Reduction of stored NOx on Pt/Al2O3 and Pt/BaO/Al2O3 catalysts with H-2 and CO

Abstract

in situ Fourier transform infrared spectroscopy, coupled with mass spectrometry a the efficiency of nitrate reduction with CO and H-2 on Pt/Al-2-O-3 and Pt/BaO/Al2O3 NOx storage reduction (NSR) catalysts. Surface nitrates NO2 adsorption. and their reduction efficiencies were examined oil the catalysts together with the analysis of the gas-phase were generated by NO2 composition in the presence of the two different reductants. H-2 was found to be a more effective reducing agent than CO. In particular, the reduction of surface nitrates proceeds very efficiently with H-2 even at low temperatures (similar to 420 K). During reduction with CO2 isocyanates form and adsorb on the oxide components of the catalyst; however, these surface isocyanates readily react with water to form CO2 and ammonia. The NH3 at higher temperatures (> 473 K) to produce N-2. In the absence of H2O the NCO species are stable to high temperatures and are removed from the catalyst only when they react with NOx thermal decomposition products to form N-2 and CO2 The results of this study point to a complex reaction mechanism involving tile removal of Surface oxygen atoms from Pt particles by either H-2 or CO2 the direct reduction of stored NOx with H-2 (low-temperature NOx reduction), the formation and subsequent hydrolysis of NCO species, and the direct reaction of NCO with decomposing NOx (high-temperature NOx reduction). (c) 2006 Elsevier Inc. All rights reserved