Dinitrosyl intermediate for N2O formation from reaction of NO on Mo(110)

Abstract

The adsorption and subsequent reaction of nitric oxide (NO) on Mo(110) has been studied by temperature programmed reaction, electron energy loss, and infrared reflectance absorbance spectroscopies. The predominant reaction pathway for a saturated NO overlayer is dissociation to atomic nitrogen and oxygen; in fact, for low NO coverages, dissociation is the only reaction and largely takes place below 300 K. At NO coverages above 65% of θsat, evolution of N2O, N2, and NO is also observed at low temperature. Temperature programmed reaction of isotopically mixed overlayers demonstrates that N2O formation occurs via reaction of two intact NO molecules, suggestive of a dimeric surface intermediate. Electron energy loss and infrared spectroscopies identify three ν(NO) features which are assigned to three distinct species; the frequencies of the ν(NO) peaks in the infrared spectrum of a saturated 14NO overlayer at 100 K are 1860, 1821, and 1720 cm−1. The 1860 and 1720 cm−1 features are assigned to monomeric NO. Based on the infrared spectrum of a mixed overlayer of 14NO and 15NO, and on comparison to reference spectra of NO adsorbed on MoO3, the 1821 cm−1 peak is identified as νs(NO) of a surface dinitrosyl complex, i.e., two NO molecules bound to one Mo site. The weakly bound NO with the stretch frequency of 1860 cm−1 is associated with NO desorption, while the dinitrosyl leads to low-temperature N2 and N2O formation and some dissociation.