Investigation of metal state in metal-containing zeolite catalysts by DTA and ESR methods

Thermal stability and its influence on the catalytic activity in CO oxidati on of Cu, Pd and Pd-Cu zeolite systems were investigated. The increasing of catalytic activity in the first cycle of reaction is connected with the th ermal decomposition of complex ions and consequently with the changing of m etal state in catalyst in the case of Cu/ZSM-5 catalyst. This activity does not relate to initial zeolite with complex ions, but to the metal ions wit h the decreasing ligands number in the coordination sphere of metal ion. Ac cording to the EPR spectrum the copper ions form clusters in zeolite channe ls due to the spin changed interaction. It was established ESR method that 1.8% Cu/ZSM-5 catalyst in a reduced form has copper (I and II) ions by. The Pd/ZSM-5 catalysts with different metal content have high catalytic activi ty below the temperature decomposition in contrary to Cu-containing zeolite s. On the one hand, it may be connected with the partial reduction of Pd io ns during CO oxidation and, on the other hand, with the ability of Pd ions to form the respective label complexes with reagents as additional ligands. The same character of relation between thermal stability and catalytic act ivity for Pd-Cu/ZSM-5 catalyst was observed.