Improved activity of Ho-modified Mn/Ti catalysts for the selective catalytic reduction of NO with NH.

A series of Ho-modified Mn/Ti catalysts with various content of Ho were prepared by impregnation method, and the low-temperature catalytic performance was tested. Techniques of BET, SEM, XRD, H-TPR, and XPS were carried out to research the effects of Ho modification on the physicochemical properties of Mn/Ti catalysts. Results showed that appropriate Ho addition could reduce the starting temperature of Mn/TiO catalyst to 100 °C. 0.2HoMn/Ti exhibiting a wider temperature range of 140~220 °C with nearing 100% NO conversion. It was found that the 0.2HoMn/TiO catalyst possessed a better dispersion of active component, enhanced redox capacity, a higher concentration of Mn species, and a larger amount of O content on the catalyst surface, which are all likely predominant factors related to the excellent SCR activity. Additionally, Ho improved the Lewis acid sites and enhanced the adsorption and activation ability of NH, as well as the NO to NO oxidation ability. The selective catalytic reduction with ammonia (NH-SCR) deNO mechanism over HoMn/Ti catalysts obeyed both the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms under low-temperature reaction conditions.