Reduction of stored NO x on Pt/Al2O3 and Pt/BaO/Al2O3 catalysts with H2 and CO

• Published in: Journal of catalysis 2006-04, Vol.239 (1), p.51
• Main Authors: Tamás Szailer, Kwak, Ja Hun, Do Heui Kim, Hanson, Jonathan C, Charles H.F. Peden, János Szanyi
• Format: Article
• Language: English
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2006.01.014

In situ Fourier transform infrared spectroscopy, coupled with mass spectrometry and time-resolved X-ray diffraction, were used to study the efficiency of nitrate reduction with CO and H2 on Pt/Al2 O3 and Pt/BaO/Al2 O3 NO x storage reduction (NSR) catalysts. Surface nitrates were generated by NO2 adsorption, and their reduction efficiencies were examined on the catalysts together with the analysis of the gas-phase composition in the presence of the two different reductants. H2 was found to be a more effective reducing agent than CO. In particular, the reduction of surface nitrates proceeds very efficiently with H2 even at low temperatures (∼420 K). During reduction with CO, 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 thus formed in turn reacts with stored NO x at higher temperatures (>473 K) to produce N2 . In the absence of H2 O, the NCO species are stable to high temperatures and are removed from the catalyst only when they react with NO x thermal decomposition products to form N2 and CO2 . The results of this study point to a complex reaction mechanism involving the removal of surface oxygen atoms from Pt particles by either H2 or CO, the direct reduction of stored NO x with H2 (low-temperature NO x reduction), the formation and subsequent hydrolysis of NCO species, and the direct reaction of NCO with decomposing NO x (high-temperature NO x reduction).