was observed in the absence of copper) and (ii) the Si/Al ratio of the zeolite [8], (iii) the preparation method of the parent Na-ZSM-5 [9]. The effect of admixed dioxygen and water vapour to the feed stream has been reported too [10]. 

In liquid phase the copper-ion exchange was carried out by stirring about 25 g sample in 0.05 M Cu-acetate solution at room temperature for 24 hours, the exchanged sample was washed, dried and calcined at 773 K for 5 hours. 

Composition of samples and copper ion-exchange level were determined by X-ray fluorescence (XRF) analysis. 

They also have tried to explain copper state in the zeolite type catalysts used in the reduction reaction of NOx with hydrocarbons in the presence of a greater amount of oxygen in the reaction medium, therefore under distinctly oxidizing conditions. They evidenced the importance of copper excess in such catalysts (the level of copper ion exchange in ZSM-5 over 100%) and confirmed the literature data which show that copper is present on the surface of these catalysts under two forms (Cu2+, Cu+) [6, 9],... 

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