Chapter II.3 Catalytic Decomposition of Nitrogen Monoxide

IR-Spectroscopic Study of Complex Formation of Nitrogen Oxides (NO, N2O) with Cationic Forms of Zeolites and the Reactivity of Adsorbed Species in CO and CH4 Oxidation

The formation of complexes and disproportionation of nitrogen oxides (NO, N2O) on cationic forms of LTA, FAU, and MOR zeolites was investigated by diffuse-reflectance IR spectroscopy. N2O is adsorbed on the samples under study in the molecular form and the frequencies of the first overtone of the stretching vibrations ν10-2 and the combination bands of the stretching vibrations with other vibrational modes for N2O complexes with cationic sites in zeolites (ν30-1 + ν10-1, ν10-1 + δ0-2) are more significantly influenced by the nature of the zeolite. The presence of several IR bands in the region of 2400-2600 cm-1 (the ν10-1 + δ0-2 transitions) for different zeolite types was explained by the availability of different localization sites for cations in these zeolites. The frequencies in this region also depend on the nature of the cation (its charge and radius). The data can be explained by the specific geometry of the N2O complex formed, presumably two-point adsorption of N2O on a cation and a neighboring oxygen atom of the framework. Adsorption of CO or CH4 on the samples with preliminarily adsorbed N2O at 20-180 °C does not result in any oxidation of these molecules. NO+ and N2O3 species formed by disproportionation of NO are capable of oxidizing CO and CH4 molecules to CO2, whereas NOx is reduced simultaneously to N2 or N2O. The peculiarities in the behavior of cationic forms of different zeolites with respect to adsorbed nitrogen oxides determined by different density and localization of cations have been established.

Effect of active component addition and support modification on catalytic activity of Ag/Al2O3 for the selective catalytic reduction of NOx by hydrocarbon - A review

The effect of active component addition and support modification of Ag/Al₂O₃ has been reviewed to examine their contribution to HC-SCR of NOx. This review has depicted the possible mechanisms of reduction of NO by hydrocarbon using metal/metal oxide doped Ag/Al₂O₃. The addition of second metal results in the maximum formation of well dispersed Ag_n^δ+ clusters. Specifically, addition of Au improves the low-temperature activity of the catalyst. However, the role of second metal also depends on the pretreatment to the catalyst and nature of the reductants. The support modification of Ag/Al₂O₃ by the addition of different metal oxides has also been reviewed. Modification by MgO showed improvement in activity besides sulfur tolerance. In situ DRIFT study demonstrates that the modification by MgO leads to the inhibition of sulfate formation of Ag and Al₂O₃. Enhancement in activity after second metal addition and support modification attributed to the synergistic effect and improved surface properties of Ag/Al₂O₃ catalyst.

Pollution by nitrogen oxides: an approach to NO(x) abatement by using sorbing catalytic materials

This article summarises the abatement of NO(x) pollution by using sorbing catalytic materials with special relevance to the challenge presented in fixed installations sources. A general vision of the origins of the different pollutants, with emphasis on nitrogen oxides formation, is presented as introduction. The impact of NO(x) pollution comprises additionally a quick view of its toxicity and environmental effects. Actual solutions are presented especially the case of the selective catalytic reduction (SCR) process with its advantages and difficulties. The new concepts for NO(x) abatement are also analysed. In such a way, updated information on solid sorbents for NO(x) removal is provided by including metal oxides, spinelles, perovskites, double-layered cuprates, zeolites, carbonaceous materials, heteropolyacids (HPAs), and supported heteropolyacids. The possibility of reducing those sorbed NO(x) is also underlined. Sorption mechanisms are analysed and clarified by emphasising convergence and disagreement points.

Assignment of Nonclassical [Cu(CO)(n)](+) (n = 1, 2) Complex Ions in Zeolite Cages

A time-resolved FT-IR technique combined with an isotopic tracer method has been applied to study CO adsorbates on Cu(+) ions in copper ion-exchanged zeolites. Three kinds of monocarbonyl species were found to adsorb strongly on Cu-zeolite samples after admission and subsequent evacuation of gas phase CO at room temperature. Their absorption bands were observed at 2146-2160, 2128-2150, and 2097-2129 cm(-1), respectively, dependent on the zeolite structures. In the presence of gaseous CO, the monocarbonyl species at 2146-2160 cm(-1) (so called nonclassical [Cu(CO)](+) complexes) could react with a CO molecule to form a dicarbonyl species [Cu(CO)(2)](+) with nu(sym) bands at 2169-2180 cm(-1). The reactivity of the nonclassical [Cu(CO)](+) complexes was dependent on the zeolite structures, ferrierite > mordenite > ZSM-5 > X-type left harpoon ovet right harpoon offretite/erionite left harpoon ovet right harpoon Y-type > L-type. The remaining two types of monocarbonyl species have little been affected by gas phase CO.