LOW-TEMPERATURE CO OXIDATION OVER AU/TIO2 AND AU/SIO2 CATALYSTS

After a high-temperature reduction (HTR) at 773 K, TiO2-supported Au became very active for CO oxidation at 313 K and was an order of magnitude more active than SiO2-supported Au, whereas a low-temperature reduction (LTR) at 473 K produced a Au/TiO2 catalyst with very low activity. A HTR step followed by calcination at 673 K and a LTR step gave the most active Au/TiO2 catalyst of all, which was 100-fold more active at 313 K than a typical 2% Pd/Al2O3 catalyst and was stable above 400 K whereas a sharp decrease in activity occurred with the other Au/TiO2 (HTR) sample. With a feed of 5% CO, 5% O2 in He, almost 40% of the CO was converted at 313 K and essentially all the CO was oxidized at 413 K over the best Au/TiO2 catalyst at a space velocity of 333 h-1 based on CO+O2. Half the chloride in the Au precursor was retained in the Au/TiO2 (LTR) sample whereas only 16% was retained in the other three catalysts; this may be one reason for the low activity of the Au/TiO2 (LTR) sample. The reaction order on O2 was approximately 0.4 between 310 and 360 K, while that on CO varied from 0.2 to 0.6. The chemistry associated with this high activity is not yet known but is presently attributed to a synergistic interaction between gold and titania.