IN-SITU ESR MONITORING OF CUH-ZSM-5 UP TO 500-DEGREES-C IN FLOWING DRY MIXTURES OF NO(NO2), C3H6(C2H5OH), AND EXCESS O-2

A flow cell was used for ESR monitoring of the state of copper ions in Cu-ZSM-5 in situ at 20-500 degrees C in a He stream containing C3H6 ( or C2H5OH), NO, and O-2. The gas mixtures approximate those in the sel ective catalytic reduction of NOx, save for the absence of steam. At r oom temperature, in propene flow, the formation of an oligomeric, carb onaceous material is accompanied by the reduction of a significant par t of the Cu2+ cations. Heating of the sample at 200-300 degrees C lead s to quantitative reduction of the cupric ions. Ethanol is a less acti ve reductant, and its sorption at 20-100 degrees C results only in a c oordination change of the Cu2+ by Octahedral complex formation. The on set of the reduction of the Cu2+ ions in the [C2H5OH + He] flow is at similar to 200 degrees C. The equilibrium oxidation state of the coppe r in CuH-ZSM-5 depends on both the temperature and the composition of the gas mixture. At 500 degrees C in the presence of propene or ethano l and in an excess of oxidant, the condition prevailing during SCR, vi rtually all the copper remains in the Cu2+ state. At lower temperature s, in the 200-350 degrees C range, in the same gas mixtures, a partial reduction of the Cu2+ ions takes place. High-temperature oxidation of the propene is accompanied by coke deposition on the outer surface of the zeolitic crystals. (C) 1995 Academic Press, Inc.