INVESTIGATION OF CO OXIDATION AND NO REDUCTION ON 3-WAY MONOLITH CATALYSTS WITH TRANSIENT-RESPONSE TECHNIQUES

The kinetics of CO oxidation and NO reduction reactions over alumina a nd alumina-ceria supported Pt, Rh and bimetallic pt/Ph catalysts coate d on metallic monoliths were investigated using the step response tech nique at atmospheric pressure and at temperatures 30-350 degrees C. Th e feed step change experiments from an inert flow to a flow of a reage nt (O-2, CO, NO and H-2) showed that the ceria promoted catalysts had higher adsorption capacities, higher reaction rates and promoting effe cts by preventing the inhibitory effects of reactants, than the alumin a supported noble metal catalysts. The effect of ceria was explained w ith adsorbate spillover from the noble metal sites to ceria. The step change experiments CO/O-2 and O-2/CO also revealed the enhancing effec t of ceria. The step change experiments NO/H-2 and H-2/NO gave nitroge n as a main reduction product and N2O as a by-product. Preadsorption o f NO on the catalyst surface decreased the catalyst activity in the re duction of NO with H-2. The CO oxidation transients were modelled with a mechanism which consisted of CO and O-2 adsorption and a surface re action step. The NO reduction experiments with H-2 revealed the role o f N2O as a surface intermediate in the formation of N-2. The formation of N-N bonding was assumed to take place prior to, partly prior to or totally following to the N-O bond breakage, High NO coverage favors N 2O formation. Pt was shown to be more efficient than Ph for NO reducti on by H-2.