IN-SITU ESR MONITORING OF THE COORDINATION AND OXIDATION-STATES OF COPPER IN CU-ZSM-5 UP TO 500-DEGREES-C IN FLOWING GAS-MIXTURES .1. INTERACTION WITH HE, O-2, NO, NO2, AND H2O

A flow cell was designed for the monitoring of the state of copper ion s in Cu-ZSM-5 in situ at high temperatures by e.s.r. In thoroughly pur ified He or in vacuum there is no spontaneous reduction of the cupric ions up to 500 degrees C. The formation of adsorption complexes betwee n isolated Cu2+ cations and NO molecules at 20 degrees C leads to a me asurable change in coordination. Strong adsorption complexes of Cu2+ w ith NO2 are formed on treatment of CuH-ZSM-5 by an [NO + O-2] mixture, Bonding of Cu2+ ions with such strong ligands as NO2 or H2O attenuate s the spin-lattice interaction between Cu2+ and the zeolitic framework . The number of Cu2+ ions in CuH-ZSM-5 is quantified by the use of the e.s.r. signal of frozen, dilute water solutions of CuSO4 as a referen ce. In the samples used in this work the e.s.r. signal is associated w ith all the copper introduced into ZSM-5 by ion-exchange.