N2O IN NO REDUCTION BY CO OVER PT/NAX ZEOLITE

摘要

Pt/NaX zeolite (3 Pt atoms per unit cell) was prepared by vacuum decomposition of [Pt(NH3)(4)](2+). NO + (CO)-C-13 and N2O + (CO)-C-13 reactions were studied under static conditions at 180, 205 and 230 degrees C and followed by temperature programmed desorption (TPD) of surface species adsorbed in zeolites during the reaction. The effect of different NO/CO ratios and of the added oxygen was examined for the former reaction. The experimental results agree with the assumption that N2O (and (CO2)-C-13) is (are) the primary product(s) released into the gaseous phase below 230 degrees C; above 205 degrees C, the complete reduction to N-2 occurs. N2O could be a very rapidly decomposing surface intermediate for this complete reduction, and can act together with the recombination of N atoms. Nitrous oxide released into the gas phase cannot serve as the reaction intermediate, because its reduction by CO proceeds much more slowly than that of NO. The formation of nitrous oxide in the NO + CO reaction is, in addition to low temperatures, enhanced by the increased NO/CO ratio and by the presence of oxygen. The latter effect can be due to the occupation of Pt active sites by adsorbed oxygen and/or by the oxidation of NO to higher oxides which decompose, yielding N2O (together with NO and oxygen). [References: 23]