Highly active oxidation catalysts have been made by treating dehydrated zeolite NaY with excesses of the neutral tetranuclear copper(II) precursor (mu(4)-O)L(4)Cu(4)Cl(6) (A, L = N,N-diethylnicotinamide) in methylene chloride, followed by methylene chloride washing, drying and oxidation with O-2 at 220 degrees C. The loaded samples contain from 3.4 to 14.3% w/w total copper, depending on the amount of A used. Previous measurements with a different ’titration’ loading method together with analytical and spectroscopic data for materials loaded with different excesses of A indicate 2.9-13.8% w/w copper on the zeolite surface (50 m(2)/g) due to a zeolite-solution equilibrium with A. Oxidation of the most heavily loaded sample with O-2 gives a catalyst that is ten times more active per gram for CO oxidation than bulk CuO at 450 degrees C. The most lightly loaded sample oxidizes CO 115 times faster than bulk CuO on a per gram CuO basis. Turnover numbers at infinitely dilute CuO loading approach 75% of the TON for bulk CuO, suggesting that CO oxidation on bulk CuO involves more than one CuO site. Prospects for catalyst development through transmetallation chemistry and different loading methods are discussed.