CATALYTIC BEHAVIOR AND STRUCTURE OF ACTIVE SPECIES OF CU-Y ZEOLITE IN OXIDATION OF CARBON-MONOXIDE

The catalytic behavior of activated Cu-Y zeolite in CO oxidation at low temperatures was investigated by temperature-programmed reduction (TPR) and extended X-ray absorption fine structure (EXAFS) measurements. An active Cu species was formed by a sequence of preliminary evacuation, reduction with hydrogen, and reoxidation with oxygen. Maximum formation of the active species was observed at 523, 673, and 473 K in each step of the treatment, respectively. With increase in amount of this species estimated from the TPR spectra, the catalytic activity of the zeolite increased proportionally, whereas the activation energy remained unchanged. In the treatment with CO, the active species was directly and reversibly reduced into Cu metal clusters at low temperature, while the original Cu2+ species were reduced to Cu+ at high temperature. It was indicated from detailed analysis of the EXAFS data that small CuO clusters could function as catalytic centers in CO oxidation via the reversible redox mechanism. © 1990 American Chemical Society.