Reduction of stored NOx on Pt/Al2O3 and Pt/BaO/Al2O3 catalysts with H2 and CO

• DOI: 10.1016/j.jcat.2006.01.014
• Publication Date: 2006-02-10T12:29:39Z
• Authors: T SZAILER; J KWAK; D KIM; J HANSON; C PEDEN; J SZANYI
• Keywords: Selective catalytic reduction; Selective Reduction; Nitrogen oxides

Abstract 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 H 2 on Pt/Al 2 O 3 and Pt/BaO/Al 2 O 3 NO x storage reduction (NSR) catalysts. Surface nitrates were generated by NO 2 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. 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 (∼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 CO 2 and ammonia. The NH 3 thus formed in turn reacts with stored NO x at higher temperatures (>473 K) to produce N 2 . In the absence of H 2 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 N 2 and CO 2 . The results of this study point to a complex reaction mechanism involving the removal of surface oxygen atoms from Pt particles by either H 2 or CO, the direct reduction of stored NO x with H 2 (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).