Preparation, characterization and catalytic performance of Ag-modified mesoporous TiO₂ in low-temperature selective ammonia oxidation into nitrogen and water vapour

Mesoporous TiO₂ was prepared by evaporation induced self-assembly (EISA) and used as a support for silver with loadings of 1.5 or 10 wt%, respectively. Silver deposited on commercial TiO₂ (anatase) and γ-Al₂O₃ served as reference catalysts. The mesoporous TiO₂ were calcined at 500, 600, 700 and 800 °C in order to obtain anatase and/or rutile phases. The materials were characterized with respect to structural (XRD, TEM, UV-vis-DRS) and textural parameters (N₂ adsorption-desorption), acidic properties (NH₃-TPD, FTIR studies), redox properties (H₂-TPR), and were applied as catalysts for the selective ammonia oxidation into nitrogen and water vapour (NH₃-SCO). The catalytic performance (activity and N₂ selectivity) was favoured over (1.5 wt%)Ag-doped mesoporous TiO₂ calcined at 600 °C. Thus, mesoporous TiO₂ with the predominant anatase phase, as a support guaranteed the formation of easily reducible highly dispersed oxidized silver species. Furthermore, these species were converted into Ag⁰ and possibly Ag_n^δ+ clusters through in situ H₂-pretreatment of catalysts. While mainly metallic silver catalyzed the decomposition of N₂O into N₂ and surface oxygen species, leading to higher N₂ selectivity in NH₃-SCO.