Low temperature FT-IR studies of NO adsorption on aluminum oxide and supported palladium

Low temperature FT-IR spectroscopy has been utilized to study the adsorption and thermal decomposition of NO on Al2O3 and Al2O3-supported palladium. At 110 K the nitric oxide adsorbs molecularly and reversibly via H-bonding to isolated surface -OH groups forming the (NO)(2) dimer. The dimer formation was characterized by symmetric and antisymmetric v(N-O) stretching modes at 1871 and 1761 cm(-1), respectively. However, upon warning the adsorbed (NO)(2) dimer decomposes to form adsorbed nitrous oxide. The reactive species is thus shown to be the adsorbed dimer, which cannot be formed at temperatures greater than 140 K for lack of H-bonding. As the palladium loading is increased, there is a gradual decrease in (NO)(2) dimer formation with an increase in chemisorbed Pd-NO because of adsorption site transfer from Al2O3 to Pd. (C) 2001 Elsevier Science B.V. All rights reserved.