Catalytic Automotive Pollution Control Without Noble Metals

Abstract

Abstract The catalytic activity for the NO reduction and the CO oxidation, and the influence of several parameters on this activity, has been studied for Cu and Cu-Cr catalysts on pelleted and monolithic supports. It has been shown that 10 wt% Cu-Cr/Al2O3 catalysts are very effective for NO reduction, CO and HC oxidation. The highest activity is obtained at a Cu/Cr ratio of 2. Monolithic-type catalysts exhibit a three-way catalyst behaviour, comparable to noble metal catalysts under the same conditions. The conversion performance under oscillating compositions is even better than under stationary composition conditions. The presence of O2 leads to an inhibition of the NO reduction by CO. NO does not affect the CO oxidation. In the NO reduction with CO at low NO conversions predominantly N2O is formed, whereas at higher conversion levels the N2O formation passes through a maximum and at higher temperatures (T > 523 K) only N2 is observed. The catalyst system deactivates at higher temperatures (> 775 K) in stoichiometric CO/NO/O2 mixtures, but the original activity returns in an overall oxidizing environment at 623 K. The CO oxidation activity level of a freshly prepared catalyst under reducing conditions is higher than under oxidizing conditions, after thermal treatment in a stoichiometric mixture this is the reversed case. A tentative explanation is given. Cu catalysts prepared from EDTA complexes and a La-stabilized alumina-support appear to have a high thermal stability and a final activity comparable to that of the Cu-Cr catalysts.