Av. Kucherov et al., TRANSFORMATIONS OF CU ZSM-5 SYSTEM UPON HIGH-TEMPERATURE REDUCTIVE AND OXIDATIVE TREATMENTS/, Microporous materials, 7(1), 1996, pp. 27-34
Interaction of O-2 with Cu/ZSM-5 samples (0.5-2.8 wt.% Cu) precalcined
in air at 500 or 800 degrees C and then reduced under different condi
tions was studied. The treatment of the samples precalcined at 500 deg
rees C by H-2 at the same temperature leads to a quantitative reductio
n of copper with formation of large (30-60 nm) Cu-0 crystals. A milder
treatment of CuH/ZSM-5/(500) (300 degrees C, C3H6) also results in a
total reduction of Cu2+, but a noticeable portion of the copper (about
20%) is retained inside the zeolitic channels either as disperse Cu-0
crystals or as Cu+ ions. For the CuH/ZSM-5 samples precalcined above
800 degrees C, the treatment by H-2 or C3H6 at 500 degrees C results i
n the reduction of only about 3/4 of the CU2+ to Cu-0, and about 1/4 o
f the cupric ions preserve the valent state Cu2+. The reducibility of
isolated cupric cations is related to the coordination state of Cu2+ i
n ZSM-5, which in turn, depends on the temperature of the oxidative pr
ecalcination.