SPECTROSCOPIC CHARACTERIZATION OF THE FE/ZRO2 SYSTEM .2. NO ADSORPTION AND CO-NO REACTION

The NO adsorption on Fe/ZrO2 (Fe, 1 wt %) has been studied, mainly by FTIR technique, on samples reduced at temperatures between 500 and 773 K; On all these samples NO is adsorbed in large quantities, forming three or four nitrosylic species, strongly bonded to different Fe2+ coordinatively unsaturated (cus) sites and absorbing in the stretching NO region 1825-1700 cm(-1). Some dissociative NO adsorption, with partial oxidation of ferrous sites and formation of N2O and NO2- species, is shown on the sample reduced at T greater than or equal to 623 K. On the sample reduced at 773 K a small amount of iron is reduced to Fe-0 and adsorbs CO, forming carbonylic clusters. These species are not perturbed by NO adsorbed at room temperature (RT), whereas the carbonylic reversible species adsorbed on the ferrous sites are displaced by NO at RT. At 473 K the CO-NO mixture fully reacts, producing N-2 in the gas phase plus carbonate groups and:small amounts of isocyanates, which spilled over onto the support.