Zeolite CuNaY

Figure 4 ESR spectrum (low eld components) of CuNaY zeolites dehydrated at 800° C and taken at room temperature in the X-hand as a function of degree of exchange (numbers on the left)...

Figure 5. ESR spectrum (low field components) of CuNaY zeolite (a = 29%) in the Q-band taken al room temperature as a function of dehydration temperature (numbers on the right are pretreatment temperatures)...

Beyer et al. (27) carried out a detailed kinetic study on CO oxidation over CuNaY zeolite after various pretreatments. The results obtained were explained in terms of the relative concentrations of the species Cu2 +, Cu+, and Cu° present in each catalyst. 

Catalytic hydrogenation of carbon dioxide was studied for the simultaneous synthesis of methanol and dimethyl ether (oxygenates). Various combinations of methanol synthesis catalysts and methanol dehydration catalysts have been examined for the hydrogenation. The hybrid catalyst of Cu/ZnO/CraOs and CuNaY zeolite was found to be very efficient for the production of oxygenates. 

CuNaY zeolites were prepared by ion exchange of zeolite NaY with an aqueous 0.03 M solution of Cu(N03)2 ( Merck, pro analysi) at 300 K. After washing and drying at ambient temperature, the composition determined by AAS was CUj, i,Na2j jY. The samples were pressed into self-supporting wafers of about 8 or 80 mg cm thickness for IR and X-Ray measurements, respectively. They were dehydrated in vacuo up to 12 h at temperatures between 625 and 575... 

The reduction of the copper ions in activated CuNaY zeolite depends on the partial pressure of both hydrogen and water. A reduction by hydrogen to copper metal only occurs if the pressure of water exceeds a certain limit. Otherwise the reduction will be incomplete and stable Cu(I) phases show up. The increased mobility of copper ions due to the availability of strong ligands seems to be important. Only these ions are able to be reduced to copper atoms by molecular hydrogen followed by an agglomeration to clusters. 

A number of transition metal ion-exchange zeolites are active for acetylene trimerization (159, 160), and the criterion for activity appears to be an even, partially filled d-orbital, i.e., d8 (Ni2 +, Co+), d( (Fe2+), d4 (Cr2 + ). This has led to the suggestion that the mechanism must involve a complex in which there is simultaneous coordination of two acetylene molecules to the transition metal ion. The active oxidation state for CuNaY butadiene cyclodimerization catalysts has been unambiguously defined as monovalent copper (172-180). The d10 electronic configuration of Cu+ is consistent with the fact that isoelectronic complexes of Ni° and Pd° are active homogeneous catalysts for this reaction. The almost quantitative cyclodimerization selec-... 

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). 

From EPR parameters conclusions on the coordination polyhedra and kind of ligands in copper complexes in various zeolites and oxides have been derived. Different gn values can be associated with different reducibilities of the copper ions. From EPR results the following sequence of increasing covalent bond character of the zeolite-Cu interaction is obtained CuNaA[Pg.230]

Studies on the State of Copper anc the Formation of its Oxidic and Metallic Phases in Zeolite CuNaY... 

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