FTIR studies of butane, toluene and nitric oxide adsorption on Ag exchanged NaMordenite

Abstract

In this work, we studied the adsorption of butane, toluene and nitric oxide on NaMordenite exchanged with different amounts of silver. The reactions that occurred when the adsorbed hydrocarbons interacted with NO and the effect of water adsorption were also addressed. Different silver species were formed after ion exchange and they were detected by TPR analysis. Highly dispersed Ag2O particles were reduced at temperatures lower than 300 °C whereas Ag+ exchanged ions showed two TPR peaks, which can be ascribed to species exchanged at different mordenite sites. The TPD experiments after adsorption of NO at 25 °C showed that the only desorbed species was NO2 which was formed by the total reduction of Ag2O particles. When the adsorbed butane was exposed to NO (1000 ppm), isocyanate species were formed on Ag+ ionic sites as well as Ag+– (NOx)–CO species. Toluene adsorption was stronger than butane since adsorbed toluene molecules were held even at 400 °C. The characteristic bands of the aromatic ring C=C bond was observed as well as that of methyl groups interacting with Ag+ and Na+ ions. However, the appearance of carboxylic groups at temperatures above 300 °C in inert flow indicated the partial oxidation of toluene due to Ag2O species present in the samples. After contacting adsorbed toluene with NO, different FTIR bands correspond to organic nitrocompounds, isocyanate, cyanide and isocyanide species adsorbed on Ag+ ions, were detected. The presence of water inhibited the formation of NO2 species and the hydrocarbon adsorption on Na+ sites but did not affect the toluene-Ag+ interaction.