Comparative study of Pt-based catalysts on different supports in the low-temperature de-NOx-SCR with propene

Pt-based catalysts have been prepared using supports of different nature (gamma -Al2O3, ZSM-5, USY, and activated carbon (ROXN)) fur the C3H6-SCR of NOx in the presence of excess oxygen. Nitrogen adsorption at 77 K, pH measurements, temperature-programmed desorption of propene, and Hz chemisorption were used for the characterization of the different supports and catalysts. The performance of these catalysts has been compared in terms of de-NO, activity, hydrocarbon adsorption and combustion at low temperature, and selectivity to N-2. Maximum NO, conversions for all the catalysts were achieved in the temperature range of 200-250 degreesC. The order of activity was, Pt-USY > Pt/ROXN similar to Pt-ZSM-5 much greater than Pt/Al2O3. At temperatures above 300 degreesC only Pt/ROXN maintains a high activity caused by the consumption of the support, while the other catalysts present a strong deactivation. Propene combustion starts at the same temperature for all the catalytic systems ((similar to 160 degreesC). Complete hydrocarbon combustion is directly related to the acidity of the support, thus determining the temperature of the maximum NO, reduction. The support play an important role in the reaction mechanism through the hydrocarbon activation. N2O formation was observed for all the catalysts. Nz selectivity ranges from 15 to 30% with the order, Pt/ROXN > Pt-USY similar to Pt/Al2O3 > Pt-ZSM-5. The catalytic systems exhibit a stable operation under isothermal conditions during time-on-stream experiments. (C) 2001 Elsevier Science B.V. All rights reserved.