PECULIARITIES OF THE REDUCTION AND OXIDATION OF THE CU ZSM-5 SYSTEM/

The interaction of O-2 at 20-650 degrees C with Cu/ZSM-5 samples (0.5- 2.8 wt % Cu), which were precalcined in air at 500 or 800 degrees C an d then reduced under different conditions, was studied. For the sample s precalcined at 500 degrees C, the copper reduction by hydrogen also proceeds quantitatively with the formation of Cu-0 crystals (30-60 nm) on the outer surface of the zeolite. A milder treatment (300 degrees C, C3H6) of the CuH-ZSM-5 samples precalcined at 500 degrees C leads t o the total reduction of Cu2+, but some portion of the copper (similar to 20%) either forms dispersed Cu-0 crystals inside the zeolite chann els or is retained as Cu+ ions. Using the samples with 1.27 and 1.5 wt % Cu precalcined at 900 and 800 degrees C as examples, it is shown th at, upon their treatment by H-2 or C3H6 at 500 degrees C, the reductio n of only similar to 3/4 of Cu2+ to Cu-0 takes place, and similar to 1 /4 of the cupric ions preserve the Cu2+ valence state. The reducibilit y of Cu2+ cations in ZSM-5 is related with the coordination state of t he cupric ions.