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

Abstract

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 Agnδ+ 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.